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Net zero emissions.

Some actions, like using electricity from a fossil fuel-fired power plant, lead to greenhouse gases entering the atmosphere. These greenhouse gas “emissions” are the root cause of climate change. Other actions help reduce emissions, like building a solar farm that lets us run that fossil fuel-fired power plant less—or even, like planting trees , take some greenhouse gases back out of the atmosphere.   A person or organization with net zero emissions is one that takes both kinds of actions, such that their positive and negative impacts on the climate are considered to effectively balance out. This is an important strategy, because it can be very hard, expensive, or even impossible to emit no greenhouse gases at all. By lowering one’s own emissions as much as possible, and then “canceling out” any remaining (or “residual”) emissions, an organization can reach net zero emissions and stop contributing to the buildup of greenhouse gases and their effect on the climate.

Net zero organizations

A growing number of organizations, from companies and universities to cities and countries, are pledging to reach net zero emissions.   Ideally, they would do this by eliminating all their emissions. Most organizations, however, will find they can only reduce their own emissions so far. (For instance, they may need to buy electricity from a local electric grid that still runs partly on fossil fuels.) To reach net zero, these organizations will need to either take actions that remove some greenhouse gases from the atmosphere, or help someone else reduce their emissions—like by buying equipment to capture methane at their local landfill. These actions could be considered to have “negative emissions.”   Organizations don’t always take on these negative emissions projects themselves. Many choose to buy carbon offsets , paying someone else with more expertise to trap methane, plant trees, or otherwise keep greenhouse gases out of the atmosphere. Carbon offset projects can be located anywhere in the world, giving organizations more options to invest in larger or more economically efficient projects than they could carry out alone.

Scope 1, 2, and 3 emissions

To achieve net zero emissions, organizations must first know how much they emit. This can be more complicated than it may appear.

In counting up its emissions , an organization should always include both “scope 1” (or  direct ) emissions, and “scope 2” emissions. 1

• Scope 1: Greenhouse gases the organization itself puts into the atmosphere—for instance, by burning gas to heat its buildings .  
• Scope 2: Greenhouse gases produced by the utilities the organization buys—for instance, when buying electricity from a fossil fuel-fired power plant.

Organizations may also choose to include some or all of their “scope 3” emissions.

• Scope 3: Greenhouse gases produced by other goods and services the organization uses—for instance, by the cars employees use to commute, by flights for business travel, and by disposal of the organization’s waste.

Scope 3 emissions are not always included in plans to reach net zero emissions, however, in part because they can give rise to double counting. When an employee drives a gas-powered car to work, are those emissions the responsibility of the employer, the employee, the car manufacturer, or the oil company who sells the gasoline?

A net zero planet

There is an important, practical reason for the focus on net zero. As long as humans keep adding greenhouse gases to the atmosphere, climate change will continue to get worse. Only when the whole planet reaches net zero emissions will the climate begin to stabilize.   For this reason, almost every country on Earth signed the Paris Agreement in 2015, pledging to reach net zero emissions in time to hold global warming to no more than 2° C and strive for no more than 1.5° C. According to the Intergovernmental Panel on Climate Change , meeting the stronger 1.5° C goal would require the whole world to reach net zero emissions by 2050. 2 Many organizations make net zero pledges in line with these global targets , wanting to “do their part” to achieve a net zero world.   Global net zero emissions, however, are especially hard to achieve. Once humans reduce worldwide emissions as much as possible, the only way to “cancel out” any residual emissions will be to actively take greenhouse gases back out of the atmosphere. Still, it is not impossible to have a net zero planet: in fact, it must be the goal of climate action if we are to finally stabilize climate change. It is even possible to go further, and take more greenhouse gases from the atmosphere than we emit. With worldwide “net negative” emissions, it may be possible to reverse some (but not all) of the catastrophic effects of climate change .

Related terms

Carbon neutrality and net zero carbon emissions are similar terms to net zero emissions, but are narrower in scope: they only address the addition and removal of carbon dioxide (CO 2 ) from the atmosphere. CO 2 is the most common and impactful greenhouse gas released by human activities, but not the only one: true net zero emissions must also consider the other greenhouse gases including methane, nitrous oxide, and fluorinated gases.

Climate neutrality is an even broader term that considers everything humans do that might influence the climate. For instance, the Earth’s snow cover helps reflect light back into space, cooling the planet. Human activities that reduce snow cover would not be “climate neutral,” even if they emit no greenhouse gases at all.

Net negative emissions is a goal that goes even further than net zero: removing more greenhouse gases from the atmosphere than one emits. If the entire world were to achieve net negative emissions, it could potentially reverse some of the climate change we have already caused.

Published December 16, 2022.

1 For more information on Scope 1, 2, and 3 emissions and what is included in each category, see World Economic Forum, " What is the difference between scope 1, 2 and 3 emissions, and what are companies doing to cut all three? "

2 Intergovernmental Panel on Climate Change: “ Climate Change 2021: The Physical Science Basis .” The same report estimates that the weaker 2° C goal would require worldwide net-zero emissions by around 2070.

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It’s possible to reach net-zero carbon emissions. here’s how.

Cutting carbon dioxide emissions to curb climate change is possible but not easy

Curbing climate change means getting more electricity from renewable sources, such as wind power.

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By Alexandra Witze

January 27, 2023 at 7:00 am

Patricia Hidalgo-Gonzalez saw the future of energy on a broiling-hot day last September.

An email alert hit her inbox from the San Diego Gas & Electric Company. “Extreme heat straining the grid,” read the message, which was also pinged as a text to 27 million people. “Save energy to help avoid power interruptions.”

It worked. People cut their energy use. Demand plunged, blackouts were avoided and California successfully weathered a crisis exacerbated by climate change. “It was very exciting to see,” says Hidalgo-Gonzalez, an electrical engineer at the University of California, San Diego who studies renewable energy and the power grid.

This kind of collective societal response, in which we reshape how we interact with the systems that provide us energy, will be crucial as we figure out how to live on a changing planet.

Earth has warmed at least 1.1 degrees Celsius since the 19th century, when the burning of coal, oil and other fossil fuels began belching heat-trapping gases such as carbon dioxide into the atmosphere. Scientists agree that only drastic action to cut emissions can keep the planet from blasting past 1.5 degrees of warming — a threshold beyond which the consequences become even more catastrophic than the rising sea levels, extreme weather and other impacts the world is already experiencing.

The goal is to achieve what’s known as net-zero emissions, where any greenhouse gases still entering the atmosphere are balanced by those being removed — and to do it as soon as we can.

Scientists say it is possible to swiftly transform the ways we produce and consume energy. To show the way forward, researchers have set out paths toward a world where human activities generate little to no carbon dioxide and other greenhouse gases — a decarbonized economy.

The key to a decarbonized future lies in producing vast amounts of new electricity from sources that emit little to none of the gases, such as wind, solar and hydropower, and then transforming as much of our lives and our industries as possible to run off those sources. Clean electricity needs to power not only the planet’s current energy use but also the increased demands of a growing global population.

Once humankind has switched nearly entirely to clean electricity, we will also have to counter­balance the carbon dioxide we still emit — yes, we will still emit some — by pulling an equivalent amount of carbon dioxide out of the atmosphere and storing it somewhere permanently.

Achieving net-zero emissions won’t be easy. Getting to effective and meaningful action on climate change requires overcoming decades of inertia and denial about the scope and magnitude of the problem. Nations are falling well short of existing pledges to reduce emissions, and global warming remains on track to charge past 1.5 degrees perhaps even by the end of this decade.

Yet there is hope. The rate of growth in CO 2 emissions is slowing globally — down from 3 percent annual growth in the 2000s to half a percent annual growth in the last decade, according to the Global Carbon Project , which quantifies greenhouse gas emissions.

There are signs annual emissions could start shrinking. And over the last two years, the United States, by far the biggest cumulative contributor to global warming, has passed several pieces of federal legislation that include financial incentives to accelerate the transition to clean energy. “We’ve never seen anything at this scale,” says Erin Mayfield, an energy researcher at Dartmouth College.

Though the energy transition will require many new technologies, such as innovative ways to permanently remove carbon from the atmosphere, many of the solutions, such as wind and solar power, are in hand — “stuff we already have,” Mayfield says.

How to hit net-zero carbon emissions by 2050

In a 2021 report, the International Energy Agency described the steps necessary to ensure that by 2050 the amount of carbon dioxide emitted into the atmosphere globally balances the amount being taken out. This chart shows how carbon dioxide emissions would have to drop across sectors to bring planetwide emissions from roughly 34 billion metric tons annually to net-zero.  

The current state of carbon dioxide emissions

Of all the emissions that need to be slashed, the most important is carbon dioxide, which comes from many sources such as cars and trucks and coal-burning power plants. The gas accounted for 79 percent of U.S. greenhouse gas emissions in 2020. The next most significant greenhouse gas, at 11 percent of emissions in the United States, is methane, which comes from oil and gas operations as well as livestock, landfills and other land uses.

The amount of methane may seem small, but it is mighty — over the short term, methane is more than 80 times as efficient at trapping heat as carbon dioxide is, and methane’s atmospheric levels have nearly tripled in the last two centuries. Other greenhouse gases include nitrous oxides, which come from sources such as applying fertilizer to crops or burning fuels and account for 7 percent of U.S. emissions, and human-made fluorinated gases such as hydrofluorocarbons that account for 3 percent.

Globally, emissions are dominated by large nations that produce lots of energy. The United States alone emits around 5 billion metric tons of carbon dioxide each year. It is responsible for most of the greenhouse gas emissions throughout history and ceded the spot for top annual emitter to China only in the mid-2000s. India ranks third.

Because of the United States’ role in producing most of the carbon pollution to date, many researchers and advocates argue that it has the moral responsibility to take the global lead on cutting emissions. And the United States has the most ambitious goals of the major emitters, at least on paper. President Joe Biden has said the country is aiming to reach net-zero emissions by 2050. Leaders in China and India have set net-zero goals of 2060 and 2070, respectively.

Under the auspices of a 2015 international climate change treaty known as the Paris agreement, 193 nations plus the European Union have pledged to reduce their emissions. The agreement aims to keep global warming well below 2 degrees, and ideally to 1.5 degrees, above preindustrial levels. But it is insufficient. Even if all countries cut their emissions as much as they have promised under the Paris agreement, the world would likely blow past 2 degrees of warming before the end of this century. 

Every nation continues to find its own path forward. “At the end of the day, all the solutions are going to be country-specific,” says Sha Yu, an earth scientist at the Pacific Northwest National Laboratory and University of Maryland’s Joint Global Change Research Institute in College Park, Md. “There’s not a universal fix.”

But there are some common themes for how to accomplish this energy transition — ways to focus our efforts on the things that will matter most. These are efforts that go beyond individual consumer choices such as whether to fly less or eat less meat. They instead penetrate every aspect of how society produces and consumes energy.

Such massive changes will need to overcome a lot of resistance, including from companies that make money off old forms of energy as well as politicians and lobbyists. But if society can make these changes, it will rank as one of humanity’s greatest accomplishments. We will have tackled a problem of our own making and conquered it.

Here’s a look at what we’ll need to do.

Make as much clean electricity as possible

To meet the need for energy without putting carbon dioxide into the atmosphere, countries would need to dramatically scale up the amount of clean energy they produce. Fortunately, most of that energy would be generated by technologies we already have — renewable sources of energy including wind and solar power.

“Renewables, far and wide, are the key pillar in any net-zero scenario,” says Mayfield, who worked on an influential 2021 report from Princeton University’s Net-Zero America project , which focused on the U.S. economy.

The Princeton report envisions wind and solar power production roughly quadrupling by 2030 to get the United States to net-zero emissions by 2050. That would mean building many new solar and wind farms, so many that in the most ambitious scenario, wind turbines would cover an area the size of Arkansas, Iowa, Kansas, Missouri, Nebraska and Oklahoma combined.

How much solar and wind power would we need?

Achieving net-zero would require a dramatic increase in solar and wind power in the United States. These maps show the footprint of existing solar and wind infrastructure in the contiguous United States (as of 2020) and a possible footprint for a midrange scenario for 2050. Gray shows population density of 100 people per square kilometer or greater.

Such a scale-up is only possible because prices to produce renewable energy have plunged. The cost of wind power has dropped nearly 70 percent, and solar power nearly 90 percent, over the last decade in the United States. “That was a game changer that I don’t know if some people were expecting,” Hidalgo-Gonzalez says.

Globally the price drop in renewables has allowed growth to surge; China, for instance, installed a record 55 gigawatts of solar power capacity in 2021, for a total of 306 gigawatts or nearly 13 percent of the nation’s installed capacity to generate electricity. China is almost certain to have had another record year for solar power installations in 2022.

Challenges include figuring out ways to store and transmit all that extra electricity, and finding locations to build wind and solar power installations that are acceptable to local communities. Other types of low-carbon power, such as hydropower and nuclear power, which comes with its own public resistance, will also likely play a role going forward.

More renewable electricity globally

Renewable energy sources, such as solar, wind and hydropower, account for a larger share of global electricity generation today than they did in 2015. The International Energy Agency expects that trend to continue, projecting that renewables will top 38 percent in 2027.

Get efficient and go electric

The drive toward net-zero emissions also requires boosting energy efficiency across industries and electrifying as many aspects of modern life as possible, such as transportation and home heating.

Some industries are already shifting to more efficient methods of production, such as steelmaking in China that incorporates hydrogen-based furnaces that are much cleaner than coal-fired ones, Yu says. In India, simply closing down the most inefficient coal-burning power plants provides the most bang for the buck, says Shayak Sengupta, an energy and policy expert at the Observer Research Foundation America think tank in Washington, D.C. “The list has been made up,” he says, of the plants that should close first, “and that’s been happening.”

To achieve net-zero, the United States would need to increase its share of electric heat pumps, which heat houses much more cleanly than gas- or oil-fired appliances, from around 10 percent in 2020 to as much as 80 percent by 2050, according to the Princeton report. Federal subsidies for these sorts of appliances are rolling out in 2023 as part of the new Inflation Reduction Act , legislation that contains a number of climate-related provisions.

Shifting cars and other vehicles away from burning gasoline to running off of electricity would also lead to significant emissions cuts. In a major 2021 report , the National Academies of Sciences, Engineering and Medicine said that one of the most important moves in decarbonizing the U.S. economy would be having electric vehicles account for half of all new vehicle sales by 2030. That’s not impossible; electric car sales accounted for nearly 6 percent of new sales in the United States in 2022, which is still a low number but nearly double the previous year .

Make clean fuels

Some industries such as manufacturing and transportation can’t be fully electrified using current technologies — battery powered airplanes, for instance, will probably never be feasible for long-duration flights. Technologies that still require liquid fuels will need to switch from gas, oil and other fossil fuels to low-carbon or zero-carbon fuels.

One major player will be fuels extracted from plants and other biomass, which take up carbon dioxide as they grow and emit it when they die, making them essentially carbon neutral over their lifetime. To create biofuels, farmers grow crops, and others process the harvest in conversion facilities into fuels such as hydrogen. Hydrogen, in turn, can be substituted for more carbon-intensive substances in various industrial processes such as making plastics and fertilizers — and maybe even as fuel for airplanes someday.

In one of the Princeton team’s scenarios, the U.S. Midwest and Southeast would become peppered with biomass conversion plants by 2050, so that fuels can be processed close to where crops are grown. Many of the biomass feedstocks could potentially grow alongside food crops or replace other, nonfood crops.

Solar and wind power trends in the United States

The amount of electricity generated from wind and solar power in the United States has surged in the last decade. The boost was made possible in large part by drops in the costs of producing that energy.

Cut methane and other non-CO 2 emissions

Greenhouse gas emissions other than carbon dioxide will also need to be slashed. In the United States, the majority of methane emissions come from livestock, landfills and other agricultural sources, as well as scattered sources such as forest fires and wetlands. But about one-third of U.S. methane emissions come from oil, gas and coal operations. These may be some of the first places that regulators can target for cleanup, especially “super emitters” that can be pinpointed using satellites and other types of remote sensing .

In 2021, the United States and the European Union unveiled what became a global methane pledge endorsed by 150 countries to reduce emissions. There is, however, no enforcement of it yet. And China, the world’s largest methane emitter, has not signed on.

Nitrous oxides could be reduced by improving soil management techniques, and fluorinated gases by finding alternatives and improving production and recycling efforts.

Sop up as much CO 2 as possible

Once emissions have been cut as much as possible, reaching net-zero will mean removing and storing an equivalent amount of carbon to what society still emits.

One solution already in use is to capture carbon dioxide produced at power plants and other industrial facilities and store it permanently somewhere, such as deep underground. Globally there are around 35 such operations, which collectively draw down around 45 million tons of carbon dioxide annually. About 200 new plants are on the drawing board to be operating by the end of this decade, according to the International Energy Agency.

The Princeton report envisions carbon capture being added to almost every kind of U.S. industrial plant, from cement production to biomass conversion. Much of the carbon dioxide would be liquefied and piped along more than 100,000 kilometers of new pipelines to deep geologic storage, primarily along the Texas Gulf Coast, where underground reservoirs can be used to trap it permanently. This would be a massive infrastructure effort. Building this pipeline network could cost up to $230 billion, including $13 billion for early buy-in from local communities and permitting alone.

Another way to sop up carbon is to get forests and soils to take up more. That could be accomplished by converting crops that are relatively carbon-intensive, such as corn to be used in ethanol, to energy-rich grasses that can be used for more efficient biofuels, or by turning some cropland or pastures back into forest. It’s even possible to sprinkle crushed rock onto croplands, which accelerates natural weathering processes that suck carbon dioxide out of the atmosphere.

Another way to increase the amount of carbon stored in the land is to reduce the amount of the Amazon rainforest that is cut down each year. “For a few countries like Brazil, preventing deforestation will be the first thing you can do,” Yu says.

When it comes to climate change, there’s no time to waste

The Princeton team estimates that the United States would need to invest at least an additional $2.5 trillion over the next 10 years for the country to have a shot at achieving net-zero emissions by 2050. Congress has begun ramping up funding with two large pieces of federal legislation it passed in 2021 and 2022. Those steer more than $1 trillion toward modernizing major parts of the nation’s economy over a decade — including investing in the energy transition to help fight climate change.

Between now and 2030, solar and wind power, plus increasing energy efficiency, can deliver about half of the emissions reductions needed for this decade, the International Energy Agency estimates. After that, the primary drivers would need to be increasing electrification, carbon capture and storage, and clean fuels such as hydrogen.

The trick is to do all of this without making people’s lives worse. Developing nations need to be able to supply energy for their economies to develop. Communities whose jobs relied on fossil fuels need to have new economic opportunities.

Julia Haggerty, a geographer at Montana State University in Bozeman who studies communities that are dependent on natural resources, says that those who have money and other resources to support the transition will weather the change better than those who are under-resourced now. “At the landscape of states and regions, it just remains incredibly uneven,” she says.

The ongoing energy transition also faces unanticipated shocks such as Russia’s invasion of Ukraine, which sent energy prices soaring in Europe, and the COVID-19 pandemic, which initially slashed global emissions but later saw them rebound.

But the technologies exist for us to wean our lives off fossil fuels. And we have the inventiveness to develop more as needed. Transforming how we produce and use energy, as rapidly as possible, is a tremendous challenge — but one that we can meet head-on. For Mayfield, getting to net-zero by 2050 is a realistic goal for the United States. “I think it’s possible,” she says. “But it doesn’t mean there’s not a lot more work to be done.”

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Renewable energy – powering a safer future

Energy is at the heart of the climate challenge – and key to the solution.

A large chunk of the greenhouse gases that blanket the Earth and trap the sun’s heat are generated through energy production, by burning fossil fuels to generate electricity and heat.

Fossil fuels, such as coal, oil and gas, are by far the largest contributor to global climate change , accounting for over 75 percent of global greenhouse gas emissions and nearly 90 percent of all carbon dioxide emissions.

The science is clear: to avoid the worst impacts of climate change, emissions need to be reduced by almost half by 2030 and reach net-zero by 2050.

To achieve this, we need to end our reliance on fossil fuels and invest in alternative sources of energy that are clean, accessible, affordable, sustainable, and reliable.

Renewable energy sources – which are available in abundance all around us, provided by the sun, wind, water, waste, and heat from the Earth – are replenished by nature and emit little to no greenhouse gases or pollutants into the air.

Fossil fuels still account for more than 80 percent of global energy production , but cleaner sources of energy are gaining ground. About 29 percent of electricity currently comes from renewable sources.

Here are five reasons why accelerating the transition to clean energy is the pathway to a healthy, livable planet today and for generations to come.

1. Renewable energy sources are all around us

About 80 percent of the global population lives in countries that are net-importers of fossil fuels -- that’s about 6 billion people who are dependent on fossil fuels from other countries, which makes them vulnerable to geopolitical shocks and crises.

In contrast, renewable energy sources are available in all countries, and their potential is yet to be fully harnessed. The International Renewable Energy Agency (IRENA) estimates that 90 percent of the world’s electricity can and should come from renewable energy by 2050.

Renewables offer a way out of import dependency, allowing countries to diversify their economies and protect them from the unpredictable price swings of fossil fuels, while driving inclusive economic growth, new jobs, and poverty alleviation.

2. Renewable energy is cheaper

Renewable energy actually is the cheapest power option in most parts of the world today. Prices for renewable energy technologies are dropping rapidly. The cost of electricity from solar power fell by 85 percent between 2010 and 2020. Costs of onshore and offshore wind energy fell by 56 percent and 48 percent respectively.

Falling prices make renewable energy more attractive all around – including to low- and middle-income countries, where most of the additional demand for new electricity will come from. With falling costs, there is a real opportunity for much of the new power supply over the coming years to be provided by low-carbon sources.

Cheap electricity from renewable sources could provide 65 percent of the world’s total electricity supply by 2030. It could decarbonize 90 percent of the power sector by 2050, massively cutting carbon emissions and helping to mitigate climate change.

Although solar and wind power costs are expected to remain higher in 2022 and 2023 then pre-pandemic levels due to general elevated commodity and freight prices, their competitiveness actually improves due to much sharper increases in gas and coal prices, says the International Energy Agency (IEA).

3. Renewable energy is healthier

According to the World Health Organization (WHO), about 99 percent of people in the world breathe air that exceeds air quality limits and threatens their health, and more than 13 million deaths around the world each year are due to avoidable environmental causes, including air pollution.

The unhealthy levels of fine particulate matter and nitrogen dioxide originate mainly from the burning of fossil fuels. In 2018, air pollution from fossil fuels caused $2.9 trillion in health and economic costs , about $8 billion a day.

Switching to clean sources of energy, such as wind and solar, thus helps address not only climate change but also air pollution and health.

4. Renewable energy creates jobs

Every dollar of investment in renewables creates three times more jobs than in the fossil fuel industry. The IEA estimates that the transition towards net-zero emissions will lead to an overall increase in energy sector jobs : while about 5 million jobs in fossil fuel production could be lost by 2030, an estimated 14 million new jobs would be created in clean energy, resulting in a net gain of 9 million jobs.

In addition, energy-related industries would require a further 16 million workers, for instance to take on new roles in manufacturing of electric vehicles and hyper-efficient appliances or in innovative technologies such as hydrogen. This means that a total of more than 30 million jobs could be created in clean energy, efficiency, and low-emissions technologies by 2030.

Ensuring a just transition , placing the needs and rights of people at the heart of the energy transition, will be paramount to make sure no one is left behind.

5. Renewable energy makes economic sense

About $7 trillion was spent on subsidizing the fossil fuel industry in 2022, including through explicit subsidies, tax breaks, and health and environmental damages that were not priced into the cost of fossil fuels.

In comparison, about $4 trillion a year needs to be invested in renewable energy until 2030 – including investments in technology and infrastructure – to allow us to reach net-zero emissions by 2050.

The upfront cost can be daunting for many countries with limited resources, and many will need financial and technical support to make the transition. But investments in renewable energy will pay off. The reduction of pollution and climate impacts alone could save the world up to $4.2 trillion per year by 2030.

Moreover, efficient, reliable renewable technologies can create a system less prone to market shocks and improve resilience and energy security by diversifying power supply options.

Learn more about how many communities and countries are realizing the economic, societal, and environmental benefits of renewable energy.

Will developing countries benefit from the renewables boom? Learn more here .

What is renewable energy?

Derived from natural resources that are abundant and continuously replenished, renewable energy is key to a safer, cleaner, and sustainable world. Explore common sources of renewable energy here.

Why invest in renewable energy?

Learn more about the differences between fossil fuels and renewables, the benefits of renewable energy, and how we can act now.

Five ways to jump-start the renewable energy transition now

UN Secretary-General outlines five critical actions the world needs to prioritize now to speed up the global shift to renewable energy.

What is net zero? Why is it important? Our net-zero page explains why we need steep emissions cuts now and what efforts are underway.

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It’s time to stop burning our planet, and start investing in the abundant renewable energy all around us." ANTÓNIO GUTERRES , United Nations Secretary-General

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Review article, sustainable energy transition for renewable and low carbon grid electricity generation and supply.

• Industrial Engineering Department, Durban University of Technology, Durban, South Africa

The greatest sustainability challenge facing humanity today is the greenhouse gas emissions and the global climate change with fossil fuels led by coal, natural gas and oil contributing 61.3% of global electricity generation in the year 2020. The cumulative effect of the Stockholm, Rio, and Johannesburg conferences identified sustainable energy development (SED) as a very important factor in the sustainable global development. This study reviews energy transition strategies and proposes a roadmap for sustainable energy transition for sustainable electricity generation and supply in line with commitments of the Paris Agreement aimed at reducing greenhouse gas emissions and limiting the rise in global average temperature to 1.5°C above the preindustrial level. The sustainable transition strategies typically consist of three major technological changes namely, energy savings on the demand side, generation efficiency at production level and fossil fuel substitution by various renewable energy sources and low carbon nuclear. For the transition remain technically and economically feasible and beneficial, policy initiatives are necessary to steer the global electricity transition towards a sustainable energy and electricity system. Large-scale renewable energy adoption should include measures to improve efficiency of existing nonrenewable sources which still have an important cost reduction and stabilization role. A resilient grid with advanced energy storage for storage and absorption of variable renewables should also be part of the transition strategies. From this study, it was noted that whereas sustainable development has social, economic, and environmental pillars, energy sustainability is best analysed by five-dimensional approach consisting of environmental, economic, social, technical, and institutional/political sustainability to determine resource sustainability. The energy transition requires new technology for maximum use of the abundant but intermittent renewable sources a sustainable mix with limited nonrenewable sources optimized to minimize cost and environmental impact but maintained quality, stability, and flexibility of an electricity supply system. Technologies needed for the transition are those that use conventional mitigation, negative emissions technologies which capture and sequester carbon emissions and finally technologies which alter the global atmospheric radiative energy budget to stabilize and reduce global average temperature. A sustainable electricity system needs facilitating technology, policy, strategies and infrastructure like smart grids, and models with an appropriate mix of both renewable and low carbon energy sources.

• The Paris Agreement of 2015 set targets to be realized to limit greenhouse gas emissions and related global warming with the objective of reducing greenhouse gas emissions and global average temperature rise.

• The cumulative effect of the Stockholm, Rio, and Johannesburg conferences made sustainable energy development (SED) a very important factor in the sustainable development.

• The energy transition seeks to transform the world order with respect to development and environment and particularly the use of energy in its many forms with priority to electricity.

• Sustainable energy transition should incorporate the three dimensions of sustainable development of social, environment and economic in addition to technical and political/institutional dimension.

• A sustainable global electricity transition will entail increased use of renewable energy sources particularly wind and solar, nuclear energy as a low carbon energy source, electrification of transport and thermal processes in industry, bioenergy, and waste to energy conversion, shift from coal and petroleum to natural gas, hydrogen as a fuel with low carbon footprint, increased energy efficiency.

• This transition can only take place successfully through collaboration between players locally and international with effective facilitating policy framework, facilitating infrastructure and technology development and adaptation, use of smart grids and various modelling and optimization facilities in decision support.

1 Introduction

Decarbonization of the global energy systems is one of the greatest and most important challenges facing man in the 21st Century. The energy sector is vital in tacking the climate change since it accounts for about two thirds of global carbon dioxide ( Quitzow, 2021 ). Energy in form of electricity and primary energy resources drive the prosperity of the world economy ( Quitzow, 2021 ). From the 1970s, the global gross domestic product (GDP) has grown by about 4.5 times, while the consumption of primary energy has grown from 155.22 EJ in 1965 to 556.63 EJ in the year 2020. The total proved energy reserves of the dominant fuels, i.e., oil, natural gas, and coal at the end of 2020 could last just 53.5 years for oil, 48.8 years for natural gas, and 139 years for coal ( BP, 2021 ). These fossil fuels account for 85% of the total primary energy consumption globally. The current era is faced with the challenge of global warming as the most prominent environmental issue thus reduction of carbon emissions is at the center of global environmental policy. It is therefore important to understand the relationship between economic development and energy consumption, and effectively improve energy efficiency for a better relationship and sustainable development ( Barasa Kabeyi and Olanrewaju, 2022 ; Jin et al., 2022 ). Electricity plays a very important role in modern economies as it provides a rising share of energy generation and consumption in all countries ( Solarin et al., 2021 ). Electricity demand is poised to increase further due to increasing household incomes, and electrification of transport and thermal energy applications as well as continues growth for digital connected devices and air conditioning ( International Energy Agency, 2019 ). Energy is a critical requirement for sustainable development and therefore optimum selection of low carbon and green energy sources remains a key objective for all nations ( Bhowmik et al., 2020 ). Electric power plays an important role in human life because all vital activities and operations today need electricity directly or indirectly ( Beaudin and Zareipour, 2015 ; Bayram and Ustun, 2017 ).

Electricity as a form of energy is extremely important for socioeconomic development. Global electricity generation stood at 4,114 GW in 2005 and increased to 5,699.3 GW in 2014 and it continues to grow annually. Fossil fuel-based electricity accounted for over 60% of this generation in 2014 and 42% of CO 2 . There is need to develop evaluation index system and models for sustainable electricity generation to sustainably cope with this ever growing demand ( Li et al., 2016 ). According to the emissions gap report, the total greenhouse gas emissions in 2018 was about 55.3 GtCO 2e of which 37.5 GtCO 2 were on account of fossil fuels combustion in various operations and activities including electricity generation [ United Nations Environmental Program(UNEP), 2019 ].

Energy sustainability or energy for sustainable development is a challenge for many countries developed and developing countries. There is need for a transition roadmap to renewable energy sources that may be unique to each country based on local resources and prevailing circumstances ( Iddrisu and Bhattacharyya, 2015 ). Energy transition is a reality for all nations because of the targets set in the Paris agreement. The global community is developing decarbonization plans aimed at reducing greenhouse gas emission in a sustainable manner ( Kabeyi and Olanrewaju, 2020b ). The process is unique to different countries because the transition is affected by local social and economic conditions. The complexity and comprehensiveness of the energy transition is influenced by the diversity of actors involved in their interests which are often in conflict with one another ( Krzywda et al., 2021 ). Electricity is a very important form of end-use energy, and it is a leading factor for economic growth and development. However, electricity generation is a leading source of greenhouse gas emissions which cause global warming and climate change which threatens sustainable development. This is because most of the global electricity is generated from fossil fuel sources of energy. Electricity accounts for a significant share of the three components that make up total energy production and consumption are electricity, transport, and heating ( Ritchie and Roser, 2021 ). The main challenges facing the electricity sector are the ever growing electricity demand, growing need to reduce greenhouse gas emissions and the need realize zero-net carbon emissions in power generation in line with the Paris Agreement which seeks to limit the increase in average global temperature to 1.5°C ( Colangelo et al., 2021 ). This calls for an energy transition from the fossil fuel dominated electricity mix to one dominated by renewable sources of energy and low carbon nuclear as well as clean fuel and conversion technologies ( Kabeyi and Olanrewaju, 2020b ; Kabeyi and Olanrewaju, 2021a ).

The world has so far witnessed three typical energy transitions. The first transition involved replacement of wood with coal as the main energy source. In the second transition, oil replaced coal as the dominant energy resource. In the third transition, there is global commitment to replace fossil fuels with renewable energy. As in 2018, 80% of the global energy was derived from fossil fuel energy resources with 36% being petroleum, 13.2% for coal, and 31% was from natural gas ( Lu et al., 2020 ). Energy transition refers changes undertaken in fundamental processes in charge of evolution of human societies that drive and are driven by technical, economic, and social changes ( Smil, 2010 ). It is a new path for economic development and innovation that does not compromise the environmental integrity and sustainability motivated by challenges caused by greenhouse gas emissions, climate change and natural resource depletion ( Mostafa, 2014 ). Energy transition consists of processes of structural changes to the subsystems of society which lead to greater sustainability in the society ( Barasa Kabeyi, 2019a ). Therefore energy transitions call for changes in existing policies, technology as well as supply and demand patterns for electricity and other energy resources ( Mostafa, 2014 ). The world is said to be undergoing a fourth energy transition today having witnessed three energy transitions in the past. The main objective of this fourth transition is to fight the global climate change through decarbonization of the energy supply and consumption patterns ( Mitrova and Melnikov, 2019 ). Therefore a sustainable energy transition system must be driven by the climate change agenda, technology developments and innovation, increased energy efficiency, competitive economies, enhanced energy security, development of affordable energy solutions and measures and modernization of the energy sector from traditional energy systems ( Smil, 2010 ; Mitrova and Melnikov, 2019 ). The International Renewable Energy Agency (IRA) defines energy transition as the pathway in the transformation of the global energy sector from fossil-dominated mix to zero-carbon by the second half of the 21st century ( Inglesi-Lotz, 2021 ).

The selection criteria for development sustainable energy transition should consider the environmental, technical, social, institutional, and economic dimensions of sustainability. While choosing or selecting energy sources for electricity generation, the choice of conversion technology and cost involved play a crucial role in modern economies and societies ( Bhowmik et al., 2020 ; Kabeyi and Olanrewaju, 2020b ). With continuous increase in global population and socio-economic activities leading to increased urbanization, and industrialization around the world, the demand for natural energy resources and more so renewable energy is gradually increasing ( Ebrahimi and Rahmani, 2019 ). It is notable that the world’s population has grown by 2.5 times since 1950, while energy demand over the same period has grown by 7 times ( Şengül et al., 2015 ). These increasing energy demand is predominantly met by fossil fuel combustion and nuclear power plants ( Tunc et al., 2012 ). With ever increasing energy demand, the related challenges are depletion of fossil fuel reserves, their price volatility, and global climate change which have attracted much attention to renewable energy sources and other low carbon and cheap sources of energy for power generation. As a result, many countries have adopted policies, strategic and operational measures to support the growth of renewable energy sources and other sustainable energy measures in the energy transition ( Ebrahimi and Rahmani, 2019 ).

Sustainable energy transitions require formulation of effective policies that promote the biomass resources, increased use of renewable and low carbon sources and penalize as well as discourage the use of fossil fuels and unsustainable natural resource use. Directing agricultural resources toward food production ( Andress et al., 2011 ). Renewable energy like solar, wind power, or hydropower can be used as viable options for generating electricity. Solar power plants, for example, could be constructed in countries with vast expanses of desert land. With developing countries like China having huge coal reserves and high electricity demand, coal fired power plants will continue to dominate electricity generation in these countries and options like clean coal technologies and carbon capture and sequestration are critical options. Production of hydrogen from coal is another strategy. For countries with high electricity demand, nuclear power generation is an option for reducing GHG emissions although with a danger of proliferation for politically unstable governments with weapons agenda. Large scale penetration of renewable energy requires development of advanced batteries, high efficiency conversion technologies, and stable and resilient grids to absorb variable renewable energy sources. Electrification of transport with most electricity coming from low carbon and green sources is another strategy for the sustainable energy transition ( Andress et al., 2011 ).

There are various strategies, measures and technologies that can be used to improve sustainability. They include energy efficiency, increasing the contribution of renewable energy in electricity generation, use of Carbon Capture and Storage (CCS) in fossil and biomass power plants, use of low carbon nuclear power, use of hydrogen in the transportation sector and reductions in the demand for energy and electrification as well as use of biofuels in transport services. The main challenges facing various options and technologies include lack of acceptance and behavioral changes as well as cost limitations and availability of cheap fossil fuels ( Hildingsson and Johansson, 2016 ).

1.1 Problem Statement

Most of the electricity generated globally is comes from fossil fuel-based power plants. These energy resources are generally expensive, scarce, exhaustible, polluting, and insecure since not all nations are endowed with the primary resources hence a source of energy insecurity, while the combustion of fossil fuels produces greenhouse gases like carbon dioxide (CO 2 ), Sulphur dioxide (SO 2 ), Nitrous oxides (NOx), which are the main causes of the global warming that is threatening the very existence of humanity and mother nature. This concern is the main motivation behind sustainable energy transition by increased use of renewable and low carbon clean energy sources especially solar, wind, biomass, hydro and nuclear. These renewable and low carbon sources improve and widen power supply, enhance long term access and utility in energy production, decrease dependence on fossil fuel, and reduce greenhouse gas emissions ( Rathor and Saxena, 2020a ; Nguyen et al., 2020 ).

Natural increases in CO 2 concentrations have historically been warming the Earth during ice age cycles for millions of years. These warm episodes are said to have started with slight increase in solar radiations reaching the Earth due to a slight wobble in Earth’s axis and path of rotation around the Sun that caused some notable warming. This phenomenon caused the warming of oceans leading to an increase in carbon dioxide (CO 2 ) emissions from the oceans. However, CO 2 concentration never exceeded 300 ppm during these periods that took place about a million years ago. Before the industrial revolution that started in of mid-1700s, the global average amount of carbon dioxide was about 280 ppm ( Lindsey, 2021 ). Figure 1 shows the historical growth of CO 2 emissions and concentration between 1750 and 2020.

FIGURE 1 . Concentration of carbon dioxide emissions between the year 1750 and 2020 ( Lidsey, 2020 ).

Figure 1 shows that the global CO 2 emissions remained constant between 1750 and about 1840 where they started to increase rapidly. The atmospheric concentration increased slightly between 1750 and 1960 before the rate increased between 1960 and the year 2020 mainly due to higher level of industrial activities and increasing use of fossil fuels. Therefore, it is the entry of fossil fuels in the energy mix that triggered rapid increase in CO 2 emissions as the level of industrialization developed.

Fossil fuels continue to dominate the current energy systems and therefore significantly contribute to the global carbon dioxide (CO2) and other greenhouse gases emissions to the atmosphere. To realize the global climate targets and avoid destructive climate change, there is need for a global transition in electricity generation, transmission, and distribution and as well as its consumption. Humanity must strike a balance between developmental needs and the environmental conservation and protection. The main challenges facing renewable energy sources is resource availability, resource access, resource location, security of supply, sustainability, and affordability ( Samaras et al., 2019 ). The growing demand for electricity has led to increased demand and consumption of fossil fuels and growing level of economic activities have contributed to growth of the greenhouse gas emissions and consequently, global warming ( Wang, 2019 ). The transition challenges are further compounded by the fact that efforts to promote more sustainable, more resilient, and equitable energy disrupts economic, political, and institutional relationships. As a result, issues of power and politics are now central themes in sustainability transition in energy sectors ( Lenhart and Fox, 2021 ).

This study examined sustainability in energy and particularly electricity generation systems and the challenges and opportunities of sustainability. The overall objective was to lay a framework for a sustainable transition to a green and low carbon electricity grid system as a contribution to the global effort to fight the climate change and greenhouse gas emissions. Various pathways to sustainable electricity generation are examined and proposals made on a feasible roadmap to a sustainable energy transition, particularly grid electricity generation, transmission, distribution, and consumption. The transition acknowledges the significance of nonrenewable sources and their main challenges of intermittence and variability as the global community seeks to transition to green energy sources. Using a critical discourse analysis, the study attempts to develop a roadmap that can be adopted by nations based on their local conditions to sustainably transition their electricity production and supply. Of particular concern is how the available energy sources can be used to realize the Paris targets without compromising the socio-economic and environmental set up and hence achieve sustainable energy transition.

1.2 Rationale of the Study

The Paris Agreement of the 21st UNFCCC Conference of Parties (COP21) of 2015 seeks to limit average global temperature increase below 2°C above pre-industrial levels look for measures to limit the average temperature rise to 1.5°C the pre-industrial temperature. This calls for drastic measures to reduce anthropogenic emissions and removals by sinks of greenhouse gases by second half of 21st century ( Lawrence et al., 2018 ). Studies have shown that the climate is changing mostly because of the anthropogenic activities. The report by Intergovernmental Panel on Climate Change (IPCC) for 2021 indicates that several climate changes are already irreversible but adds that we still have hope for the future if action is taken. To mitigate further changes ( Inglesi-Lotz, 2021 ). The climate is very important to man and other living organisms on the planet, yet there is overwhelming evidence that the world is facing changing climatic conditions due to the greenhouse effect as demonstrated by the increase in average global temperature, high incidents of climate related issues like drought, storms and desertification ( Wallington et al., 2004 ). The global anthropogenic activities have led to about 1°C rise in average global temperature above prehistoric level and is further projected to reach 1.5°C between the year 2030 and 2052 if current greenhouse gas emission rates are maintained ( Fawzy et al., 2020 ).

