Sustainable energy

The Solar Settlement at Schlierberg, Germany, is powered sustainably, using solar power and extreme energy efficiency.

Sustainable energy is energy produced and used so that it meets the needs of the present without compromising the needs of future generations. This includes environmental aspects such as greenhouse gas emissions in addition to social and economic aspects such as energy poverty.

In general, renewable energy sources such as solar, wind, hydroelectric power and geothermal energy are considered to be sustainable. However, aspects of some renewable energy projects, such as the clearing of forests for the production of biofuels, can cause severe environmental damage. Nuclear power is a low-carbon source and has a safety record comparable to wind and solar, but its sustainability has been debated due to concerns about nuclear proliferation, nuclear waste, and accidents.

The energy transition to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is one of the greatest challenges facing humanity in the 21st century. Nearly a billion people still lack access to electricity and over 2.5 billion relying on smoky fuels such as wood, charcoal or animal dung to cook. Energy production and consumption are responsible for over 70% of greenhouse gas emissions that cause climate change, contributes to water scarcity and biodiversity loss, and can cause toxic waste. The Paris Agreement to limit climate change and the United Nation's Sustainable Development Goals aim for a rapid transition to sustainable energy. Governments use several policies to achieve these goals, such as energy efficiency standards, carbon pricing and a phase-out of fossil fuel subsidies.

Costs of wind, solar, and batteries have fallen rapidly and are projected to continue falling due to innovation and economies of scale. Moderate amounts of wind and solar energy, which are variable energy sources, can be integrated into the electrical grid without additional infrastructure such as grid energy storage and demand-response measures. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly. A sustainable energy system is likely to see is shift towards more use of electricity in sectors such as transport, energy conservation and the use hydrogen produced by renewable electricity or with carbon capture and storage.

Definitions and background

The concept of sustainable development, for which energy is a key component, was described by the United Nations Brundtland Commission in its 1987 report Our Common Future. It defined sustainable development as development that "meets the needs of the present without compromising the ability of future generations to meet their own needs." This description of sustainable development has since been referenced in many definitions and explanations of sustainable energy. No single interpretation of how the concept of sustainability applies to energy has gained worldwide acceptance. The UN Economic Commission for Europe, and various scholars in the field, include several aspects of sustainability in their working definitions:

• Environmental aspects include greenhouse gas emissions, impacts on biodiversity and ecosystems, the production of hazardous waste and toxic emissions, water consumption, and depletion of non-renewable resources.
• Economic and social aspects include having reliable energy be affordable for all people, and energy security so that each country has constant access to sufficient energy.

Sustainable development

See also: Sustainable Development Goal 7

The energy transition to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is one of the greatest challenges facing humanity in the 21st century, both in terms of meeting the needs of the present and in terms of effects on future generations. Improving energy access in the least-developed countries, and making energy cleaner, are key to achieving most of the United Nations 2030 Sustainable Development Goals, which cover issues ranging from climate action to gender equality. Sustainable Development Goal 7 calls for "access to affordable, reliable, sustainable and modern energy for all" by 2030.

Environmental issues

Renewable energy sources (a part of sustainable energy approaches) have increased from 2000 to 2019 but coal, oil, and natural gas remain the primary global energy sources.

The current energy system contributes to many environmental issues, including climate change, air pollution, biodiversity loss, the release of toxics into the environment and water scarcity. Energy production and consumption are responsible for 72% of annual human-caused greenhouse gas emissions as of 2014. Generation of electricity and heat contributes 31% of human-caused greenhouse gas emissions, use of energy in transport contributes 15%, and use of energy in manufacturing and construction contributes 12%. An additional 5% is released through processes associated with fossil fuel production, and 8% through various other forms of fuel combustion.

The combustion of coal releases precursor elements which form into ground-level ozone and acid rain, especially if the coal is not cleaned before combustion. An estimated 3 million people die each year as a consequence of outdoor air pollution from particulates, with major contributions from coal and biomass burning. Meeting the Paris agreement goals that limit global warming to a 2 °C increase could save about a million of those lives per year worldwide from reduced air pollution alone by 2050. Outdoor air pollution death rates are concentrated in low-income and middle-income countries, and in urban areas worldwide.

Co-benefits of such climate mitigation strategies, such as air quality health effects, "can offset costs of climate policy implementation," with monetized benefits usually surpassing levelized electricity cost from renewable sources.

Environmental impacts extend beyond the byproducts of combustion. Oil spills at sea harm marine life and may be accomanied by fires which release toxic gases into the atmosphere. Around 10% of global water use goes to energy production, mainly for cooling thermal energy plants. In already dry regions, this contributes to water scarcity. Bioenergy production, coal mining and processing and oil extraction also require large amounts of water.