Electricity generation accounts for about 26% of total greenhouse gas emissions making it an important target for emissions control in the war against climate change ( Kabeyi and Oludolapo, 2020a ). The Intergovernmental Panel on Climate Change (IPCC) sought to stabilize the atmospheric air carbon concentration with a target to limit concentration to 350 ppm for CO 2 while maintaining temperature rise of 2° C above the preindustrial level, a target that was ratified by many nations globally. This calls for limitation in the consumption of fossil fuels particularly in electricity generation and transport industries through substitution with renewable energy sources and electrification of transport among other measures. This calls for massive expansion in power generation capacity using renewable energy and low carbon energy sources ( Burger et al., 2012 ). The future of humanity as defined by the sustainable development goals in the face of climate change has made sustainability the concern for all major systems including energy or electricity generation, supply and consumption systems ( Vine, 2019 ). There is need for a shift from current dependence on fossil fuels for power generation, transport, and thermal applications ( Burger et al., 2012 ).

The global greenhouse gas emissions can be presented based on economic activities that lead to their production and emission. Greenhouse gases are mainly released by electricity and heat generation in the energy and related sectors, manufacturing activities, industrial operations, transportation, agriculture and forestry as well as the building industry ( Marcus, 1992 ). The sources of greenhouse gases can be classified into five economic sectors. These sectors are energy, industry, transport, buildings and AFOLU, i.e., agriculture, forestry, and other land uses ( Lamb et al., 2021 ). In Figure 4 below, the greenhouse gas emissions by sector are presented for the years 1990–2018 for the entire world and across 10 ten global regions, namely Asia pacific, Africa, East Asia, Eurasia, Europe, Latin America, Middle east, North America, South Asia, and Southeast Asia. Figure 2 below shows the contribution of greenhouse gases by five economic sectors.

FIGURE 2 . Greenhouse gas contribution by economic sector ( Boden et al., 2017 ; Lamb et al., 2021 ).

From Figure 2 , it is noted that the energy sector inn form of electricity and heat production is the largest contributor of green house gases with about 34%, industry at 24% followed by agriculture, forestry and other land activities accounting for 21%, transportation with 14%, while buildings contributed about 6% while the building sector is least with 6% in 2018 ( Lamb et al., 2021 ). Figure 2 further demonstrates that for the African region, most emissions.

The greenhouse gas emissions (GHG) for 2018 were about 11% (5.8 GtCO 2 eq) higher than GHG emission levels in 2010 (51.8 GtCO 2 eq). The energy sector accounted for close to 1/3rd of the increase in GHG emissions between 2010 and 2018 of about 1.9 GtCO 2 eq, followed by industrial sector with 1.8 GtCO 2 eq which was about 30% of the increase, then the transport accounted for 1.2 GtCO 2 eq or 20% of the increase. Emissions that came from AFOLU increased by about 0.72 GtCO 2 eq equivalent to 12% increase while the buildings sector recorded the lowest increase in emissions with about 0.22 GtCO 2 eq, or 4% ( Lamb et al., 2021 ).

A sustainable energy transition should address the energy sources, energy conversion, transmission, and consumption especially the leading sectors in energy consumptions like heat and power production, transport related activities including fuel use and conversion. These measures include a shift from fossil fuel sources to renewable and low carbon sources, efficient conversion technologies, electrification of transport with most electricity coming from renewable resources, energy conservation measures and elimination of unnecessary energy demand and consumption.

Energy is far much more than just the technical infrastructure. It is through the energy transition that we realize emergence of innovative business models and organization that drives the establishment of new practices and procedures, and new ways of life, reassign responsibilities, reorganize governance, and redistributes power structure. It is for these reasons that the sustainable energy transition calls for consideration of the social, technical, economic, political, and institutional dimensions of sustainability in addressing challenges of the energy sector in order to sustainably shift to a low-carbon economy and electricity systems which is the main focus of this research ( Quitzow, 2021 ).

2 Methodology and Novelity of the Study

In this study, low-carbon energy transitions options and strategies are considered governed and proposed in line with broader sustainability goals and requirements as specified by the dimensions of sustainability. The study sought to identify conflicts and synergies between low-carbon strategies and the attainment of both short term and longer-term environmental, economic, technical, social, and institutional objectives. The research framework is organized across the five dimensions of sustainable energy and specifically electricity development which are environmental, economic dimensions, social aspects, technical dimensions, and institutional, political dimensions. The study adopted secondary method of data collection and analysis from recent primary and secondary data found in original research findings and reports from credible peer reviewed sources. This would facilitate the voice of the common people, professional, experts, and authorities as well as governments for a cleaner global future. For this research, the term primary data refers to the data originated and carried out and presented as peer reviewed academic and professional papers and reports through personal interviews with the expert team or analysis based on primary data and presented as original reports or peer reviewed journal article. Therefore, this study is a review of the energy sustainable transitions globally. Published literature in the form of technical reports, peer reviewed journals and conference papers were reviewed by the authors. The study is a survey using credible literature from peer reviewed journals papers and energy data from various authorities globally.

Most studies on sustainable energy transition are narrow in scope as they tend to concentrate on the environmental dimension of sustainability. Researchers that look at sustainability more wholistically also tend to concentrate on the three pillars of sustainability, namely economic, environmental, and social dimensions of sustainability ( Kabeyi, 2019a ; Barasa Kabeyi, 2019b ; Krzywda et al., 2021 ). Past reviews also concentrate on energy sustainability in general. However, in this study, the focus is electricity as a secondary form of energy derived from primary sources of energy like wind, solar, hydro, nuclear, coal, and gas through indirect conversion through a generator or direct conversion as in fuel cells and solar photovoltaics.

In most studies undertaken on energy transitions, the focus has been on energy technologies and sources with main objective being minimizing emissions. Others have gone further to address variability and intermittence and to rank sources in order of potential within the framework of the three pillars of sustainability. This study is unique as it looks at technical and institutional dimensions in addition to the economic, social, and environmental and hence the role of energy storage and electrification of transport which induces additional variability to demand side. The study also brings into focus the role of the smart grid in managing the dynamic nature of electricity demand and supply in decentralized generation and with the intermittence and variability of wind and solar. The study therefore recognizes that social foundations and human behaviors have a significant role to play in the future sustainability of the energy sector ( Inglesi-Lotz, 2021 ). Therefore, the study pays attention and extensively analyses to energy and electricity models and modelling tools that wholistically considers sustainability in the energy sector and electricity systems.

3 Greenhouse Gas Emissions and Their Environmental Impacts

Greenhouse effect refers to a natural process that has taken place over millions of years but was first discovered by Jean Baptiste-Joseph de Fourier in 1827 ( Wallington et al., 2004 ; Wang, 2019 ). Greenhouse gas effect is the long-term increase in the temperature of the planet Earth as a result of accumulation of greenhouse gases in the atmosphere ( İpek Tunç et al., 2007 ). The discovery of greenhouse effect was demonstrated experimentally by John Tyndall in 1861 and quantified in 1896 by Svante Arrhenius. In the work of Svante Arrhenius, the author observed that the release of large amounts of CO 2 emissions from the combustion of fossil and doubling of atmospheric CO 2 concentration warmed the Earth by 5–6°C, as compared to current climate models which predict a 1.5–4.5°C rise by doubling the concentration of CO 2 ( Kabeyi and Oludolapo, 2020a ; Kabeyi and Oludolapo, 2020b ). Greenhouse gas effect results from the interaction between solar energy and greenhouse gases in the atmosphere. The work of Roger Revelle and Hans Suess in 1957, remarked that the build-up of carbon dioxide in the atmosphere constituted a large-scale geophysical experiment whose consequences were unknown and so should be monitored and controlled. As a result, the year 1958 was designated as the International Geophysical Year. This marked the beginning of the ongoing program of continuous measurements of atmospheric CO 2 levels at Mauna Loa, Hawaii, in the United States by Charles Keeling. This measurement demonstrated that the levels of carbon dioxide were rising steadily from 315 ppm in 1958 to 370 ppm in 2001 ( Wallington et al., 2004 ).

The global climate change is one of the leading challenges facing humanity today ( del RíoJaneiro, 2016 ). This is because the climate has been changing over time with manifestations like the global increase in average temperature, rising sea level, heat waves, several incidents of flooding, both stronger and frequent ocean waves, and drought in many parts of the world ( Intergovernmental Panel on Climate Change(IPCC), 2007 ; Butt et al., 2012 ). The United Nations Framework Convention on climate change, attributes these directly or indirectly to human activities that change the atmospheric composition leading variation in the natural climate as observed over a long period of time. There has always been evidence that the global climate has been changing since the beginning of creation, but the current rate is alarming with several consequences already being witnessed today.

Greenhouse gases like carbon dioxide (CO 2 ) can absorb and radiate thermal energy. It is this greenhouse effect that warms the Earth and keeps its average annual temperature above the freezing point which implies that normal global warming maintains life and so is necessary ( Lindsey, 2021 ). Although carbon dioxide (CO 2 ) is less potent than methane and nitrous oxide, it is more abundant and stays longer in the atmosphere thereby making it more significant. It is for this reason that the increase in atmospheric carbon dioxide is responsible for about two-thirds of the total energy imbalance and temperature rise. Additionally, carbon dioxide has a negative impact to the sea water because when dissolved in ocean water, CO 2 reacts with water molecules to produce carbonic acid which lowers the PH of the ocean water. It is for this reason that the PH of the ocean’s water has reduced from 8.21 to 8.10 since the beginning of the industrial revolution. This is quite significant because a drop by 0.1 in PH causes about 30% increase in acidity of the ocean. The biological effect of ocean acidification is interference with marine life’s ability to extract calcium from the water to build their shells and skeletons ( Lindsey, 2021 ).

The global atmospheric of carbon dioxide (CO 2 ) has been increasing particularly on the account of fossil fuel combustion in powerplants, transport and several industrial processes. This is not sustainable because the fossil fuels took many millions of years to form, only to be returned to the atmosphere in just few years, hence their lack of renewability [ United Nations Economic and Social Commission (ESCAP), 2016 ]. It is estimated that the last time the atmospheric CO₂ amounts were relatively higher was about 3 million years ago, when temperature was 2–3°C (3.6–5.4°F) above the pre-industrial era, and the sea level was 15–25 m (50–80 feet) higher than it is today ( Lindsey, 2021 ). Industrialization is the main cause for the steady rise in the concentration of carbon dioxide between 1970 and 2020 because of the use of fossil fuels in transportation, industry, and power generation. This trend is demonstrated in Figure 3 .

FIGURE 3 . Changes in carbon dioxide concentration between 1970 and 2020 ( Lindsey, 2021 ).

From Figure 3 , it is noted that the concentration of atmospheric carbon dioxide has increased steadily from about 328 ppm in 1970 to 412.5 ppm in 2020 up from 409.8 ppm in 2019 having increased steadily from the value of 328 in 1970. The annual rate of increase in CO 2 in the atmosphere is about 100 times faster than previous natural increases over the past 60 years, e.g., last ice age 11,000–17,000 years ago. Additionally, the ocean has absorbed enough carbon dioxide to lower its pH by 0.1 units causing a 30% increase in ocean acidity ( Lindsey, 2021 ). Although the concentration dropped in 2020, global energy-related CO 2 emissions stood 31.5 Gt, which contributed to CO 2 that made atmospheric concentration reach about 50% higher than it was at the beginning of the industrial revolution ( International Energy Agency, 2021a ).

3.1 Greenhouse Gases in Power Generation

Electricity and heat generation is a leading source of CO 2 emissions and they generated 13 billion tons of CO 2 emissions accounting for 41% of all CO 2 emissions coming from fuel combustion globally in 2017. This was due to the use of fossil fuels to generate about 16,947 TWhrs of electricity representing 63% of the total electricity generation ( Solarin et al., 2021 ) At the global scale, the key greenhouse gases emitted by human activities are carbon dioxide, methane, nitrous oxide, and F gases. Energy supply is the largest contributor to global greenhouse gas emissions. About 35% of total anthropogenic GHG emissions in 2010 originated in the energy sector. The global annual growth in greenhouse gas emissions from energy supply sector increased from 1.7% per year in 1990–2000 to 3.1% in 2000–2010 mainly due to faster economic growth which increase demand for heat and electricity consumption. Most of these heat and power demand is met by fossil fuel sources of energy ( Bruckner et al., 2014a ).

3.1.1 Carbon Dioxide (CO 2 )

The Natural increases in CO 2 concentrations have been warming the Earth over time with increase in temperature during ice age cycles over millions of years. These warm episodes or interglacial started with a small increase in sunlight when the Earth had a tiny wobble in its axis of rotation around the Sun. This event led to some warming of the Earth’s surface and oceans causing increased release of carbon dioxide. The extra CO 2 in the atmosphere only magnified the initial natural warming. Among the anthropogenic greenhouse gases, CO 2 is responsible for about 60% of the greenhouse gas effect ( İpek Tunç et al., 2007 ). With the industrial revolution, manmade sources have become significant sources of atmospheric carbon dioxide through activities like fossil fuel combustion for power generation, transportation, industrial as well as domestic activities ( Lindsey, 2021 ). Other leading sources are industrial chemical reactions and operations like cement production. Carbon dioxide is mainly removed from the atmosphere or sequestration through photosynthesis [ United States Environmental Protection Agency (EPA), 2017 ]. When carbon dioxide is heated, it absorbs and radiates heat in the form of thermal infrared energy. This radiation has the positive side because without it, the annual average temperature would be just close to 60°F. However, with the rapid increase in greenhouse gas emission, additional heat has been trapped leading to raising planet Earth’s average temperature above the pre-industrial level.

3.1.2 Methane (CH 4 )

Methane is generated from various natural and artificial processes like anerobic digestion and during the production and transport of fossil fuels like coal, natural gas, and oil [ United States Environmental Protection Agency (EPA), 2017 ]. Therefore, methane is added to the atmosphere through natural and anthropogenic sources, with 30% of the methane flux originating from natural sources while about 70% is contributed by anthropogenic sources ( Wallington et al., 2004 ).

3.1.3 Nitrous Oxide (N 2 O)

Food production particularly the use of fertilizers is the primary source of N 2 O emissions. As well as fossil fuel combustion in power generation, industry, and transportation as a product of combustion and wastewater treatment process ( Viet et al., 2020 ). Nitrous oxide (N 2 O) is the third most abundant well mixed greenhouse gas after CO 2 and CH 4 with a life span of about 130 years. The natural sources of N 2 O come from soils and the oceans. Anthropogenic emissions originate from biomass combustion, fossil fuel combustion, and industrial production of adipic and nitric acids, and nitrogen fertilizer use in agriculture ( Wallington et al., 2004 ).

3.1.4 F Gases

The F gases result from industrial processes, refrigeration systems, and the use of some consumer products associated with emissions of F-gases. These gases include hydro fluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF 6 ). Hydro fluorocarbons, perfluorocarbons, sulfur hexafluoride, and nitrogen trifluoride are synthetic, and come from industrial processes. These Fluorinated gases are occasionally used as substitutes for ozone-depleting substances , e.g., chlorofluorocarbons, hydro chlorofluorocarbons, and halons. These gases have high global warming potential gases even though they are released in small quantities [ United States Environmental Protection Agency (EPA), 2017 ].

Figure 4 below shows the global composition of the greenhouse gases in the atmosphere ( Lamb et al., 2021 ).

FIGURE 4 . Global greenhouse gas emissions by gas ( Boden et al., 2017 ).

From Figure 4 , it is noted that carbon dioxide remains the dominant greenhouse gas with most of it coming from fossil fuel combustion in industry, heat, and power generation which accounts for 65% of global emissions. Other sources of carbon dioxide are agriculture and forestry related activities which contribute 11% of the greenhouse gas emission in form of CO 2 . Methane is the second largest greenhouse gas accounting for 16% of greenhouse gas emissions, followed by nitrous oxide and F-gases respectively with 6 and 2% contribution respectively.

The global average CO 2 concentration in 2018 was about 407.4 ppm with uncertainty of + and −0.1 ppm. Today, carbon dioxide levels are the highest over the past 800,000 years ( Lindsey, 2021 ). Over 400 billion metric tons of carbon dioxide has been released to the atmosphere from fossil fuels combustion and cement production since the year 1751, of which about 200 billion metric tons originate from fossil fuel combustion since the late 1980s.

In 2014, the global carbon emissions to the atmosphere were about 36 billion tons, which is approximately 1.6 times the 1990s rates, an increase which has been associated with average global temperature rises ( Gamil et al., 2020 ). Close to 9,855 million metric tons of fossil-fuel based carbon dioxide emissions were emitted between 2013 and 2014, representing an increase of 0.8%. Liquid and solid fuels accounted for 75.1% of the global carbon emissions from fossil-fuel burning and cement production in 2014. Gaseous fuel accounted for 18.5% of the emissions which is about 1,823 million metric tons of carbon emissions from fossil fuels in 2014. In 2014, emissions from cement production were 568 million metric tons of carbon indicating, which shows a more than double increase in the last decade to represent 5.8% of global CO 2 emissions from fossil-fuel burning and cement production. Emissions from gas flaring, which accounted for about 2% of global emissions during the 1970s, reduced to less than 1% of global carbon emissions from fossil-fuel ( Boden et al., 2017 ). These statistics show that fossil fuel combustion which mainly comes from power generation and cement production in the manufacturing industry are leading polluters of the atmosphere in terms of carbon emissions.

3.2 Global Warming/Greenhouse Effect

Global warming is the effect of the imbalance between the heat received by the Earth and, the heat reradiated to the space. Terrestrial longwave radiative flux is emitted by the Earth’s surface beyond the 3–100 µm wavelength range while the surface incoming radiation is shortwave solar radiation also called global irradiance or solar surface irradiance. This is the radiation flux density reaching a horizontal unit of Earth surface in the 0.2–3 µm wavelength range ( Ming et al., 2014 ). Global warming refers to the process which leads to the average rise in the Earth’s temperature and that of the atmospheric layers close to Earth because of human activities. Climate change on the other hand is the phenomenon where other climatic factors change due to global warming. Any slight increase in the ocean temperature causes hydrological events which effectively change the physical and chemical characteristics of the water. Aquatic life is affected by change in water as it affects their life cycle, physiology, and behaviors ( Ninawe et al., 2018 ).

Global warming potential (GWP) is a measure of how much a given mass of a chemical substance adds to global warming over a specified time. It refers to the ratio of the warming caused by a substance to the warming caused by a similar mass of carbon dioxide. These therefore allocates 1 as the global warming potential of carbon dioxide. Water has the lowest global warming potential of 0, while Chlorofluorocarbon-12 has a high global warming potential of 8,500. Chlorofluorocarbon-11 has GWP of 5,000. Several hydrochlorofluorocarbons and hydrofluorocarbons have GWP potentials varying between 93 and 12,100 based on a 100-years period ( Demirel and Demirel, 2014 ). The three-time scales used to compute the GWP are 20, 100 or 500 years respectively. The main greenhouse gases from fossil fuel combustion are nitrous oxide (N 2 O), methane (CH 4 ) and carbon dioxide (CO 2 ). The value of the three main greenhouse gases varies in GWP for the time scales used in evaluation, i.e., 20, 100, and 500 years. The GWP of CO 2 is used as a reference in the computation of the relative GWP of other gases ( MacLeod et al., 2011 ; Demirel and Demirel, 2014 ). Table 1 below shows the relative global warming potential (GWP) for water, carbon dioxide, methane and nitrous oxide based on the 20-, 100- and 500-years’ time scale.

TABLE 1 . Global warming potential for various substances/gases ( MacLeod et al., 2011 ; Demirel and Demirel, 2014 ).

From Table 1 , it is noted that the global warming potential of the major greenhouse gases various in value over the three timescales. It shows that N 2 O has the highest individual and average GWP followed by methane and carbon dioxide while water has no global warming potential.

Carbon dioxide accounts for about 60% of the anthropogenic greenhouse gases which are the cause the greenhouse gas effect with use of fossil fuels especially in power being cited as the major cause ( İpek Tunç et al., 2007 ; Tunc et al., 2012 ). The global increase in carbon emissions was about 1.4 ppm before 1995 but thereafter increased to 2.0 ppm ( Owusu and Asumadu-Sarkodie, 2016 ). Carbon dioxide concentration has grown from 277 ppm in 1750 to 397 ppm in 2014 representing about 43% and peaked at 400 ppm between March and December 2015 ( Berga, 2016 ). According to Moriarty and Honnery (2019) and Lindsey (2021) , the concentration of CO 2 in the atmosphere passed 407 ppm in 2018 with energy sector emerging as the largest emitter of the greenhouse gases ( Intergovernmental Panel o, 2007 ; Butt et al., 2012 ; Berga, 2016 ; Owusu and Asumadu-Sarkodie, 2016 ). In 2010, the energy supply sector contributed 35% of all the anthropogenic greenhouse gas emissions realized. The emissions increased at average rate of 1.7% between 1990 and 2000 which increased to average of 3.1% between 2000 and 2010 on account of rapid economic growth experienced due to increased use of coal in the energy mix ( Sagan, 2011 ). Fossil fuel sources like coal, heavy fuel oil and natural gas used in power generation are significant sources of greenhouse gases ( Butt et al., 2012 ), yet fossil fuels inform of gas and coal account for over 60% of global electricity generation ( International Energy Agency, 2018 ).

With the increase in energy demand and continuous use of fossil fuels in power generation, a 62% increase in CO 2 emissions is expected between 2011 and 2050 with two thirds of these emissions coming from China and India ( Butt et al., 2012 ). It is for this reason that the Intergovernmental panel on climate change (IPCC) recommended that greenhouse gas emissions should be reduced by 50–80% by the year 2050 to avoid serious consequences of global warming, ( Butt et al., 2012 ). Among the potential consequences are more frequent extreme weather events like heat waves, storms, flooding and droughts, stress due to higher temperatures for plants and humans, rising sea level, and altering occurrence of pathogenic organisms ( Streimikienea et al., 2012 ).

3.3 Other Impacts of Greenhouse Gas Emissions

Besides global warming, some gaseous emissions have other significant negative impacts to the global and local environment. They include contamination of air by pollutants like Sulphur oxides, nitrogen oxides, particulate matter, and volatile organic compounds, which are released into the atmosphere by the combustion of fossil fuels in power plants, vehicles exhausts, industry, and building and equipment. Whereas some pollutants harm human health directly, others lead to atmospheric chemical reactions that yield harmful conditions like depletion of ozone layer besides global warming. This pollution can be controlled or limited through fuel substitution and conversion technologies that are less polluting ( United States Department, 2015 ). For example, power plants should be equipped with pollution monitoring and control systems like desulphurization systems, carbon capture systems and fuel substitution technologies.

The rise in sea level and its acidification is another threat to the global environment and mankind. GHG emissions in the atmosphere lead to changes include sea-level rise, and an increase in the frequency and intensity of certain extreme weather events like drought and storms. Carbon dioxide is also by the oceans, leading to ocean acidification. The solution is increased use of nonpolluting energy sources, carbon capture and energy efficiency measures ( Nag, 2008 ; United States Department, 2015 ; Kabeyi and Olanrewaju, 2020b ).

4 Global Electricity Generation

The ever-growing electricity demand is the main reason for growth in global CO 2 emissions from electricity which have now reached a record high. The commercial availability of low emissions generation technologies and energy sources has placed electricity at the center of the global effort to combat climate change and pollution. Decarbonization of electricity has a significant potential to provide a platform for CO 2 emissions reduction by means of increased use of electricity-based fuels such as hydrogen and biofuels. Renewable energy sources and efficiency in resource use and generation has a special role to play in increasing access to electricity globally ( International Energy Agency, 2019 ).

The shift and growth in electricity demand adopts two distinct global routes or paths. For most developed countries, demand growth is linked to increasing digitalization and electrification which is largely offset by energy efficiency measures and improvements in process energy efficiency. For the developing countries like China and India, the reasons for growing electricity demand are the growing incomes and better quality of life, industrialization, and growing services sector. It is also worth noting that the developed countries account for about 90% of global electricity demand growth, and the trend may remain so until the year 2040 ( International Energy Agency, 2019 ).

Today, Industry and building sectors are the main users of electricity accounting for over 90% of global electricity demand. Moving forward, the main drivers of electricity demand growth are motors in industry which may account for over 30% of the total growth to 2040. It is projected that industrial and domestic space cooling will account for 17% while large electrical appliances are projected to account for 10% growth while electric vehicles are projected to account for 10% growth in electricity demand. Further growth in electricity demand of about 2% is projected to come from provision of electricity access to 530 million first time users of electricity. The Sustainable Development Scenario, projects that electric vehicles will become a leading source of electricity demand moving to the future towards the year 2040 ( International Energy Agency, 2019 ).

The global energy demand and supply has been growing with supply increase of about 60% between 1990 and 2016 when supply hit 568 EJ. The international bunkers was 16.3 EJ in 2016 accounting for 3% of global total energy supply and was marked by a double growth since 1990, an indication of growing activity and hence energy consumption internationally [ United Nations(UN), 2019 ]. The global electricity generation more than doubled between 1990 and 2016, to reach about 25,000 TWh. Between 1990 and 2016, the largest absolute growth in terms of energy sources came from coal with about 5,300 TWh representing +116% growth. Natural gas supply reached 3,500 TWh representing a growth of +213%.

Renewable sources of energy represented by mainly solar, wind grew by +2,224% or 1,370 TWh over the same period. This was the fastest growth recorded for renewable sources of energy. However, over 75% of electricity in 2016 came from non-renewable sources, mainly from thermal energy accounting for 65% or 16,186 TWh and nuclear 10% or 2,608 TWh. On the positive note, between 2000 and 2016, 50% of new electricity generating capacity came from renewable energy sources [ United Nations(UN), 2019 ; Wanga et al., 2020 ]. Figure 5 below shows the changes in total energy supply between 1971 and 2019.

FIGURE 5 . World total energy supply between 1971 and 2019 ( United Nations, 2019a ; International Energy Agency, 2021b ).

From Figure 5 above, it is noted that between 1971 and 2019, the proportionate composition of primary energy mix has been changing. The total primary energy consumption increased from 254 EJ in 1973 to 606 EJ in 2019. Biofuels and wastes reduced from 10.5% in 1973 to 9.3% in 2019. Coal consumption increased from 24.7% of total primary energy consumption to 26.8% in 2019. Oil reduced from 46.2% in 1973 to 30.9% in 2019. Natural gas increased from 16.2% of consumption in 1973 to 23.1%. Nuclear increased from 0.9 to 5% while hydro increased from 1.8 to 2.5% of total primary energy consumption in 2019 ( International Energy Agency, 2021b ).

Fossil fuels generated 61% of global in the year 2020 while combined nuclear, wind and solar accounted for 35% of global electricity generation in the year. Solar energy also surpassed oil in global electricity generation 2020 where solar accounted for 3.2% compared to oil that contributed 2.8% of global electricity generation for the year 2020 ( World Energy Data, 2021 ). Figure 6 below shows global electricity generation from different sources for the year 2020.

FIGURE 6 . World electricity generation by source for 2020 ( BP, 2021 ).

From Figure 6 , it is noted that for the year 2020, fossil fuels contributed 61.3% of global electricity production, 35.2% was on account of combination of nuclear, hydro, and solar, other renewable s accounted for 2.6% while other sources accounted for 0.9%. Coal contributed 35.1% of global electricity while gas accounted for 23.4% of global electricity.

5 Sustainable Energy Development

The road to a sustainable energy future has twin challenges of energy access and mitigation of global warming by control of greenhouse gas emissions ( Kaygusuz, 2012 ). Energy is at the center of several Sustainable Development Goals. They include expansion of electricity access, improving clean cooking fuels, curbing pollution, and reducing wasteful energy subsidies. Goal number 7 also referred to as SDG 7–aims to ensure access to reliable, affordable and modern energy for all by the end of the next decade ( Birol, 2021 ). The global adoption of energy specific sustainable development goals was an important milestone towards a more sustainable and equitable society. Although energy must be at the heart of efforts to lead the world to a more sustainable pathway, the current and planned policies fall well short of realizing the critical energy-related sustainable development targets. On the positive note, there is tremendous progress in delivering universal electricity access (SDG 7.1.1) for Asia and parts of sub-Saharan Africa ( Birol, 2021 ). As in the year 2012, about 1.4 billion people globally had no access to electricity of which 85% are based in rural areas. It is projected that by the year 20130, about 2.8 billion people globally will be relying on traditional forms of energy mainly biomass, which is an increase from 2.7 billion people in the year 2012 ( Kaygusuz, 2012 ), where the number of people without access to electricity declined to 1.1 billion in 2016, from about 1.7 billion in the year 2000. However, it is projected that more than 670 million people will still have no access to electricity in 2030. Therefore a lot more remains to be done in terms of electricity access ( Birol, 2021 ).

Lack of access to affordable electricity and reliance on the inefficient and unsustainable traditional energy like fuelwood, charcoal, agricultural waste, and animal dung) are a clear manifestation as well as an indicator of poverty. Modern energy sources and electricity plays an important role in socio-economic development ( Tracey and Anne, 2008 ; Kaygusuz, 2012 ). Reliable electricity and light lengthen the day activities hence provide extra hours for economic activities. Positive contribution of electricity includes saving women and children from exposure to poisonous smoke and long hours of looking for firewood. Hospitals can better sterilise instruments and store medicines in refrigerators. Electricity improves manufacturing and service enterprises by extending the quality and range of their products hence creating more jobs and higher wage ( Kaygusuz, 2012 ).

5.1 Sustainable Development

There is need to eliminate energy poverty to achieve the Millennium Development Goals but in a way that takes the world away from dependence on the fossil fuels to avoid global warming by moving rapidly towards a green economy ( Vezzoli Vezzoliet al., 2018 ) . The three interlinked objectives that must be achieved by the year 2030 to realise sustainable energy for all are ensuring universal access to modern energy services, double the share of renewable energy in the global energy mix and double the rate of energy efficiency improvement ( Kaygusuz, 2012 ; Vezzoli Vezzoliet al., 2018 ).

Philosophers, economists and scientists introduced the closely related concepts of sustainable development and sustainability in the 18th, 19th, and early 20th centuries ( Seghezzo, 2009 ). Sustainable development can further be defined socio-economic growth that delivers the traditional positive progress and targets in an ecologically acceptable manner and with due regard of the future generations’ welfare and rights to the same ( Kabeyi and Olanrewaju, 2020b ; Kabeyi and Oludolapo, 2021a ). Sustainable is defined as sustained growth, or sustained change or can also be defined simply as development that is successful ( Lélé, 1991 ). Sustainability is necessary in energy and other resources exploitation so as man exploits resources to meet his ever-growing energy demand, he does not compromise the ability of future generations to meet their own energy needs and a stable environment ( Broman and Robèrt, 2017 ; Kabeyi and Olanrewaju, 2020b ). Because of these requirement and expectations, society must strike a balance between economic growth and the social wellbeing of the society as a whole, now and in future to realize sustainability, which is a technical, political and economic challenge ( Dyllick and Hockerts, 2002 ). Therefore, the concepts of sustainable development and sustainability has the objective of achieving economic advancement and progress while at the same time conserve the value and integrity of the environment. This calls for a tradeoff between environmental sustainability goals and economic development objectives and targets ( Emas, 2015 ).

The publication of Carson’s book called “Silent Spring” in 1962 was used as the starting point of the global concern over proper use of natural resources. This can be demonstrated by what emerged 10 years later in 1972 as the “Club of Rome” that styled itself as an independent analysts and think tank who later published a book called “The Limits to Growth” ( Jacobs et al., 1987 ; Intergovernmental Panel o, 2007 ; Akella et al., 2009 ). In this book, the authors observed that if the global economy and population grew unchecked, the planet Earth’s natural resources would approach depletion at a point in future. These narrative led to the formation of the UN “World Commission on Development and Environment”, also called the Brundtland Commission, named after its chair, Gro Harlem Brundtland, who was a former Norwegian Prime Minister ( Seghezzo, 2009 ; University of Alberta, 2021 ). The “Brundtland Commission” released its final report that was entitled, “Our Common Future” 4 years later that defined sustainable development. The report defined sustainable development as a positive change that meets the needs of the present generation without compromising the ability of future generations to meet their own needs in future ( World Commission on Envir, 1987 ; University of Alberta, 2021 ). Therefore the concept of sustainable development is more concerned with whether what is acceptable today and is acceptable or not acceptable to the next generation ( Jonathan, 2001 ). Today, the strategies for sustainable development aim at promoting harmony and wellbeing among human beings and between humanity and Mother nature. Obviously, energy especially in the form of electricity has a central role in any effort to achieve sustainable development. From the use of wastes by industry to generate power and stabilize the grid, and conversion of polluting and eye soring slaughterhouse waste to clean electricity and create jobs keeping humanity clean and healthy fee of diseases, poverty, and physical harm ( Kabeyi and Olanrewaju, 2021b ; Kabeyi and Olanrewaju, 2021c ; Kabeyi and Olanrewaju, 2021d ; Kabeyi and Olanrewaju, 2021e ).

Sustainable development and the concept of sustainability calls for integration of economic benefits, social considerations and progress with environmental protection and considerations for maximum positive outcome ( Mohamad and Anuge, 2021 ). The United Nations General Assembly in 2015 adopted the 2030 Agenda for sustainable development which as a framework of 17 sustainable development goals (SDGs). This agenda calls for sustainable development which recognizes need to reduce poverty and guarantee equity and integrity of the entire global human community. These 2030 agenda calls for member countries to protect the planet Earth from further degradation by taking sustainability measures which include sustainable resource production and consumption, and sustainable management and conservation of the Earth’s natural resources and prevent climate change ( United States Department, 2015 ; Kabeyi and Oludolapo, 2020a ).

There is inherent interdependence between environmental stability and the economy which then lays a strong foundation for sustainable development ( Emas, 2015 ). There is however need for public policy that promotes investment in economic and industrial activities that seek to protect the natural environment, promote human, and social capital, and prevent the damage caused by pollution, social clashes, resource waste, and greenhouse gas emissions which are both indicators and effects of unsustainable practices ( United States Department, 2015 ). Fortunately, policies that seek to protect the environment and mother nature also promote innovation and profitability by organizations, and this should encourage enforcement, either voluntarily or by legislations. Promotion of innovation and strict environmental regulations can enhance competitiveness and hence economic performance and progress. The link between the environmental integrity and development provides a strong rationale for environmental protection ( Liu, 2014 ; Kabeyi and Olanrewaju, 2020b ).

The use of polluter pay principle in environmental protection requires authorities to impose penalties upon those who pollute the environment and hence make them bear the cost of their impact instead of leaving it with the environment or others. There is need to integrate economic, environmental, and social objects across sectors, territories, and even generations if sustainable development can be achieved. This implies that energy policy should be an integral part of the entire national and international agenda and should be therefore be integrated in other policies touching on the economy, society and the environment ( Emas, 2015 ). Sustainable energy development should also be taken as a continuous process integrating all aspects of national, local, and international development agendas ( Mohamad and Anuge, 2021 ). Therefore, sustainable energy development can only be realized through integration of energy objectives, development goals and environmental protection to avoid conflict by creating a critical synergy.

5.2 Relationship Between Sustainable Development and Energy

Energy is currently recognized as one of the most important factors that influence the rate of progress as well as sustainable development of all nations ( Kolagar et al., 2020 ). To meet the ever-growing energy demand especially electricity, increase access to electricity for the billions of people with no access to electricity and high-quality low carbon fuels, as well as to reduce greenhouse gas emissions requires a radical shift from the fossil-fuel focused energy systems. There is need for a new energy paradigm to encourage the transformation of the predominantly fossil fuel-based energy systems. Sustainability is an important paradigm in the global energy transition where all dimensions of sustainability are addressed any policy formulation and implementation, planning, operation, and dispatch of the energy resources in both generation and consumption ( Davidsdottir and Sayigh, 2012 ). For a longtime, energy did not seriously factor in sustainable development. However, sustainable development and sustainability issues now play a central role in energy and electricity by anchoring the evolution of the sustainable development paradigm ( Iddrisu and Bhattacharyya, 2015 ; Kabeyi and Olanrewaju, 2021f ).

Specific energy projects influence the economic, social, and environmental dimensions of the sustainability country or region. The triangular approach to the three dimensions of sustainable development consisting of economic, social, and environmental is used to assess the sustainability of a specific energy project ( Kolagar et al., 2020 ). Figure 7 below illustrates the triangular approach in energy project assessment.

FIGURE 7 . The dimensions of sustainability and their interrelationships ( Kolagar et al., 2020 ).

From Figure 7 , it is noted that the three dimensions of sustainability are held together by the institutional state. The economic state is the main driver of social and environmental states with the institutional state playing the coordination role.

It is at the Stockholm conference, energy was identified as a source of environmental stress, thus linking energy to the environmental dimension of sustainable development. The United Nations Conference on Environment and Development (UNCED) which was also referred to as the “Earth Summit,” that was held in Rio de Janeiro, Brazil, from 3 to 14 June 1992 led to the Rio Declaration on Environment and Development, that had no specific reference to energy. Energy was however a central them theme in Chapter 9 in Agenda 21 on the protection of the atmosphere in which energy was identified as a major source of atmospheric pollution ( Quitzow, 2021 ). Agenda 21 further illustrated the need to draw a balance between economic growth, energy consumption, and its environmental impacts. Although the Commission for Sustainable Development (CSD) was established by the Rio conference of 1992, it is in 1997 when energy was placed in the agenda of the Commission for Sustainable Development ( Gibbes et al., 2020 ; Kolagar et al., 2020 ). Based on the progress of the Commission for Sustainable Development (CSD9), the 2002 Johannesburg conference made direct reference to energy as crucial for sustainable development. It is in this conference that energy was addressed within the three dimensions of sustainable development, i.e., economic, social, and environmental. The conference further clearly treated energy as a specific issue of concern rather than a subset of other issues as it was in the Rio Conference. There was strong and specific emphasis on energy use and its social attributes like access to high-quality energy as a basic human right. It is therefore from the Johannesburg conference of 2002 that the social dimension of energy was incorporated in addition to environmental and economic dimensions which had already been incorporated curtesy of the Rio and Stockholm conferences ( Gibbes et al., 2020 ; Kolagar et al., 2020 ).

Important energy issues that affect sustainability are energy research and development, training and capacity building, and technology development and transfers. Therefore, it is the cumulative effect of the Stockholm, Rio, and Johannesburg conferences that the notion of sustainable energy development (SED) as a very important factor in the sustainable development was mooted by linking energy to the environmental dimension in the Stockholm conference, economy in the Rio conference and society in the Johannesburg conference. Over time, energy consumption and energy development have become a specific issue in the three dimensions of sustainable development.

It is Article 8 from the Johannesburg declaration that we get the most comprehensive definition of sustainable energy development. Therefore, sustainable energy development involves improving access to reliable, affordable, economically viable, socially acceptable, and environmentally sound energy services and resources that consider the national specificities and circumstances. These can be achieved through means like enhanced rural electrification, decentralized electricity generation, greater use of renewable energy, use of clean gaseous and liquid fuels and improved energy use efficiency while recognizing the poor and vulnerable and their right of access to clean energy ( Davidsdottir and Sayigh, 2012 ).

5.3 Characteristics of Sustainable Energy

For energy sources and systems to contribute to sustainable development, they should possess the following characteristics.

• Energy resources and systems are sustainable if they are renewable or perpetual in nature.

• Sustainable energy system should not be wasteful but efficiently produced and used with minimum resource wastage.

• Sustainable energy and energy systems should be economically and financially viable.

• Energy is sustainable if the source is secure and diverse.

• Sustainable energy and energy systems should be equitable or readily accessible, available, and affordable.

• Sustainable energy development should bring positive social impacts.

• Sustainable energy should be associated with minimal environmental impacts ( Kolagar et al., 2020 ).

5.4 Themes/Goals of Sustainable Energy Development

By combining the characteristics or features of the Johannesburg definition with the International Atomic Energy Agency (IAEA) definition, there ae four central goals/themes of sustainable energy development. These are.

5.4.1 Improving Energy Efficiency

This involves improvement in economic and the technical efficiency of energy systems in generation and consumption. With investment in efficient energy systems, costs will reduce as well as output from available energy resources This can be achieved through technology transfer, research, and development and good energy management practices ( Kolagar et al., 2020 ).

5.4.2 Improving Energy Security

Energy security covers the security of both supply and the energy resources infrastructure. Energy security refers to the availability of energy at all times in various forms, in sufficient quantities, and at fair prices that are affordable and predictable. Therefore, for energy to be regarded as secure, it must meet all dimensions of sustainable energy and development. Strategies to improve energy security include decentralizing power generation, wide use of renewable energy resources, investment in redundancy, diversifying energy sources, enhancing supply, more use of local energy resources. Common indicators of energy insecurity include power rationing, frequent blackouts, energy related conflicts and price instability and supply instability ( Gibbes et al., 2020 ; Kolagar et al., 2020 ).

5.4.3 Reduce Environmental Impact

Sustainable energy development calls for reduction in emission of greenhouse gas emissions, which cause global warming. This can be achieved through reduction in the lifecycle environmental impact of energy systems use and production or generation. Other strategies include waste recycling and treatment and adoption of clean technologies that ensure that disposal of wastes does not exceed the Earth’s assimilative capacity ( Kolagar et al., 2020 ). Decarbonization of the energy supply is a very important function in the transition to low carbon energy grid and economy. Besides technology, the deployment of a powerplant depends on the availability of resources, socioeconomic impact, and smooth integration with the existing electricity system. Energy system planners should consider all these to determine and prioritize energy projects and programs ( Colla et al., 2020 ).

5.4.4 Expand Access, Availability, and Affordability

Sustainable energy should be reliable in supply and access at affordable price or cost and quality. There is need to expand energy resources to ensure supply reliability. Goals one and two correspond to the economic dimension of sustainable development, while the third goal deals with environmental dimension of sustainable development. On the other hand, the fourth goal deals with the social dimension of sustainable development. Progress towards sustainable energy development can be measured by various indicators which are critical in the energy transition to sustainable energy ( Davidsdottir and Sayigh, 2012 ).

6 Sustainable Energy and Electricity Generation

Sustainable energy or electricity refers to the generation and supply of electricity in a way that does not compromise the ability of future generations to meet their own energy or electricity needs ( Hollaway and Bai, 2013 ). It can also be defined as energy sources that do not get depleted in a time frame that is relevant to humanity and hence contribute to the sustainability of all species ( Lund and Lund, 2010 ). Sustainable Energy, just like sustainable development requires significant changes in the way things are done and the exact things that we do with effects on the industrial, production, social infrastructure, and value systems. The development of clean energy would unlock many challenges to sustainable development ( Kabeyi and Oludolapo, 2020c ; Kabeyi and Olanrewaju, 2021a ; Kabeyi and Olanrewaju, 2022 ). Sustainability is a major concern today as a direct result of the serious concerns over the climate change, of which electricity generation is an important contributor ( Vine, 2019 ). Electricity is a critical product needed to support life, welfare, and global sustainable development ( Berga, 2016 ). Currently, humanity is faced with a significant challenge to realize new sustainable development Goals (SDGs) by the year 2030 ( Berga, 2016 ; Kabeyi and Oludolapo, 2020b ). Sustainable development and its correlation with energy became a significant global concern and issue in the 2002 Johannesburg world summit on sustainable development ( CS-UNIDO, 2008 ) . Determination of the most appropriate energy systems in an electricity mix is considered as a strategic approach in realization of sustainable development ( Ebrahimi and Rahmani, 2019 ; Kabeyi and Olanrewaju, 2020b ). Electricity generation systems can be assessed by a five-dimensional approach consisting of environmental, economic, social, technical, and institutional sustainability as a strong measure of energy sustainability ( Ebrahimi and Rahmani, 2019 ). Therefore, sustainability in energy development seeks to achieve technical sustainability, political or institutional sustainability, social sustainability, environmental sustainability, and economic sustainability which is greatly realized by the development and use of renewable energy resources ( Kabeyi, 2020a ). Figure 8 illustrates the five main dimensions of energy sustainability.

FIGURE 8 . Dimensions of energy sustainability ( Kabeyi, 2020a ).

Figure 8 above summarizes the main dimensions of energy sustainability particularly electricity. The main dimensions of sustainability in energy development and consumption are environmental, social, political, economic, and technical sustainability.

6.1 Technical Sustainability

Technical sustainability of electricity generation refers to the ability to meet the current and future demand in a safe and efficient manner with the use of clean sources of energy and technology ( Kabeyi, 2020a ). Unsustainable production and consumption of energy resources is the main cause of environmental damage in many organizations and countries globally ( Liu, 2014 ). To realise sustainable development calls for changes in industrial processes and systems, in terms of the type and quantity of energy and other resources for waste management, emission control as well as product and service range or type ( Krajnc and Glavic, 2003 ). Through the development and adoption of appropriate technology, humanity can make development of energy sustainable. Engineering and technology are closely linked to sustainability, but the engineering input so sustainability must be in partnership with other interests by application of constraints to the three pillars of sustainability which are social, environmental, and economic pillars. All engineering systems, products, operations, services, and infrastructure have designed and actual life after which they should be subjected to sustainability analysis by application of three measures in order of priority. These measures are reuse, recycle, and disposal ( The Royal Academy of Engineering, 2005 ).

For evaluation of energy or electricity sources, a number technical and operational indicators have to be analyzed ( Dobranskyte-Niskota et al., 2009 ). The typical technical evaluation criteria for energy systems and sources include efficiency, exergy efficiency, primary energy ration, system reliability, maturity, and safety ( Şengül et al., 2015 ). Other important powerplant performance indicators in power plant generation are specific fuel consumption, specific emissions, power plant availability, load factor, among others.

The transformative and disruptive potential of rapid technological changes, and the danger of using primitive technologies should be avoided for a sustainable transition. Even with advanced science, technology and innovation policies, and technologies, it is unlikely to deliver progress regarding global development unless the environment nurtures learning and innovation for effective management of innovation systems. Both national and international policies should promote international technology assessment and foresight and cooperation including collaborations and technology transfer. This cross border partnerships and cooperation will facilitate rapid sustainable energy development ( United Nations, 2019b ).

6.2 Environmental Sustainability

Environmental sustainability is concerned with managing the negative impact of energy production and use to the society and to magnify or extend the good ones. The environment should never be allowed to absorb more than it can contain, naturally or artificially ( Iddrisu and Bhattacharyya, 2015 ). Environmental sustainability is concerned with the integrity of natural environment and its ability to remain resilient and productive in support of humanity ( Kolagar et al., 2020 ). Environmental sustainability is further concerned with the integrity and carrying capacity of the natural environment to sustain humanity as a waste sink and source of raw materials ( Mensah, 2019 ). Thus, the environment or ecological dimension of sustainability is concerned with preservation of the environment and habitats, especially against the impacts of waste disposal, excessive consumption of Earth’s resources, and greenhouse gas emissions. The gases that lead global warming include, carbon dioxide, methane, and nitrous oxides. Carbon emissions in the atmosphere have increased from about 280 ppm by volume during pre-industrial times to over 400 ppm today representing more than 40% increase. In the United States, fossil fuel consumption results in average annual emission of about 5.3 billion metric tons of CO 2 into the atmosphere ( Nag, 2008 ). The origin of these carbon emissions is from energy consumption, non-energy use and industrial processes like iron and cement production.

The typical environmental evaluation criteria of energy systems include emission levels for SO 2 , NO x , CO 2 , particulate emissions, non-methane volatile organic compounds, land use and requirements ( Şengül et al., 2015 ). The main environmental dimension indicators for energy technology assessment include: GHG emissions, environmental external costs, radionuclides external costs, severe accidents perceived in future and fatal accidents from the experience. Additional environmental indicators are land use and solid waste. Life cycle emissions of GHG emissions in kg (CO 2-eq .)/kWh are selected to assess electricity generation technologies according policies like the EU environmental policy on climate change mitigation ( Streimikienea et al., 2012 ). GHC emissions in kg CO 2 eq./kWh were selected instead of external costs of GHG emissions because of the large uncertainties related to evaluation of external costs of GHG emissions. Climate change is the dominating environmental concern of the international environ-mental political discussion of today. Global warming is not only an issue for the environment, but rather for human society, since rising global temperatures might have serious consequences on the economy and social life. The indicator reflects the potential negative impacts of the global climate change caused by emissions of greenhouse gases to produce 1 kWh of electricity. This indicator was used in almost all studies on energy technologies assessment survived ( Streimikienea et al., 2012 ).

Therefore, an environmentally sustainable energy systems should maintain a stable resource base, avoiding energy resource over-exploitation, and avoid depleting non-renewable resources through development of adequate substitutes. These approaches include biodiversity maintenance, atmospheric stability, as well other ecosystem functions that are not necessarily economic resources ( Jonathan, 2001 ).

6.2.1 Atmospheric Temperature Changes

For the world to have a stable atmosphere, it is recommended to maintain temperature increase of 1.5–2°C above preindustrial level which then translates to 400–450 ppm of CO 2 equivalence ( Dyllick and Hockerts, 2002 ). The most widely accepted climate change scenarios and projections predict annual temperature increase of 1–3.5°C in coming decades based on existing scenarios ( Butt et al., 2012 ), hence the need for more global commitment. The Intergovernmental panel on climate change (IPCC) predicted that greenhouse gas emissions (GHG) will lead to global temperature increase of between 1.1 and 6.4°C by the end of the 21st Century with cities like London, Los Angeles and Phoenix having already experienced about 1°C average temperature rise within a decade. The United Kingdom (UK) is expected to experience temperature rise of about 3.5°C by 2050 which will also be accompanied by increased winter precipitation of up to 20% as well as increased incidences of storms ( Hulme et al., 2002 ; Intergovernmental Panel o, 2007 ). This predicted temperature rise is higher than the target set by the Paris Conference of 2015 (COP21) of 2°C above pre-industrial levels ( Berga, 2016 ; Lu, 2017 ). These statistics paint a picture of a world that is already missing its targets that are necessary to save mother nature and humanity.

6.2.2 Ecological Sustainability

Ecologically sustainability requires organizations to use only natural resources that are consumed at rates that are below their natural reproduction or replenishment rates or at a rate less than the development rate of substitute products or resources. They should also ensure that emissions which have potential of accumulation should not be allowed to accumulate at rates that are more than the capacity of the natural removal or absorption from the ecosystem system ( Kabeyi, 2019a ; Barasa Kabeyi, 2019b ; Kabeyi, 2020b ). Sustainable organizations should never engage in actions or activities that degrade any part of their eco-system ( Dyllick and Hockerts, 2002 ). Natural resources should be consumed by mankind at rates that allow them to replenish themselves ( University of Alberta, 2021 ). Therefore, environmentally sustainable systems should maintain a stable resource base free from over exploitation of energy resources. Ecological sustainability also advocates for maintenance of biodiversity, stability of the atmosphere, and other economic and non-economic ecosystem functions and resources ( Jonathan, 2001 ), while non-renewable resource substitution by renewable sources is a solution for the depleting ad polluting resources like fossil fuels namely petroleum, coal, and gas.

Environmental management and protection are a significant indicator of peoples’ culture, values, and ethical principles. Ethics involve making decisions based on acceptable values. This calls for social movements that constitute useful sources of cultural values and environmental movement to influence the environment is managed ( Kabeyi, 2018a ; Kabeyi, 2018b ). Therefore, sustainable environmental management is a result of multiple actors and factors. Environmental management for sustainability is concerned with control of interaction with the environment to protect and enhance human health and welfare together with environmental quality. Energy production, conversion, delivery, and end use can have serious environmental consequences to air, land, and water quality which are important for preservation of human life. These environmental issues related to energy are discussed below ( Kabeyi and Olanrewaju, 2020b ).

6.2.3 Water Pollution

Energy-related processes impact on water through discharge of water polluting solid and liquid wastes, thermal pollution from waste process heat, and excessive consumption of freshwater, and negative impact on aquatic life. Chemical contaminants like acids from mining operations, and discharge of coal ash to water bodies, radioactive wastes from nuclear power plants as well as oil spills from diesel power plants are common scenes from power plants ( Raja et al., 2006 ; Rajput, 2010 ). Although considered as gaseous and hence air contaminant, Carbon dioxide (CO 2 ) causes acidification of oceans with serious negative impacts on aquatic life. Process improvements and technology can help mitigate this pollution of water from energy related activities ( Nag, 2008 ; United States Department, 2015 ). Buried nuclear wastes can cause contamination of underground water source. Energy-related atmospheric emissions of conventional pollutants such as particulates, sulfur, and nitrogen compounds have been reduced through improved combustion strategies and exhaust scrubbing while transition to cleaner energy sources is also proving to be effective ( Raja et al., 2006 ; Nag, 2008 ; Rajput, 2010 ; Kabeyi, 2020a ). Used brine can also contaminate surface water in geothermal powerplants in powerplants with no reinjection ( Kabeyi, 2019b ; Kabeyi, 2020c ). Some technologies may not be water polluting but the process through which the plant and equipment are producing may be highly polluting.

6.2.4 Land Contamination

Energy and power generation related activities contaminate or pollute land in various ways . Land pollution takes many forms like deposition of atmospheric pollutants with precipitation, direct discharge, and accumulation of pollutants like coal ash from coal power plants. Oil spills from diesel power plants, soil extraction or excavation for fuel mining and production or associated with energy plant and infrastructure siting and development. Although regarded as clean power sources, wind, and solar power plants occupy huge tracts of land which may no longer be used for other economic activities like farming and human settlements. Cases of induced seismicity have been experienced in geothermal power development and generation which affects land use ( Barasa Kabeyi, 2019a ; Kabeyi, 2020c ; Kabeyi et al., 2020 ). Radioactive wastes from nuclear power plants may also be buried underground rendering the area useless for other economic activities ( Rajput, 2010 ). While liquid and gaseous emissions and effluents still must be handled by nuclear power plants. Buried nuclear wastes can cause contamination of underground water source. Energy-related atmospheric emissions of conventional pollutants such as particulates, sulfur, and nitrogen compounds have been reduced through improved combustion strategies and exhaust scrubbing while transition to cleaner energy sources is also proving to be effective ( Raja et al., 2006 ; Nag, 2008 ; Rajput, 2010 ; Kabeyi, 2020a ). Lack of reinjection in geothermal power plants can lead to land contamination by the used geothermal fluid ( Kabeyi, 2020c ; Kabeyi and Olanrewaju, 2021a ).

6.3 Economic Sustainability

Economic sustainability in energy and electricity production and use refers to the ability to meet demand in a cost-effective manner. It also a measure of access to requisite financing for energy resource development. The cost-effective operation will ensure that the energy system is s economically viable and feasible and hence makes the investment attractive to investors and financiers ( Kabeyi, 2020a ). All economies are made up of markets where transactions are made. The main activity in an economy is production of goods and services, distribution and consumption ( Mensah, 2019 ). Therefore, economic dimension of energy sustainability is concerned with the viability of individuals and organizations, products, and services in production and consumption of energy or electricity, distribution, and interactions.

Economic sustainability seeks to maintain the operational stability in terms of liquidity and cash flow and ensure fair or reasonable income and benefits to investors and other stakeholders in energy systems ( Dyllick and Hockerts, 2002 ). Electricity is the most multipurpose energy carrier globally, and therefore it is highly linked to human and economic development ( Bazmi and Zahedi, 2011 ). For economic sustainability to thrive, organizational policies, and operations should not retard economic progress, development, or affluence of society ( Hasna, 2007 ). It is through economic sustainability that humanity can maintain independence and have unlimited access to the required energy resources. Economic sustainability is realized from energy systems if they remain intact while activities and processes are equitably accessible to all to secure their livelihoods in a fair manner ( University of Alberta, 2021 ). Therefore, energy or electricity system must continuously produce goods and services to manage debts, pay bills, pay workers ensure sectorial balance with stable agricultural and industrial production ( United States Department, 2015 ). Energy systems and organizations should remain profitable and useful from one generation to another generation ( Kabeyi, 2018b ). Therefore, this implies that energy systems are economically sustainable if they are operated profitably by investors or organizations.

Energy costs are embedded in every commodity and service in an economy and therefore the economy requires better and efficient energy technologies to reduce energy costs leading to affordable electricity. This will enhance the level of economic activities through better supply reliability, reduced import bill, and a bigger market for energy goods and services. This leads to higher gross domestic product and balance of payments at a macroeconomic level ( United States Department, 2015 ). The various elements of economic dimension of energy sustainability of include corporate sustainability, energy costs, supply disruption loses, energy import bills, energy technology, and service market.

Renewable energy projects make use of local labor from rural areas, businesses, local material and business, local investors, and other services. Therefore revenue from renewable energy electricity revenue is invested back to local communities in form of taxes, payments for materials and labor as well as profits to investors which leave more economic benefits than imported fossil fuels or imported grid power ( Kumar and Okedu, 2019 ). Different renewable energy sources have different socioeconomic value. For example, biofuel projects create more jobs as compared to jobs created by solar and wind powerplants which gives the different projects a unique rank in socioeconomic evaluation of energy options. The cost and price of generated electricity is another important economic aspect of power generation projects and has a bearing on electricity sustainability ( Akella et al., 2009 ).

In economic evaluation of energy systems, typical evaluation criteria include total cost of investment, operation, and maintenance cost, fuel cost of generation, electricity cost, net present value (NPV), service value and equivalent cost of the energy system ( Şengül et al., 2015 ). The Economic dimension in sustainability assessment of energy technologies and projects is significant since energy or electricity supply cost influences technology adoption and penetration. Indicators that address economic dimension of energy sustainability assessment in electricity and heat generation and supply include the private or investors costs involved, the fuel price increase sensitivity, energy or plant average availability factor, costs involved in grid connection, energy or plant peak load response, and energy security of supply. Very important economic investment indicators are private costs, availability factor and costs of electricity grid connection ( Streimikienea et al., 2012 ). Goods and services should be produced in a continuous manner in an economically sustainable system to be realized. Should produce goods and services continuously, to maintain sustainable levels of debt, and ( Jonathan, 2001 ).

6.3.1 Energy Costs

Several factors influence the cost of energy and electricity and hence the price paid by consumers. These factors include the type of primary energy commodity used, availability of supplies or resources, primary sources price or cost, the capital costs of the power plant and operating costs incurred to convert or process the supplies into energy services like electricity, and prevailing energy demand. The variation in energy cost for various sources of energy leads to market competition among energy resources and services, with alternatives sources of energy. Unfortunately, the costs associated with energy security and environmental factors are often not fully included in the market price of energy sources. Reduced energy costs generally contribute to improved performance in many sectors of the economy, hence the need for low-cost energy and electricity supply. The reduction in cost of solar and wind power generation can significantly affect the competition with other, more traditional generation options like fossil fuels ( United States Department, 2015 ).

Energy systems respond to changes in input price and technology at different rates to in the energy sector and markets. The price of energy responds to the supply and prevailing demand which is dynamic. The factors influencing price include inventory level, level of economic activities, political factors, environmental factors, and market speculation which can drive market price volatility. These instability and volatility in energy price makes planning complicated and difficult, and hence negatively impact the entire economy. It is desirable to have a diversified portfolio comprising of many different sources of energy supply and enabling technologies to provide feasible options that can allow one to hedge the risk of being dependent on a single energy supply ( United States Department, 2015 ).

6.3.2 Energy Related Disruption and Losses

Energy disruptions can occur on the supply side, consumer side or transmission and distribution infrastructure any time, whether planned or not. Any electric power outage causes substantial economic costs and losses to the businesses and activities most of which depend on electricity. As an example, study by Lawrence Berkeley National Laboratory in 2006 on the cost of power outages estimated that disruptions to the U.S. electric power system cost between $22 and $135 billion per year with common causes identified as weather-related events like falling trees, and equipment failures like transformer failures. In another study, it was found outage-related costs ranging from $20 to $50 billion per year for weather-related outages alone. These losses are worse off if damages due to extreme weather events like Hurricanes are considered. The solution to this significant loss is improvements to the transmission and distribution systems ( United States Department, 2015 ). Sustainable engage should not only be affordable but reliable in supply, generation, and transmission.

6.3.3 Energy Import Liabilities

Energy business has significant impact on the balance of payment positions for importing and exporting countries for example the US spent approximately $190 billion in 2014 on petroleum imports. Oil importing countries must content with energy insecurity and fluctuating price and supply of petroleum. Electricity can also be imported and exported between countries leading and sharing of resources with resource rich countries especially with desirable renewable and low carbon sources like hydro and nuclear. Reducing dependence on energy imports reduces the impact of supply disruptions while promoting local investment in sustainable energy options ( United States Department, 2015 ).

6.3.4 Energy Technology Markets

Electricity generation and distribution is a big business in all countries while production and export of energy resources like fossil fuel sustains many countries’ economies with some almost entirely dependent on oil and gas exports. Other commercial primary resources include coal while some countries have relied on charcoal business to generate significant revenue. Export of energy production equipment like generators, turbines, boilers, and other plant equipment represents a substantial market opportunity for many countries like the United States and often generate high-value jobs. The International Energy Agency (IEA) predicts that clean energy will supply between $7 trillion and $10 trillion investment in electricity generation of which $6 trillion will be renewable sources and $1 trillion in low carbon nuclear power generation over between 2015 and 2025. It is observed further about two-thirds of this investment will be done in emerging economies. Additionally, energy efficiency investments will account for a further $8 trillion of investment ( United States Department, 2015 ).

6.4 Social Sustainability

Social sustainability is concerned with the rights of the community as measured by the level of social acceptance and access to the energy resource and systems by the people ( Iddrisu and Bhattacharyya, 2015 ). Social sustainability is the ability to preserve desirable social values, institutions, traditions, and social characteristics of the society before and after a project or an intervention. It is also concerned with social justice and therefore addresses aspects like labour practices, variance in production standards, and promotion of equity among all people ( Kabeyi, 2018c ; Kabeyi, 2019a ; Kabeyi, 2019c ). Social sustainability can be achieved by the selection and development of technology and powerplants that provide adequate power and employment to local communities and that don’t interrupt or interfere with their established way of living and value system ( Liu, 2014 ; Kabeyi, 2020a ; Kolagar et al., 2020 ). Therefore, social sustainability implies that people are important because development is basically about the people themselves. Principles that should be applied in energy development to realize social sustainability include accountability, empowerment, participation, cultural identity, and institutional stability ( Mensah, 2019 ).

At institutional level, sustainability is grounded in environmental initiatives which were sometimes referred to as green corporate initiatives. This is the ability of an organization to endure, take care of the needy in society and ensure institutional responsibility for greater good of the human society ( Samaras et al., 2019 ), by taking care of the world’s most vulnerable people in society. Any effort to achieve financial gains for the few while ignoring the needs of the majority is no longer acceptable, reasonable, productive, or justifiable ( Kabeyi, 2020b ). Therefore, socially sustainable organizations attempt and succeed in adding value to the communities within which they operate or do business. This is achieved by increasing the human capital base of individual partners and social capital of the community. Organizations should manage social capital in a way that stakeholders do understand the objectives and motivations for general agreement and cooperation ( Dyllick and Hockerts, 2002 ). Therefore key requirements for social sustainability of energy transformation is openness and democracy in the process ( Miller et al., 2013 ). Therefore, engaging in community social responsibility (CSR) activities is a strategy for increasing social sustainability of energy activities.

Social sustainability assumes two types of sustainability, i.e., social capital and human capital. Social capital is concerned with quality of public services like good education, water, infrastructure or a supporting culture and value system. Human capital is primarily concerned human skills, level of motivation, and loyalty of employees and business partners in their own capacity ( Dyllick and Hockerts, 2002 ). Therefore, human capital is an intrinsic phenomenon of an individual or individuals while social capital is concerned with communal or common physical projects, infrastructure or facilities meant to improve the quality of human beings in each social system. This implies that sustainable energy systems should have a positive impact on both human and social capital of the society.

Individual organizations have a critical role to play to ensure social sustainability of energy systems during the energy transition. Social sustainability requires organizations to act in a manner that creates welfare to society and all its people and should be ready to take responsibility for their actions ( Mohamed et al., 2020 ). A socially sustainable organization should internalize the social costs, develop the capital stock, exceed the social carrying capacity, enhance self-renewal of natural systems, nature openness, accountability, and democracy, enhance human choices and practice fair distribution of available but scarce energy and other resources among all stakeholders. It is necessary that social sustainability should preserve human rights and human dignity and guarantee equitable access to necessities which leads to a healthy and secure society. Communities that are healthy have fair leadership which ensures that personnel, labor, and cultural rights of all are respected to the later ( University of Alberta, 2021 ). Therefore for energy resources and electricity systems to be socially sustainable, they should be characterized by equity, reliable supply of social services, address gender equity, facilitate political stability, address accountability issues, and nature participation in their governance systems ( Jonathan, 2001 ). Social sustainability requirements call for energy practitioners, organizations, and countries, local and international organizations to go beyond just energy solutions and ensure holistic approach in as far as energy transition is concerned. Energy transition should address human physical and health, system and human safety, human rights, and dignity for sustainable energy development to be achieved.

Energy policies necessary to realize sustainability should be guided by a mixture of robust, objective, empirical, and theoretical principles that consider the impact not just to the current generation, but equally on future generations. Energy resources and electricity systems should consider socio-technical impacts on man and machines for them to be socially acceptable. Adoption of new electricity or energy technologies should bear in mind that systems are operated by man and should therefore be acceptable and comfortable by design and adequate capacity building should be done for man to be comfortable and therefore embrace new ways and systems. The impact of the technology change or acquisition on current and future financial systems, school system, labour market composition, organizational culture and political aspirations of the people should be considered in the energy transition if it has to be sustainable and avoid failure or negative perception by the people ( Miller et al., 2013 ). This implies that man is a very important aspect of the energy transition and should be at the center of the transition and be involved using various participatory methodologies, otherwise the transition may never succeed.

Any social evaluation of energy systems should consider social acceptability, expected job creation, and other social benefits of the energy systems ( Şengül et al., 2015 ). Significant social indicators for energy and electricity technologies are related job opportunities, health effects, food safety and security risk and work-related accidents and fatalities. Technology specific job opportunities in person-year/kWh indicator are based on the average amount of labor used to produce a unit of electricity ( Berga, 2016 ; Lu, 2017 ). The quality of electricity or energy related work is addressed by Work Quality indicator is based on knowledge and training of average worker in each technology chain, using an ordinal scale indicator ( Streimikienea et al., 2012 ). A system is said to be socially sustainable if it guarantees distributional equity, provides social services like education, health, guarantees gender equity as well as political accountability and adequate public participation of stakeholders ( Jonathan, 2001 ).

Therefore, social sustainability of the energy transition is concerned with the value to community, democratic participation, direct benefits through addition of human and social capital, job creation and other community benefits through activities like corporate social responsibility and respect for local customs, traditions, and beliefs.

6.5 Political and Institutional Sustainability

The development of new energy technologies, new business models, and new policy priorities and frameworks need new market participation and control models and rules and regulations which require new governance and new institutional design ( De, 2021 ; Lenhart and Fox, 2021 ). Transition historical studies show that whereas technological innovations and market actors are the main drivers of change, extensive studies claims that it is governance systems that influence the distribution of the benefits of new technologies to the society which is an important requirement of sustainability ( Kuzemko et al., 2016 ; Kabeyi, 2020a ). The road to the global low-carbon transformation should deal with the climate crisis is within reach, but this requires political actions from world leaders. There is need for action along multiple approaches and models globally that can be scaled up and adapted to suit specific national prevailing circumstances. Cost-effective a low-carbon technologies are available in many fields with several under research but the rate of adoption is still a serious concern because governments need to put in place the right policies, regulations and a facilitating legal framework for faster and successful adaption ( Watson, 2014 ; Krzywda et al., 2021 ). Political or institutional dimension of energy sustainability is concerned with governance of sustainable energy transformation at all levels. This is achieved by setting and implementing policies and regulations with different political institutions influencing governance choices ( Kuzemko et al., 2016 ). This implies that the political dimension of energy sustainability is concerned with the strategic planning and definition of the energy system and related systems and processes. Therefore, political sustainability concerns address the future structure and indicates some issue on political stability and foreign policies of the energy system ( Kabeyi, 2020a ). For development to be sustainable, there is need for adequate management of the tradeoff between social equity, protection and integrity of the environment, real economic development and progress and preservation and use of natural resources for equitable use by all ( Robyns et al., 2012 ). This can only be achieved effectively when we have the political will from all if not many nations and groups that have power to influence energy policy ( Kabeyi, 2019a ).

The institutional dimension of sustainability defines the role of local participation in the control and management of energy resources and energy systems ( Kabeyi, 2019a ; Kabeyi, 2019c ). The institutional dimension embodies elements like local ownership, participation, local contributions, local skill base, local policy and regulation, protection of investors and consumers and sharing of resources and benefits accruing. This dimension is the one that defines the system structure and framework of processes, systems and policy decisions which affect the project or investment ( Iddrisu and Bhattacharyya, 2015 ; Kolagar et al., 2020 ). There is evidence that highly or adequately institutionalized countries with efficient and effective energy related institutions are more successful in managing the energy transition. This is because the institutions encourage innovation, efficient resource allocation and set desirable policy, legal and financial measures and instruments which are enables of sustainable energy transition ( Inglesi-Lotz, 2021 ).

6.5.1 Politics and Sustainable Energy Transition

Energy activities, products and services constitute big business globally. In 2015, four out of eight top Fortune 500 companies, were energy related companies like Exxon Mobil, Chevron, Phillips 66, and General Electric. Therefore, energy represents a big portion of global economy and therefore it affects jobs, people’s incomes, company performance, profits, and personal or individual economics. Within these dynamics, politics become important especially as an enabler of business through various instruments at their disposal. Internationally, government subsidies have helped the development of new technology for solar and wind power. Many governments subsidize the oil and nuclear power industries which complicates the viability of renewable energy resources and technologies ( United States Department, 2015 ).

Politics play a leading role in the coal industry which continues to survive and thrive in many countries like the United States because of exemptions from federal pollution regulations making its use competitive. The same is true for hydrologic fracturing or fracking, which has survived in the US because of the 2005 Clean Water Act. The US government also subsidizes pipelines and supports military actions in the Middle East as a strategy to ensure a stable and reliable supply of fossil fuels. Energy has also been a leading cause of most political tensions between countries. These tensions or conflicts shape the decisions all countries make about their energy resources which ultimately affects their electricity mix so as to manage costs, security and environmental concerns besides shaping international relationships ( Dufour, 2018 ).

6.5.2 Energy Policies, Regulations, and Governance

Governments should strive to meet the growing energy demand but also meet environmental requirements. To realize these demand and sustainability challenges, Governments should develop regulations and policies that seek to meet the growing energy needs and concerns over emissions and global warming. It is necessary to develop sustainable energy policies to provide relevant and suitable policy recommendations for end-users ( Lu et al., 2020 ). Policymakers should develop sustainable solutions and a conducive environment for a sustainable energy transition. Good governance in the energy sector is an important tool to realise climate change mitigation by investing in sustainable measures and projects. There is need for public intervention by putting in place what is considered as a conducive energy transition’s regulatory framework. Renewable energy projects and other sustainable energy investments, just like any other investment, require political stability, proper regulatory frameworks, good and effective governance and secure property rights ( Inglesi-Lotz, 2021 ).

Energy policy issues are political in nature, and act as instruments through which governments can influence sustainability in the society. Governments should develop energy policies which can alter consumption habits and patterns, reduce fossil fuel dependency and environmental conservation and protection while stimulating investment and development of clean energy technologies. Interest groups represent interests from energy conservation proponents to nuclear power opponents ( Marcus, 1992 ). Interest groups representing various groups and stakeholders from energy conservation to nuclear power opponents need to be heard during policy formulation on sustainable electricity ( Marcus, 1992 ). Energy policy seeks to establish security of supply, energy affordability, and minimum impact on the environment.

Institutions in energy transition generally refers to the formal and informal rules and their enforcement ( Inglesi-Lotz, 2021 ). The quality of these institutions is measured in terms of ability to create a conducing environment characterised by the following indicators and dimensions.

6.5.2.1 Voice and Accountability

This refers to the extent to which the people in a country can choose and challenge the government of the day which limits executive authority.

6.5.2.2 Peace and Political Stability

The citizens of a country have no incentive to invest in their future in environments of political instability or civil strife. This therefore makes sustainability concerns secondary to the need for immediate survival.

6.5.2.3 Government Effectiveness

Government effectiveness is the quality of public services and the degree of freedom or independence from political pressures and interference. This creates an enabling environment for private sector investment in energy.

6.5.2.4 Regulatory Quality

Regulatory quality is the ability to formulate and implement appropriate policies and regulations that facilitate private sector growth and development. This requires that government lays down fair and uniform rules of economic engagement.

6.5.2.5 Rule of Law

Investment in sustainable energy requires suitable laws governing quality of contract enforcement, private and public property rights, effective police, and courts for arbitration and the enforcement of the rules of society.

6.5.2.6 Control of Corruption

There is need for a strong anticorruption prevention for more the more economic success as a Corruption inhibits investment and increases the cost of doing business and lowers competence and efficiency of performance which in itself and indicator of lack of sustainability ( Kabeyi, 2020b ).

6.5.2.7 Ease of Doing Business

This is a measure of the multitude of aspects that influence the extent to which the regulatory environment is facilitates business operations. Investment in sustainable renewable energy projects can delayed or abandoned by too complex and lengthy bureaucratic procedures and corruption ( Inglesi-Lotz, 2021 ).

A sustainable energy transition calls for the design of an appropriate market structure for proper performance of the energy sector in terms of prices, energy efficiency, supply, and technological innovation. Governance mechanisms directly influence the market structures and influence investment decisions. Therefore, bad or improper market structure designs and policies can lead to higher costs of the energy sector unnecessarily which impacts negatively on the welfare of consumers ( Inglesi-Lotz, 2021 ).

6.5.3 Energy Security, Risks, and System Resilience

Energy security generally refers to low probability of damage to acquired values. Energy security is best defined by the four As of energy security which refer to availability, affordability, acceptability, and access to energy resources and systems ( Cherp and Jewell, 2014 ). Energy security is therefore the degree of vulnerability on vital energy resources and systems which is influenced by the degree of exposure to energy related risks, its resilience and links to important energy and social systems. Energy security issues emerged in the early 20th century with respect to the supply of oil to the military more so in the frontline. Academic reflections on energy security emerged in 1960s and became real in 1970s with the oil crisis. It remerged in the 2000s with concerns over rapid demand growth for energy in Asia and gas supply disruptions in Europe and the current pressure over emissions and global warming concerns ( Cherp and Jewell, 2014 ; Austvik, 2016 ).

Energy systems are entangled with human and national security with reliability concerns shaping public opinion and policy as well as political decisions and agenda with implications on the economy and political systems ( Austvik, 2016 ). It is the desire of everybody and every nation to have uninterrupted supply of vital energy services and hence, energy security is a priority for all nations ( Jansen and Seebregts, 2010 ). The security concerns are robustness, i.e., resource sufficiency, system reliability, stability, and affordability; sovereignty which include protection from internal and external threats; and resilience which is ability to withstand disruptions of energy systems. For many countries, energy insecurity means lack of self-sufficiency and having aging infrastructure, while insecurity issues among developing countries additionally includes lack of adequate capacity, high energy intensity, and high demand growth that is more than ability to supply. For low-income countries, multiple vulnerabilities overlap, making them seriously energy insecure ( Jacobs et al., 1987 ).

Energy security is a very important policy driver with privatization of the electricity sector being used as a tool to secure cheaper energy supplies in some countries in the short term. However, this has led to contrary effects in some places because of stiff competition, resulting in delayed and deferred development of power plant and infrastructure caused by prolonged uncertainties on viability ( Bazmi and Zahedi, 2011 ). Renewable energy sources have the potential to help nations become independent from foreign energy supplies and mitigate risks from conflicts and other disruptions to vital energy resource supplies because most of them do not rely on imports unlike fossil fuels sources ( Ölz et al., 2007 ). A typical example of an energy conflict involved the expansion of the existing pipeline between Germany and Russia through the Baltic Sea. This caused international disputes with the US warning Germany with sanctions ( Dettmer, 2019 ). In this energy project, countries like Poland and Ukraine heavily criticized the pipeline, fearing that Russia would use it for political gain and escalate regional conflicts through arming Eastern European countries ( Gurzu, 2019 ). This is because of the concern that the pipelines can deliver gas to German directly and hence by-pass Ukraine and thus escalate the conflict with Ukraine.

In another case of energy insecurity, the first oil crisis in 1973 brought about a reduction of about 30% in the supply to of oil to Japan leading to Japanese economic downturn and recession in 1974. These reminded policy makers in Japan that energy supply is a serious security issue and should be managed ( Cheng, 2009 ; Mihut and Daniel, 2013 ). The case was similar in South Korea which was also seriously affected by the first and second oil shocks of 1973 and 1979 ( Miller et al., 2013 ; Azad, 2015 ). The supply shocks demonstrated that energy supply and national security are seriously intertwined. In 2011, the Tohoku earthquake in Japan brought about massive disruptions to energy supply after Japan was forced to shut down its nuclear power plants after the nuclear accident at Fukushima Daiichi power plant leading to increased use of fossil fuels. This caused significant increase in fossil fuel demand and supply ( McCurry, 2015 ; Energy Information A, 2020 ). Today, Japan and South Korea have shifted their electricity generation from oil based and to liquefied natural gas and coal which is steal a fossil fuel but with less environmental impact ( Korea Energy Economics In, 2017 ; Ministry of Economy, 2018 ).

In yet another case of energy insecurity, Taiwan, experienced a massive power outage in the northern half of the island in 201 that lasted 5 h causing an estimated damage of three million US dollars. Although this was partly blamed on human error, and structural challenges within Taiwan Power Corporation, a critical analysis showed that operating electricity reserves had significantly reduced from 6% to just 1% within 1 week to the blackout ( Yu, 2017 ). Therefore, adequate energy planning has an important role to play in energy supply security and that unreliable or insecure energy system can be quite destructive and costly to any economy.

There are several energy related risks to national energy and electricity security, and can be broadly categorized into physical, cyber, economic, and conflict-related risks although with significant overlaps among these categories. Energy technologies must be robust and resistant to these vulnerabilities if they must be sustainable and secure.

6.5.3.1 Physical Energy Risks

Energy security risks are related to the damage and disruption of energy supply, energy storage, and delivery infrastructures. Several energy infrastructure and assets are susceptible to damage and disruptions. Energy infrastructure include the electrical grid infrastructure system, pipelines for oil and gas, and rail transport network and infrastructure, as well as road and marine systems. Examples of damages to the infrastructure include Hurricane Sandy effects and the attacks on substation facilities and power plants as a result of extreme weather with climate change raises these risks ( United States Department, 2015 ).

6.5.3.2 Cyber Security Risks

Cyber security refers to vulnerabilities that compromise the computer-based systems and related operations and functions like data inputs, data analysis, and data processing, the real time operation and coordination of electricity supply systems, energy delivery, and end-use systems control in smart grids. There is need to validate and manage all data inputs, monitor the systems for intrusion, and the need to address other vulnerabilities which come with challenges of maintaining the integrity of these systems. Electricity networks encounter cyber security threats which increase with access to the internet and other computer supported operations as in the case of the smart grid ( United States Department, 2015 ).

6.5.3.3 Economic Energy Risks

Economic energy security risks are related to resource supply and price shocks like the oil crisis of 1973 and 1978. Energy resources that are traded internationally are particularly subject to price and supply fluctuations due to various reasons that include civil war, international war, economic sanctions, and deliberate supply control. The price and supply shocks create uncertainties for energy-dependent businesses, which then invest in energy security measures including research and development of renewable and sustainable energy systems. Supplier related risks include price and supply manipulations. Manufacture of complex energy infrastructure components is often dependent on global supply chains which can be adversely affected by long lead times, long-range shipping logistics, and price volatility ( United States Department, 2015 ).

6.5.3.4 Conflict-Related Energy Insecurity

These are risks that are related to unrest in foreign countries as well as energy fueled domestic or local conflicts. International security risks include those that involve unrest in locations that are critical to global energy supply ( Austvik, 2016 ). They include conflicts in the Middle East which seriously disrupt the supply of petroleum resources. These conflicts also cause deaths, economic meltdown, and environmental disaster like oil spills and destruction of oil resources by enemies in conflicts ( United States Department, 2015 ).

In many countries, conflicts over energy resources are a common denominator. In most of these conflicts, prevailing historical differences and injustices among neighbors has been cited in various areas like religion, tribe, race or even clans and political inclinations. For example, in Syria and Iran, the conflicts appear like they are religious in nature between Sunnis, Shiite Muslims, Kurds, Turkmen, and others while. In Nigeria, it may appear as a conflict is over energy between Muslims, Christians, and other traditional groups, while in the South Sudan, the conflict looks like just differences between the Dinka and Nuer tribes. In Eastern Europe, conflicts in Ukraine, are between Ukrainian loyalists and Russian speakers aligned with Moscow. A deep scrutiny of these conflicts highlighted place energy at the epicenter of the differences, hence the reality is that these conflicts are struggles for control over the principal source of national income which is energy ( Marcus, 1992 ; Dufour, 2018 ). Therefore, it is only through proper energy resource management that social, political, and economic conflicts can be avoided or resolved. Hence, for energy to be sustainable, governments and groups have a duty to maintain peace and stability and prevent or manage existing and potential energy conflicts within their political environment.

6.5.4 Corporate Sustainability

This is an extension of institutional and political dimension of energy sustainability ( Kabeyi and Olanrewaju, 2020b ). Organizations and individuals create social impacts that are both positive and negative, through their operational activities. Societies rely on organizations for individual and common good and benefits like employment and social infrastructure, while organizations or corporations need societies to provide workforce and other critical inputs like raw materials to sustain their operations. While we have the interdependence between organizations and society, it is only a healthy and positive society that will create good workers sought organizations ( Tharp, 2012 ). Individuals within the community or society play a significant role in developing sustainable situations and circumstances but organizations can influence this by acting sustainably in their operations and relationships with society ( University of Alberta, 2021 ). Since there is mutual dependence between institution or organizations and society, there is need to have the principle of shared value while making choices and decisions. Sustainability demands for responsibility and facilitates human creativity to develop innovative ways that will further protect the shared environment, respect for all, and empower stakeholders. For organizations, sustainability is important because it creates value and provides them with competitive advantage and leaves a greater positive value to society and stakeholders as well ( Nawaz and Koç, 2019 ).

Energy sustainability programs and activities should facilitate the bridging of the gap between laws and the requirements of good business practice, which include prevention of exploitation, transparence, and accountability to all stakeholders in business or a given system under consideration. This calls for proactive risk identification, assessment, mitigation, and management. This makes sustainability a necessary value and an integral business goal and objective of all organizations including energy companies. Long term success of business operations should incorporate social, environmental, and supply issues in all their undertakings with suppliers, customers, and all other stakeholders. This in return adds value to the respective organizations in terms of corporate reputation, brand visibility, value and equity, better risk management, easier access to capital, talent attraction and retention and higher profitability and return on investment ( Kanter, 2021 ).

Corporate sustainability involves the integration of the economic, ecological, and social aspects in business practice and operations ( Dyllick and Hockerts, 2002 ). The consumption of goods and services is pivotal to enhanced organization’s operational efficiency because sustainable use of goods and services leads to reduced generation of waste during productive operations. The general objective of sustainable corporate development is to realize economic, social, and low carbon sustainability by companies. By embracing sustainable innovation practices, organizations can reduce adverse social and economic impacts of their operations which leads to better corporate performance ( Kabeyi and Oludolapo, 2020a ; Mohamed et al., 2020 ).

Environmental sustainability of an organization is an important element of corporate sustainability since it is associated with social consequences of business activities and the environment ( Darkwah et al., 2018 ; Mohamed et al., 2020 ). An organization that is environmentally proactive should accommodate their stakeholder concerns which leads to better corporate performance and profitability. Environmentally friendly practices are positively related to corporate sustainable performance because of low carbon innovation attitude ( Rosen, 2009 ; Darkwah et al., 2018 ; Mohamed et al., 2020 ). Therefore, socially responsible corporate behavior often affects environmental sustainability.

Corporate sustainability strategies incorporate sustainable development principles into business activities and mediation of the relationship between environmental, social sustainability and technology in organizational operations. Nurturing creativity helps to increase environmental, social, and economic efficiency and effectiveness by organizations and in the process, it facilitates advancement of environmentally friendly measures. Therefore, creativity impacts green innovation within organizations and so should be encouraged ( Musango et al., 2011 ; Moriarty and Honnery, 2019 ; Mohamed et al., 2020 ).

Various elements have an impact on corporate sustainability which also affects energy sustainability. Energy activities constitute a very important social enterprise with 9 out of 12 most capitalized companies globally engaging in energy business ( Miller et al., 2013 ). Organizations that are economically sustainable have guarantee that they always have sufficient cashflow to ensure liquidity while at the same time they produce above average returns to the investment. Organizations that are ecologically sustainable consume natural resources at a pace lower than the resource reproduction or substitution and they do not pollute the environment with emissions that accumulate beyond the capacity of natural systems to absorb and assimilate them ( Kabeyi, 2018b ; Barasa Kabeyi, 2019b ; Kabeyi and Oludolapo, 2020b ; Kabeyi et al., 2020 ). They also do not engage in ecosystem degrading services. Socially sustainable companies usually add value to the communities where they operate through increment of the human capital of partners. They also improve the societal capital of surrounding communities and are transparent in their activities and operations. ( Dyllick and Hockerts, 2002 ). Therefore, corporate sustainability is a critical part of the wider energy and global sustainable transition.

Therefore, institutional dimension is a very important dimension in determining and influencing investment, competitiveness, prices, investment, and performance of energy sector. The political function sets energy sector institutions, policies and regulations that govern the energy sector and therefore directly influence choices and performance of the energy transition measures and investment.

7 Strategies for Sustainable Energy and Electricity Systems

The sustainable transition strategies typically consist of three major technological changes namely, energy savings on the demand side, generation efficiency at production level and fossil fuel substitution by various renewable energy sources and low carbon nuclear ( Lund, 2007 ; Kabeyi and Oludolapo, 2021b ; Kabeyi and Olanrewaju, 2022 ). For the transition remain technically and economically feasible and beneficial, policy initiatives are necessary to steer the global electricity transition towards a sustainable energy and electricity system. ( Bruckner et al., 2014b ; IRENA, 2018 ). Whereas renewable sources energy holds the key for sustainable energy transition, large-scale renewable energy adoption should include measures to improve efficiency of existing nonrenewable sources which still have an important cost reduction and stabilization role ( Lund, 2007 ). A resilient grid with advanced energy storage for storage and absorption of variable renewables should also be part of the transition strategies ( Kabeyi and Olanrewaju, 2020b ).

7.1 Policy Measures and Initiatives for the Energy Transition

A successful energy transition requires a stable political and economic framework, and support systems, financial measures, technical and as well as well as administrative policy measures to overcome barriers existing as a result of a distorted energy market ( Fouquet, 2013 ). At the center of any sustainable energy strategies is the objective of improving the production and use of energy resources so that they contribute to sustainable development. These requires policies that seek to widen access to reliable and affordable modern energy supplies and while mitigating the negative health and environmental impacts associated with the energy processes and systems. To increase energy supplies comes with economic burdens and so the policies should also foster real socio-economic development to sustain any expansion and access. Measures be taken to make markets work more effectively, and develop new markets while modernizing and expanding old once for efficiency and sustainability in general ( Jefferson, 2000 ).

The focus areas where policy and decision makers should act are as follows.

7.1.1 Develop a Strong Synergy Between Energy Efficiency and Renewable Energy

Policy makers policy design policies that combine the effect of bulk of energy-related decarbonization needs by 2050 in a cost-effective manner through efficient energy production and use ( Bruckner et al., 2014b ; IRENA, 2018 ).

7.1.2 Develop an Electric System in Which Renewables Provide a High Share of the Energy

There is need to transform the global energy system through fundamental shift in the way electric power systems are conceived and deployed. This calls for long-term system planning and a shift to policymaking that is more holistic and coordinated across all sectors and nations. There should be timely deployment of infrastructure and the redesign of rules and regulations to achieve cost-effective large-scale integration of solar and wind generation. With their massive potential and renewability with negligible emissions and environmental impact, wind and solar should be made the backbone of electric power systems by the year 2050 to meet the targets set in the Paris agreement ( Bruckner et al., 2014b ; IRENA, 2018 ).

7.1.3 Accelerate Electrification in Transport, Building, and Industry

There is need for deep and cost-effective decarbonization of transport and heat sectors by electrification with the bulk of power coming from renewable electricity. Where it is not possible to electrify transport, industry and buildings then other renewable solutions will have to be adopted ( Fouquet, 2013 ). Alternative sources of energy for direct use include modern bioenergy, solar thermal, and geothermal heat applications. The realization of this shift needs the deployment of an enabling policy framework and development of supporting technology and other related initiatives in urban planning, building, transport and industrial sectors ( Bruckner et al., 2014b ; IRENA, 2018 ).

7.1.4 Foster System-Wide Innovation

There is need to have continued technological innovation to achieve a successful global energy transition, just the same way new technologies have played a leading role in renewable energy development and deployment. Innovation effort must cover a technology’s full life cycle, that includes demonstration, technology deployment, commercialization, and final disposal. It is worth noting that innovation is broader than technology research and development (R&D) as it includes new approaches to existing energy systems and markets and development of new technical and business models. There is need for coordinated effort by regional, national governments, national and international actors, and the private sector to deliver the needed innovations to facilitate energy ( Bruckner et al., 2014b ; IRENA, 2018 ).

7.1.5 Align Socio-Economic Structures and Investment With the Transition

There is need for a globally integrated and holistic approach by alignment of socio-economic systems with the requirements of the energy transition. Implementation of the energy transition requires investments, in addition to those already incurred with respect to the adaptation to climate change. Faster realization of the energy transition would lower the climate change adaptation costs and in addition to reduced socio-economic disruption. This calls for alignment of the financial systems with broader sustainability and energy transition demands that today’s investment decisions made define the energy system of many years ahead. For smooth investment in energy transitions, there is need to allow urgent flows of capital investment to low-carbon solutions, avoid locking economies into a carbon-intensive energy systems and to minimize incidents of stranded assets ( Mullen and Dong, 2021 ).

A smooth and successful energy transition calls for establishment of regulatory and policy frameworks that give all relevant stakeholders a clear, firm, and long-term guarantee of energy systems transformations to meet the emissions and climate goals set. This will create economic incentives that are aligned to the environmental and social costs of fossil fuels and remove barriers to accelerated deployment of low carbon energy systems and solutions ( Mullen and Dong, 2021 ). Energy transition would require increased participation of both private and public institutional investors as well as community-based finance who should be facilitated and motivated with relevant incentives. The requirements and specifications of distributed investment needs including energy efficiency and distributed generation need to be addressed within the socioeconomic structures and investment transformation ( Bruckner et al., 2014b ; IRENA, 2018 ).

7.1.6 Ensure That Transition Costs and Benefits are Distributed Fairly

Policies put in place should ensure that the whole society should be involved in a collaborative manner and process to achieve the desired transition. Effective participation is only achievable if the energy transformation costs and benefits are shared and the transition itself is implemented in a fair and just manner. A key requirement and component of a fair and just transition is the universal energy access where all benefit. There is need for the transition scenarios and planning to incorporate access and convergence factors in the transition because there are huge disparities presently in availability of energy services, hence the need for energy services to cover all regions ( IRENA, 2018 ).

A successful energy transition will require the promotion and facilitation of a social accounting framework which enables and visualizes the transition contributions and obligations from the stakeholders in the transition. There is need to make advances in the definition and implementation of a fair context to share costs of transition while at the same time promoting and facilitate structures which enable fair distribution of the benefits of the transition. There is need to explicitly address a just transition considerations from the onset, at both macro, and micro levels, which will enable the creation of structures needed to provide alternatives that allow parties who have been trapped into the fossil fuel dynamics to participate effectively from the transition benefits.

The economic, social, political and technological realities and developments continuously influence the energy mix hence the need to have a rationale in energy system decision making in energy planning and generation deployment ( Streimikienea et al., 2012 ). Renewable energy is considered as a solution for mitigating climate change and environmental pollution; however, an important problem of the application of renewable energy systems (RESs) is that the evaluation of the sustainability of these systems is extremely complicated.

7.1.7 Specific Policy and Legal Measures

There is need to have appropriate policy frameworks, attractive prices for investors and consumers, and a facilitating regulatory framework to realize a sustainable energy transition. Whereas strategies to encourage sustainable energy systems are straightforward, there is need for wider acknowledgement of the challenges and stronger commitment to specific enabling policies ( Wanga et al., 2020 ). It is also necessary to ensure that electricity utilities have adequate generation capacity and that they are financially healthy for them to contribute to sustainable energy and power ( Karekezi and Kimani, 2002 ). Governments should play a proactive role in the transformation, but they cannot single handedly create desired change and the right speed without the involvement and participation of non-state actors to nature the transformation ( Pegels, 2010 ).

With electricity generation being an important contributor to global greenhouse gas emissions, a viable option in the transition is to decarbonize the grid electricity energy sources by use of low carbon and renewable sources ( Jefferson, 2000 ; Colla et al., 2020 ). Several measures should be put in place to ensure that energy systems promote sustainable socioeconomic development. The main challenges to overcome are expansion of access to affordable, reliable, and adequate energy supplies while addressing environmental impacts at all levels ( Jefferson, 2000 ). With the right policies, prices, and regulations in place, energy markets can achieve many of these objectives. But where markets do not operate or where they fail to protect important public benefits, targeted government policies, programs, and regulations are justified to achieve policy goals. Although strategies to encourage sustainable energy systems are straightforward, there is need for a wider acknowledgement of the challenges and a stronger commitment to specific policies aimed at enhancing sustainability ( Wang, 2019 ; Wanga et al., 2020 ).

7.2 Electricity/Energy Planning and Resource Allocation for the Energy Transition

It should be noted that a competitive and sustainable energy market is the most efficient allocator of energy resources and provides high levels of consumer service and satisfaction as expected. Thus, a key requirement for any sustainable energy strategy should be to maintain competitive market conditions. However, the market alone cannot meet the needs and expectations of the most vulnerable groups, protect, or preserve the natural environment, and ensure energy security in the face of a complex political environment. In general, governments and societies should put in place proper frameworks to enable competitive pricing and effective regulation of energy markets so as to achieve many of the objectives of sustainable energy ( Jefferson, 2000 ). Therefore, it is critical to have a working policy and supportive political environment.

The selection and deployment of energy and power systems is a multicriterial approach that considers all the dimensions of sustainable energy systems and sources. Figure 9 below illustrates the stages in multicriterial sustainable energy decision analysis.

FIGURE 9 . Planning for electricity sustainability.

Figure 9 above shows the recommended steps in the planning for sustainable energy and electricity solutions and options using the multicriteria approach. The process starts with the selection of sustainability indicators for use in selection and planning. Based on the appropriate indicators, appropriate technology is selected from the desirable specifications that were specified. In addition to the social, environmental, and economic indicators which define sustainable development, further considerations are needed to capture the technical and institutional/political dimensions which will guide in the deployment of the best or most appropriate energy and electric power systems.

The multicriteria analysis and decision making often requires the application of energy and electricity models for more effective decision making. The same will also become critical in real time electricity generation and supply for efficient deployment of powerplants and electricity supply as well as consumption by all category of consumers ( Bruckner et al., 2014b ; IRENA, 2018 ).

7.3 Renewable Energy in the Energy Transition

Renewable energy sources come from naturally occurring sources which replenish themselves through natural forces. As a source of clean energy that is inexhaustible, renewable energy sources have a significant role to play in the energy transition ( del RíoJaneiro, 2016 ). Although renewable in nature, their consumption should allow for natural replenishment for them to be renewable and competitive ( Owusu and Asumadu-Sarkodie, 2016 ). Strategies to improve access and consumption of renewable energy sources include improvement in conversion efficiency, use of energy storage technologies to deal with fluctuating nature and policies that discourage more consumption of fossil fuels ( Sasmaz et al., 2020 ). Renewable energy sources have been identified as the main solution for mitigation of greenhouse gas emissions and climate change, and environmental pollution ( Liu, 2014 ). Renewable energy sources (RES) can greatly contribute to economic, social, and environmental energy sustainability. The renewable energy sources can be used to improve energy access for most of the population because they are often locally available, reduce greenhouse gas emissions and may create local socioeconomic development opportunities through job creation and improved local economy. ( Jaramillo-Nieves and Del Río, 2010 ). Before the industrial revolution, solar energy was the most readily available form of energy for direct solar application like drying. This changed with the industrial revolution as fossil fuels became dominant source of energy. Fossil fuels constitute the main class of energy sources that cause severe environmental pollution and are thus the main target of substitution with renewable and low carbon sources. The challenge of this substitution is that it may impact negatively on human development ( Sasmaz et al., 2020 ). Sustainable social and economic development goals cannot be achieved without access to clean, reliable, and affordable energy resources and supplies ( Kabeyi and Oludolapo, 2020b ; Kabeyi and Olanrewaju, 2020b ; Sasmaz et al., 2020 ).

As the world’s population and economy keeps growing, so is the energy demand, a scenario that automatically increase the demand and consumption of conventional sources of energy, particularly fossil fuels ( United States Department, 2015 ; Owusu and Asumadu-Sarkodie, 2016 ). Renewable energy resources can be used as substitutes for fossil fuels. These sources are characteristically ideal to achieve sustainability in energy use as one of the basic requirements of sustainable development ( Wanga et al., 2020 ). Therefore, replacement of fossil fuels with renewable energy sources in electricity generation is an important measure to reduce carbon emissions ( Mohamad and Anuge, 2021 ).

There are increasing opportunities for companies to increase the use of renewable energy through development in data-driven technology which can help to better understand on real-time basis, internal energy consumption and demand, which may provide information required to control cost. Such information can assist investors in negotiating energy supply contracts that are more appropriate for their unique consumption and demand patterns ( Scheneider Electric Company, 2019 ). Energy planners face challenges in energy planning because of challenges like unequal distribution of natural resource, limited financial resources and other considerations. Factors considered in energy evaluation include economic, institutional, technological development, energy security, environmental protection, and prevailing state of the energy market ( Wanga et al., 2020 ). For energy systems to be sustainable, the consumption should bear in mind the limits of resource supply and the environmental and social impact ( Jefferson, 2000 ). Maximum advantage should be taken of immense resource supply for renewables like geothermal, solar, hydro and wind ( Jonathan, 2001 ).

Although renewable energy sources have significant advantages, their consumption is also associated with challenges like low conversion efficiency, unsteady supply, low conversion efficiency, and general variability and unpredictability in supply. These weaknesses can be addressed by technological advances and application of computer hardware and software which can enhance optimization and hence create stability and reliability in renewable energy supply and use ( Bishoge et al., 2019 ). Since energy production and consumption accounts for over two thirds of the total greenhouse gas emissions and over 80% of Carbon dioxide emissions, countries that seek to meet the long-term climate objectives of the Paris Agreement must develop measures and strategies to mitigate emissions from power plants and other energy related activities. Countries should individually and collectively tackle their challenges through right and effective energy policy measures ( Dufour, 2018 ). Countries may adopt different transition routes due to relative differences in endowment and competitiveness of renewable and nonrenewable energy resources.

Strategies and measures that can be adopted by countries to exploit their renewable energy resources include on site power generation which involves generating power at the location where it is used like photovoltaic panels installed on buildings, farm-based biogas plants, use of geothermal heat pumps located next to the building, and combined heat and power or cogeneration as well as energy saving and efficiency measures. Another strategy to use renewable and low carbon energy is the use of interconnectors whose role is to physically link different grids or countries for more interconnection needed to ensure the countries can import electricity from low carbon producers like France mainly from nuclear and Sweden and Ethiopia with huge hydro potential as a strategy for de-carbonization of their grid electricity ( Dutton, 2019 ). The purchase of green power through Renewable Energy Certificates (RECS) also known as green tags, green energy certificates, also called tradable renewable certificates is another important strategy in promoting electricity generation from renewable sources ( Wanga et al., 2020 ).

7.3.1 Renewable and Non-Renewable Energy Options in the Transition

Through sustainable energy, the dependence on fossil fuel sources is reduced while increasing the use of renewable sources of energy thus reducing greenhouse gases. Renewable energy technologies may be divided into three generations. The first generation commenced in the nineteenth century and relied on hydropower biomass and geothermal energy. The second generation started in the 1980s and consisted of consists of tidal, wind power, wave power, and solar energy. The third stage or generation is still under development today and is based on gasification, bio-refinery, and ocean thermal power ( Hollaway and Bai, 2013 ). As the global fossil fuel reserves and nuclear diminish, the world has an urgent need to increase the use of renewable energy resources and diversify other available resources and efficiency options. Currently renewable energy power generation has focused on solar photovoltaic (PV), hydro, and wind energy resources with limited use of geothermal and biomass. This is despite the abundance of these energy resources, underlined, for instance, by the importance of sugar-mill power generation ( CS-UNIDO, 2008 ).

There is a global energy transition back to renewable energy, after a century of fossil fuel dominance. Solar energy, wind, bioenergy and geothermal among others will play a leading role in the current transition ( Moriarty and Honnery, 2019 ). The transition will however require creativity and enhanced innovation in form of technology and institutional reforms ( Pegels et al., 2018 ). There are various options for future use of renewable energy.

1) Electricity from Intermittent wind, solar, and wave energy.

2) Dispatchable electricity from hydropower, i.e., major, mini, micro, and others based on resource availability.

3) Energy in form of thermal dispatchable power from solar, geothermal, and biomass.

4) Direct use of thermal energy from bioenergy and low-temperature geothermal energy for heating and cooling applications.

5) Biochemical conversion like biomass to biogas and fermentation to produce gaseous and liquid forms energy ( Moriarty and Honnery, 2019 ).

7.3.1.1 Hydropower

Hydroelectric plants convert energy in moving water to electricity. Conventional hydropower plants have a reservoir developed behind a dam to supply water to the hydraulic turbine for generation of a highly flexible, dispatchable electricity supply. Hydropower can be combined with wind, solar and other sources to supply reliable steady and affordable grid electricity. Hydropower can also be exploited from, run-of-the-river resources which have less environmental impact but with overreliance on steady supply of rain water whose supply is unsteady and unpredictable. Apart from power generation, reservoirs can control floods, supply water, and power from stored water even during drought ( Wikipedia, 2021 ). Hydroelectric electric power plants are useful for grid electricity sustainability particularly during peak hours where plants that generate flexible and cheaper electricity are on high demand ( Kolagar et al., 2020 ).

In 2017, whereas fossil fuels supplied 16,947 TWh or 63% of the total global electricity generation, 4,222 TWh or 16% came from hydropower ( BP, 2021 ) while in 2020, hydropower contributed 16% of global electricity generation as fossil fuels supplied 61.3% of global electricity ( International Energy Agency, 2019 ; BP, 2021 ). Hydropower is environmental-friendly and releases much less greenhouse gases (GHG) compared to fossil fuel sources like oil, natural gas, coal, and diesel. Hydropower also provides energy security as it decreases reliance on fossil fuels, besides other benefits of developing dams like irrigation, supply of water for industrial and domestic use, flood control and employment opportunities ( Solarin et al., 2021 ).

Hydropower has very low emission which vary with the size of the reservoir. Decomposing organic matter release methane and carbon dioxide while deforestation affects the local hydrology and promotes desertification besides displacing many people from their settlements ( Wikipedia, 2021 ).

7.3.1.2 Solar Energy

Solar energy is cheap because the cost of solar energy is usually negligible, beyond the initial cost outlay. The operational costs of solar are also significantly lower than the conventional power plants. Solar is an important source of energy security since it is locally available. Energy security which is guaranteed by solar energy makes a country less susceptible to external interruptions or events which may influence supply or cost. Socially and economically, solar power generation creates employment opportunities, for example in the year 2018, the solar photovoltaic industry supported more than over 3.6 million jobs globally ( Solarin et al., 2021 ). The main challenge facing solar energy is variability and intermittence in supply and relatively low electricity conversion efficiency.

7.3.1.3 Geothermal Energy

Geothermal energy is produced by drilling deep into the Earth’s crust for harnessing to generate electricity or thermal energy. Feasible geothermal resources are available where the thermal gradient is above 30°C/km, permeable rock structure, natural or artificial water replenishment, and an impervious cap rock. Geothermal contributes less than 1% of global electricity generation even though we have significant potential such that it can meet the entire energy needs of humanity at current rates of consumption ( Barasa Kabeyi, 2019a ; Kabeyi, 2020c ).

As a renewable energy resources, geothermal energy is constantly replenished from neighboring hotter regions and the radioactive decay of naturally occurring isotopes deep in the Earth’s crust. The greenhouse gas emissions from geothermal-based electricity are less than 5% of total emissions from coal-based electricity generation ( Kabeyi and Olanrewaju, 2022 ). The risks associated with geothermal energy exploitation include the risk of inducing earthquakes, water and soil pollution from brine, and releases toxic emissions like hydrogen sulphide and greenhouse gas emissions like carbon dioxide ( Kabeyi and Olanrewaju, 2021f ). The main challenge facing geothermal electricity generation is long project development period, high upfront risks and huge project costs for conventional technologies which also have low electricity conversion efficiency. The adoption of wellhead generators as a project development option can reduce the period and risks involved in development of geothermal powerplants ( Kabeyi and Oludolapo, 2020a ; Kabeyi et al., 2020 ; Kabeyi and Olanrewaju, 2021a ).

7.3.1.4 Wind Energy and Power

Wind has been used by man for a very long period to drive windmills, pumps, sailing ships and mechanical energy for industrial processes. Wind turbine generators are used to generate electric power and provided about 6% of global electricity in 2019 ( Enerdata, 2021 ). Wind generated electricity is competitive with nuclear and natural gas and is cheaper than electricity from coal Other than installing onshore, wind turbogenerators can be installed offshore where wind is stronger but will cost more in construction and maintenance ( Dreyer, 2021 ).

Wind generators have environmental impact in form of visual impact on the landscape. collisions between turbine blades with birds and bats is common while noise and flickering lights can cause annoyance and constrain human settlement near the installations ( Wang and Wang, 2015 ). Advantages of wind power is low construction energy and the plants have low water requirements but need more land and the turbine blade materials are not fully recyclable ( Huang et al., 2017 ).

7.3.1.5 Bioenergy

Bioenergy is energy that comes from biomass which is organic material that comes from animals and plants. Biomass produce heat and electricity on combustion and can also be converted into biofuels like biodiesel, ethanol, methanol, etc. for use in combustion engines ( Ayompe et al., 2021 ). Biomass or bioenergy resources include solid and liquid waste, industrial and domestic wastewater, forest resource waste, agricultural waste, and livestock waste ( Kabeyi, 2020a ). All countries around the word have bioenergy in one form or another. This makes biomass an important energy or electricity source that guarantees energy security with limited environmental harm ( Kolagar et al., 2020 ).

The feedstocks used to include how they are grown, harvested, and processed determines the climate impact of biomass sources of energy. As an example, burning wood fuel produces carbon dioxide which can be offset by photosynthesis in fast growing energy trees and well-managed forest cover since trees absorb carbon dioxide as they grow. The negative impact of bioenergy crops is that they displace natural ecosystems, cause soil degradation, and also they consume water resources and synthetic fertilizers which have some carbon value. About a 1/3 of wood used globally is unsustainably harvested and consumed. Additionally the harvesting and processing of bioenergy feedstocks requires energy for harvest, drying, and transportation which adds to its carbon footprint as greenhouse gases are emitted, although in significantly less quantities than fossil fuels ( Correa, 2019 ).

7.3.1.6 Hydrogen Energy

Hydrogen produces electricity with zero emissions at the point of usage. However, the overall lifecycle emissions of hydrogen are determined by the production process used in its production. Currently, hydrogen is mainly produced from fossil fuel sources ( Chant, 2021 ). The main method of hydrogen production is by steam methane reforming where hydrogen is made by chemical reaction between steam and methane. About 6.6–6.9 tons of CO 2 are emitted by of this process to produce one ton of hydrogen ( Bonheure et al., 2021 ). Carbon capture process can then be used to remove a large percentage of the CO 2 produced making the process cleaner. Although the overall carbon footprint of hydrogen as a fuel is yet to be fully established, it remains a cleaner fuel than natural gas, biogas or methane ( Griffiths et al., 2021 ).

In another method of hydrogen production, electrolysis by use of electricity can be used to split water molecules to hydrogen fuel. However, the process is more expensive compared to methane reforming and sustainability requires that the electricity is from green sources which for now is still a challenge in many parts of the world. Hydrogen fuel can be produced during surplus of intermittent renewable electricity and stored for use during peak and when the variable renewable disappears ( Palys and Daoutidis, 2020 ). Hydrogen can also be processed into synthetic fuels sources of energy like ammonia and methanol ( Blank and Molly, 2020 ).

Research and development are encouraged to develop hydrogen electrolyzers for use in large-scale production of hydrogen for power generation competitively. Hydrogen produces intense heat suitable for industrial production of steel, cement, glass, and chemicals. Therefore, hydrogen can act as a clean fuel in the steal steelmaking, can act as a clean energy carrier and simultaneously as low-carbon catalyst in place of coke ( Blank and Molly, 2020 ). The main limitation of hydrogen as an energy carrier is high storage and distribution costs since it is explosive and occupies a large volume. The gas also embrittles pipes hence it needs special handling facilities which have to be developed ( Griffiths et al., 2021 ).

7.3.1.7 Natural Gas

It is important to note that several cities globally have reached or are reaching epidemically poor-quality atmospheric air quality requirements and urgently need to reduce pollution from engines emissions. There is need for an immediate remedy to pollution caused by urban diesel vehicles. Natural gas as a fuel is also cheaper than refined petroleum products. In most markets around the world [ Group of Experts on Pollution & Energy (GRPE), 2001 ].

Besides direct combustion, natural gas has more hydrogen atoms making it an excellent raw material or feedstock for hydrogen production by using high-temperature steam also called, steam methane reforming, and by partial oxidation. Steam reforming and partial oxidation both produce “synthesis gas,” that produces more hydrogen when reacted with water. These processes make natural gas a pathway to the hydrogen future. This is mainly because several aspects of hydrogen and natural gas distribution and storage, fueling, station siting, and training of technicians and drivers are similar. Hence knowledge from handling of natural gas will make the transition to a hydrogen fuel smoother. Hydrogen and natural gas can also be blended with hydrogen to make transportation fuel. These can take the form of 20% by volume hydrogen also called Hythane or 30% by volume hydrogen called HCNG ( Werpy et al., 2010 ).

7.3.1.8 Marine Energy

This energy resource has one of the smallest contributions to the global energy market. Marine energy consists of tidal power, which is a maturing technology and wave power, which is steal under early stages of research and development as well as ocean thermal energy. A typical example of these resources is the Two Tidal Barrage Systems in France and in South Korea which account for 90% of world marine energy production. The environmental impact of small and single marine energy devices is little except for larger devices are less well known ( Wikipedia, 2021 ). Tidal power is a form of green energy resource, as it emits near zero greenhouse gases and occupies less space per unit power. The largest tidal powerplant project globally is the Sihwa Lake Tidal Power Station in South Korea, which has installed capacity of 254 MW established in 2011, as a development to a 12.5 km-long seawall that was built in the year 1994 to for flood control and support of farming ( Husseini, 2021 ). Tidal power has the benefit of predictability as the gravitational forces of celestial bodies won’t be going anywhere soon. The equipment is also about four times longer lasting than wind equipment and the plant has high power density with limited surface area requirements ( Wikipedia, 2021 ; Husseini, 2021 ).

The Ocean Thermal Energy Conversion (OTEC) is a marine technology that utilizes the solar energy absorbed by sea water to generate electricity. It takes advantage of the thermal difference between cooler deep waters and warmer shallow or surface ocean waters to operate a heat engine to generate work. The main challenge is that the temperature difference is small which poses a challenge to the technical and economic sustainability ( World Energy Council, 2013 ). This calls for more research and development for ocean thermal energy.

7.3.1.9 Nuclear Power

Nuclear power plants have been in operation since 1950s as sources of low carbon base load electricity. Nuclear power plants operate in over 30 countries generating over 10% of global electric power ( Rhodes, 2021 ; World Nuclear Association, 2021 ). As of the year 2019, over 25% of the low carbon electricity was generated from nuclear making it the 2nd largest source after hydropower. The main environmental benefit of nuclear power is that the lifecycle greenhouse gas emissions including that of mining and processing of uranium are close to emissions from renewable energy sources ( Bruckner and Fulton, 2014 ). Additionally, its land requirement per unit power output is or less than that of the major renewables, and it doesn’t pollute the local environment. Although uranium ore is a non-renewable resource, its available quantities can provide power for hundreds to thousands of years to come. Therefore, increased use of nuclear power will reduce emissions and related environmental impact ( Bruckner and Fulton, 2014 ; Dunai and De Clercq, 2019 ).

The main sustainability challenges of nuclear power generation which should be addressed are challenges of nuclear waste handling and disposal, weapon proliferation, and catastrophic accidents ( Gill et al., 2014 ). There is need to manage radioactive nuclear waste over long time scales before final disposal ( Gill et al., 2014 ), while low energy fissile material created is a feasible raw material for low energy nuclear applications including military use in weapon development ( Gill et al., 2014 ). Statistically, nuclear energy has caused fewer accidents and pollution related deaths than fossil fuel ( Ritchie, 2021 ). The challenge to the investment and hence development of nuclear power is politically motivated and is mainly over fear for weapons proliferation ( Gill et al., 2014 ).

The main challenges facing nuclear power development is long developing period, and high cost of capacity and powerplant development, hence the need to reduce cost and delivery time ( Timmer, 2021 ). Technology options include Fast breeder reactors which are capable of recycling nuclear waste hence reduce disposal challenges by reducing waste but they are yet to be commercially deployed ( Joint Research Centre, 2021 ). In terms of energy security, countries with no Uranium can resort to the use of thorium rather than uranium ( Gill et al., 2014 ). Another sustainable option is use of Small modular reactors which are smaller, cheaper and faster to deploy. While their modularization allows flexibility in capacity development for countries with low electricity demand. Modular units also generate less waste and have less risks of explosion ( Bruckner and Fulton, 2014 ; Gill et al., 2014 ).

7.3.1.10 Coal and Petroleum Resources

Coal is a leading source of energy for grid electricity while countries like Poland rely on coal for significant energy applications and source of revenue to the economy. Poland for example is the largest producer of hard coal and the second largest producer of lignite in the European union followed by Germany. Therefore, coal is an important economic product for several countries, besides being a secure energy resource. Due to abundant supply of coal as a secure energy source, coal accounted for 76.8% of its electricity in Poland. For Germany, which is another leading producer of coal, it accounted for 35.6% of electricity generation, followed by the United Kingdom which produced 5.1% of its electricity from coal. The entire European union produced 18.9% of its electricity from coal. Poland produced 68.3 million tons of hard coal in 2019, which was an 85 reduction over the 2018 production. Of all coal produced, 60.1% was consumed by the energy sector, 24.6 was used by the industry and construction while households used 15.2%. The coal industry has a positive social value worth noting. For example, in 2019, coal mining employed 94% of people in coal mining or 78,500 people in Upper Silesian Basin, of Poland while the remaining 6% worked at the Bogdanka mine in the Lublin province of Poland with monthly salaries in 2020 being twice the average salary in Poland ( Krzywda et al., 2021 ).

Although coal is a fossil fuel with huge environmental impact, it will continue to play an important role in power generation with application of clean coal technologies. Gradual substitution is recommended as coal rich economies continue transition to renewable and low carbon energy resources and diverse their economies to substitute declining coal revenue.

7.3.1.11 Shift to Natural Gas From Coal and Petroleum Fuels

The switching from coal and diesel to natural gas in power generation has significant benefits in terms of sustainability. Natural gas generates about half the emissions of coal when used in power generation and about two-thirds the emissions of coal when applied in heat production. Additionally, natural gas produces less air pollution than coal, but the challenge is to limit gas leakages since methane is highly potent as a greenhouse gas ( Information Adminitstr, 2021 ).

The shift from coal to natural gas reduces emissions as a short term measure but does not provide a long term path to the desirable net-zero emissions. Therefore these transition has the danger of causing carbon lock-in and stranded assets which must be written off or they are allowed to continue operating against the emission targets ( Gürsan and de Gooyert, 2021 ; Plumer, 2021 ).

7.3.2 Benefits and Challenges of Renewable Energy

There is a relationship between total greenhouse gas emissions and consumption of renewable energy resources. For example between 1990 and 2012, greenhouse gas emissions (GHG) in European Environmental Agency (EEA) with 33 member countries reduced by 14% while GHG emissions per capita declined by 22% over the same period ( European Environment Agen, 2016 ) due to increased use of renewable energy, a scenario that was also witnessed in the United States between 2006 and 2014 ( Owusu and Asumadu-Sarkodie, 2016 ). This brings both environmental and socioeconomic benefits with less environmental impact through substituting polluting fossils with renewable and low carbon energy sources and creation of jobs and social capital in the society [ United States Environmental Protection Agency (EPA), 2017 ].

Renewable energy sources and technologies are competitive energy options particularly for remote areas but encounter barriers to their diffusion like lack of access to capital for the for low and medium-income population. There is need for financing for renewable energy technologies, such as solar PV, micro-hydro, wind power for water pumping and electric power generation, bio digesters and biogas installation costs and improved woodstoves production and installation ( Kabeyi and Oludolapo, 2021b ). Other barriers include:

1) Lack of competitiveness since most of these renewable energy power plants have higher investment and energy costs as compared to conventional or nonrenewable options particularly in terms of initial cost of the project.

2) Uncoordinated planning, policy and legal and financial instruments has ensured that renewable energy renewable energy projects need support against nonrenewable sources in form carbon tax, tax incentives and subsidies and regulations support to enhance their diffusion and interconnection to electricity grid and general adoption.

3) There is Lack of information, supportive infrastructure, and maintenance, for example in some cases, there is lack of technologies and infrastructure or capabilities to develop renewable energy projects or markets ( Kabeyi and Oludolapo, 2021b ).

7.4 Decentralized and Distributed Power Generation

Power transmission and distribution networks where initially conceived and designed to distribute electricity from central power stations to consumers kilometers away. This approach is no longer valid because of the increasing presence of distributed generation systems that are mainly based on variable renewable energy sources and a growing number of variable load users like, plug-in electric cars connected to the grid and lower voltage points ( Zarco-Soto et al., 2021 ). There has been a shift to the use of small and distributed powerplants as the world gradually adopts the use of renewable sources of energy for grid electricity generation which requires a bi-directional flow of power through transformers ( Colangelo et al., 2021 ). The centralized model of power generation and distribution has dominated the electricity sector in many countries while distributed energy resources (DER), are slowly being accommodated and remain dominant in remote and isolated areas. The decentralization of electricity generation gathered momentum when economies of scale stopped being significant factor owing to innovation and technology development. The main motivation was the use of diesel engines and gas turbines and the adoption of smart grids. Traditionally, decentralised systems consisted of dispatchable resources; but we have increasing use of non-dispatchable PV as a recent development. The development of decentralised generation is such that today, the global annual distributed generation capacity additions have surpassed the centralized electricity systems ( Mitrova and Melnikov, 2019 ).

For maximum use of DER technologies to be achieved, there is need to develop a systemic architecture and put in place policy measures in the power sector to balance the interests of new players with the existing centralized model players. However, an optimal combination of centralized generation and DER seems to be the most effective and efficient approach in the energy transition. This implementation requires principles and mechanisms for seamless for the integration of the centralized and decentralized for reliability in operations ( Mitrova and Melnikov, 2019 ). The main system benefit distributed renewable energy sources is that it leads to increase in nodal voltages. The growing use of variable loads on distribution networks like electric cars puts significant pressure on the need for nodal voltage control through a flexible and resilient electricity grid that goes beyond mere decentralization of grid power generation ( Zarco-Soto et al., 2021 ). With the new decentralized generation technologies, economies of scale have been turned upside down with improved viability of small energy systems. Increased use of information technologies has generated new opportunities for energy e infrastructure management in a less hierarchical and flexible manner. This combined with consumer demands for control over their energy systems has created energy communities (ECs) on the agenda hence higher opportunities for transition towards more sustainable energy through improvement in efficiency, less emissions, reduced costs, and hence a sustainable energy future.

7.5 Transition From Traditional to Smart Grids

About 10% of the total grid power is lost to transmission and distribution of which 40% is lost at the distribution side alone in the traditional grid ( Rathor and Saxena, 2020b ). The solutions to the energy or electricity related pollution and losses are significant reduction in use of fossil fuels, increased use of renewable energy sources like photovoltaics and wind, use of fuel cells and integration of energy and battery storage systems and use of plug-in electric cars ( Conejo et al., 2010 ; Azzouz et al., 2015 ; Rathor and Saxena, 2020b ). The world has witnessed significant advances in technology which includes development of better electricity carriers, decentralization of generation and increasing contribution of variable renewable sources energy to grid electricity and electrification of transport which introduces unpredictable load on the grid. All these developments call for development and use of smart grids. The smart grid uses computer programs and hardware to manage electricity generation and distribution resources and hence can help in optimization of the energy mix of both renewable and non-renewable energy for sustainable power generation and supply through smart grids. Smart grids can facilitate increased absorption of variable renewable sources of energy like wind and solar and thus displace fossil fuels from the grid. They enhance decentralization of generation provide the infrastructure and capacity needed to facilitate increased use of renewable energy help increase participation of all stakeholders in the operation and power delivery between sources and users in a two-way manner. This will greatly contribute to the dream of a sustainable grid electricity system.

The current global trend is to develop digital technologies for the entire economies and hence digitalization of the power systems is part of the global technological transition. Digitalization of electricity sector brings opportunities particularly the increased absorption of variable renewable like wind and solar which makes control very difficult ( Schiffer and Trüby, 2018 ). Lack of system flexibility reduces its resilience and hence capacity to absorb the variable sources of energy hence the need to adopt power system digitalization as a transition strategy ( Mitrova and Melnikov, 2019 ). Digitalization of operation and controls in power-generating and supply assets will increase efficiency, security of power systems as well as resilience more efficient, the electric grid more secure and resilient, thus reducing emissions and the threat of global climate change.

7.6 Research and Development of Sustainable Energy Technologies

It is not practical to achieve significant contribution of the intermittent renewable energy sources like solar, wind and hydro in power production without a combination of flexible dispatch able power, a reliable electricity transmission system, energy storage facilities, the smart grids, and demand side electricity management. To realize maximum renewable energy contribution, it is necessary to develop effective business models and policies, modern innovative energy technologies, system operational flexibility, and efficiency through continues research and development ( Gielen et al., 2019 ). The technology and approaches to enable sustainable electricity include the development of smart grids and replacement of the traditional electricity grid, decentralization of grid electricity generation and use which will lead to better absorption of renewable energy and adequate participation of consumers in demand management, electrification transport, development of energy storage technologies, demand side management strategies through measures like time dependent electricity tariff system and smart solutions like smart meters for consumers within a smart grid. Most of the critical technologies for the energy transition like smart grids and cheaper energy storage technologies are still under research and development and require funding and other forms of research support to mature.

7.6.1 Carbon Capture and Storage

Carbon capture and storage technology is an effective technology to absorb emissions, either by natural processes in bio crops or industrial scale plant processes. This process is known as bioenergy with carbon capture and storage (BECCS) can lead to net CO 2 removal from the atmosphere while carbon dioxide and other emissions from powerplants and other process plants can be absorbed and stored or buried. Unfortunately, BECCS may lead to net positive emissions based on how the biomass is produced, harvested, transported, and processed. Biomass material is grown, harvested, and transported ( Ayompe et al., 2021 ).

7.6.2 Energy Storage

Energy storage is an important solution to intermittent renewable energy supply and hence a critical aspect of a sustainable energy system. Various storage methods for use include pumped-storage hydroelectricity ( Hunt, 2020 ), and batteries especially lithium-ion batteries ( Blanco and Faaij, 2018 ). The challenge with batteries is that they have limited storage periods which calls for more research into storage technology for both utility-scale batteries and low energy density batteries makes them impractical for the very large energy storage needed to balance inter-seasonal variations in energy production. Other than pumped hydro storage and power-to-gas like hydrogen needs further research ( Koohi-Fayegh and Rosen, 2020 ).

7.6.3 Fuel Cells in Sustainable Electricity

Fuel cells are electrochemical systems that convert chemical energy of a fuel like hydrogen and oxidizing agent often oxygen to electricity through a pair of redox reactions. Unlike batteries they continuously require supply of fuel and oxygen to sustain the process. In batteries the chemical energy comes from metals and their ions or oxides that are already in the battery except for flow batteries ( Saikia et al., 2018 ). The fuel cell will produce power continuously on condition that there is a steady supply of the fuel and oxygen and are more efficient than combustion systems. The heat generated in the process of power generation can be put into thermal application thus further increasing the efficiency through cogeneration. They are able to reduce building facility energy service cost by 20–40% ( Fuel Cells, 2000 ).

Stationary fuel cells are often used for commercial, industrial, and residential primary and backup electricity generation and can be very useful for power supply in remote locations, like spacecraft, isolated weather stations, large parks, telecommunication communication centers, off grid stations including research stations, remote military applications, and standby power supply sources for power stations ( Saikia et al., 2018 ). The main advantage of fuel cell systems like hydrogen fuel cells is that they are compact, light, and have limited moving parts to attend to hence low maintenance and can realize 99.9999% reliability ( Fuel Cells, 2000 ).

7.6.4 Electrification Transport Industrial Processes and Rural Areas

It is possible to reduce emissions faster in electricity systems than many other systems because as in 2019, about 37% of global electricity generation came from low-carbon sources, i.e., renewables and nuclear energy with the rest coming from coal and other fossil fuel sources ( Bruckner et al., 2014b ). Phasing out coal fired power plants is among the easiest and fastest ways to controlling greenhouse gas emissions and in its place increase the share of renewable and low carbon electricity generation ( Ritchie, 2021 ). A leading limitation in provision of universal access to electric power is rural electrification where both off-grid and on-grid systems based on renewable energy can power villages who predominantly rely on wood fuel, kerosene and diesel generators for heat lighting and power ( Rosen, 2009 ). Wider access to reliable electricity would lead to less use of kerosene lighting particularly for the developing countries ( United Nations Develpment programme, 2016 ).

Electrification of transport is significant because transport sector accounts for about 14% of global greenhouse gas emissions which can be reduced by use of electric cars, buses, and electric trains that consume green electricity ( Bigazzi, 2019 ). The various climate change scenarios predict extensive electrification and substitution of direct fossil fuel combustion with clean electricity for heating building and for transport ( Miller et al., 2013 ). A deliberate climate policy should see double increase in energy share from electric power by 2015 from the 20% of the year 2020 ( Bruckner et al., 2014b ; IRENA, 2018 ; United Nations Develpment programme, 2016 ).

7.6.5 Energy Efficiency and Conservation

Energy efficiency and conservation have potential to provide a means to achieve global emissions and climate change targets set by the Paris agreement and other national and international protocols. Energy efficiency and conservation measures will lead to reduction in greenhouse gas emissions, reduce fuel consumption, reduce the load and strain on the electricity grid, and reduce cost of both generation and cost of electricity consumed ( Clark and Clark, 2019 ). The main challenge facing adoption of efficiency and conservation measures is lack of appropriate technology and high capital requirements which creates financial management risk and undetermined return-on-investment and hence undetermined payback periods which significantly limit their adoption ( Clark and Clark, 2019 ). Significant amount of energy in many forms including heat, electricity and even primary resource id lost or wasted through transmission, heat loss, and application of inefficient technology. This is a huge cost to consumers who must pay for the lost energy as more energy is consumed to carter for the losses resulting in more pollution for every extra unit consumed due to losses ( Department of Energy, 2021 ). Therefore, putting in place various energy efficiency measures is one of the easiest and cost-effective means of combatting climate change, limit emissions and related pollution, reduce energy costs and improve the competitiveness of businesses ( Department of Energy, 2021 ). In a sustainable energy scenario by the International Energy Agency, energy efficiency is expected to deliver more than 40% of targeted reduction in energy-related greenhouse gas emissions between 2020 and 2040 as a strategy to put the world on track to achieve international emissions and related climate change targets ( Clark and Clark, 2019 ; International Energy Agency, 2021c ).

7.6.6 Microgrids

Microgrids are becoming an important solution in the sustainable energy transition by improving reliability and resilience of electric power grids, necessary to manage distributed clean energy resources like wind and solar photovoltaic (PV) as well as generation to reduce emissions as well as supply power to off grid locations ( Wilson, 2021 ). A microgrid can be defined as a group of interconnected loads and distributed energy resources existing in a well-defined electrical boundary that is operated as single controllable unit with respect to the grid. It can connect and disconnect from the main grid to enable it to operate in both grid and off grid mode ( Valencia et al., 2021 ; Wilson, 2021 ).

A grid basically consists of a power source, consumers, wires to connect them, and a system to control generation and supply. On the other hand, a microgrid is a grid but a smaller version of it. A microgrid can cover one or several buildings and can be used to supply power to critical infrastructure, remote or small communities or business and industrial installation ( Valencia et al., 2021 ). Microgrids enable supply of clean and efficient energy, with more resiliency, and improves the operation and stability of the local electric power systems ( Wilson, 2021 ). Microgrids constitute a very important segment of the energy transition representing a shift from centralized power towards more localized and distributed generation solutions. The main benefit of microgrids is ability to isolate from the central or larger grid hence a feasible and attractive option for cities, rural areas, industrial parks, suburbs, and remote installations. With use of microgrids, it possible to balance generation from variable renewable power sources such as solar, wind, and hydro and conventional sources like gas-fueled combustion turbines, coal, and diesel powerplants ( Wilson, 2021 ).

7.7 Earth Radiation Management and the Solar Radiation Management

The current global warming mitigation efforts and future commitments are inadequate to achieve the Paris Agreement temperature targets. Although the various techniques show the physical potential to contribute to limiting climate change, many are still in the early stages of development. For this reason, the climate geoengineering techniques provide alternative or additional measures to contribute to meeting the Paris Agreement temperature goals ( Lawrence et al., 2018 ). The best way so far to reduce global warming is reduction in the anthropogenic emissions of greenhouse gases. However, the global economy with its ever-growing population cannot do without energy most of which is generated from fossil fuels. Replacing this energy with carbon dioxide-free renewable energies, and energy efficiency is a long term, costly, and difficult venture. By use of geoengineering schemes which use solar radiation management technologies to modify terrestrial albedo or reflect incoming shortwave solar radiation back to space provide an alternative solution to the challenge of global warming ( Lenton and Vaughan, 2009 ). We also have power-generating systems that have potential to transfer heat from the Earth surface to the upper layers of the troposphere and then to the space ( Ming et al., 2014 ). The main objective of Geoengineering is to stabilize global climate, reduce global warming and reduce anthropogenic climate changes by two main strategies namely, shortwave (0.3–3 μm) reflection where sunlight is reflected back and then secondly the use of carbon dioxide removal technologies ( Ming et al., 2014 ).

The solar radiation management geoengineering systems work by the parasol effect, i.e., reducing solar incoming radiation, but the carbon dioxide still traps the reduced heat both day and night over the entire world. The effect of solar radiation management would be only experienced during the day particularly at the equator ( Ming et al., 2014 ).

8 Results and Discussion

A good concept of sustainable development should facilitate social equity, prevent environmental degradation, and maintain a sound economic base. There is need for sustainable preservation of natural capital for sustained economic production and equity in intergeneration equity in resource exploitation. Fulfillment of basic health and participatory democracy is crucial in energy resource planning and exploitation to ensure sustainability. Sustainable transition requires governments to use policy instruments and an effective institutional mechanism to deliver working solutions to a sustainable energy future. The three main dimensions of sustainable development are economic, social, and environmental sustainability. However, sustainability in energy resource use and electricity systems has extra dimensions of technical, and political or institutional sustainability.

Humanity has increased the concentration of carbon dioxide in our atmosphere, amplifying Earth’s natural greenhouse effect. This is still ongoing and hence a continuous threat to the global environment. The global average amount of carbon dioxide hit a new record high in 2020: of 412.5 ppm. The annual rate of global increase in atmospheric CO 2 over the last 60 years is about 100 times faster than previous natural increases like those that occurred at the end of the last ice age about 11,000–17,000 years ago. As a result, the ocean has absorbed enough carbon dioxide to lower its PH by 0.1 units, from 8.21 to 8.10 since the beginning of the industrial revolution which represents about 30% increase in acidity of the ocean. This is dangerous to aquatic ecological balance due to the biological effect of ocean acidification which interferes with marine life’s ability to extract calcium from the water to build their shells and skeletons.

The energy sector is the largest contributor of global carbon dioxide emissions and second largest contributor of non-carbon dioxide greenhouse gas emissions globally. With electricity being the leading source of greenhouse gases, which are the cause of global warming, any effort to minimize greenhouse gases should address emissions from power generation. Sustainable grid electricity requires facilitating technologies and infrastructure like smart grids, decentralization of generation. A mixture of options is necessary to lower the unit cost and carbon intensity of energy systems to achieve a truly sustainable energy with low carbon world. Energy related GHG emissions are a result from conversion and delivery sectors like extraction/refining, power generation and direct transport of energy carriers in pipelines, cables, ships, tracks an end use sectors and industries like transport, buildings and construction, manufacturing, agriculture, forestry, households, and waste and hence cannot be blamed entirely on one sector or process alone.

The Intergovernmental panel on climate change (IPCC) predicted that a greenhouse gas emission (GHG) will lead to global temperature increase of between 1.1 and 6.4°C by the end of the 21st Century. The world would experience about 62% increase in CO 2 emissions between 2011 and 2050 if energy demand and use of fossil fuels to meet the demand does not change. To maintain ecologically sustainability, organizations should consume natural resources whose consumption rates are lower than the rate of natural replenishment or reproduction. Where substitutes exist, the rate of consumption should be lower than the rate of substitute development. The greenhouse gas emissions should be reduced by between 50 and 80% by the year 2050 if the world must avoid the looming consequences of global warming. The composition of atmospheric carbon dioxide (CO 2 ) has been rising as summarized in Table 2 above.

TABLE 2 . Increase in CO 2 concentration between 1750 and 2018.

Table 2 shows that between 1750 and 2020, the atmospheric concentration of carbon dioxide has increased from 277 to 412.5 ppm representing an increase of 48.92%.

For a stable atmosphere, the global average temperature increase should be maintained between 1.5 and 2°C above the preindustrial level which translates to atmospheric carbon dioxide concentration of 400–450 Energy resources are sources of various past and current political and social conflicts and therefore it is through proper energy resource management that many social, political, and economic conflicts can be avoided or resolved globally. Countries can use renewable energy sources like solar, wind and even hydro to enhance their national energy security because these resources do not need international trade to secure them and hence cushions countries against energy instigated insecurity.

Today, industry and building sectors are the main users of electricity accounting for over 90% of global electricity demand. Moving forward, the main drivers of electricity demand growth are motors in industry which may account for over 30% of the total growth to 2040, industrial and domestic space cooling will account for 17% while large electrical appliances are projected to account for 10% growth and electric vehicles are projected to account for 10% growth in electricity demand. Further growth in electricity demand of about 2% is projected to come from provision of electricity access to 530 million first time users of electricity. The sustainable development scenario, projects that electric vehicles will become a leading source of electricity demand moving to the future towards the year 2040. Therefore, a sustainable electricity transition should prepare for wider use of variable renewables, low carbon nuclear power, electrification of transportation and industrial processes, better and efficient conversion, and efficient energy use technologies and electrification of thermal application of energy.

Table 3 , it is noted that fossil fuels in the form of coal, natural gas and oil contributed 61.3% of the global electricity generation in the year 2020. Low carbon nuclear and renewable energy sources which should be the basis of the sustainable electricity transition accounted for about 38% of global electricity with undefined sources accounting for about 0.7% of the global electricity generation in the year 2020.

TABLE 3 . The global electricity generation can be summarized in Table 3 below.

A sustainable electricity transition calls for eventual transition of the 61.3% of the global electricity production to low carbon and renewable energy sources. In the short and to some extend middle term, natural gas can substitute oil and coal although with the risk of delaying the zero emissions transition and creating transition related carbon lock-in and stranded assets by developing natural gas infrastructure. Since countries with huge coal and oil reserves may find it unsustainable to make immediate transition, increase in the share of natural gas, and investment in efficient technologies like cogeneration and clean coal technology can reduce the carbon footprint.

Sustainable energy transition should address the five major dimensions. They are technical, social, economic, environmental, and institutional dimensions. These dimensions of energy sustainability are summarized in Table 4 below.

TABLE 4 . The five dimensions of energy sustainability.

From Table 4 , it is noted that there are five dimensions of energy sustainability namely environmental, economic, social, technical, and institutional/political sustainability which can be used to design and analyses energy sustainability measures.

Various energy resources have been identified as potential solution to the global transition. They are discussed in summary form in Table 5 below.

TABLE 5 . Summary of energy options for the global transition.

From Table 5 , it is noted that both renewable and nonrenewable sources of energy have a role to play in the energy transition. The nonrenewable sources like coal and oil are abundant in several countries and therefore are readily available and offer energy security. The steady release of energy by fossil fuel sources is important for reliability and stability and hence quality which are sustainable energy requirements. However, their high carbon footprint, finite supply, price, and supply interruptions and resource related conflicts make fossil fuels unreliable and unsustainable source of energy and hence the need for gradual substitution with renewable and low carbon sources of energy. The use of highly efficient conversion technology and clean coal as well as carbon capture and sequestration can greatly reduce the carbon footprint of fossil fuel sources. For natural gas, controlling leakages along the entire supply chain is paramount due to the high global warming potential of methane which is the main constituent of natural gas.

Solar and wind offer the greatest potential but suffer from unpredictable and unreliable supply challenge hence the need for advanced energy storage facilities. For grid electricity, the unreliability and unpredictable supply nature of wind and solar is a danger to energy security and the grid stability for the traditional grid. However, the use of smart grids with ability to absorb small scale producers and variable supply will greatly increase the absorption of wind and solar energy as well as small hydro sources and decentralized generation.

Various strategies or methods that can be adopted to reduce carbon emissions and hence realize the global energy/electricity transition are summarized in Table 6 below.

TABLE 6 . Summary of sustainable energy transition strategies.

From Table 6 above it is noted that various technological strategies can be adopted separately or in combination to reduce emissions and hence achieve a sustainable energy transition. They include electrification of transport which requires efficient and cost-effective energy storage systems and a resilient electricity grid to handle multiple variable consumer and supplier load. This creates the need to transition from the traditional grid to a more resilient smart grid. Electrification of the rural populations that are not electrified also provide an opportunity for increased use of renewable sources of electricity especially through decentralized generation systems. The use of decentralized generation will widen feasible grid connected generation which mostly comes from renewable energy sources. Energy efficiency by consumers will reduce demand and wastage hence avoid emissions while efficiency in generations leads to less fuel consumption and hence emissions and reduced environmental impact.

Although fossil fuels are major contributors of greenhouse gas emissions leading to global warming, most of them are price competitive, have steady release of energy hence the power plants operate at high load and capacity factors with high reliability of electricity supply, and thus provide grid stability. Therefore, their consumption now and soon is key to a stable and reliable electricity grid which is a key requirement of energy sustainability. The consumption of fossil fuels should be reduced but they will continue to supplement the intermittent and unpredictable but abundant wind and solar energy which have the key to the future sustainable energy supply in a highly optimized electricity generation and supply system where technology will play a key role in planning and decision support. The carbon footprint of fossil fuels used in power generation should minimized by adoption of efficient conversion technologies like cogeneration and trigeneration to minimize which reduce fuel consumption and maximize generation from limited energy resources. Other technologies include dual fuel diesel power, use f biofuel substitutes fuel blending with biofuels and use of combined cycle powerplants. Therefore, a sustainable transition for now should involve increase in energy efficiency to reduce the total demand and wastage of fossil fuels in an optimized system in which the grid absorbs all variable renewables. The smart grid and advanced storage technologies will play a significant role in the sustainable electricity transition.

From this study, the technical options to the energy transition can be grouped into three categories. They are substitution technologies, carbon capture and sequestration and climate geoengineering techniques.

9 Conclusion

Sustainable development cannot be achieved without sustainable energy which facilitates sustainable electricity generation. Whereas sustainable development can be analyzed within three dimensions representing the three pillar of sustainable development namely economic, social and environmental dimensions, sustainable energy is best analyzed with five dimensions namely social, economic, environmental, institutional or political, and technical, The sustainable transition strategies typically consist of three major technological changes namely, energy savings on the demand side, generation efficiency at production level and fossil fuel substitution by various renewable energy sources and low carbon nuclear. For the transition to remain technically and economically feasible and beneficial, policy initiatives are necessary to steer the global electricity transition towards a sustainable energy and electricity system. Whereas renewable sources energy holds the key for sustainable energy transition, large-scale renewable energy adoption should include measures to improve efficiency of existing nonrenewable sources which still have an important cost reduction and stabilization role. A resilient grid with advanced energy storage for storage and absorption of variable renewables should also be part of the transition strategies. The world has so far witnessed three typical energy transitions. The first transition involved replacement of wood with coal as the main energy source. In the second transition, oil replaced coal as the dominant energy resource. In the third transition, there is global commitment to replace fossil fuels with renewable energy. Through the cumulative effect of the Stockholm, Rio, and Johannesburg conferences, sustainable energy development (SED) was identified as a key requirement for sustainable development and so energy was linked energy to the environmental dimension in the Stockholm conference, economy in the Rio conference and society in the Johannesburg conference. Sustainable development is expected to bring economic and progress in an environmentally benign manner free from wastage, pollution, destructive emissions, and social strive in a facilitating political environment. Sustainable development has got three main dimensions of economic, social, and environmental aspects while sustainable energy has got two additional dimensions of technical and institutional or political environment.

The greatest sustainability challenge facing humanity today is the greenhouse gas emissions and the global climate change with fossil fuels led by coal, natural gas, and oil contributing 61.3% of global electricity generation in the year 2020. Through sustainable energy, the dependence on fossil fuel sources is reduced while increasing the use of renewable sources of energy thus reducing greenhouse gases. Renewable energy technologies may be divided into three generations. The first generation commenced in the nineteenth century and relied on hydropower biomass and geothermal energy. The second generation started in the 1980s and consisted of consists of tidal, wind power, wave power, and solar energy. The third stage or generation is still under development today and is based on gasification, bio-refinery, and ocean thermal power. Electricity is the most dominant form of energy deriving its supply from both renewable and nonrenewable sources. The optimum operation of the grid electricity system is influenced by many dynamic variables which must be determined and controlled, managed, or accommodated to deliver reliable, affordable, and clean electricity. Sustainable grid electricity transformation needs competitive and cost-effective financing mechanisms to accelerate the transition, needs reliable energy supplies, and application of effective business and operation modelling tools that can deliver sustainable electricity which also needs new technology and data capability to analyze, and optimize results on real-time basis and in medium- and long-term planning.

Technology has very important role to play in the transition to a low carbon electricity grid and economy. Technology options to facilitate the energy transition will include rapid digitalization of the energy sector which will enhance its flexibility and resilience to absorb variable renewable sources of energy particularly wind and solar. Important technology include transition from the traditional grid based on centralized generation to smart grids which support decentralized generation and ability to absorb the fluctuating renewable energy sources like solar and wind and fluctuating demand like electric cars while guaranteeing a stable and reliable electricity supply. Decentralization and enhanced use of variable renewables will further be enhanced by use of microgrid technology. With use of microgrids, it possible to balance generation from variable renewable power sources such as solar, wind, and hydro and conventional sources like gas-fueled combustion turbines, coal, and diesel powerplants. Since greenhouse gas emissions come from sectors like extraction/refining, power generation and direct transport, agriculture, industry, and homes, electrification of all industries and homes with power coming from renewable sources of energy will greatly succeed in cutting down global emissions. The broad strategies adopted for sustainable transition include liberalisation and restructuring of electricity and other energy markets which is made attractive by ever growing energy demand globally. Key polices adopted should aim at making electricity markets work better. More research and development into efficient, environmentally friendly, and competitive technology is needed to facilitate innovation and diffusion of sustainable energy technologies. To successful implement these policies calls for reduction unit cost of electricity and affordable cost of appropriate energy carriers and services, plus regulations to increase efficiency and reduce energy related environmental for greater public benefits.

The implementation of effective sustainable energy technologies to minimize carbon emissions will require the use of renewable and low carbon sources of energy and adoption of three main strategies namely conventional mitigation, negative emissions technologies which capture and sequester carbon emissions and finally technologies which alter the global atmospheric radiative energy budget to stabilize and reduce global average temperature. Besides low emissions, a sustainable electricity grid system should be stable and supply reliable, affordable, and socially acceptable electricity.

Although there is no consensus on quantitative factors and their magnitude there is agreement on the need for supportive policies, regulations, programmes, and international commitments. Other measures are the development and expansion of financial sector, and improvement on the performance and quality of energy sector institutions. This study concludes that both renewable and non-renewable sources of energy have a leading role to play in the short and long-term energy transition. They include energy sources like solar, wind, hydro, hydrogen, bioresources, marine energy, nuclear, natural gas substitute of other fossil fuels and application of clean and efficient technologies for existing fossil fuel and non-renewable systems. Important strategies include electrification of thermal applications and household, and technologies like smart grids and energy storage for variable renewables and carbon capture and sequestration, cogeneration, and energy efficiency measures to limit consumption and wastage of energy resources. Waste to energy and particularly in form of electricity will minimize solid waste load and reduce environmental pollution like water and soil contamination. With the grid connecting different energy sources and infrastructure, decision support systems and optimization models will play a key role in realizing cost effective and environmentally friendly and reliable electricity generation and supply. Technology measures to control global warming can be classified into three broad categories of carbon capture and sequestration, emission mitigation strategies and technologies that alter the radiative properties of incoming and outgoing solar radiations.

10 Recommendations for Future Research

This study lays the foundation for further research into technical and non-technical measures to ensure a sustainable transition to a low carbon electricity grid from different sources, both renewable and nonrenewable and will form a firm foundation for effective policy formulation and implementation necessary to drive the energy transition globally. Further research into practical details of the technologies and measures is recommended to guide the actual implementation of the transition measures and strategies like smart grids, decentralized generation, energy storage, decentralized generation, and computerization and optimization of electricity generation, transmission, and distribution resources to facilitate a sustainable energy future. The study further recommends identification and development of transition specific energy and electricity models to aid in planning and execution of sustainable energy and electricity production, supply and consumption by end users, utilities, and prosumers.

Author Contributions

MK developed the draft manuscript with OO reviewing and making further input including editorial.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Acknowledgments

The authors sincerely acknowledge the contribution of all individuals, reviewers, and editors for their contribution towards the production of this manuscript.

Abbreviations

CHP, Combined heat and power; CO 2-eq , Carbon dioxide equivalent; CSR, Corporate social responsibility; EJ, Exajoules; GHG, Greenhouse gases; KenGen, Kenya Electricity Generating Company PLC; KWS, Kenya Wildlife Services; PPM, Parts per million; NEMA, National Environment Management Authority.

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Keywords: renewable energy, sustainable electricity, energy and electricity sustainability, energy transition, energy security, energy transition strategies, global climate change, greenhouse gas emissions

Citation: Kabeyi MJB and Olanrewaju OA (2022) Sustainable Energy Transition for Renewable and Low Carbon Grid Electricity Generation and Supply. Front. Energy Res. 9:743114. doi: 10.3389/fenrg.2021.743114

Received: 17 July 2021; Accepted: 28 December 2021; Published: 24 March 2022.

Reviewed by:

Copyright © 2022 Kabeyi and Olanrewaju. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Moses Jeremiah Barasa Kabeyi, [email protected] , [email protected]

This article is part of the Research Topic

Advances Towards Deep Decarbonization of Energy Systems

The green energy economy is here - but it needs to grow bigger quicker, says the IEA

The problem, says the IEA in a landmark report, is that it’s proving harder than expected to ditch fossil fuels as economies recover from COVID-19. Image:  Unsplash/RawFilm

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Stay up to date:, sdg 13: climate action.

• We are making progress towards a new green energy economy, according to a landmark report from the International Energy Agency.
• The problem is we’re going nowhere near fast enough to achieve net zero by 2050.
• Government pledges to cut emissions only go a fifth of the required distance.
• So we need to act now to accelerate the sustainable energy transition.

How fast is the world really moving towards net-zero carbon? Not fast enough according to the International Energy Agency (IEA), although there are signs that a new green energy economy is starting to emerge.

The problem, says the IEA in a landmark report, is that it’s proving harder than expected to ditch fossil fuels as economies recover from COVID-19, prompting the agency to warn that governments must move faster to implement the climate pledges they’ve already made.

But even if all the pledges were implemented in full, they would only go one-fifth of the way needed to limit emissions enough to peg the rise in global temperatures at 1.5C, the level targeted in the Paris Climate Accord of 2015 .

A virtuous cycle

The IEA’s World Energy Outlook 2021 report says there are encouraging signs that change is starting to happen, prompted partly by the COVID-19 pandemic which dampened energy demand and saw electric vehicles claim a bigger market share.

“The new energy economy will be more electrified, efficient, interconnected and clean,” says the IEA. “Its emergence is the product of a virtuous circle of policy action and technology innovation, and its momentum is now sustained by lower costs.”

In most countries, solar and wind energy are already the cheapest sources of electricity generation. Clean technology is generating employment and investment and spurring international collaboration, says the report.

Analyzing the actual policies countries are pursuing, as opposed to their pledges, the report says that even though global electricity demand is forecast to double to 2050, a gradual decline in energy emissions is still possible.

Rebound in coal use

But this would fall far short of what is needed to get to net-zero carbon by 2050 – and is in danger of being offset by rises in emissions from other sources, particularly from industries like cement and steel and transport, as emerging markets develop their infrastructure.

Governments have only invested around one-third of the money needed to “jolt the energy system onto a new set of rails,” says the report, with the biggest shortfalls in developing countries.

The energy sector is central to the fight against climate change , having contributed almost three-quarters of the emissions responsible for the increase in global average temperatures of 1.1C since the pre-industrial age, the report says.

Although lockdowns in the first half of 2020 depressed demand for coal, by the fourth quarter of the year, the economic recovery in some nations meant coal consumption grew 3.5% above the level for 2019 contributing to a resurgence in CO2 emissions. The trend continues in 2021.

“For all the advances being made by renewables and electric mobility, 2021 is seeing a large rebound in coal and oil use. Largely for this reason, it is also seeing the second-largest annual increase in CO2 emissions in history,” says the IEA.

Have you read?

How to accelerate the energy transition in developing economies, explained: why renewables became so cheap so fast, this is how ai will accelerate the energy transition, a clear signal needed from governments.

Speaking at the report launch, IEA Executive Director, Dr Fatih Birol , said: “The world’s hugely encouraging clean energy momentum is running up against the stubborn incumbency of fossil fuels in our energy systems.”

The focus was now on the COP26 climate summit in Glasgow in November , he added. “Governments need to resolve this at COP26 by giving a clear and unmistakable signal that they are committed to rapidly scaling up the clean and resilient technologies of the future.

Calling for a boost to investment in clean energy, he added, “this needs to happen quickly”. Two-fifths of the emission cuts needed to get to net zero would come from measures which can pay for themselves – by improving efficiency or using wind or solar where it is the cheapest energy source – he said.

The World Economic Forum warned that the transition to clean energy must be rooted in economic, political and social practices, including changes to the way we live, work, produce and consume materials if we are to make progress irreversible.

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What is green energy? What to know about renewable, clean power like solar and wind energy

The world is in the midst of a shift away from fossil fuels and towards carbon-neutral energy sources , a change expected to be as momentous as the coal that enabled the Industrial Revolution in the 1700s. 

The United States has pledged to become carbon neutral by 2050, just 27 years from now. It's a move that 69% of Americans support  and one that would mitigate climate change , clean the air and make power cheaper .

But what does green energy mean, actually? Is it wind turbines, solar panels, natural gas or nuclear? Who decides and what are the guidelines?

What to know about clean, green energy:

What does green energy mean? 

Renewable energy is electricity produced by fuel sources that renew themselves and do not diminish when humans tap them for power. Think the sun, the wind, plants and the heat at the Earth's core. These include electricity from solar panels, wind turbines, hydroelectric dams and what's known as biomass, which is burning wood, crop waste or garbage.

How does climate change affect you? : Subscribe to the weekly Climate Point newsletter

READ MORE : Latest climate change news from USA TODAY

For 2023, 16% of US electricity will come from solar and wind projects, according to the U.S. Energy Information Administration. Hydroelectric power produces 6% of U.S. electricity. Biomass, which includes ethanol blended into gasoline , made up about 5% of total US energy consumption.

Renewables also include geothermal energy, which means making power from naturally occurring underground reservoirs of very hot water and steam. Mostly available in the western United States, geothermal power is still a tiny proportion of US energy but already produces enough electricity to power 2.7 million homes. For comparison, geyser-filled Iceland gets 66% of its primary energy from geothermal power.

Why is it called green energy?

Like many ecologically friendly initiatives, "green" energy has gotten its name because it is good for the planet. 

It has become common to label clean, renewable projects "green" to remind people that they are intended help lead to a healthier, greener, more sustainable planet. Green racing , Green New Deal  and green plane fares  are other examples.

While scientists agree green energy helps fight climate change, it's important to remember that not everything with the "green" label is actually better. It can also be used as a form of "greenwashing" where a company tries to make a product or policy seem environmentally friendly when it in fact isn't.

Green energy helps fight climate change

The shift to renewable energy is important because most of these power sources don't produce greenhouse gasses that drive climate change . These gases, especially the carbon dioxide produces when coal, oil or natural gas are burned, create a "blanket" in the atmosphere that holds in heat.

Since humans began burning large amounts of coal at the beginning of the Industrial Revolution, later adding oil and natural gas, the amount of carbon dioxide in the atmosphere has increased from 280 parts per million to 418 parts per million. 

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Is renewable energy the same as green energy?

In general, renewable and green energy mean the same thing . 

The U.S. Environmental Protection Agency defines green power as a subset of renewable energy, including all renewable energy resources that provide the greatest environmental benefit and the lowest environmental cost.

In practice, this means all renewable energy sources with the exception of large hydroelectric resources that can have "environmental trade-offs on issues such as fisheries and land use."

Is solar power green energy? Is wind? Definitions explained.

Here's a cheat sheet:

• Green energy: Wind, solar, small hydro, geothermal, biomass
• Renewable energy: Wind, solar, all hydro, geothermal, biomass
• Carbon neutral: Wind, solar, hydro, nuclear, geothermal, biomass
• Conventional: Coal, natural gas, oil, nuclear

What is carbon-neutral energy?

Carbon-neutral energy is energy that is produced without emitting greenhouse gases into the atmosphere.

Renewable energy sources – wind, solar, hydroelectric, biomass and geothermal – are all considered carbon-neutral energy production, although building them (and all energy plants) does produce carbon. The major energy source that's carbon neutral but not renewable is nuclear power. 

America's 92 nuclear power plants produce about 20% of US electricity and about 50% of the nation's carbon-neutral energy. 

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What are conventional energy sources?

Conventional power is energy that comes from the burning of fossil fuels including coal, natural gas and oil. Power from the nuclear fission of uranium is also considered conventional. These fuels all have environmental costs from mining, drilling and extraction and all but nuclear power emit greenhouse gases. 

Elizabeth Weise covers climate change and the energy transition for USA TODAY. Reach out to her at [email protected]. 

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Technologies and perspectives for achieving carbon neutrality

1 CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China

48 University of Chinese Academy of Sciences, Beijing 100049, China

Jean Damascene Harindintwali

Zhizhang yuan.

2 Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China

3 Key Laboratory for Agro-Ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha 410125, China

Faming Wang

18 South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China

19 Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China

4 Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China

Zhigang Yin

17 Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China

5 International Research Center of Big Data for Sustainable Development Goals, Beijing 100094, China

6 Key Laboratory of Digital Earth Science, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China

20 State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China

Scott X. Chang

21 Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2E3, Canada

Linjuan Zhang

22 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China

Jörg Rinklebe

23 Department of Soil and Groundwater Management, Bergische Universität Wuppertal, Wuppertal 42285, Germany

Zuoqiang Yuan

24 CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Liaoning 110016, China

Qinggong Zhu

25 Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China

Leilei Xiang

Daniel c.w. tsang.

26 Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong, China

27 Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 101400, China

28 Institute of Marine Science and Technology, Shandong University, Qingdao 266273, China

29 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430000, China

Matthias Kästner

30 Department of Environmental Biotechnology, Helmholtz Centre for Environmental Research – UFZ, Leipzig 04318, Germany

Yong Sik Ok

31 Korea University, Seoul 02841, Korea

Jianlin Shen

Dailiang peng.

32 Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China

Damià Barceló

33 Catalan Institute for Water Research ICRA-CERCA, Girona 17003, Spain

Yongjin Zhou

Zhaohai bai.

34 Key Laboratory of Agricultural Water Resources, Hebei Key Laboratory of Soil Ecology, Center for Agricultural Resources Research, Institute of Genetic and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang 050021, China

35 CAS Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China

36 The Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Zhiliang Tan

Liu-bin zhao.

37 Department of Chemistry, School of Chemistry and Chemical Engineering, Southwest University, Chongqing, 400715, China

38 Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China

Jinxing Zheng

39 Institute of Plasma Physics, Chinese Academy of Sciences, Anhui 230031, China

Nanthi Bolan

40 School of Agriculture and Environment, Institute of Agriculture, University of Western Australia, Crawley 6009, Australia

Xiaohong Liu

Changping huang, sabine dietmann.

41 Institute for Informatics (I 2 ), Washington University, St. Louis, MO 63110-1010, USA

42 Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China

43 Key Laboratory of Surface Processes and Resource Ecology, Faculty of Geographical Science, Beijing Normal University, Beijing 100875, China

44 CAS Key Laboratory of Renewable Energy, Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China

Ferdi Brahushi

45 Department of Agro-environment and Ecology, Agricultural University of Tirana, Tirana 1029, Albania

Tangtang Zhang

46 Key Laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Chinese Academy of Sciences, Lanzhou 730000, China

Xianfeng Li

47 Shenyang Agricultural University, Shenyang 110866, China

Nianzhi Jiao

7 Joint Laboratory for Ocean Research and Education at Dalhousie University, Shandong University and Xiamen University, Halifax, NS, B3H 4R2, Canada, Qingdao 266237, China, and, Xiamen 361005, China

8 Institute of Marine Microbes and Ecospheres, Xiamen University, Xiamen 361101, China

9 State Key Laboratory of Marine Environmental Science and College of Ocean and Earth Sciences, Fujian Key Laboratory of Marine Carbon Sequestration, Xiamen University, Xiamen 361005, China

Johannes Lehmann

10 School of Integrative Plant Science, Section of Soil and Crop Sciences, Cornell University, Ithaca, NY 14853, USA

11 Institute for Advanced Studies, Technical University Munich, Garching 85748, Germany

Yong-Guan Zhu

12 Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, 1799 Jimei Road, Xiamen, 361021, China

13 State Key Laboratory of Urban and Regional Ecology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, 100085, China

Hongguang Jin

Andreas schäffer.

14 Institute for Environmental Research, RWTH Aachen University, Aachen 52074, Germany

James M. Tiedje

15 Center for Microbial Ecology, Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI 48824, USA

Jing M. Chen

16 Department of Geography and Planning, University of Toronto, Ontario, Canada, M5S 3G3

Global development has been heavily reliant on the overexploitation of natural resources since the Industrial Revolution. With the extensive use of fossil fuels, deforestation, and other forms of land-use change, anthropogenic activities have contributed to the ever-increasing concentrations of greenhouse gases (GHGs) in the atmosphere, causing global climate change. In response to the worsening global climate change, achieving carbon neutrality by 2050 is the most pressing task on the planet. To this end, it is of utmost importance and a significant challenge to reform the current production systems to reduce GHG emissions and promote the capture of CO 2 from the atmosphere. Herein, we review innovative technologies that offer solutions achieving carbon (C) neutrality and sustainable development, including those for renewable energy production, food system transformation, waste valorization, C sink conservation, and C-negative manufacturing. The wealth of knowledge disseminated in this review could inspire the global community and drive the further development of innovative technologies to mitigate climate change and sustainably support human activities.

Graphical abstract

Public summary

• • Carbon neutrality may be achieved by reforming current global development systems to minimize greenhouse gas emissions and increase CO 2 capture
• • Harnessing the power of renewable and carbon-neutral resources to produce energy and other fossil-based alternatives may eliminate our dependence on fossil fuels
• • Protecting natural carbon sinks and promoting CO 2 capture, utilization, and storage are conducive to mitigating climate change
• • This review presents the current state, opportunities, challenges, and perspectives of technologies related to achieving carbon neutrality

Introduction

Industrialization, the engine for economic expansion and urbanization, has accelerated the development of different sectors in association with the growth of the global population and affluence. 1 , 2 By 2050, the world's population is expected to grow from 7.8 billion in 2020 to 9.9 billion, requiring 80% more energy and 70% more food, when the accompanying increase in living standards is considered. 3 , 4 Over the past two centuries, the world economy has heavily depended on the overexploitation of natural resources and the alteration of the life-supporting biogeochemical cycles and processes in the biosphere. 5 The current boom in the use of petroleum resources and deforestation is a response to the pressure to meet the growing demand for energy, food, and other commodities. 4 , 6 These eco-unfriendly practices are the root causes of the increased emissions of anthropogenic sources of global greenhouse gases (GHGs), the primary drivers of climate change. In 2016, energy and food systems accounted for more than 90% of all global emissions of GHGs (mainly in the form of CO 2 ). 7 It is expected that GHG emissions will increase by 50% by 2050, mainly due to the expected 70% increase in energy-related CO 2 emissions. 4 , 8 If these emissions keep rising at their current rate, it will push the carbon (C) cycle out of its dynamic equilibrium, leading to irreversible changes in the climate system. Therefore, concerted efforts to reduce C emissions and increase C sequestration have to be initiated through a variety of socio-economic and technological interventions. 9 , 10

In response to the ever-increasing global greenhouse effect, all countries signed a landmark United Nations climate agreement in Paris on December 12, 2015, to jointly tackle GHG emissions and combat climate change. 11 Under the 2015 Paris agreement, all countries agreed to keep warming below 2.0°C and make an effort to curb global warming to less than 1.5°C by achieving C neutrality by 2050. 12 , 13 The global average temperature in 2020 was 1.2°C warmer than the pre-industrial temperature, and the effects of this warming are felt globally. 14 Based on the current climate data, there is an urgent need to accelerate our efforts to reduce atmospheric GHG concentrations to reverse global climate change.

To achieve C neutrality and sustainably support human activities, it is of utmost importance to reduce fossil fuel and food C emissions while promoting C sequestration in terrestrial and marine ecosystems. 15 Different strategic paths to achieve C neutrality have been mapped out in different countries 16 , 17 but, due to the magnitude of the fluxes involved, reducing C emissions to net-zero is challenging. According to the International Energy Agency, 18 if the world is to become C neutral by 2050, the extraction and development of new crude oil, natural gas, and coal must stop in 2021. In this regard, investment in research and adoption of renewable energy from C-free sources (i.e., sunlight, tide, wind, water, wave, rain, and geothermal power) and biomass (i.e., organic materials from plants or animals) are the key to bridging the gap between the rhetoric and reality of net-zero CO 2 emissions.

Renewable resources can provide more than 3,000 times the current global energy demand. 19 The global demand for renewable energy (in the form of electricity, heat, and biofuels) has expanded considerably in the past decade, with the share of renewables in global electricity production growing from 27% in 2019 to 29% in 2020. 20 Despite this progress in renewable energy use, the pace of transition from conventional to renewable energy is not fast enough, and the world is not on track to achieve C neutrality and sustainable development by 2050. Therefore, more effort is needed to transform the energy sector into a climate-neutral hub. This can be accomplished through the collaborative work of various multidisciplinary research teams and the application of integrated approaches developed as a result of recent scientific and technological advances in civil and environmental engineering, biotechnology, nanotechnology, and other areas. In addition to the development of renewable energy, the management of food systems also needs to be optimized to increase production efficiency and reduce C emissions. This can be achieved through the development of new technologies for better fertilizer production and precision agriculture, integrating crop-livestock production systems, and developing C-neutral food production systems. Given that the world is unlikely to substantially reduce fossil fuel-based CO 2 emissions in the short term, harnessing the power of natural resources and processes to remove CO 2 from the atmosphere presents a feasible route toward C neutrality. To mitigate climate change, various potential strategies for enhancing C capture from the atmosphere through industrial means and C sequestration in terrestrial and marine ecosystems are being investigated. These include bioenergy with C capture and storage; 21 enhanced rock weathering by spreading crushed minerals, which are naturally capable of adsorbing CO 2 on land or in the ocean; 22 afforestation and reforestation; 23 soil C sequestration via biochar, compost, direct biowaste incorporation, and conservation tillage, among others; 24 , 25 , 26 ocean fertilization through the application of iron or/and other nutrients for promoting the growth of photosynthetic plankton; 27 coastal wetlands restoration; and direct air capture using chemicals to remove CO 2 directly from the atmosphere. 28 It is necessary to evaluate the practicality, cost, acceptability, and usefulness of each of those so-called negative emission technologies (NETs) in mitigating climate change and its influence on global ecosystems and human activities.

There have been many reviews exploring pathways to C neutrality, with the focus on renewable energy sources, 19 , 29 C capture and storage in terrestrial and marine ecosystems, 22 , 30 , 31 , 32 , 33 , 34 , 35 and food system transformations. 36 , 37 , 38 , 39 , 40 , 41 However, to the best of our knowledge, no review has compared the strengths and challenges of all available new technologies toward C neutrality or highlighted uncertainties associated with those new technologies in climate change mitigation.

This review focuses on new technologies designed to accelerate our race to C neutrality in different areas, including those for renewable energy, sustainable food systems (increasing soil C sequestration and reducing C emissions), sustaining the health of Earth's largest C stores (restoration and protection of marine and forest ecosystems), and C-neutral chemical industrial production. The information disseminated in this review is expected to inspire the global scientific community and stimulate interest in further research on new pathways to achieve C neutrality and the United Nations Sustainable Development Goals.

Technologies for renewable energy

The overconsumption of energy from non-renewable resources increases energy scarcity, greenhouse gas emissions, climate change, and environmental degradation, posing threats to mankind. As a result, the ecological awareness of humankind and the transition to low-C or C-free energy are more concerning now than at any time in the past. A series of policies have been developed on a global scale 42 , 43 to address those concerns.

Among clean energies, renewables, such as solar energy, wind power, and ocean energy, are regarded as some of the most important and efficient means to achieve C neutrality. In addition to nuclear and H 2 energy, which have the advantages of low resource consumption and low pollution risk, and are identified as the strategic approach to ensure national energy security and to achieve the goal of "C neutrality," bioenergy is also key to reorganizing the structure of energy supply and consumption. Core technologies for renewable energy ( Figure 1 ), and the effects of these technologies on realizing C neutrality, are discussed below. In particular, the future development and feasible progress of these technologies are also presented.

Core technologies for renewable energy production

Solar energy

Solar energy is an inexhaustible resource. Because of its clean, renewable, and ubiquitous nature, solar energy can play an important role in the global renewable energy supply. 44 Currently, fossil sources (e.g., oil, coal, and natural gas) still dominate the total energy consumption across the world. In contrast, solar energy, hydropower, wind power, and tidal energy, which do not produce C emissions, only constitute a small part of the energy consumption. To achieve C neutrality, it is essential to increase renewable energy use. Thus, replacing traditional fossil fuel with renewable energy from sunlight is highly desirable and crucial for reducing CO 2 emissions and decarbonizing energy systems toward C neutrality.

The rapidly developing photovoltaic technology has been recognized as a powerful method to harness solar energy. 45 Conventional thin-film solar cells using inorganic semiconductors, such as silicon, gallium arsenide (GaAs), copper indium gallium selenide, and cadmium telluride (CdTe) materials, have been industrialized on a large scale, as they have high power conversion efficiencies and salient operational stability. Some newly emerging solar cells, such as organic solar cells, perovskite solar cells, quantum dot solar cells, and other integrated devices, have been developed as promising photovoltaic technologies in recent years. 45 , 46 , 47 , 48 , 49 This new generation of solar cells can complement traditional solar cells and will act as alternative low-cost photovoltaic technologies in many specific areas to provide power generation and thus effectively reduce CO 2 emissions. Although their power conversion efficiencies have reached more than 18%, it is necessary to further improve the efficiency and stability of large-area solar cells and reduce the product manufacturing and decarbonization costs. In addition, solar cell panels and photovoltaic grid-connected systems are also essential to electricity generation and may accelerate our race to C neutrality. Recent research showed that installing solar panels on rooftops may decrease GHG emissions by 57% in the near term (approximately 10 years) and achieve C neutrality in the long term (about 30 years). 50

Solar thermal technologies rely on photothermal conversion to achieve heat, steam, and electricity production for C-neutral operations, unlike photovoltaic techniques. When solar thermal technologies, such as concentrated solar power systems, are employed in commercial and residential sectors to replace natural gas as a source of energy, an obvious reduction in both energy consumption of fossil fuels and CO 2 emissions has been observed. 51 , 52 Besides photovoltaic and solar thermal technologies, some strategies to convert solar radiation into stable chemical fuels also provide feasible ways for large-scale utilization and storage of solar energy toward energy decarbonization. For instance, great efforts have been made on solar hydrogen production, demonstrating an extremely attractive route to produce hydrogen fuel by adopting renewable solar energy or solar-derived power to electrolyze water. 53 , 54 Note that hydrogen fuel is an ideal clean energy source to deliver C-free emissions, showing a great potential to reduce GHG emissions. Recently, a new concept of liquid sunshine has been proposed for combining solar energy with captured CO 2 and water to generate green liquid fuels, such as methanol and alcohol, which may deliver an ecologically balanced cycle between generation and utilization of CO 2 in global production systems. 55

Solar energy represents an ideal solution to meet the energy demands in a low-C and C-free society. Owing to the low-operating costs, a series of useful measures based on solar energy techniques are good candidates to reduce C emissions and utilize CO 2 to form clean energy storage, thereby playing an irreplaceable role in the realization of C neutrality. The next decades will require accelerated development of advanced energy conversion/storage technologies and large-scale deployment of solar energy combined with clean resources to promote integrated pathways to C-neutral energy systems.

Wind energy

Wind results from the motion of air due to uneven heating of the Earth's surface by the Sun. This means that wind power could be regarded as indirect solar energy. 56 Like solar energy, wind energy will play a critical role in realizing "C peak and C neutrality."

The Earth has abundant wind resources, which are mainly distributed in grasslands, deserts, coastal areas, and islands. 57 The site location has a significant impact on the economy, technicality, and implementation of wind energy. The world attaches great importance to and vigorously supports the development of wind power. However, one of the issues that hinders wind energy utilization is the noise generated by wind turbines. Strategies to reduce or minimize the noise produced by wind turbines and further utilize wind sources sensibly are urgently needed. Another concern with wind energy production is that wind turbines may have an adverse effect on birds via collisions, disruptions, or habitat destruction if they are located inappropriately.

Although the wind resource on Earth is abundant, the uneven distribution of wind resources across the landscape poses a challenge to the transport of electrical energy produced by wind turbines. And the unpredictable nature of winds in terms of speed and direction will result in a variable and unstable phase, amplitude, and frequency for the generation of electricity, which may make it difficult to be integrated into the grid, resulting in a waste of wind energy. The cost of installing a wind turbine is currently quite high, which also hinders the widespread adoption of this technology. It is necessary to devote more efforts to exploring and developing wind energy technology to meet the needs of energy users.

Ocean energy

Ocean energy refers to the energy contained in the water body in the ocean and is both renewable and clean. The ocean energy reserve is enormous globally and is enough to power the entire world. There are typically five different energy forms: tidal energy, wave energy, ocean current energy, thermal energy, and osmotic energy. The tidal, wave, and current energies are mechanical energy. The research of exploiting ocean energy was started a few decades ago. The geographical distribution varies broadly for different energy forms, and the harnessing technologies are also quite different.

Tidal energy is the energy contained in the tide, including the potential energy related to the water level and the kinetic energy of the tidal current. The tide originates from the gravitational interaction of sea water with the Moon or the Sun. Tidal energy is estimated to be about 1,200 TWh per year, which is relatively low among all ocean energy forms 58 due to limited locations from where tidal energy can be harvested. The tidal barrage is adopted to harvest the potential energy of tides, which is relatively technologically mature. Early tidal barrages started to operate in the 1960s, and tidal energy now has the largest share of ocean energy being exploited (Khare et al., 2019). Harnessing tidal current power mainly relies on turbines, although other types of devices are also under development.

Wave energy is the kinetic and potential energy in water waves, which is widely distributed. It essentially comes from wind, which transmits part of its kinetic energy to the water at the ocean surface. The potential of wave energy globally is 29,500 TWh per year. 59 The technology for harvesting wave energy is less mature than that for tidal energy, and many different types of devices are being tested on a small scale toward commercialization. The major device forms include point absorber, attenuator, oscillating water column devices, and overtopping devices. Besides traditional large devices using electromagnetic generators, new technologies based on triboelectric nanogenerator networks are also being developed toward effective harvesting of wave energy economically. 60

Ocean current energy is reserved in the large circulations of sea water globally. It is the kinetic energy in the water flow. The supply of this source of energy is stable with little fluctuation. It can be extracted using turbines. The device needs to be deployed in deep sea and far from the shore; thus, less effort has been devoted to harnessing this type of energy.

Thermal energy originates from the Sun's irradiation, which heats the upper layer of the sea water, making its temperature different from the water in the deep sea. Such temperature differences can be exploited for electricity generation mainly based on thermal cycles. Due to the high-temperature difference required for improved efficiency, this form of energy is mainly distributed in the tropical region. The potential for this energy is estimated to be 44,000 TWh per year. 61 The utilization of this form of energy is still at the research stage by universities and research institutes.

Osmotic energy, also called salinity gradient energy, is the energy that exists between water bodies with different salt concentrations. The salinity of sea water is not homogenous globally; for example, a salinity gradient is formed in estuaries where fresh water meets salt water. The harness of such energy relies on high-performance membranes that are robust in sea water. Two main technologies are being tested at present: pressure-retarded osmosis and reversed electrodialysis. 59 Osmotic energy is still a conceptual energy source and is not ready for commercialization.

The ocean energy reserve is enormous globally and is enough to power the entire world. Technologies to harvest tidal and wave energy are on the verge of commercialization. Technologies for harvesting ocean current energy, thermal energy, and osmotic energy are still in their early development stage. Major challenges of exploiting ocean energy lie in the economic cost-competitiveness and technological reliability in severe ocean environments. By overcoming these challenges, ocean energy will provide the world with abundant clean energy.

Biomass is a renewable source of energy that originates from plants. The most important sources of biomass are agricultural and forestry residues, biogenic materials in municipal solid waste, animal waste, human sewage, and industrial wastes. Biomass provides 13%–14% of the annual global energy consumption. 62 Various processes are used to convert biomass into energy, including the following.

Thermochemical conversion of biomass includes gasification, pyrolysis, and combustion. Combustion produces approximately 90% of the total renewable energy obtained from biomass. 63 Pyrolysis can convert biomass into solid, liquid, or gaseous products by thermal decomposition at temperatures around 400°C–1,000°C in the absence of oxygen, producing components such as acids, esters, and alcohols. 64 Gasification converts carbonaceous materials into combustible or synthetic gas by reacting the air, oxygen, or vapor at a temperature of over 500°C, preferably over 700°C, yielding gases such as H 2 , CO, and CH 4 . 64 , 65

Chemical conversion converts vegetable oils and animal fats into fatty acid esters through esterification or/and transesterification to produce biodiesel. The transesterification process is necessary since raw materials are composed of triglycerides, which are not a useable fuel. Triglycerides are converted into methyl or ethyl esters (biodiesel) using a mostly alkaline catalyst in the presence of methyl or ethyl alcohol, respectively. Rapeseed oil (accounting for 80%–85%) and sunflower oil (accounting for 10%–15%) are major vegetable oils used for biodiesel production. 63

Biochemical conversion converts biomass into liquid fuels (e.g., alcohols and alkanes), natural gas (e.g., hydrogen and methane), different types of bio-products (e.g., carotenoids, omega-3 and omega-6 fatty acids), as well as other chemical building blocks (e.g., acetic acid and lactic acid) using microbes and enzymes as the catalyst. 66 The most popular biological conversions are fermentation and anaerobic digestion.

The most common biomass feedstock used for biological conversion is lignocellulosic biomass, such as agricultural and forestry residues. Lignocellulosic biomass is the most abundant and widely available renewable resource in the world, mainly composed of three heterogeneous biopolymers, namely cellulose, hemicellulose, and lignin. Three major steps are involved in cellulosic bioethanol production: (1) pre-treatment, (2) enzymatic hydrolysis, and (3) fermentation. Pre-treatment uses physical, chemical, or physicochemical methods to improve biomass accessibility by enzymes. Enzymatic hydrolysis splits cellulose and hemicellulose into monomer sugars, such as glucose, xylose, and mannose. The conversion of biomass-derived sugars into ethanol by Saccharomyces cerevisiae has received most research and development efforts. Another method for producing butanol is through fermentation, specifically through an acetone/butanol/ethanol process that is predominantly carried out by Clostridia strains. 67 Anaerobic digestion consists of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. These reactions break down the macromolecules in the biomass into simpler molecules with the generation of biogas in an anaerobic environment. One of the advantages of anaerobic digestion lies in the potential of the biogas to be used directly in ignition gas engines and gas turbines.

Despite the presence of abundant biomass resources, there is still a need for work on the use of biomass to produce energy, with main efforts needed to increase productivity and reduce costs to further expand the share of such renewable energy in the total energy consumption. 68 Some of the issues that need to be resolved are the high cost of transporting the biomass to the site for bioenergy production through various conversion processes and the sustainability of the production of bioenergy feedstocks.

Hydrogen has been a necessity for industrial use over the past two hundred years. The demand for hydrogen (currently >80 Mt per annum) has grown more than three times since 1975 and continues to rise. Up to now, H 2 is almost entirely produced from fossil fuels, consuming around 6% of global natural gas and 2% of global coal, resulting in emissions of around 830 Mt of CO 2 per year. 69 Recently, hydrogen energy has drawn a great deal of interest because it can be used to establish a fully renewable energy system similar to an electricity grid, providing the sector integration needed for energy system transition and decarbonize energy end uses. 70

Hydrogen production using renewable energy has a strong likelihood of both technological and economic viability in the near future. The decreasing costs of renewable energy and the increase in variable renewable power supplies' market share have put significant roadblocks in the way of cheap water electrolysis. 71 With the fast development of artificial intelligence, deployment and learning-by-doing are expected to reduce electrolyzer costs and supply chain logistics. After H 2 production via electrolysis, safe and low-cost hydrogen storage and transportation technology need to be developed. Hydrogen can be stored in gas, liquid, and solid states. 72 , 73 As of now, none of these technologies are mature for establishing a hydrogen economy. In addition, hydrogen offers the lowest cost option for long-term energy storage, such as inter-seasonal; however, the ability to store large quantities of hydrogen at low costs with a high safety is still a challenge. Underground H 2 storage in large salt caverns and hydrogen transport via existing and refurbished gas pipelines are available at low cost to support long-term energy storage and sector coupling. However, equipment standards need to be adjusted and are also limited by geographical conditions. 74 , 75

Hydrogen fuel cell technologies have developed rapidly and are ready for commercialization, to the point that we now see commercial sales of hydrogen-powered passenger cars, such as Mirai, Clarity, and Nexo, and heavy-duty vehicles, trains, and ships. The main issue now is to reduce the cost while maintaining an acceptable level of durability and efficiency. 76 Other opportunities that pay more attention to the handling of energy-intensive commodities produced with hydrogen—synthetic organic materials/pharmaceuticals, iron and steel making, building/marine bunkers or feedstock to produce ammonia/methanol, and so on—seem to be prime markets. We now need to develop scale-up technologies, increase energy use/conversion efficiencies, optimize the upgrade of H 2 industrial structures, and lower costs to enable widespread use of H 2 energy. There needs a long-term devotion to fundamental understanding and development of new strategy/technology and infrastructure.

Nuclear energy

Nuclear energy is a major contributor to clean energy, accounting for 40% of low-C electricity generation worldwide, and avoids about 1.7 Gt CO 2 emissions a year globally. Therefore, nuclear energy is a strategic approach to ensure national energy security and achieve C neutrality. Nuclear energy is mainly generated through nuclear fission, while nuclear fusion technology is at the R&D stage. However, the future development of nuclear fission energy is highly uncertain for several reasons: rising costs, challenges with the disposal of radioactive spent fuel, plant safety, and risks for nuclear weapons proliferation. Therefore, Gen IV reactor nuclear fission systems have been proposed 77 based on the following considerations: safety, reliability, physical protection, cost-effectiveness, sustainability, and proliferation resistance. Furthermore, Gen IV reactor systems are key pillars of a sustainable and low-C energy mix, which can support environmental stewardship in both the electric and non-electric energy sectors. 78

Molten salt reactors (MSRs) are in the framework of the Generation IV International Forum because of their nuclear safety and sustainability. 79 In 2011, the Chinese Academy of Sciences launched the “Thorium molten salt reactor nuclear energy system” project to realize effective thorium energy utilization and comprehensive utilization of nuclear energy for 20–30 years. The small modular design of MSRs can reduce the R&D challenge and difficulty of large commercial MSRs while increasing their economic return and safety. Near-term deployable MSRs will have safety performance comparable with or better than that of evolutionary reactor designs. In addition, the MSR uses high-temperature molten salt as the coolant, which can be combined with the molten salt energy storage system of concentrating solar power stations to realize various regions and large-capacity heat storage systems. In this case, MSR plays the role of baseload energy source and can provide regulation and supplement the unstable and intermittent renewable energy. A reliable energy supply can be ensured even under long-term severe weather conditions. An MSR with an outlet temperature above 700°C can also be applied to high-temperature electrolysis hydrogen production. 80 In short, advancing MSR research will play an important role in the transition to sustainable clean energy and in accelerating global efforts to achieve C neutrality. Nuclear fusion, the dominant reaction that powers the Sun, is another nuclear energy type besides atomic fission. Nuclear fusion produces no long-lived radioactive waste. There is no risk of a meltdown, such as that which might occur with a fission reactor, because a fusion reactor shuts down within a few seconds when interference occurs. Thus, fusion energy is regarded as the optimal energy source of the 21st century, which will benefit our effort to achieve C neutrality. A tokamak, a piece of equipment that confines plasma using magnetic fields, is the most widely researched configuration for fusion power generation worldwide, and it is regarded as the most suitable solution for future fusion power plants that can achieve steady-state operation. Based on the experience obtained from small- and mid-sized tokamaks, the International Thermonuclear Experimental Reactor (ITER) is being constructed as the world's largest tokamak through the cooperation of seven countries: China, EU, Japan, South Korea, Russia, US, and India. The goal of ITER is to demonstrate sustainable deuterium-tritium plasma formation to create a 500 MW fusion power (Q = 10) for a duration of 300–500 s. 81 According to the roadmap of fusion energy development, the construction of demonstration power plants (DEMO) will be the last step before building a fusion power plant. China, 82 the EU, 83 and Japan 84 have carried out their studies on DEMO, and the engineering design of the Chinese Fusion Engineering Testing Reactor was completed in 2021.

Geothermal energy

Geothermal energy is non-carbon-based heat energy contained in the interior of the Earth, with the advantages of stability, continuity, and high capacity. 85 It will play an important role in providing a stable and continuous basic load in the future energy structure.

As the primary form of utilization of geothermal energy, geothermal power generation utilizes natural geothermal steam (or low-boiling working fluid steam heated by geothermal fluid) to drive a turbine to generate electricity. At present, geothermal power generation technologies mainly include dry steam power, flash power, and binary power systems. 86

Direct utilization of geothermal energy occurs in the form of thermal energy, which is usually applicable to medium- to low-temperature geothermal resources. At present, direct geothermal utilization technologies mainly include ground source heat pumps, geothermal heating, geothermal refrigeration, geothermal greenhouse, and geothermal drying. 87

As a country with a high geothermal utilization rate, geothermal energy in Iceland provided 62% of the country's energy production in 2020, helping it achieve the goal of a zero-carbon country in the future. 88 In 2021, the US Department of Energy's (DOE) Frontier Observatory for Research in Geothermal Energy selected 17 projects for up to $46 million in funding for cutting-edge, domestic, and carbon-free enhanced geothermal projects. 89 Turkey is one of the fastest-growing countries in geothermal energy, with a geothermal power generation capacity of 1,549 MW as of 2020. 88

In 2020, global geothermal utilization achieved an annual CO 2 emission reduction of about 300 million tons, and it has achieved an annual CO 2 emission reduction of about 100 million tons in China. The building area of shallow and deep geothermal heating is close to 1.4 billion m 2 , which makes a great contribution to carbon reduction for buildings. Geothermal energy plays an important role in clean heating in northern China, and a number of major projects have emerged; for example, the "Xiongxian model" Beijing Sub-center, Beijing Daxing International Airport, among others.

Energy storage

The electricity produced from most renewables is random and intermittent, which hinders the widespread application of renewables. 90 Therefore, developing energy storage technology is pivotal to improving electricity output reliability and stability from renewables. 91

Energy storage technologies can be divided into mechanical, electromagnetic, electrochemical, and phase change energy storage. Mechanical energy storage technologies, such as pumped hydro 92 , 93 , 94 and compressed air energy storage, 95 , 96 , 97 are currently the mainstream technologies for electric energy storage. Although pumped hydro is the most mature technology for large-scale energy storage, its use is restricted by site availability and the large initial investment. Compressed air energy storage is considered to be the least-cost storage technology but relies on the availability of naturally occurring caverns to reduce overall project costs.

Electrochemical energy storage technologies are one of the most promising electric energy storage applications because of their high efficiency and flexible design. Based on market prospects, battery technologies, one of the representative electrochemical energy storage technologies, can be divided into two types: (1) alkali (lithium, sodium, potassium)-based batteries, or advanced lead-C batteries for portable electronic devices and electric vehicles, and (2) flow batteries for renewable energy integration, microgrid, and power grid peaking. Lithium-ion batteries have already dominated our daily life because of their desirable electrochemical performance in both energy density and power density, as well as the advances in their system design and manufacturing. 98 , 99 Their upfront cost remains a big challenge for stationary applications because of the limited supply of lithium. As a result, sodium-ion batteries emerge as a promising alternative for their economic feasibility. Due to the higher redox potential of Na/Na + and larger ionic radius (as compared with Li/Li + ), sodium-ion batteries are currently suffering from low energy density and poor cycling stability. Compared with lithium- or sodium-ion batteries, solid-state lithium batteries have the advantages of high energy density and improved safety, making them very promising for next-generation energy storage applications. However, their application is confronted with many problems that need to be addressed, e.g., the large interfacial resistance between solid electrolyte and electrode and the limited power density. Moreover, the revolutionary technologies that dramatically increase safety and reliability remain urgently needed for the aforementioned battery types. 100 , 101 Hence, innovative materials design and development of control strategy that can endow alkali-based batteries with high safety, high energy density, and long life cycle can further accelerate the progress of these energy storage technologies.

In contrast, flow batteries are well suited for large-scale energy storage applications because they have high safety, high efficiency, and flexibility. 102 The vanadium flow battery, led by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, has been developed as one of the most mature technologies and is currently at the commercial demonstration stage. 103 Currently, the world's largest vanadium flow battery project (200 MW/800 MWh) is being built in Dalian, Liaoning. 104 , 105 Different from vanadium flow batteries, zinc-based flow batteries have attracted great attention in distributed energy storage due to their advantages of low cost and high energy density. Some zinc-based flow batteries are currently at the demonstration stage. However, the issues of zinc dendrite/accumulation, limited areal capacity, and reliability need to be overcome to realize their commercialization and industrialization. In addition to vanadium flow batteries and zinc-based flow batteries, a growing interest in novel flow battery systems, especially investigations on novel organic or inorganic redox couples have emerged. 106 , 107 , 108 Although many research papers have been published and demonstrated the promise for energy storage applications, these flow batteries are currently in the early stages of their development.

Different energy storage technologies have different reliability, cost, efficiency, scale, and safety. These technologies complement each other, and their applications are dependent on many aspects, such as energy storage time, site requirements, and environmental concerns. Coupled with renewables, the development of energy storage technologies will contribute to reducing CO 2 emissions and achieving C neutrality.

Technologies for enhanced carbon sink in global ecosystems

Global ecosystems contribute to the release and capture of CO 2 , methane (CH 4 ), and nitrous oxide (N 2 O) ( Figure 2 ), and influence the atmospheric GHG composition and the climate. Over the last 50 years, the removal of about one-third of anthropogenic GHG emissions has been attributed to terrestrial ecosystems. 109 In the process of producing high quality and large quantity of food for a growing affluent population, global food systems are important GHG sources and account for more than one-third of the global anthropogenic GHG emissions, of which 71% came from agricultural crop-livestock production systems and land-use change activities. 110 Forest ecosystems are one of the most important global C sinks and absorb 45% of anthropogenic GHG emissions, 111 with 85%–90% of terrestrial biomass produced in forest ecosystems. The ocean covers more than 70% of the Earth's surface and plays an important role in capturing CO 2 from the atmosphere. Currently, 22.7% of the annual CO 2 emitted from human activities is sequestered into the ocean ecosystem. 112

Overview of global GHG influx (Gt CO 2 -eq year −1 ), and strategies to promote GHG reduction and absorption in global ecosystems

To prevent irreversible deterioration from global climate change, the biosphere must increase biomass production and food supply with lower GHG emissions, remove CO 2 from the atmosphere and store it as organic C in the biosphere, contributing to C neutrality. In this sense, we emphasize optimizing crop-livestock production systems, promoting forest ecosystem health with soil C sequestration, and utilizing soils and marine ecosystems as natural C sinks. These can provide breakthrough technologies for C reduction and immobilization in terrestrial and marine ecosystems ( Figure 2 ) and are further discussed in the following subsections.

Carbon emission reduction in agricultural food production systems

The GHG emissions from agricultural food production systems have increased by around one-third during the past 20 years. Emissions are mainly due to the increase in crop and animal production, 113 with 4.2 Gt CO 2 -eq year −1 from enteric fermentation, manure and pasture management, and fuel use in livestock production, 3.6 Gt CO 2 -eq year −1 from synthetic N fertilizer application and crop production for human and animal food, and 3.3 Gt CO 2 -eq year −1 from changes in land use for crop-livestock production systems. 114 Given the uncertainties surrounding the large-scale implementation of C capture and storage technologies in food production systems, 113 alternative technologies or approaches are needed to mitigate a substantial portion of GHG emissions from agricultural production systems. For example, we need to change our eating habits to diets with less animal-based but more plant-based foods. How to convince people to change their diet on a large scale is a sociological and behavioral question and will not be discussed in this article.

Crop production management. Optimization of fertilizer and water use in croplands can greatly reduce GHG emissions in crop production systems. 115 New synthetic N fertilizer types, such as slow- and control-release N fertilizers, and N fertilizers with urease and nitrification inhibitors, need to be developed to enhance N use efficiency. 116 Better cropping systems, fertilization, and irrigation practices, and the use of advanced digital agriculture technologies, such as multi-sensor drone technology to allow farmers to manage crops, soil, fertilization, and irrigation more effectively and precisely, can reduce N fertilizer input and N 2 O emissions. 117 , 118 For example, intermittent irrigation can substantially reduce the production of CH 4 and increase CH 4 oxidation, and thus can be an important choice to mitigate CH 4 emissions from rice fields. 119 , 120

Breeding crop varieties with a high N use efficiency (NUE) can reduce the N fertilizer application rate and reduce the emission of nitrogen oxides. Using transgenic and gene-editing technology, the introduction of proliferating cell factor domain proteins, such as OsTCP19-H, into modern rice varieties has been shown to enhance NUE. 66 Multi-sensor drone-based technology to conduct plant phenotyping can evaluate NUE under different N dosages, thereby allowing the selection of superior genotypes with high NUE. 100 In addition, the development of inhibitors for methanogenesis or the addition of biochar in rice paddies has a large technical potential to reduce CH 4 emissions. 121 , 122 Other options include using microbes to help crops fix N, thus saving N fertilizers and reducing the footprint of the N fertilizer industry. 111

Animal production management. Manipulation of enteric fermentation is one of the key strategies to mitigate CH 4 emissions in ruminant livestock production systems. Methane is natural by-product disposal of hydrogen during enteric fermentation and released by methanogenic archaea. Methane inhibitors can be developed by inhibiting H 2 metabolism for methanogenesis. 123 Such inhibitors include alternative electron sinks, phytocompounds, ionophore antibiotics, and oil. 124 , 125 , 126 Among these, 3-nitrooxypropanol is the latest developed and promising inhibitor for methanogenesis, 127 which has been shown to reduce methane emissions in ruminant animals by up to 40%. 128 , 129 Vaccination, by inducing the host immune system to create antibodies capable of suppressing methanogens, has the potential to reduce CH 4 emissions and is particularly beneficial for pasture-based systems. 130 Given that ruminants fed with forage diets account for 70% of global ruminant methane emissions, 131 breeding new highly digestible forage species with increased non-fiber carbohydrates and less lignified fiber, as well as a high concentration of secondary plant metabolites, such as tannins, saponins, and essential oils, can be worthwhile.

Manure management practices could substantially mitigate indirect GHG emissions by optimizing grazing-land management, generating on-farm energy, and producing organic fertilizers that have a low emission factor. 132 The development of technologies spanning the entire manure management chain, such as advanced in-vessel composting to reduce C and N losses and reverse osmosis for concentrating and recovering N from liquid manure for long-distance transportation, may maximize the potential for recycling C and N from manure. Using manure to produce insect or fungal proteins is another value-added technology that may replace soy and fish proteins in animal feed and reduce GHG emissions associated with feed production. 133

Animal breeding techniques are to genetically select highly productive animals with less GHG emission intensity, 134 thereby reducing the number of animals required to produce the same amount of food. Shotgun metagenomics provides a platform to identify rumen microbial communities and genetic markers associated with CH 4 emissions, allowing the selection of cattle with less CH 4 emissions. 135 , 136 , 137 Other high technologies include the use of cloned livestock animals and manipulation of traits by controlling target genes with improved productivity.

Revolutionary technologies for agricultural food production. The development of biotechnology, automatic control technology, and artificial intelligence has made it possible to produce vegetables, fruits, and meats in a factory setting. Plant-based meat and cell-based meat can be produced artificially from non-animal sources. Tempeh and tofu are traditional plant-based meats; new plant-based meats include proteins extracted from plants or fungi, then formulated and processed into meat substitutes. 39 Innovative technologies, such as shear cells and 3D printing, are utilized to improve the taste and texture of plant-based meat. Cell-based meat is produced through the development of stem cell and large-scale cell culture technologies and thus has a taste and texture similar to real meat. 138 However, obstacles to commercializing cell-based meat still exist, such as how to scale up, regulatory approval, and the high production cost. Significant progress has been made in recent years, and signals point to commercialization soon. 39

Other novel biotechnology strategies include metabolic engineering to enable microbial utilization of using CO 2 , CH 4 , and other C1 feedstocks for the production of microbial proteins rich in essential amino acids. 139 , 140 These proteins can be used as substitutes for animal proteins. Current advances in biotechnology provide a powerful platform for the production of protein-rich feed or food additives in the form of fungal, algae, yeast, and bacterial cell biomass. 141 However, raising public awareness and obtaining regulatory approval of microbial proteins as feed or food additives still present major challenges requiring imminent actions to improve sustainable food supply with low C emissions.

A plant factory is an indoor vertical farming system that allows continuous food production throughout the year without being affected by seasonal changes and weather conditions. All environmental parameters, such as light level, temperature, moisture, and air composition, are intelligently controlled in a closed system. Several pilot plants demonstrate the feasibility of large-scale production requiring agricultural land. 142 Factories have been built for the commercial production of vegetables, fruits, and medicinal plants. Such systems can achieve extremely high productivity and low GHG emissions without altering land-use change compared with the traditional systems. 143 , 144 The high initial investment can be recovered quickly through the high rate of return from the operation, and the environmental impact from the operation can be minimized if renewable energy is used to run the plant factory.

Carbon sink in terrestrial ecosystems

Terrestrial ecosystems are vitally important C sinks on Earth. The global forest net C sink is estimated at 10.7 Gt CO 2 -eq year −1 , 112 which is mainly distributed in temperate regions. 145 Grasslands cover around 26% of the ice-free land on Earth and store around 34% of the global terrestrial C. 146 Soils of these grasslands store about 343 Gt C, which is about 50% more than the amount stored in forest soils and acts as a sink for about 1.83 Gt CO 2 -eq year −1 . Despite the large C stock size, the annual C input rate and turnover times are subject to considerable uncertainty. 147 Agricultural soils can be an important C pool and contribute about 3.30 Gt CO 2 -eq year −1 to C sequestration, 148 although agricultural food production is related to GHG emissions. 149 Terrestrial ecosystems could increase C sequestration readily by restoring vegetation and incorporating organic soil amendments. 150 , 151 , 152 In addition to these terrestrial ecosystems, inland waters also emit CO 2 to the atmosphere, known as CO 2 evasion. The global inland water CO 2 evasion rate was estimated to exceed 7.70 Gt CO 2 -eq year −1 . 153 Furthermore, a substantial amount of terrestrial C sequestered through photosynthesis and from chemical weathering is transported laterally along the inland water continuum from terrestrial ecosystems to the ocean. Previous research indicates that anthropogenic perturbations have increased the flux of C 154 to inland waters by up to 3.67 Gt CO 2 -eq year −1 since pre-industrial times, with over 40% of this additional C returning to the atmosphere via CO 2 evasion and 50% sequestered in sediments, leaving only 10% for the open ocean.

Factors driving the terrestrial carbon sink. Temperature, precipitation, and solar radiation are the three key climatic factors that influence plant photosynthesis and thus the C sink size of terrestrial ecosystems. 155 A great deal of soil C has been lost from natural ecosystems due to the influence of climate change and human disturbance. 156 , 157 A favorable climate (especially high precipitation) was directly associated with high biomass production and species diversity, which could promote soil organic carbon (SOC) stock, thus offsetting the negative impact of favorable climate on SOC. 158 , 159 However, the SOC storage and favorable climates (e.g., high temperature and precipitation) are consistently negatively related in shrub lands and forests, but not in grasslands. 160 Other factors, such as atmospheric CO 2 concentration, and growing season, also influence the absorption of CO 2 by terrestrial ecosystems. 161

Anthropogenic disturbances (e.g., N deposition, P fertilization, pesticides, 162 road density, grazing, fire) have substantially altered ecosystem functions and services across different biomes, thus affecting C sink strength in terrestrial ecosystems. 163 The growth of terrestrial plants is widely limited by soil N and P availabilities. Therefore, adding these nutrients to the soil could enhance plant production and ecosystem C sequestration. 164 , 165 However, ecosystem C storage depends on the balance between production and decomposition. 166 If the stimulation of decomposition is more than production caused by fertilization, there would ultimately be a net C loss from the ecosystem. 167 The magnitude of nutrient limitation is determined by the environmental conditions, the variability of plant properties, and the potential physio-biochemical machinery of the autotrophs. 168

Grasslands are one of the largest terrestrial ecosystems, and grazing is the primary land use of grasslands globally. 169 Through herbivory, trampling, and defecation of livestock, grazing induces changes in vegetation abundance and community composition and affects the ecosystem's capacity to fix C. Yet, grazing also regulates a series of C release processes: plant respiration related to biomass loss and microbial C mineralization associated with changes in the soil environment. Ultimately, these jointly affect the C sink function. 170 In recent years, overgrazing has become one of the dominant causes of grassland degradation. A high percentage of rangelands worldwide suffers from overuse of the land, such grasslands support a declining livestock number and, consequently, economic and social problems are created in the communities supported by those grasslands. 171 All of these would have a profound impact on the ecosystem C cycle and deserve more attention.

Technologies for enhancing carbon sinks. Nature-based NETs on land rely on biomass C sequestration through interventions, such as reforestation and afforestation, sustainable forest management, soil C sequestration from increased inputs to soils, and biochar additions. 22 , 172 , 173 A recent study suggests that there is a significant reduction of global CO 2 emission from an increase in forest coverage, from a mean of 4.3 (between 1991 and 2000) to 2.9 (between 2016 and 2020) Gt CO 2 -eq year −1 . During this period, forest land was a C sink globally, but its strength was decreasing, which could be attributed to the removed forest land counterbalancing the C emission from net forest conversion (i.e., deforestation). 174 Therefore, maintaining forest area is the basis of enhancing the C sink of terrestrial ecosystems. Since the late 1970s, China has implemented six major ecological restoration projects, covering 44.8% of China's forests and 23.2% of its grasslands. 175 , 176 The total annual C sink of the project area was 132 Tg C year −1 in 2001–2010, over half of which was attributed to the implementation of these projects. 176 Furthermore, for C sequestration in forest ecosystems, optimizing forest management strategies such as selection of suitable tree species, rotation length, and fertilization regimes are effective ways to increase the amount of forest C sequestration. 177 , 178 , 179 Regulating stands into a more complex vertical structure will lead to faster growth and greater C sequestration in forests because multilayered canopies will occupy a range of light environments, resulting in high light acquisition and light-use efficiency. 180 , 181 Since the SOC storage of broad-leaved forests is significantly higher than that of coniferous forests, afforestation should use mixed species planting and trees should be arranged according to the tree species' shade tolerance and successional characteristics. 182 Fertilization, usually with N or P, could relieve plants from nutrient limitation and allow them to sequester more C in stems and soils. For example, excess N deposition can significantly increase soil C in N-rich tropical forests. 183

Promoting sustainable grazing management practices, including appropriate stocking rates, introducing beneficial forage species, and allowing sufficient rest time for plant recovery between grazing, livestock rotation, and adopting silvopasture in livestock production systems, can help reduce GHG emissions and increase C sinks in grazing lands/pastures. 147 For example, when agroforestry systems, such as silvopasture, are applied in suitable locations, C is sequestered in soil as well as in tree biomass, which could promote C uptake by expanding the niches from which water and soil nutrients are drawn, lengthening the growing season, and enhancing soil fertility when N-fixing species are included as part of the system. 184

The use of organic fertilizers and crop residues in agricultural soils enhances C sequestration, and new technologies need to be developed to improve the C sequestration efficiency, e.g., by repeated changes of redox conditions similar to rice paddies 185 and by promoting microbial diversity 152 and abundance in SOC with powering the “microbial C pump” and improved storage of microbial necromass in soils. 185 , 186 This may need additional fertilizing measures when leaving crop residues in (poor) agricultural soils. Biochar amendments can also be an effective approach to increase SOC stocks due to the stable (on a millennium timescale) nature of the C contained in the biochar. 187 , 188 Soil acidification due to atmospheric nitrogen deposition in forest and grassland and excessive nitrogen fertilizer application in croplands should also be avoided to reduce the loss of soil inorganic C. 189 , 190 Application of crushed calcium- and magnesium-rich silicate rocks to soils is proposed for large-scale CO 2 removal. 191 This technology was called enhanced rock weathering, which increases soil alkalinity, and thus atmospheric CO 2 can be converted into dissolved inorganic C to be finally transported to the ocean, where the stored C has a long lifespan via land surface runoff. Peatlands make up 60% of the wetlands in the world and play a crucial role in the C cycle. Raising water tables and avoiding draining peatlands should be executed to conserve the vital C stored in peatlands. 192

Carbon sink in marine ecosystems

The total amount of C stored in the ocean is about 44 times greater than that in the atmosphere, and the stored C has a mean residence time of several hundred years. 112 , 193 , 194 Atmospheric C fixed and stored in these marine ecosystems is referred to as blue C. 195 , 196

Ocean carbon sinks and coastal blue carbon. Several physical and biological processes determine the ocean C sink size. The "solubility C pump" removes atmospheric CO 2 as air mixes with and dissolves into the upper ocean. The "biological C pump" is the photosynthetic absorption of atmospheric CO 2 by ocean microorganisms, 193 and transported to the deep ocean as sinking biogenic particles or as dissolved organic matter, resulting in long-term sequestration of C in the deep ocean. 197 However, the fate of most of this exported material is remineralization to CO 2 . 197 During this process, a portion of the fixed C is not mineralized but is stored for millennia as recalcitrant dissolved organic C. Jiao et al. 197 proposed that microorganisms play a vital role in this process and described it as a microbial C pump. The microbial C pump sequesters C by producing recalcitrant dissolved organic C with a lifespan of >100 years 198 and was regarded as the invisible hand behind a vast C reservoir. 199 The estimated magnitude of the microbial C pump in the world ocean is 0.2 Tg C year −1 , and some models suggest that climate change would enhance C sequestration by the microbial C pump. 198 The scientific understanding of ocean solubility C pump, biological C pump, and microbial C pump provides a practical and consistent foundation for the research and potential sustainable management of C cycling between land and ocean.

Although the original concept of blue C proposed in 2009 refers to the C that is captured by marine ecosystems covering both coastal and open ecosystems, 200 practical research and development of blue C have predominantly involved coastal wetlands, such as mangrove, seagrass, and salt marsh. 201 , 202 These coastal ecosystems are highly productive in photosynthetically sequestering atmospheric CO 2 , 203 and a varying fraction of C is buried in tidally inundated suboxic and anoxic sediments and thereby largely prevented from returning to the atmosphere. 204 Globally, tidal marshes and mangroves capture 196.72 Tg CO 2 per year, which is 30% of the organic C deposited on the ocean floor. 205 It was estimated that seagrass ecosystems accumulate 176–411 Tg CO 2 -eq year −1 . 203 The C stored in these coastal ecosystems as blue C can be preserved over millennia, together with the continuous accretion of soil and sediment organic C driven by sea-level rise, the C sequestration efficiency in marine ecosystems is much higher than that of terrestrial ecosystems. 205 , 206

Practice for blue carbon management. The sustainable management, conservation, and restoration of these marine ecosystems are vital to support the provision of C sequestration and other ecosystem services that humans depend on. 207 One possible way to increase blue C is to promote microbial C sequestration in marine ecosystems by reducing the application of chemical fertilizers on land ( Figure 2 ), as initially proposed by Jiao et al. 208 This suggests the need to adopt land-sea integrated strategies to achieve C storage and sustainable development. In addition to halting untreated sewage flow into rivers, the reduction of chemical fertilization in agriculture may minimize anthropogenic nutrient flux to marine ecosystems, thereby reducing the mobilization of dissolved organic C for degradation and respiration. 209 This process may reduce the eutrophication and red tides in rivers and oceans and increase the deep ocean C sequestration through the microbial C pump.

Due to the importance of coastal ecosystems in storing large amounts of C and providing other ecological functions, policies to protect and restore coastal and open water ecosystems need to be strengthened. 201 , 205 , 210 Preventing the conversion of these ecosystems to other land uses and restoring degraded coastal wetlands can increase C sequestration. 211 , 212 Recent simulations suggested that the protection and restoration of global coastal wetlands can provide half of forest soil C migration potential by 2030. 211

Although coral calcification is accompanied by the release of CO 2 into the atmosphere, the importance of coral reefs as a C sink in the ocean cannot be ignored 213 because they rapidly convert inorganic C into carbonate minerals, principally as calcium carbonate (CaCO 3 ) accretion. Coral reefs need to be protected and restored to improve their ability to adapt to climate change.

The implementation of sustainable practices in all industries that impact the ocean and coastal ecosystems, including mariculture and tourism, is also needed. For example, mariculture has a huge potential for the development of negative C emissions in the ocean. However, the C sequestration process of bivalves and seaweed farming is complicated, and the scientific principles and processes are gradually being recognized and are yet to be resolved. 214 Technological approaches and policies are needed in mariculture to implement the C sequestration, such as expanding mariculture space and increasing unit yield, sustainable development of mariculture, integrated multi-trophic aquaculture, blue C engineering through ocean ranching, and artificial marine upwelling. 214

In short, marine ecosystems, including coastal wetlands and open waters, are considered the largest C sink on Earth. Coastal ecosystems producing blue C are also some of the most efficient natural ecosystems to bury C into sediments. Improving these marine ecosystems' C sequestration or negative C emission capacity is a fundamental opportunity for achieving C neutrality. Protection and restoration of marine ecosystems is the first step and the quickest way to enhance C sequestration. Eco-engineering practices and approaches, such as land-sea integrated strategies for C sequestration, sustainable mariculture, and marine artificial upwellings, are also needed to increase C sequestration in marine ecosystems. Theoretical underpinnings, experimental scenarios, and ultimate technological viability plans for negative C emissions in the ocean require further in-depth investigations to increase ocean C storage. Public and government support for further blue C research could lead to eco-solutions for sustainable marine ecosystem management and innovative climate change mitigation technologies.

Tackling the carbon footprint of global waste

Zero waste biochar as a carbon-neutral tool. Driven by the extensive expansion of food, urban, and industrial systems, billions of tons of solid waste are generated globally every year. It is estimated that, by 2050, the amount of waste generated annually in the world will jump from 2.01 billion tons in 2016 to 3.4 billion tons. 215 Despite having only 16% of the world's population, high-income countries produce 34% of the world's waste. According to the US Environmental Protection Agency, solid waste landfills are the third-largest source of CH 4 emissions in the United States, emitting the same amount of CH 4 as almost 21.6 million passenger vehicles driven for an entire year or annual CO 2 emissions from energy use of nearly 12 million households in 2019. 216 The most common way to treat the waste is open waste burning, which promotes the emission of GHGs, carcinogenic compounds, and other toxic substances, thereby posing long-term threats to the environment and human health. 217 Addressing these problems associated with waste landfills and open waste burning is far more expensive than creating and running safe waste management systems. Therefore, it is essential to find and develop alternative methods to deal with the ever-increasing volume of solid waste. Ideally, such alternatives should be cost-effective, based on eco-friendly processes, contribute to climate change mitigation, promote sustainable development, and lead to economic and ecological benefits. In this way, the thermochemical conversion of solid waste into biochar can bring multifunctional benefits to the circular economy in addition to climate change mitigation and C sequestration.

Biochar, a fairly new term but an ancient tool, is a porous solid material that is produced from the treatment of feedstocks at high temperatures (300°C–900°C) under limited oxygen or oxygen-free conditions. 218 , 219 The thermochemical decomposition of feedstocks into biochar can be carried out by various methods, including pyrolysis, hydrothermal carbonization, torrefaction, gasification, and traditional carbonization. 220 Among these methods, pyrolysis is widely employed to produce biochar since it preserves one-third of the feedstocks as persistent biochar products while also generating bio-oils and non-condensable gases. 221 A plethora of organic resources, such as crop residues, 222 forest residues, livestock manure, food wastes, industrial biowastes, municipal biowastes, and animal carcasses, are feedstocks that can be used to produce biochar for different purposes. 223 , 224 Some researchers have made great progress by investigating the pyrolysis of plastic waste for char production, 225 , 226 while others have studied the co-pyrolysis of organic materials and plastics. 227 Char production from fossil-fuel-derived materials neither constitutes a way to withdraw carbon dioxide from the atmosphere nor qualifies as a soil amendment (and is therefore not called biochar) but has application as construction material. Interestingly, biochar can be produced on many different scales, from large industrial to small household scale, and can also be produced on farmland. 228 Therefore, bio(char) production from widely distributed waste has socio-economic and environmental significance in the race to achieve C neutrality. The possibility of producing biochar with multiple functions in a sustainable way positions the biochar industry as a viable hub to create a more sustainable and prosperous future for all people and the environment. 218

Biochar for sustainable development. In addition to cleaning up wastes, biochar also plays a key role in a variety of human activities in the realization of a circular economy and sustainable development ( Figure 3 ). Driven by the possibility to create either a highly charged surface and multiple functional groups or hydrophobic surfaces, biochar is emerging as an effective and safe natural adsorbent that can capture CO 2 229 and remove diverse organic contaminants 152 (e.g., antibiotics, aromatic dyes, agrochemicals, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons) and inorganic contaminants (e.g., phosphate, ammonia, sulfide, and heavy metals) from solid, aqueous, and/or gaseous media. 137 , 230 , 231 , 232 As a soil amendment, it can improve plant productivity and photosynthesis rate by enhancing the physical, chemical, and biological properties of the soil, 233 thereby contributing to C sequestration in terrestrial ecosystems and mitigating climate change. 234 Biochar addition to agricultural soils has improved soil water availability, water holding capacity, and nutrient availability, 235 , 236 , 237 increased soil microbial biomass and activity, 238 reduced risk of crust formation and soil erosion, 239 enhanced antibacterial activity, 240 and reduced mobility and toxicity of environmental pollutants in the soil. 241 , 242 By supplementing it with nutrients and microorganisms, biochar may be used as a carrier material for agricultural inputs, thus increasing the nutrient use efficiency, viability, and activity of the inoculated microorganisms in the soil. 243 Biochar can also serve as a source of nutrients for plant growth and suppress soil-borne, pathogen-based diseases to alter the agricultural environment. 242 , 244 In addition, biochar can also reduce the emission of CH 4 , N 2 O, and other air pollutants during the degradation of biomass in the soil, mainly by adsorbing free C and N compounds to its surface, changing the properties of the systems. 245 For example, biochar used as a soil amendment can reduce soil CH 4 emissions by 39.5%, 246 and soil N 2 O emissions by 30.92%. 247 Furthermore, biochar has been shown to mitigate the emission of GHGs (CH 4 , N 2 O, and CO 2 ) during composting, and its application is highly recommended for optimizing the composting process and conservation of C, N, and other compost minerals. 187 , 248 Therefore, the conversion of agricultural waste into biochar to improve soil health is regarded as a promising strategy for storing soil nutrients and reducing GHG emissions. 249

Zero waste biochar as a carbon-neutral tool for sustainable development

Owing to its controllable and tailorable electrical conductivity and inherent functional groups, biochar could be easily designed to have photonic, electronic, acoustic, and bio/redox interactions with other reactive substances, making it a viable alternative to replace unsustainable solid C-based catalysts. 250 , 251 , 252 , 253 , 254 In addition, the possible use of biochar in the manufacturing of value-added construction materials has been explored. 255 , 256 For instance, in a study, Das et al. 257 obtained wood polypropylene composites with enhanced physical and mechanical properties after mixing wood and malleated anhydride polypropylene with biochar, suggesting that biochar with a high surface area may act as a reinforcing filler in the production of biocomposite materials.

Research on waste valorization using biochar as a low-cost C-based additive in the manufacturing of construction and building materials has produced promising results. 258 , 259 Biochar can replace cement in ultra-high-performance concrete 260 and strengthen the interface bond between cement matrix and polypropylene fiber. 261 Other benefits include improving cement composite flexural strength by 66%, toughness by 103%, and compressive strength by 40%–50%, 262 reducing the water permeability and adsorption of the mortar, thereby enhancing the impermeability of the biochar-enriched mortar. 263 With the help of the C-negative manufacturing process, biochar occupies a special position in the production of green cement and concrete. It may become a key tool for building a better world for the progress of human civilization.

Besides its usage in environmental protection and sustainable development activities, biochar application as a feed additive in animal production systems is also gaining more attention. More recently, it has been shown that adding biochar to animal feed reduces ruminant methane generation, improves animal growth and health, egg production, and suppresses disease occurrence, thus boosting animal productivity. 264 In addition, there is a possibility that biochar may find its application in the human healthcare industry, but it has yet to be explored.

Although biochar may contribute to a sustainable platform to realize the goal of C neutrality and zero waste, not all forms of biochar are environmentally friendly or beneficial. 249 This is because the effectiveness of biochar depends on its physical and chemical properties, which are affected by various production factors and operating settings, such as the type of raw material and the thermochemical conversion process used to produce the biochar, temperature, time, and heating rate, etc., in addition to the post-production processes. 265 , 266 For example, when used as a soil amendment, biochar with an excessively high pH, too much ash, or high concentrations of residual organic and inorganic toxicants may negatively impact plants and beneficial microorganisms in the soil. 267 Therefore, it is necessary to develop an in-depth understanding of suitable raw materials and production conditions to obtain biochar with the characteristics required for a specific application.

Many recent studies have shed light on biochar's constructive features and potential applications in promoting a circular economy and mitigation of climate change toward sustainable development. For instance, Ghodake et al. 228 investigated the connection between feedstock source, production conditions, and physicochemical properties of biochar, bringing together aspects required for establishing viable systems for the production of biochar with desired attributes. Bolan et al. 223 discussed the trends in biochar applications in different areas, including crop-livestock production, environmental remediation, direct climate change, air pollution mitigation, chemical and materials industry, and construction industry. Beyond elucidating multi-purpose benefits of biochar, Bolan et al. 223 also summarized the negative side of biochar applications, stressing the need for biochar life-cycle analysis from an environmental, energy, economic perspective before its intended use. Although the above reviews offered a wealth of information on waste valorization, they focused only on biochar generated from biomass wastes, leaving out char made from plastic wastes, which can be effective in environmental remediation. 225

To achieve sustainable development in a C-neutral world, in addition to the need to decentralize biochar production units and increase public awareness of its multifunctional values, there is a need to determine the critical factors for the biochar system to advance its potential in GHG reduction, carbon dioxide removal, and environmental protection. Because the properties and applicability of biochar are significantly different due to different pyrolysis conditions and types of raw materials, future development in biochar optimization should focus on feedstock pre-treatment, pyrolysis process, operating factors, and product yield. Finally, integrating ecological strategies to optimize the process of biochar production, characterization, and life-cycle analysis, and formulating standards based on models and experimental routes will enable policymakers, biochar producers, users, and other relevant stakeholders to work together toward C neutrality.

Carbon sequestration in bio-based products. Using biomass to transform, reuse, and recycle CO 2 is a sustainable way to mitigate climate change and promote a circular bioeconomy. Potentially, all fossil fuel products can be produced from biomass. In addition to providing bioenergy, inedible biomass can replace non-renewable fossil fuel resources in the industrial production of plastics, lubricants, medical devices, paint, and other valuable commodities. 268 This is not a myth because recent scientific and technological advances in various fields, including biotechnology, nanotechnology, and nanobiotechnology, have paved the way for the utilization of biomass for the truly sustainable development of global production systems. For instance, microorganisms, especially bacteria, can use most biological resources, such as starch, fatty acids, cellulose, sugars, proteins, and other organic materials, as sources of nutrients and convert them into various monomers appropriate for the production of biopolymers. 269

Unlike traditional polymers derived from fossil fuels, biopolymers are in line with our principles of C neutrality and sustainable development, as they are directly or indirectly derived from photosynthetic plants that capture CO 2 from the atmosphere. Starch-based polymers are the most widely used and cost-effective biomaterials due to their biodegradability, biocompatibility, tensile strength, and thermal efficiency, and account for 50%–80% of the global bioplastics and biopolymers market. 270 Plastics from different biomass feedstocks, their uses, and their environmental impacts compared with petrochemical plastics have been thoroughly documented. 271 , 272 , 273 , 274 , 275 Undoubtedly, harnessing the power of biomaterials can reduce the C footprint and environmental impact of petroleum-based polymers, offering a wider range of applications than conventional polymers. Different bio-based materials are now extensively tailored using cutting-edge technologies to offer sustainable innovative materials with the properties required for specific applications. 276 , 277 For instance, fibrillated cellulose obtained from renewable sources, due to its mechanical, thermal, optical, and fluid properties, is a multifunctional nanomaterial that may be utilized to produce materials spanning from composites, nanofillers, and macrofibers to thin films, gels, and porous membranes. 277 In addition, modification and functionalization of wood materials using nanotechnology processes can provide large-scale bio-templates with improved properties. These wood-based materials can be used to implement the concept of hierarchically structured nanomaterials for large-scale applications in various advanced technologies, including energy storage, solar-steam-assisted desalination, water treatment, and production of lightweight structural materials, plastic, electronics, glass, and ionic devices. 276

The application of wood nanotechnology for producing bioinspired functional materials, with a particular emphasis on novel nanotechnological approaches for developing new wood-based materials, has been developed for sustainable use in various production systems. 276 , 278 , 279 These advances in the development of a circular bioeconomy are a promising path toward C neutrality as C will be stored in these bio-based products.

Technologies for CO 2 capture, utilization, and storage

The CO 2 capture, utilization, and storage (CCUS) technology comprises three different processes: separating CO 2 from emission sources, CO 2 conversion and utilization, transportation, and storage underground with long-term isolation from the atmosphere.

The CCUS is a necessary technology to realize the CO 2 emission reduction target. 280 The International Energy Agency (IEA) forecasts that the task of reducing emissions cannot be accomplished only by improving energy use efficiency and adjusting the energy structure, but also 19% of CO 2 emissions must be captured and stored to keep global temperature rise below 2°C by 2050. 281 Without CCUS, the total cost of CO 2 reduction will rise by 70% by 2050. 281 The technology in C capture and utilization is summarized in Figure 4 .

The roadmap for CO 2 capture technology development in the industry

CO 2 capture and storage

The concept of CO 2 capture and storage (CCS) was first developed in 1977, 282 and it has gone through three stages of development so far. The first stage, from 1977 to 1996, was the technology development phase. In 1989, the Massachusetts Institute of Technology launched the first CCS technology project. While financially supporting CCS projects, the Norwegian government imposed a C dioxide tax in 1991 to ensure that the country can meet its climate goals. As a result, the C tax promoted the operation of the world's first platform-based C dioxide capture facility at the Sleipner gas field. 283 The second stage from 1997 to 2018 was the large-scale demonstration phase of the technology. In 2005, the IPCC released a special report on CCS, which identified CCS as one of the important emission reduction technologies. Subsequently, Australia, the United States, Canada, the United Kingdom, and other countries developed corresponding regulations or modified existing regulations for CCS to solve the regulatory problems of large-scale CCS demonstration projects. At the same time, international organizations, such as the IEA and CSLF, have developed CCS technology roadmaps to advance CCS demonstrations and applications. Those technology roadmaps are updated as the technology develops. By the end of 2018, there were 23 commercial CCS facilities in operation or under construction, including four operational and two projects under construction. The third phase began in 2018, and CCS technology entered the early stages of commercialization. It was marked by the US amendment of tax 45Q, which provides a tax credit of up to $50/t CO 2 for CCS projects. Since then, the number of large-scale commercial CCS projects has gradually increased.

Current status of carbon capture technology. At present, the technical routes of CO 2 capture mainly include post-combustion capture, pre-combustion capture, and oxygen-fuel combustion. Post-combustion separates CO 2 from the exhaust gas and is one of the simplest ways of CO 2 recovery in energy systems. The gas separation technologies used in post-combustion capture technology include physical absorption, chemical absorption, membrane separation, etc. Due to a large amount of post-combustion flue gas treatment and low CO 2 concentration, the chemical absorption method is the most suitable separation technology for post-combustion CO 2 capture. The advantage of post-combustion capture is that it can be operated easily, and there is no need to modify the power generation system too much. Due to N 2 dilution, the concentration of CO 2 in the tail gas of an energy system is usually very low (generally, the concentration of CO 2 in the tail gas of coal-fired power plants is 10%–15%, and that of natural gas power plants is even lower, about 3%–5%), and the amount of tail gas treatment is large. When using the chemical absorption method to separate CO 2 from the exhaust gas of coal-fired power plants, the energy consumption is about 0.37–0.51 MWh/t CO 2 , which means that 90% CO 2 separation will reduce the efficiency of the energy system by 11.0–15.0 percentage points, and the unit investment of a power plant increases by 50%–80%. The current research focus of post-combustion separation is to find efficient absorbers and optimize the separation process to reduce the energy consumption of CO 2 separation. However, the fundamental reason for the high energy consumption of post-combustion separation is the low CO 2 concentration in the tail gas. It is difficult to significantly reduce the energy consumption of separation only by improving the absorbers and optimizing the process.

The way to separate CO 2 before combustion is called pre-combustion. Fuel is gasified into syngas (mainly composed of CO and H 2 ), then CO in the syngas is converted into CO 2 and hydrogen and, afterward, CO 2 is separated from H 2 . Since the CO 2 separation takes place before the fuel combustion process and the fuel gas has not been diluted by nitrogen, the CO 2 concentration in the syngas is over 30%. The results show that 90% CO 2 capture before IGCC combustion can reduce the net power efficiency by 8.0–10.0 percentage points, 284 which is smaller than that of post-combustion capture. However, for IGCC pre-combustion, advanced coal gasification technologies and gas turbines fueled by hydrogen-rich gas need to be further developed.

Oxygen combustion is proposed because of the defect that conventional air combustion can dilute CO 2 . The fuel is burned in an environment of oxygen and CO 2 , and a part of the flue gas is returned to the system for circulation. The concentration of CO 2 in the flue gas can be more than 95%. The oxygen required is produced mainly by air separation, including the use of polymeric films, pressure-swing adsorption, and cryogenic technologies. The advantage of oxygen combustion is that the flue gas mainly consists of CO 2 and vapor, and thus the energy consumption of CO 2 separation is close to zero. However, due to the need for oxygen production, the power consumption of the air separation unit is large, and the power output of the system is still reduced greatly (around 10%–25%). Meanwhile, the air separation will increase the additional investment of the system. If 90% CO 2 is captured, the net power efficiency will decrease by 10.0–12.0 percentage points for oxygen combustion. 284 The bottleneck of improving the efficiency of the oxygen combustion system is the development of efficient air separation technology.

Current status of CO 2 transportation. CO 2 transportation means the process of transporting the captured CO 2 to use or the storage area. In some aspects, CO 2 transportation is similar to the transportation of oil or gas, which includes pipelines, ships, railways, roads, and so on, among which pipeline transportation technology has the most potential for application. In recent years, there have been many practices for CO 2 pipeline transportation around the world. For example, the United States has built a trunk pipeline network of more than 5,000 km. At present, CO 2 transportation in China is mainly based on low-temperature storage tanks by road transportation. In the area of low-pressure CO 2 transportation, we can learn from the experience of mature oil and gas pipeline transportation; meanwhile, the research on high-pressure, low-temperature, and supercritical CO 2 transportation has just started.

Current status of CO 2 storage. CO 2 storage refers to storing the captured CO 2 in geological structures through engineering and technical means. It could achieve long-term isolation of CO 2 from the atmosphere. Different storage geological bodies mainly include the storage of onshore saline aquifers, the storage of saline aquifers on the seabed, and the exhausted oil and gas field storage and other technologies. At present, long-term safety and reliability are the main obstacles to CO 2 geological storage technology development.

Challenges and future technology development directions. The CO 2 capture technologies currently being demonstrated and commercialized around the world are mainly post-combustion separation technologies. However, such technologies have high energy consumption and cost and have limited potential for reduction. In the early stage of CCS technology promotion, post-combustion technology is relatively simplistic and has low technical difficulty. This type of technology is often used in CCS demonstration projects. It could achieve CO 2 emission reduction effects in the short term. However, in the long run, since the nature of this type of technology is to use more energy in exchange for CO 2 emission reduction, using it as the main technology for long-term CO 2 emission reduction will cause countries to pay unbearable energy and economic costs. For this reason, if the application of CCS technology needs to be promoted on a large scale, countries must develop low-energy, low-cost CCS technologies suitable for developing countries for the clean utilization of coal, such as new poly-generation technology, chemical chain technology, NET with multi-energy complementary technology CO 2 capture, etc.

Chemical-power poly-generation technology with low energy consumption CO 2 capture . Chemical-power poly-generation refers to the technology of producing both synthetic fuels/chemical products (such as methanol, dimethyl ether, and other alternative fuels) and electricity. Chemical-power poly-generation technology can achieve not only substantial energy savings in the chemical and power industries but also produce coal-based alternative fuels to reduce our dependence on fossil fuels and reduce CO 2 emissions on a large scale at the cost of low energy consumption. 285 , 286 , 287 Efficient gasification and gas turbines fueled by hydrogen are future breakthroughs of poly-generation technologies.

Flameless chemical-looping combustion technology. The "flameless" chemical-looping combustion is essentially different from the traditional "flame" combustion: through two gas-solid reactions, no contact between fuel and air is realized. Thus, the gas product is high concentration of CO 2 and H 2 O, and the CO 2 can be recovered without the separation process. CO 2 can be separated with zero energy consumption. The use of a "flameless chemical-looping combustion" has opened a new way to control GHGs. The special report on the capture and storage of CO 2 by IPCC emphatically pointed out: "Chemical looping combustion is a way to achieve 100% capture of CO 2 . It is a promising way to control greenhouse gases." 284 In the 1990s, Chinese scholars took the lead in discovering the new phenomenon of high-concentration CO 2 enrichment in chemical-looping combustion. 288 The IEA and the US DOE have identified the chemical chain as the primary new direction for zero emissions of fossil energy in the future. Oxygen carriers with high reactivity, mechanical properties, and cycle index still need to be further developed. New reactors suitable for chemical-looping combustion and heat integration of the whole system also need further investigations.

Negative emission technology: Fossil energy combined with biomass and solar energy. With the gradual decrease in the proportion of fossil energy and the increase in the proportion of renewable energy consumption, the CCS technology coupled with fossil energy and biomass/solar energy could achieve negative emissions. It could be used for the areas that have to be emitted to achieve C neutrality. The development of this kind of multi-energy complementary technology still needs to develop system integration theory and solve the problems of space-time complementation between fossil energy and renewable energy.

The safety and reliability assessment of CO 2 storage. At present, the storage potential and long-term safety are the main obstacles to the large-scale deployment of CO 2 geological storage technology. Due to the complex sedimentary history, tectonic structures, and diagenesis processes of sedimentary systems and resource deposits in a history of a geological era. The spatial distributions of aquifer layers and oil fields suitable for CO 2 storage lack sufficient technologies to obtain detailed geological data because of the limitations of technologies and interpretations; and then, the assessments of the CO 2 storage capacities face extreme difficulties. Long-term risk and safety issues also face the challenges of current understandings and technology levels.

Therefore, technical innovations are keys to the large-scale deployment of CO 2 geological storage. The breakthrough of these key technologies and methods can provoke the process of realizing C neutrality targets in the future to develop efficient and safe CO 2 geological utilization and storage theory, methods, technology, software, and related equipment. Among various vital technologies, establish the site characterization and site evaluation technical system; construct the specialized system for collaborative optimization of C storage and underground resource recovery; form a safe CO 2 transportation technology system of various options; the development of "sky-surface-underground" integrated monitoring, risk prediction, and risk mitigation technology system; and finally integrate the full-chain CCUS project at scale to systematically and creatively solve the key scientific, technical, software and equipment problems facing CCUS scale and commercialization.

CO 2 utilization

The CO 2 chemical utilization refers to processes of converting CO 2 into other high-value chemicals under certain conditions of temperature, pressure, and the presence of a catalyst. The CO 2 chemical utilization can directly realize the conversion and utilization of CO 2 and has a certain direct emission reduction effect. 289 Meanwhile, this type of technology can also form a new chemical synthesis route to replace the utilization of fossil fuels or raw materials. The C flow from the lithosphere to the atmosphere will be transformed into a new model that circulates in the atmosphere, which has a huge indirect emission mitigation effect and has important application prospects in future C-neutral scenarios. To facilitate CO 2 conversion, diverse routes, such as thermochemical catalysis, photochemical catalysis, electrochemical catalysis, and others (enzymatic catalysis and organometallic catalysis) have been developed, and substantial advances have been made in recent years.

Thermochemical catalysis. Among various approaches for CO 2 conversion, the thermochemical processes have been intensively investigated, and some have been commercialized. In thermochemical catalysis, the integration of CO 2 into certain organic substrates to form new C–X bonds in catalytic sequences would broaden the reaction pathway to produce valuable chemicals. Generally, new covalent bonds between CO 2 and substrate molecules can be formed by constructing C–X bonds, including C–H, C–O, C–N, and C–C bonds. 290 (1) The generation of C–H bonds originates from the hydrogenation of CO 2 to produce syngas, CH 4 , HCOOH, and alcohols. 291 , 292 , 293 (2) The construction of C–O bonds is established via the cycloaddition of epoxides with CO 2, the condensation of 1,2-based polyols with CO 2 , oxidative cyclization of olefins with CO 2 , and carboxylative cyclization of propargyl alcohols with CO 2 to afford organic carbonates. 294 , 295 , 296 (3) Catalytic formation of C–N bonds resulting from the reactions of CO 2 with various amines to the synthesis of N-containing compounds. Various N-containing compounds, including oxazolidinones, quinazolines, ureas, imidazolinones, and benzimidazoles, can be produced via these routes. 297 , 298 , 299 , 300 (4) The formation of C–C bonds is through a direct carboxylation reaction (i.e., carboxylation of CO 2 with alkenes, alkynes, or aromatic heterocycles), affording carboxylic acid derivatives as the target products. 301 , 302 However, from a thermodynamic point of view, many catalytic reactions are thermodynamically unfavorable and/or need harsh reaction conditions (i.e., high pressure and high temperature) because CO 2 is thermodynamically stable and kinetically inert. Therefore, photochemical and electrochemical catalysis have been prompted as attractive alternative techniques for a sustainable and environment-friendly pathway.

Photochemical catalysis. Photoelectrochemical reduction of CO 2 has gained increasing interest as it can enhance CO 2 efficiency under mild conditions. In a typical photochemical reaction, the inexhaustible solar light is used as an energy source, and CO 2 photoreduction can be carried out using various semiconductors photocatalysts under light irradiation. An efficient photocatalyst should possess the following properties: (1) fast migration of multiple electrons from photocatalytic centers to CO 2 ; (2) easy adsorption of reactants onto the catalyst and desorption of products into the system; (2) more negative potential of the photocatalyst's conduction band bottom level than the redox potential of CO 2 is required; and (4) the photogenerated holes on the valence band of the photocatalyst should be consumed by oxide species. Therefore, an efficient photocatalytic CO 2 conversion can be promoted via optimization of the light harvesting, fast charge transfer, together with abundant active centers that can adsorb and/or activate CO 2 . 303 Recently, several semiconductors, including metal oxide/sulfide (e.g., TiO 2 , ZnO, ZnS, SrTiO 3 , and CdS) and their modified materials, are most widely investigated for the photocatalytic reduction of CO 2 to fuels. 304 , 305 Many valuable fuels, such as CO, CH 4 , CH 3 OH, HCOOH, and C 2+ products have been generated through proton-assisted multiple electron-transfer processes. 306 , 307 , 308 , 309 , 310 To improve the catalytic efficiency, many efforts have been made via morphological control, structure architecture, heterojunction construction, surface defect engineering, and doping with heteroatoms.

Electrochemical CO 2 reduction. The electrochemical CO 2 reduction reaction (CO 2 RR), enabling the conversion of intermittent renewable electricity from sunlight and wind into storable fuels and useful chemical products, is an important approach for CO 2 conversion and utilization to meet the requirement of C neutrality. 13 , 311 , 312 Since the pioneering works by Hori et al., 313 , 314 massive efforts have been devoted to boost the catalytic performance of electrochemical CO 2 RR, especially within the past decade. 315 , 316 , 317 , 318 , 319 , 320 , 321 There has been increasing mechanistic understanding as well as many encouraging signs of experimental progress on this complicated multi-electron and multi-proton transfer reaction system. 192 , 315 , 322 , 323 , 324 , 325 , 326

Theoretical simulations using density functional theory (DFT) have become a powerful tool for providing mechanistic insights into microscopic processes at electrode/electrolyte interface and obtaining critical thermodynamic and kinetic data. A significant difference between electrocatalysis and classical catalysis is that both the reaction thermodynamics (reaction free energy) and kinetics (activation barrier) can be effectively modulated by the applied electrode potential. A simple way to treat the electrode potential effect was developed by Nørskov et al. 327 The combination of the proton-coupled electron-transfer model with the computational hydrogen electrode model was applied to explain the unique ability of copper to convert CO 2 into hydrocarbons. The onset potential and potential-determining steps ascertained from thermodynamic computations are useful in determining the catalytic activity toward a certain reduction product based on linear scaling relations and the volcano model (Sabatier's principle). 328 , 329

Other catalysis. Enzymatic and organometallic conversions of CO 2 have also emerged as attractive alternatives in certain applications. Various useful reduction products such as CO, HCOOH, carboxylic acids, and cyclic carbonates have been successfully obtained. 330 , 331 , 332 , 333 However, development in these fields is still in its infancy; considerable effort needs to be dedicated to understanding structural features controlling the catalytic activity and achieving practical catalysts suitable for the conversion of CO 2 to useful chemicals. 334

Future challenges and key technologies of CO 2 catalysis. Although significant efforts have been made over the past several years, the conversion of CO 2 into fuels and chemicals is still challenging in overcoming both thermodynamic and kinetic barriers. For thermal catalysis, the number of valuable and spontaneous reactions of CO 2 with other chemicals is very limited. Deep insights in seeking new reactions in which CO 2 reacts with multi-compounds simultaneously will provide more opportunities for CO 2 conversion. For photochemical and electrochemical catalysis, large-scale application of CO 2 transformation has not been realized. One of the main obstacles in developing rational strategies for catalysis is that the complexity of catalysts hinders the efforts of the active sites. Therefore, much more work needs to be carried out to enhance the existing routes' efficiency and explore efficient catalysts and reaction mediums. In addition, the products for photocatalysis and electrocatalysis are still limited due to the relatively poor efficiency or unfavorable operating conditions. Seeking more reactions in which CO 2 reacts with other compounds may open ways to produce long-chain C products in photochemical and electrochemical systems. To approach the neutral cycle in the future, we must continue developing more efficient catalytic systems to accelerate industrialization. For electrocatalytic CO 2 reduction, this field still faces challenges of (1) slow electron-transfer kinetics, (2) large overpotential, and (3) unsatisfactory selectivity, restricting its practical application and technological commercialization. 335 , 336 All of the above three important performance indexes are intrinsically related to the kinetic properties of catalytic processes. The current density and overpotential reflect the polarization relation of electrochemical rate, while the faradic efficiency stands for the distribution relation of parallel reaction rate. Thus, intensively kinetic studies based on first-principles calculations and simulations are crucial whether interpreting the electrocatalytic performance of reported catalysts or promoting catalytic properties by designing new catalysts. Microkinetic models are needed to use the DFT-calculated activation energy barriers to determine the reaction rates, the catalytic activity, the product distribution, and the current density under real experimental conditions. 312

In addition to improving energy efficiency and adjusting the energy structure through renewable energies, CCUS is a necessary solution for achieving C neutrality. The role of CCUS in carbon emission reduction depends on its competition with renewable energy with energy storage. When the target of C neutrality is proposed, it is hoped that renewable energy may replace almost all fossil fuels. However, this hope seems to be impracticable as renewable power is not stable and cannot meet the requirement of energy safety. Although large-scale energy storage can enforce the stability of renewable powers, its total cost and environmental impacts need to be reconsidered. In addition, the transition to renewable energies may mean that there needs to be a complete reconstruction or retrofit of current fossil fuel-based energy production, transmission, and supply systems, and this cost is huge. Also, innovative CCUS technologies can be cost-competitive to renewable powers. Thus, in consideration of the stability and safety of energy supply, environmental impacts, and total cost, CCUS may play a big role in realizing C neutrality in the future. High cost and high energy consumption are still the main challenges for CCUS in the power, steel, and cement industries. Opportunities with low-cost CO 2 capture exist in the chemical industry and may contribute to around 0.4–1.0 billion tons of CO 2 emission yearly in China. CCUS can be combined with clean fuel productions, such as hydrogen production from fossil fuels, and will a play role in the future. There are only two examples of large-scale CCUS technology in power sector currently, and they both adopt post-combustion technologies. The high investment and energy consumption of the two demonstrations indicate that CCS needs technological innovations to reduce its cost further. Low-cost chemical-looping combustion, renewable energy poly-generation, and hybrid renewable fossil fuel energy systems are promising technologies that can help build a C-neutral world. However, the above innovative technologies are at the early stage of R&D and may play an important role after ten years (more than one billion tons of CO 2 emission reduction per year in China). Furthermore, the conversion of CO 2 into valuable chemicals and fuels can also reduce several million tons of CO 2 emissions per year in China.

Carbon neutrality based on satellite observation and Digital Earth

In the area of satellite observation and Digital Earth technology, the support for C neutralization includes the rapid monitoring of global GHG concentration, ground land cover change, and the spatial analysis of global natural C sink, which plays an important supporting role in the assessment of when to achieve the peak of C emissions and the potential of a natural C sink.

Satellite observations of CO 2 emissions

At present, greenhouse gas observation methods include ground-based monitoring and satellite remote sensing. A global network of greenhouse gas observation stations was established in the early stage to provide accurate greenhouse gas concentration data. 337 However, due to the limitation of the number of sites, the spatial resolution is often not sufficient to meet global C flux calculation needs. Three CO 2 satellites were launched successively, including GOSAT launched by Japan in 2009, 338 OCO-2 launched by the United States in 2014, 339 and TANSAT launched by China in 2016, 340 which significantly improved the ability of C flux observation. In addition to CO 2 observation, the Sentinel-5P satellite launched by Europe has achieved good results in CH 4 , NO 2 , CO, O 3 , and other gas inversions. Among them, NO 2 , as the gas produced by fossil energy combustion, the photochemical lifetime of which is only a few hours, can effectively track the emission source. 341 , 342 It is often used as a barometer of economic stagnation or recovery in various countries during the COVID-19 pandemic. 343 It is expected that, in 2025, the European Space Agency will launch a new satellite by combining CO 2 and NO 2 observations together. 344

Digital Earth for carbon neutrality

Digital Earth will integrate a massive amount of data mainly from satellite observation, and develop models, simulate or predict current or future global ecosystems at multiple resolutions in space and time, and then visualize the results. These new technologies and features will provide very powerful benefits for C neutrality and C trading for the following two reasons: (1) the C cycle is influenced by many natural and human factors. 345 Many current models cannot effectively simulate these factors and estimate the C sink. Its estimation is complex, and results from many models differ considerably. 346 However, Digital Earth, which combines these models and comprehensive data, can provide a platform to run these models and compare or validate their results to get a more realistic global C sink. (2) The Principle of Common and Separate Responsibilities was clearly stated in United Nations Framework Convention on Climate Change in 1992. It was adopted in the Kyoto Protocol in 1997, which was widely accepted because countries at different stages of development have different capacities to deal with international environmental issues. Different countries or regions differ in C emissions and sequestration and, consequently, different levels of responsibilities for C neutrality. 347 Global C estimation or prediction and even their driving mechanisms are conducted and shown on Digital Earth at the pixel level. It is apparent that to find the spatial distribution and differences among countries or regions which will bring great convenience to quantify the responsibility for C neutrality taken by governments and the C trading among countries or regions. Moreover, these digital replicas of the global C estimation and their driving mechanisms are helpful to provide essential information for climate and C neutrality policymaking.

Conclusions and future perspectives

Carbon is one of the most important elements that contribute to the existence of life on Earth. Since the Industrial Revolution, C-based resources have been exploited to produce energy, food, and other commodities, affecting the global ecosystems in countless ways. The extensive use of fossil fuels and deforestation to promote anthropogenic activities and urbanization are entwined with global climate change, which stems from the greenhouse effect associated with increased atmospheric CO 2 and other GHGs. Currently, the international community is confronted with developing cost-effective and sustainable methods for minimizing C emissions and promoting C sequestration. As the global community is moving towards C neutrality, there is a need to revise our understanding of the current state of C flows in the total environment. Therefore, it has become imperative to switch from non-renewables to renewables that sustain current production systems and address climate change issues to protect human health and the environment. As presented in this review, harnessing the power of renewable resources in energy, food, and industrial production systems and promoting C sequestration in terrestrial and marine ecosystems are seen as possible routes towards C neutrality and achieving sustainable development goals. However, the current level of research has not overcome the major challenges to efficiently use renewable resources in production systems and prevent us from depending on fossil fuels. Many problems still require scientific, socioeconopolitical, and technological solutions to adopt practices that reduce GHG emissions in current global production systems. These include:

• 1. Given that the potential of global renewable energy resources surpasses global energy demand, the most pressing research needs in sustainable development are enhancing the current renewable energy production trend to phase out the use of fossil fuels. Increasing the amount of power and heat generated from C-free sources (i.e., sun, wind, and ocean) is one aspect of this, but so is the production of biofuels and hydrogen from biomass. The intermittency of wind, solar and other renewable energy sources is one of the major challenges limiting the replacement of fossil fuels with renewable energy. Energy storage is the apparent answer to the intermittency of some of the renewable energy sources. However, the scalability and cost-effectiveness of energy storage are subject to many constraints and limitations. Energy storage development and promotion entail scientific and technological challenges, as well as economic and regulatory concerns that must be addressed in order to drive investment and competition in the energy storage industry. Improving energy efficiency (including residential heating/cooling) has a major impact on reducing GHG emissions in our daily lives. Therefore, more research is needed to fully understand how to maximize energy efficiency and support C-neutral economic growth. As there is a clear link between energy conservation and climate change mitigation, efforts to minimize energy consumption in end-use sectors will contribute to sustainable development as well as carbon neutrality targets.
• 2. Considering that unsustainable management practices in food systems, spanning from the production and application of chemical fertilizers to waste landfilling and burning, continue to account for a significant portion of GHG emissions, more research is needed to reduce emissions from food systems and enhance sinks of C and other important nutrients (i.e., nitrogen, potassium, phosphorus, and sulfur). To achieve this, developing new methods for further optimization of waste recycling and nature-based processes in agroecosystems, along with the technological development of food factories, has the potential to reduce the need for chemical fertilizers and sustainably support human activities. Given that biochar has multifunctional values in addition to carbon sequestration, as discussed in this review, there is a need to integrate ecological strategies to optimize biochar production, characterization and life cycle analysis, and to formulate model-based standards and experimental evidence to spur biochar-assisted sustainable development. Since terrestrial and marine ecosystems are the largest C reservoirs on Earth, strengthening policies that promote afforestation and reforestation and use of C-negative materials to conserve terrestrial ecosystems and sustainable management of aquatic ecosystems could contribute to increasing C sequestration, thereby mitigating climate change.
• 3. Even though the CCUS approach has a pivotal role to play in our pursuit of carbon neutrality, the adoption of current CCUS technologies is hampered by their high energy consumption and costs. Carbon capture and storage in the power industry require scientific and technological innovations to achieve low or even net-zero energy use. Polygeneration, chemical looping combustion, and technologies that combine fossil fuels and renewable energy sources for capturing CO 2 could open a new era for CCUS. At the same time, the conversion of CO 2 to fuels and chemicals is also a promising possibility, but the obstacles of thermodynamics and kinetics need to be overcome.
• 4. Given the utmost relevance of monitoring GHG emissions from space to ensure the world is on track to meet its climate change mitigation goals, the accuracy and spatiotemporal resolution of monitoring GHG emissions from satellites need to be further strengthened so as to monitor greenhouse gas emission sources and rates more comprehensively and timely. The capacity and accuracy of satellites in monitoring terrestrial ecosystem biomass also need to be improved. Remote sensing monitoring of marine carbon sink potential needs new theoretical breakthroughs. Carrying out accurate carbon budget calculation based on land-sea-air joint observation is an important basis for carbon peak and carbon neutralization decision-making.

In summary, this review sheds light on the current status, challenges, and prospects of technologies for building a carbon-neutral future. However, to bridge the gap between the C-neutral world rhetoric and reality, the urgent need to restructure global development systems and protect natural resources requires swift and collaborative actions by researchers, policymakers, investors, and consumers around the world, aiming at reducing GHG emissions and promoting carbon sequestration in technical and natural systems. Furthermore, the global scientific and technological innovations that foster the green economy must be financially and strategically rewarded to accelerate the trend towards carbon neutrality.

Acknowledgments

This work was partially supported by the National Key R&D Program of China (2020YFC1807000), the National Natural Science Foundation of China (41991333, 41977137, 31922080, 32171581, 52173241, 21776294, 21773267, 21872160, 51776197, 21677149), the Youth Innovation Promotion Association of Chinese Academy of Sciences (2011225, 2016275, 2019189, 2019182, 2021347, 2017241, Y202078, 2019170, Y202042), the Key Program of Frontier Sciences, Chinese Academy of Sciences (QYZDJ-SSW-DQC035), the Outstanding Youth Fund of Natural Science Foundation of Jiangsu, China (BK20150050), ‬the Guangdong Basic and Applied Basic Research Foundation (2021B1515020011), the Center for Health Impacts of Agriculture (CHIA) of Michigan State University, the ANSO Scholarship for Young Talents in China, the Natural Science Foundation of Fujian Province for Distinguished Young Scholars (2019J06023) and the Joint Fund of the Yulin University and the Dalian National Laboratory for Clean Energy (YLU-DNL Fund 2021005), German Research Foundation (DFG 5174188, 5245626, 5422173, 5471428, 40956283, 214367779, 160523647, 272843), and Hunan Province Science and Technology plan ( 2020NK2066). Fang Wang was partially supported by a fellowship from the Alexander von Humboldt Foundation for experienced researchers. We thank WG-46, Joint PICES/ICE Working Group on Ocean Negative Carbon Emission (ONCE) for their useful discussions.This work is dedicated to the 10th anniversary of the Youth Innovation Promotion Association of Chinese Academy of Sciences.

Author contributions

Fang W., J.D.H., D.C.W.T., S.X.C., M.K., D.B., K.W., X.H., S.D., J.G., C.X., N.J., Y.Z., H.J., A.S., J.M.T., J.M.C., and L.X. conceived, organized, and revised the manuscript. Zhizhang Y., Zhigang Y., Linjuan Z., Liang X., Y.-G.Z., Y.Z., H.C., J.Z., X.L., and Y.G. wrote and revised technologies for renewable energy. M.W., Faming W., Y.F., J.R., Leilei X., Z.Y., X.J., J.L., Y.S.O., W.C., J.S., Z.B., B.L., Z.T., N.B., M.L., J.L., and F.B. wrote and revised technologies for enhanced carbon sink in global ecosystems. S.L., L.L., Q.Z., N.W., W.Z., B.Z., Liu-bin Z., X.L., N.S., and T.Z. wrote and revised section technologies for carbon capture, utilization, and storage. L.H., D.P., and C.H. wrote and revised carbon neutrality based on satellite observations and Digital Earth. All authors discussed and approved the final manuscript.

Declaration of interests

The authors declare no competing interests.

Published Online: October 30, 2021

Lead contact website

Fang Wang: http://sourcedb.issas.cas.cn/yw/rc/fas/201412/t20141230_4283668.html .

Jing M. Chen: http://faculty.geog.utoronto.ca/Chen/Chen's%20homepage/home.htm .

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Next-generation battery ecosystem for a carbon-neutral lifestyle

Produced by

EcoFlow’s proprietary bi-directional inverter system, X-stream, allows for efficient electric power conversion between direct current and alternating current. Credit: EcoFlow

The global push for carbon neutrality has spurred the development of clean energy solutions, but most innovations to cut emissions have focused on making changes at the industry level. EcoFlow, founded in 2017 and based in Shenzhen, has been developing environmentally friendly and convenient power appliances for household use, featuring a renewable energy ecosystem and fast-charging battery technology.

“Progression towards carbon neutrality requires both top-down and bottom-up approaches, and we see significant market potential in filling the need for green-power storage products on the consumer front,” says Lei Wang, EcoFlow co-founder and CEO.

A BloombergNEF report from 2021 estimated that there will be 20 times more global energy storage installations in place by the end of 2030, with about 25% located at homes and businesses.

The demand, as Wang sees it, is driven by people seeking next-generation power for homes and businesses. Growing cases of massive power outages caused by natural disasters or grid production limitations are only adding to that need.

Consumer-level innovations

EcoFlow was among the first companies to start designing renewable energy systems, mainly portable power stations for the consumer setting — a big market, considering household consumption is estimated to contribute 60% of greenhouse gas emissions.

After working at drone tech leader DJI’s battery R&D department, Wang wanted to bring renewable energy to households in ways that could make a bigger impact on people’s daily life.

While the rapid adoption of electric cars has fuelled the advancement of lithium-ion batteries, creating unprecedented opportunities for the energy storage industry, EcoFlow aims to bring a more comprehensive set of power solutions for multiple scenarios both indoor and outdoor that span clean power generation, storage and end use.

EcoFlow’s portable power stations (the name for power banks in the company’s line of products) stand apart due to a proprietary bi-directional inverter system called X-stream, allowing for efficient electric power conversion between direct current and alternating current.

The inspiration came from the USB Type-C connector system, Wang explained. Through a Type-C portal, electric power may flow in two directions: a laptop can charge a phone, and we can charge a laptop with the help of an adaptor.

Conventional power stations need a tailored adapter to charge up their batteries from a wall outlet. Plus, the output of electric power to appliances may also require device-specific adapters especially for small gadgets such as phones and laptops.

With bi-directional inversion, X-stream can negate the need for adapters. Doing so makes the power station smaller and easier to carry around. From a manufacturing perspective, even the design contributes to carbon reduction by using fewer materials.

EcoFlow DELTA Pro portable power bank offers rapid speed and big capacity. Credit: EcoFlow

More importantly, by minimizing the steps of AC-DC conversions, the bi-directional inversion system cuts energy losses and boosts transmission efficiency. For users, that means rapid recharging. Powered by X-stream, the EcoFlow DELTA Pro portable power stations of 3.6 kWh capacity can be fully charged from a 240 V AC wall outlet in 1.8 hours.

To be user-friendly and environmentally sustainable, compact power stations should offer more than just rapid speed and a large capacity. The company is incorporating solar panels as one of several possible recharge input options, and is also exploring supporting other renewable energy sources such as wind power.

For its solar panels, EcoFlow developed maximum power point tracking (MPPT) algorithms with a proportional integral differential (PID) controller to tackle unpredictable solar energy production. The algorithms, built in the EcoFlow Solar Tracker, can calculate the best angle for a solar panel based on sun irradiation and position. The tracker can then automatically adjust the solar panel’s orientation to ensure maximum power generation. Compared with systems without auto-adjustment, a solar panel using the solar tracker can generate 30% more energy.

Portable power station, solar panel and solar tracker are all part of a clean power ecosystem that EcoFlow is building for various energy consumption settings. By channelling energy from a smart solar panel to a power station, users could avoid the frustration of intermittent energy production intrinsic to renewable energy resources and achieve more stable output. That feature could come in handy in an outdoor setting where there are fewer wall sockets.

In the case of an emergency, a separate EcoFlow Smart Generator can serve as an additional back-up that integrates with a power station through DC charging. An EcoFlow DELTA Pro station can simultaneously receive recharging input from three sources—a solar panel, an AC outlet, and a smart generator—with the help of a Smart Extra Battery.

For users who have excessive standby power storage or who want to power a larger system, EcoFlow provides the Smart Home Panel, which can feed power units into home circuits.

To give users additional control and an overview of power use, EcoFlow provides a mobile app that allows users to manage settings, including charging and discharging levels and even prioritize which appliances get power first during blackouts.

EcoFlow’s design goal is a carbon-neutral lifestyle for every household. Credit: EcoFlow

Accelerating global transformation

For all its R&D moves, EcoFlow is built around Wang’s philosophy of “meaningful innovation”. That is, to develop new technologies that solve real problems and meet consumers’ real-world expectations.

EcoFlow has invited consumers into its R&D process through crowdfunding. The development of EcoFlow DELTA Pro, for example, was supported by a crowdfunding campaign launched on Kickstarter. The company had originally aimed for US$100,000, but eventually raised about US$12.2 million. With funders’ feedback, EcoFlow gets direct access to users’ needs, which could help the company make adjustments in future designs, Wang said.

EcoFlow’s work fits into a major global transformation, which involves the wider adoption of renewable energy as a more sustainable resource, Wang said. During this process, “electrifying everything” is the key to carbon neutrality—as evident in electrical vehicles—and smart devices are necessary to enable better penetration, he added.

“We’re offering consumers more than just a piece of equipment,” Wang said. “By adding more products in our EcoFlow energy solution ecosystem, we aim to foster a carbon-neutral lifestyle which each person and household can practice in everyday life.”

Contact Details:

Email: [email protected]

Website: ecofow.com

This advertisement appears in Nature Spotlight 2022 China’s net-zero ambitions , an editorially independent supplement. Advertisers have no influence over the content.

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Essay on One Step Towards Green And Clean Energy

One step towards green and clean energy essay -.

Energy is extremely essential to life and all living organisms. We need energy to function effectively in our everyday lives. Most of the living and nonliving organisms around us need energy for sustenance. Traditional energy sources like coal,oil,and natural gas contribute to global climate change. Burning of these fuels also causes air pollution. So we should use more renewable energy sources. Here are a few sample essays on “One Step Towards Green And Clean Energy” .

100 Words Essay On One Step Towards Green And Clean Energy

Green energy is generated from natural resources such as sunlight, wind or water. It often comes from renewable energy sources and includes wind energy, solar energy, geothermal energy and hydroelectric power .

These energy sources can help to reduce pollution and have several advantages such as minimal maintenance cost, cost savings and storage capacities. Human behavior of contaminating the earth with hazardous wastes and garbage degrades and pollutes the environment.

A good approach will be to work to transform these wastes into biogas, which is a renewable energy source. Turning to the use of green energy is an excellent strategy to alleviate global warming and maintain a clean and healthy environment.

200 Words Essay On One Step Towards Green And Clean Energy

The world needs cleaner energy sources. ‘Go green’ is an earth-friendly approach to living. It means as an individual as well as a community in a way that is friendly to the environment and is sustainable for the earth.

Advantages Of Green Energy

Green and clean energy sources have very low or zero carbon emissions. They are environment- friendly.

Another advantage is that it is irrelevant to rely on any country to supply renewable energy resources, unlike its non-renewable counterparts.

In 2019 India also announced that it would be additionally doubling its renewable energy target from 175 GW by 2022 to 450 Giga-Watt.

Green energy is really beneficial for the environment because it does not affect nature in any way. It is one of the alternative energy sources that has received distinct attention from governments and various organizations to keep the planet clean.

Green energy can reduce the effects of greenhouse gasses produced in the atmosphere by fossil fuels and other sources.

We may utilize solar-powered stoves and other solar-powered gadgets to help us harness the sun’s energy. It will aid in the conservation of energy and be convenient in the future. Moreover, good energy resources will be obtainable in the future.

500 Words Essay On One Step Towards Green And Clean Energy

The present era is the era of industrialisation, to which energy is essential. For most of this work, traditional sources of energy are used. These traditional sources of energy have detrimental effects on the environment. Hence, a helpful alternative will be to turn to sources of green and clean energy.

Green energy can be defined as a renewable energy source because it is never exhausted. It's a sustainable energy source for generations. Wind turbines are a well-known example of green and clean energy. They generate electricity by working with the wind.

This creates zero carbon emissions. Windmills are another source of renewable energy. Geothermal energy is another example of a renewable energy resource. They are found in the earth's crust. They are extracted by drilling.

India’s Steps Towards Green And Clean Energy

Recent studies have shown that India's dominance in green and clean energy is significant. The country is trying to bring a revolutionary change in the field of generating electricity through solar energy and wind energy. The government has implemented a solar pumping programme for irrigation in the fields. Different types of solar devices save electricity and gas. They will also be used by future generations.

Fusion Energy

A recent milestone in nuclear fusion research was announced by U.S Scientists. It made a breakthrough in fusion, the process that powers the sun and stars that one day could provide a cheap source of electricity. The results are good news for advocates of nuclear energy as a clean alternative to fossil fuels.

This energy source produces no greenhouse gasses and minimal waste compared to conventional energy sources. It could produce limitless, carbon-free energy to supply electricity needs without raising global temperatures and worsening climate change. Developing this kind of technology delivers a low-carbon, sustainable source of energy that helps to protect the planet for future generations.

Ways To Save Energy

Energy conservation is most important in today’s world. By conserving energy today, we can brighten our future. Here we are going to discuss some ways to save energy in our day to day life.

Use energy efficient appliances such as energy saving bulbs or air conditioners etc.

During the day, try to rely on sunlight for light rather than turning the lights on.

Turn off and unplug all appliances when not in use to prevent unnecessary use of energy.

Old appliances usually consume more electricity than required. Hence, replacing old appliances with new ones helps in staying energy efficient.

How I Save Energy

One day there was a discussion in our classroom about how to save energy. Energy conservation is achievable by using energy more efficiently. We discussed many points in our class. I followed the following measures at home and my surroundings to save fuel. These are:

Replaced filament bulbs to CFL or LED lights in our home.

Turn off all home and office electrical equipment when not in use.

Turn off lights when not in use.

Use energy star labeled equipment everywhere.

Consider adding solar panels to our rooftops.

Public transportation is one of the important ways to save energy. So, I use more public transport than private transport.

I also made my family members and other friends aware of this. Now everyone started following this as much as they can so that we save energy as much as we can.

Explore Career Options (By Industry)

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Data Administrator

Database professionals use software to store and organise data such as financial information, and customer shipping records. Individuals who opt for a career as data administrators ensure that data is available for users and secured from unauthorised sales. DB administrators may work in various types of industries. It may involve computer systems design, service firms, insurance companies, banks and hospitals.

Bio Medical Engineer

The field of biomedical engineering opens up a universe of expert chances. An Individual in the biomedical engineering career path work in the field of engineering as well as medicine, in order to find out solutions to common problems of the two fields. The biomedical engineering job opportunities are to collaborate with doctors and researchers to develop medical systems, equipment, or devices that can solve clinical problems. Here we will be discussing jobs after biomedical engineering, how to get a job in biomedical engineering, biomedical engineering scope, and salary. 

Ethical Hacker

A career as ethical hacker involves various challenges and provides lucrative opportunities in the digital era where every giant business and startup owns its cyberspace on the world wide web. Individuals in the ethical hacker career path try to find the vulnerabilities in the cyber system to get its authority. If he or she succeeds in it then he or she gets its illegal authority. Individuals in the ethical hacker career path then steal information or delete the file that could affect the business, functioning, or services of the organization.

GIS officer work on various GIS software to conduct a study and gather spatial and non-spatial information. GIS experts update the GIS data and maintain it. The databases include aerial or satellite imagery, latitudinal and longitudinal coordinates, and manually digitized images of maps. In a career as GIS expert, one is responsible for creating online and mobile maps.

Data Analyst

The invention of the database has given fresh breath to the people involved in the data analytics career path. Analysis refers to splitting up a whole into its individual components for individual analysis. Data analysis is a method through which raw data are processed and transformed into information that would be beneficial for user strategic thinking.

Data are collected and examined to respond to questions, evaluate hypotheses or contradict theories. It is a tool for analyzing, transforming, modeling, and arranging data with useful knowledge, to assist in decision-making and methods, encompassing various strategies, and is used in different fields of business, research, and social science.

Geothermal Engineer

Individuals who opt for a career as geothermal engineers are the professionals involved in the processing of geothermal energy. The responsibilities of geothermal engineers may vary depending on the workplace location. Those who work in fields design facilities to process and distribute geothermal energy. They oversee the functioning of machinery used in the field.

Database Architect

If you are intrigued by the programming world and are interested in developing communications networks then a career as database architect may be a good option for you. Data architect roles and responsibilities include building design models for data communication networks. Wide Area Networks (WANs), local area networks (LANs), and intranets are included in the database networks. It is expected that database architects will have in-depth knowledge of a company's business to develop a network to fulfil the requirements of the organisation. Stay tuned as we look at the larger picture and give you more information on what is db architecture, why you should pursue database architecture, what to expect from such a degree and what your job opportunities will be after graduation. Here, we will be discussing how to become a data architect. Students can visit NIT Trichy , IIT Kharagpur , JMI New Delhi . 

Remote Sensing Technician

Individuals who opt for a career as a remote sensing technician possess unique personalities. Remote sensing analysts seem to be rational human beings, they are strong, independent, persistent, sincere, realistic and resourceful. Some of them are analytical as well, which means they are intelligent, introspective and inquisitive. 

Remote sensing scientists use remote sensing technology to support scientists in fields such as community planning, flight planning or the management of natural resources. Analysing data collected from aircraft, satellites or ground-based platforms using statistical analysis software, image analysis software or Geographic Information Systems (GIS) is a significant part of their work. Do you want to learn how to become remote sensing technician? There's no need to be concerned; we've devised a simple remote sensing technician career path for you. Scroll through the pages and read.

Budget Analyst

Budget analysis, in a nutshell, entails thoroughly analyzing the details of a financial budget. The budget analysis aims to better understand and manage revenue. Budget analysts assist in the achievement of financial targets, the preservation of profitability, and the pursuit of long-term growth for a business. Budget analysts generally have a bachelor's degree in accounting, finance, economics, or a closely related field. Knowledge of Financial Management is of prime importance in this career.

Underwriter

An underwriter is a person who assesses and evaluates the risk of insurance in his or her field like mortgage, loan, health policy, investment, and so on and so forth. The underwriter career path does involve risks as analysing the risks means finding out if there is a way for the insurance underwriter jobs to recover the money from its clients. If the risk turns out to be too much for the company then in the future it is an underwriter who will be held accountable for it. Therefore, one must carry out his or her job with a lot of attention and diligence.

Finance Executive

Product manager.

A Product Manager is a professional responsible for product planning and marketing. He or she manages the product throughout the Product Life Cycle, gathering and prioritising the product. A product manager job description includes defining the product vision and working closely with team members of other departments to deliver winning products.  

Operations Manager

Individuals in the operations manager jobs are responsible for ensuring the efficiency of each department to acquire its optimal goal. They plan the use of resources and distribution of materials. The operations manager's job description includes managing budgets, negotiating contracts, and performing administrative tasks.

Stock Analyst

Individuals who opt for a career as a stock analyst examine the company's investments makes decisions and keep track of financial securities. The nature of such investments will differ from one business to the next. Individuals in the stock analyst career use data mining to forecast a company's profits and revenues, advise clients on whether to buy or sell, participate in seminars, and discussing financial matters with executives and evaluate annual reports.

A Researcher is a professional who is responsible for collecting data and information by reviewing the literature and conducting experiments and surveys. He or she uses various methodological processes to provide accurate data and information that is utilised by academicians and other industry professionals. Here, we will discuss what is a researcher, the researcher's salary, types of researchers.

Welding Engineer

Welding Engineer Job Description: A Welding Engineer work involves managing welding projects and supervising welding teams. He or she is responsible for reviewing welding procedures, processes and documentation. A career as Welding Engineer involves conducting failure analyses and causes on welding issues. 

Transportation Planner

A career as Transportation Planner requires technical application of science and technology in engineering, particularly the concepts, equipment and technologies involved in the production of products and services. In fields like land use, infrastructure review, ecological standards and street design, he or she considers issues of health, environment and performance. A Transportation Planner assigns resources for implementing and designing programmes. He or she is responsible for assessing needs, preparing plans and forecasts and compliance with regulations.

Environmental Engineer

Individuals who opt for a career as an environmental engineer are construction professionals who utilise the skills and knowledge of biology, soil science, chemistry and the concept of engineering to design and develop projects that serve as solutions to various environmental problems. 

Safety Manager

A Safety Manager is a professional responsible for employee’s safety at work. He or she plans, implements and oversees the company’s employee safety. A Safety Manager ensures compliance and adherence to Occupational Health and Safety (OHS) guidelines.

Conservation Architect

A Conservation Architect is a professional responsible for conserving and restoring buildings or monuments having a historic value. He or she applies techniques to document and stabilise the object’s state without any further damage. A Conservation Architect restores the monuments and heritage buildings to bring them back to their original state.

Structural Engineer

A Structural Engineer designs buildings, bridges, and other related structures. He or she analyzes the structures and makes sure the structures are strong enough to be used by the people. A career as a Structural Engineer requires working in the construction process. It comes under the civil engineering discipline. A Structure Engineer creates structural models with the help of computer-aided design software. 

Highway Engineer

Highway Engineer Job Description:  A Highway Engineer is a civil engineer who specialises in planning and building thousands of miles of roads that support connectivity and allow transportation across the country. He or she ensures that traffic management schemes are effectively planned concerning economic sustainability and successful implementation.

Field Surveyor

Are you searching for a Field Surveyor Job Description? A Field Surveyor is a professional responsible for conducting field surveys for various places or geographical conditions. He or she collects the required data and information as per the instructions given by senior officials. 

Orthotist and Prosthetist

Orthotists and Prosthetists are professionals who provide aid to patients with disabilities. They fix them to artificial limbs (prosthetics) and help them to regain stability. There are times when people lose their limbs in an accident. In some other occasions, they are born without a limb or orthopaedic impairment. Orthotists and prosthetists play a crucial role in their lives with fixing them to assistive devices and provide mobility.

Pathologist

A career in pathology in India is filled with several responsibilities as it is a medical branch and affects human lives. The demand for pathologists has been increasing over the past few years as people are getting more aware of different diseases. Not only that, but an increase in population and lifestyle changes have also contributed to the increase in a pathologist’s demand. The pathology careers provide an extremely huge number of opportunities and if you want to be a part of the medical field you can consider being a pathologist. If you want to know more about a career in pathology in India then continue reading this article.

Veterinary Doctor

Speech therapist, gynaecologist.

Gynaecology can be defined as the study of the female body. The job outlook for gynaecology is excellent since there is evergreen demand for one because of their responsibility of dealing with not only women’s health but also fertility and pregnancy issues. Although most women prefer to have a women obstetrician gynaecologist as their doctor, men also explore a career as a gynaecologist and there are ample amounts of male doctors in the field who are gynaecologists and aid women during delivery and childbirth. 

Audiologist

The audiologist career involves audiology professionals who are responsible to treat hearing loss and proactively preventing the relevant damage. Individuals who opt for a career as an audiologist use various testing strategies with the aim to determine if someone has a normal sensitivity to sounds or not. After the identification of hearing loss, a hearing doctor is required to determine which sections of the hearing are affected, to what extent they are affected, and where the wound causing the hearing loss is found. As soon as the hearing loss is identified, the patients are provided with recommendations for interventions and rehabilitation such as hearing aids, cochlear implants, and appropriate medical referrals. While audiology is a branch of science that studies and researches hearing, balance, and related disorders.

An oncologist is a specialised doctor responsible for providing medical care to patients diagnosed with cancer. He or she uses several therapies to control the cancer and its effect on the human body such as chemotherapy, immunotherapy, radiation therapy and biopsy. An oncologist designs a treatment plan based on a pathology report after diagnosing the type of cancer and where it is spreading inside the body.

Are you searching for an ‘Anatomist job description’? An Anatomist is a research professional who applies the laws of biological science to determine the ability of bodies of various living organisms including animals and humans to regenerate the damaged or destroyed organs. If you want to know what does an anatomist do, then read the entire article, where we will answer all your questions.

For an individual who opts for a career as an actor, the primary responsibility is to completely speak to the character he or she is playing and to persuade the crowd that the character is genuine by connecting with them and bringing them into the story. This applies to significant roles and littler parts, as all roles join to make an effective creation. Here in this article, we will discuss how to become an actor in India, actor exams, actor salary in India, and actor jobs. 

Individuals who opt for a career as acrobats create and direct original routines for themselves, in addition to developing interpretations of existing routines. The work of circus acrobats can be seen in a variety of performance settings, including circus, reality shows, sports events like the Olympics, movies and commercials. Individuals who opt for a career as acrobats must be prepared to face rejections and intermittent periods of work. The creativity of acrobats may extend to other aspects of the performance. For example, acrobats in the circus may work with gym trainers, celebrities or collaborate with other professionals to enhance such performance elements as costume and or maybe at the teaching end of the career.

Video Game Designer

Career as a video game designer is filled with excitement as well as responsibilities. A video game designer is someone who is involved in the process of creating a game from day one. He or she is responsible for fulfilling duties like designing the character of the game, the several levels involved, plot, art and similar other elements. Individuals who opt for a career as a video game designer may also write the codes for the game using different programming languages.

Depending on the video game designer job description and experience they may also have to lead a team and do the early testing of the game in order to suggest changes and find loopholes.

Radio Jockey

Radio Jockey is an exciting, promising career and a great challenge for music lovers. If you are really interested in a career as radio jockey, then it is very important for an RJ to have an automatic, fun, and friendly personality. If you want to get a job done in this field, a strong command of the language and a good voice are always good things. Apart from this, in order to be a good radio jockey, you will also listen to good radio jockeys so that you can understand their style and later make your own by practicing.

A career as radio jockey has a lot to offer to deserving candidates. If you want to know more about a career as radio jockey, and how to become a radio jockey then continue reading the article.

Choreographer

The word “choreography" actually comes from Greek words that mean “dance writing." Individuals who opt for a career as a choreographer create and direct original dances, in addition to developing interpretations of existing dances. A Choreographer dances and utilises his or her creativity in other aspects of dance performance. For example, he or she may work with the music director to select music or collaborate with other famous choreographers to enhance such performance elements as lighting, costume and set design.

Social Media Manager

A career as social media manager involves implementing the company’s or brand’s marketing plan across all social media channels. Social media managers help in building or improving a brand’s or a company’s website traffic, build brand awareness, create and implement marketing and brand strategy. Social media managers are key to important social communication as well.

Photographer

Photography is considered both a science and an art, an artistic means of expression in which the camera replaces the pen. In a career as a photographer, an individual is hired to capture the moments of public and private events, such as press conferences or weddings, or may also work inside a studio, where people go to get their picture clicked. Photography is divided into many streams each generating numerous career opportunities in photography. With the boom in advertising, media, and the fashion industry, photography has emerged as a lucrative and thrilling career option for many Indian youths.

An individual who is pursuing a career as a producer is responsible for managing the business aspects of production. They are involved in each aspect of production from its inception to deception. Famous movie producers review the script, recommend changes and visualise the story. 

They are responsible for overseeing the finance involved in the project and distributing the film for broadcasting on various platforms. A career as a producer is quite fulfilling as well as exhaustive in terms of playing different roles in order for a production to be successful. Famous movie producers are responsible for hiring creative and technical personnel on contract basis.

Copy Writer

In a career as a copywriter, one has to consult with the client and understand the brief well. A career as a copywriter has a lot to offer to deserving candidates. Several new mediums of advertising are opening therefore making it a lucrative career choice. Students can pursue various copywriter courses such as Journalism , Advertising , Marketing Management . Here, we have discussed how to become a freelance copywriter, copywriter career path, how to become a copywriter in India, and copywriting career outlook. 

In a career as a vlogger, one generally works for himself or herself. However, once an individual has gained viewership there are several brands and companies that approach them for paid collaboration. It is one of those fields where an individual can earn well while following his or her passion. 

Ever since internet costs got reduced the viewership for these types of content has increased on a large scale. Therefore, a career as a vlogger has a lot to offer. If you want to know more about the Vlogger eligibility, roles and responsibilities then continue reading the article. 

For publishing books, newspapers, magazines and digital material, editorial and commercial strategies are set by publishers. Individuals in publishing career paths make choices about the markets their businesses will reach and the type of content that their audience will be served. Individuals in book publisher careers collaborate with editorial staff, designers, authors, and freelance contributors who develop and manage the creation of content.

Careers in journalism are filled with excitement as well as responsibilities. One cannot afford to miss out on the details. As it is the small details that provide insights into a story. Depending on those insights a journalist goes about writing a news article. A journalism career can be stressful at times but if you are someone who is passionate about it then it is the right choice for you. If you want to know more about the media field and journalist career then continue reading this article.

Individuals in the editor career path is an unsung hero of the news industry who polishes the language of the news stories provided by stringers, reporters, copywriters and content writers and also news agencies. Individuals who opt for a career as an editor make it more persuasive, concise and clear for readers. In this article, we will discuss the details of the editor's career path such as how to become an editor in India, editor salary in India and editor skills and qualities.

Individuals who opt for a career as a reporter may often be at work on national holidays and festivities. He or she pitches various story ideas and covers news stories in risky situations. Students can pursue a BMC (Bachelor of Mass Communication) , B.M.M. (Bachelor of Mass Media) , or  MAJMC (MA in Journalism and Mass Communication) to become a reporter. While we sit at home reporters travel to locations to collect information that carries a news value.  

Corporate Executive

Are you searching for a Corporate Executive job description? A Corporate Executive role comes with administrative duties. He or she provides support to the leadership of the organisation. A Corporate Executive fulfils the business purpose and ensures its financial stability. In this article, we are going to discuss how to become corporate executive.

Multimedia Specialist

A multimedia specialist is a media professional who creates, audio, videos, graphic image files, computer animations for multimedia applications. He or she is responsible for planning, producing, and maintaining websites and applications. 

Quality Controller

A quality controller plays a crucial role in an organisation. He or she is responsible for performing quality checks on manufactured products. He or she identifies the defects in a product and rejects the product. 

A quality controller records detailed information about products with defects and sends it to the supervisor or plant manager to take necessary actions to improve the production process.

Production Manager

A QA Lead is in charge of the QA Team. The role of QA Lead comes with the responsibility of assessing services and products in order to determine that he or she meets the quality standards. He or she develops, implements and manages test plans. 

Process Development Engineer

The Process Development Engineers design, implement, manufacture, mine, and other production systems using technical knowledge and expertise in the industry. They use computer modeling software to test technologies and machinery. An individual who is opting career as Process Development Engineer is responsible for developing cost-effective and efficient processes. They also monitor the production process and ensure it functions smoothly and efficiently.

AWS Solution Architect

An AWS Solution Architect is someone who specializes in developing and implementing cloud computing systems. He or she has a good understanding of the various aspects of cloud computing and can confidently deploy and manage their systems. He or she troubleshoots the issues and evaluates the risk from the third party. 

Azure Administrator

An Azure Administrator is a professional responsible for implementing, monitoring, and maintaining Azure Solutions. He or she manages cloud infrastructure service instances and various cloud servers as well as sets up public and private cloud systems. 

Computer Programmer

Careers in computer programming primarily refer to the systematic act of writing code and moreover include wider computer science areas. The word 'programmer' or 'coder' has entered into practice with the growing number of newly self-taught tech enthusiasts. Computer programming careers involve the use of designs created by software developers and engineers and transforming them into commands that can be implemented by computers. These commands result in regular usage of social media sites, word-processing applications and browsers.

Information Security Manager

Individuals in the information security manager career path involves in overseeing and controlling all aspects of computer security. The IT security manager job description includes planning and carrying out security measures to protect the business data and information from corruption, theft, unauthorised access, and deliberate attack 

ITSM Manager

Automation test engineer.

An Automation Test Engineer job involves executing automated test scripts. He or she identifies the project’s problems and troubleshoots them. The role involves documenting the defect using management tools. He or she works with the application team in order to resolve any issues arising during the testing process. 

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Wood Pellets: Green Energy or New Source of CO2 Emissions?

Burning wood pellets to produce electricity is on the rise in Europe, where the pellets are classified as a form of renewable energy. But in the U.S., where pellet facilities are rapidly being built, concerns are growing about logging and the carbon released by the combustion of wood biomass.

By Roger Drouin • January 22, 2015

In 2011, Enviva — the United States’ largest exporter of wood pellets — opened its flagship pellet-manufacturing mill in Ahoskie, North Carolina. The plant annually converts 850,000 tons of trees and waste wood into tiny pellets that are shipped to Europe and burned in power plants for what is being touted as a renewable form of electricity.

Two years later, Enviva opened another mill 50 miles away in Northampton County, North Carolina, and by 2016 the company is expected to operate eight wood pellet mills from Virginia to Mississippi. Elsewhere in the southeastern United States, other companies are planning or rapidly building facilities to produce wood pellets. A mill planned by Biomass Power Louisiana in Natchitoches, La., will produce up to 2 million tons of the pellets annually. Drax, a British utility that’s taking steps to transform itself into a predominately biomass energy generator , has said it will open four of its own large mills to produce pellets in Mississippi, South Carolina, and Louisiana.

Demand for this purportedly green form of energy is so robust that wood pellet exports from the United States nearly doubled from 2012 to 2013 and are expected to nearly double again to 5.7 million tons in 2015. This soaring production is driven by growing demand in the U.K. and Europe, which are using wood pellets to replace coal for electricity generation and heating. The European Union’s 2020 climate and energy program classifies wood pellets as a carbon-neutral form of renewable energy, and European companies have invested billions to convert coal plants to plants that can burn wood pellets.

But as wood pellet manufacturing booms in the southeastern U.S., scientists and environmental groups are raising significant questions about just how green burning wood pellets really is. The wood pellet industry says that it overwhelmingly uses tree branches and other waste wood to manufacture pellets, making them a carbon-neutral form of energy. But many environmentalists and scientists believe current industry practices are anything but carbon-neutral and threaten some of the last remaining diverse ecosystems in the southeastern U.S., including the Roanoke River watershed surrounding the Ahoskie, N.C., plant and longleaf pine ecosystems near the large Enviva wood pellet mill in Cottondale, Fla.

Critics contend pellet manufacturers frequently harvest whole hardwood trees that can take a long time to regrow.

Critics contend that Enviva and other pellet manufacturers frequently harvest whole trees — including hardwoods from bottomland areas — that can take a long time to regrow, thus making the burning of wood pellets an overall source of CO2 emissions.

“They are cutting them down and burning them to produce energy in Europe — a practice that both degrades critical forest habitat and increases carbon emissions for many decades to come,” says Debbie Hammel, a senior resource specialist with the Natural Resources Defense Council (NRDC).

Less than a year after Enviva’s Ahoskie plant opened, the NRDC began monitoring how the facility was impacting nearby forests and what kinds of trees were being used to produce pellets. As the demand for wood to manufacture more pellets increased, the NRDC noticed forested wetlands in the Roanoke watershed begin to disappear.

“A significant portion of the wood source Enviva uses comes from natural hardwood forests,” says Hammel, noting that logging in such forested wetlands and bottomlands creates major ecological impacts, including threatening species such as wood storks and the cerulean warbler. In the opinion of Hammel and others, burning wood pellet biomass to produce electricity is far more harmful to the environment and the climate than renewable energy sources such as solar and wind power.

Industry officials say, however, that manufacturing and burning wood pellets is an important part of the mix of renewable energy options. Seth Ginther, executive director of the United States Industrial Pellet Association , says that wood pellets are a “low-cost, low-carbon alternative” to coal. In addition, he says, wood biomass is lower in sulfur, nitrogen, ash, chlorine, and other chemicals than coal and traditional fossil fuels.

Wood pellet producers are using waste wood and low-grade wood fiber in many instances, according to Ginther. This niche market is enabling some landowners to keep growing and planting trees, rather than chopping down woodlands for commercial development or agriculture. “Our industry helps encourage forest owners to reforest and replant so this market helps keep working forests working,” Ginther says.

Burning wood pellets releases as much or even more carbon dioxide per unit than burning coal.

Ginther says that the U.S.’s wood pellet industry can expect even more robust growth if the Asian commercial market or European residential market embraces the combustion of wood biomass. “The U.S. has established itself as a sustainable source of fiber for bioenergy, and we are very proud of the fact that so many European customers are looking to U.S. producers for sourcing needs,” Ginther says.

The wood pellet industry really took off in 2012, after the U.K.’s Department of Energy and Climate Change published guidelines on the direction of British renewable energy policy for the near future. The guidelines encouraged utilities to convert coal-fired generators to generators using wood biomass and gave utility companies the option to burn wood pellets to help them meet European Union air pollution and renewable energy standards. Power companies then began to turn to the southeastern United States, where logging is well-established and much less restricted than in Europe, as the primary supplier of wood pellets.

“It is the EU that has prompted this industry explosion,” Hammel says.

Some scientists say there are still more questions than answers when it comes to commercially burning wood pellets for energy, and it’s largely a matter of carbon cycle calculations. Bob Abt , a professor of natural resource economics and management at North Carolina State University, says a lot depends on the origin and type of trees used to feed the pellet mills.

Burning wood pellets releases as much or even more carbon dioxide per unit of energy as burning coal, so in order for burning pellets to be carbon-neutral the carbon emitted into the atmosphere has to be recaptured in regenerated forests, Abt says. Residual wood, such as tree thinnings and unused tree parts left over at timber mills, is the best material for wood pellets, says Abt. But he and others say that not enough of such waste wood exists to feed the growing demand for wood pellets.

So the industry has turned to whole trees.

Softwood trees such as loblolly pines grown on managed plantations can be planted and regrown relatively quickly after harvesting, and selective removal of some trees may occur in as little as 12 years. When softwood is used, carbon released during the burning of wood pellets for electricity production can then be sequestered and stored in the new trees.

But using hardwood trees from bottomlands results in a different carbon calculation, Abt says. Using these species of trees requires a much longer time to make up for the released carbon, as bottomland hardwoods grow more slowly. Abt also points out that floodplain forests, which are typically owned by smaller, private owners, tend not to be certified to adhere to sustainability standards. Regeneration in bottomlands also tends to be more variable and depends on local hydrological conditions.

When a mill consumes nearly a million tons of wood a year, it’s difficult to track where every single tree comes from, according to Abt and other experts.

But Forisk , a consulting company that tracks forest industry trends, calculates that the majority of the wood used at Enviva’s Ahoskie, N.C., mill comes from hardwood trees — including those typically found in wetland forests.

Generally, wood pellet mills in North Carolina and Virginia are more reliant on these slower-to-regrow hardwoods, while mills in Georgia, for instance, mainly utilize plantation pines, Abt says. These two different classes of trees are “on different ends of the spectrum” when it comes to both forestry management and how much carbon is released and sequestered, he notes.

More than 168,000 acres of forest are at risk of being cut down for producing wood pellets for one facility.

If the timber industry in the southern U.S. gathers up all the branches, roots, and other tree waste and uses that wood to make pellets, William Schlesinger , who is president emeritus of the Cary Institute of Ecosystem Studies and a biogeochemist who studies carbon cycles, wouldn’t have a problem with it.

The problem, he says, is when pellets are made from virgin growth and second-growth hardwoods.

“The best evidence we have is that not all the pellets are coming from wood waste, and that creates a carbon deficit,” says Schlesinger, who was one of the scientists who wrote a letter to the Environmental Protection Agency calling on the agency to create strong pollution standards for biomass energy. Schlesinger points to aerial photos distributed by the Southern Environmental Law Center showing large-diameter oak and hickory trees felled for wood pellet production at Enviva’s Ahoskie mill.

A study of the Ahoskie plant commissioned by the Southern Environmental Law Center and National Wildlife Federation found that more than 50 percent of the likely sourcing area for the Ahoskie facility is forested wetlands. More than 168,000 acres of wetland forest are at high risk of being cut down for manufacturing wood pellets at this single plant, the study said.

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The NRDC is currently undertaking a study using GPS data to map hotspots where wood pellet facilities throughout the southeastern United States are having the biggest impacts. The group plans to publish the study this spring, highlighting logging around wood pellet manufacturing facilities.

Schlesinger says recent calculations using U.S. Energy Information Administration (EIA) and International Energy Agency (IEA) data show that burning wood pellets results in major impacts on forests for very modest quantities of bioenergy. For instance, the IEA projects that to produce 6.4 percent of global electricity from burning wood biomass in 2035, the global commercial tree harvest — all trees felled except for traditional firewood — would have to increase by 137 percent.

It’s not just European utilities that may end up burning wood pellets on an industrial scale. Hammel, of NRDC, notes the possibility of a significant shift to burning wood commercially here in the United States, depending on how the U.S. Environmental Protection Agency decides to count greenhouse emissions from power plants that burn biomass.

“It would be a mistake for the EPA to give biomass energy producers a free pass on carbon accountability,” Hammel says. “Cutting down and burning trees for energy is a step in the wrong direction for the climate and our forests.”

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