Biodiversity is greatly impacted by climate change, with additional threats from fossil fuel extraction. Low-carbon sources of energy also have the potential to be detrimental to biodiversity, with the best locations for bioenergy production in places of high ecological value. Onshore wind and solar, when built in protected areas or wilderness, may also pose a risk to biodiversity.

Energy poverty

Main article: Energy poverty

World map showing where people without access to electricity lived in 2016 - mainly in sub-Saharan Africa.

As of 2016, 940 million (13% of the world) people do not have access to electricity, two-thirds of whom live in sub-Saharan Africa. In developing countries, over 2.5 billion people rely on traditional cookstoves and open fires to burn biomass (including crop residue and animal dung) or coal for heating and cooking. This practice causes harmful indoor air pollution, resulting in an estimated 1.6 to 3.8 million deaths annually, particularly among young children and women who spend much time near the hearth. Death rates from indoor air pollution are over 1,000 times as high in various low income countries compared to rich countries. As of 2017, improved access to clean cooking fuels consistently lag improvements in getting more access to electricity. Additionally, serious local environmental damage, including desertification, can be caused by excessive harvesting of wood and other combustible material.

Reliable and affordable energy, particularly electricity, is essential for health care, education, and economic development. In health clinics, electricity is required for operation of medical equipment, refrigeration of vaccines and medications, and lighting, but a 2018 survey in six Asian and African countries found that half of health facilities had no or poor access to electricity. According to a 2019 report by the IEA, in sub-Saharan Africa "current and planned efforts to provide access to modern energy services barely outpace population growth" and would still leave over half a billion people without electricity and over a billion without clean cooking by 2030.

Energy conservation

Main articles: Energy conservation and Efficient energy use

Global energy usage is highly unequal. High income ountries such as the United States and Canada use 100 times as much energy per capita as some of the least developed countries in Africa.

Increasing energy efficiency is one of the most important ways to reduce energy-related pollution while also delivering economic benefits and improving quality of life. For some countries, efficiency can improve energy security by reducing dependence on fossil fuel imports. Efficiency has the potential to slow the growth of energy demand to allow rising clean energy supplies to make deep cuts in fossil fuel use. The International Energy Agency (IEA) estimates that 40% of greenhouse gas emission reductions needed to fulfill the Paris agreement can be achieved by increasing energy efficiency. Ambitious energy pathways in line with Paris show energy usage to remain around the same between 2010 and 2030, and increase slightly by 2050.

Between 2015 in 2018, each year saw less improvement in energy efficiency compared to the previous. In transport, consumer preferences for bigger cars is part of the driver of the slowdown. Globally, governments did not strongly increase their ambitions in energy efficiency policy over this period either. Policies to improve efficiency can include building codes, performance standards, and carbon pricing. Energy efficiency and renewable energy are often considered the twin pillars of sustainable energy.

Behavioural changes are another important way to conserve energy. In the International Energy Agency scenario for reaching net zero greenhouse gas emissions in 2050, several significant behavioural changes are described, about half of them deriving from transport. In their scenario, some business flights are replaced by videoconferencing, cycling and walking increase in popularity, and more people use public transport.

Renewable energy sources

Main article: Renewable energy

The terms "sustainable energy" and "renewable energy" are often used interchangeably. However, renewable energy projects sometimes raise significant sustainability concerns. Renewable energy technologies are essential contributors to sustainable energy as they generally contribute to world energy security, and reduce dependence on fossil fuel resources thus mitigating greenhouse gas emissions.

Solar

11 MW solar power plant near Serpa, Portugal

Main articles: Solar power and Solar water heating

In 2019, solar power provided around 3% of global electricity. Most of this is in the form of solar panels based on photovoltaic cells (PV). Costs of solar PV have dropped rapidly, which is driving a strong growth in worldwide capacity. Solar panels are mounted on top of building or used in solar parks connected to the electrical grid. Typical panels convert less than 20% of the sunlight that hits them into electricity, as higher efficiency materials are more expensive. The cost of electricity from new solar farms is competitive with, or in many places cheaper than, existing coal plants.

Concentrated solar power produces heat to drive a heat engine. Because the heat is stored, this type of solar power is dispatchable: it can be produced when needed. Solar thermal heating and cooling systems are used for many applications: hot water, heating and cooling buildings, drying and desalination. Globally in 2018, it provided 1.5% of heating and cooling final energy demand.

Wind power

Main articles: Wind power and Environmental impact of wind power

Wind power stations in Xinjiang, China - an example for a sustainable energy source.

Wind turbines are turned by the kinetic energy of wind and, in 2019, their electric generators provided approximately 6% of global electricity supply. Wind farms consist of many individual wind turbines, which are connected to the electric power transmission network. New onshore wind is often cheaper than existing coal plants, and competitive with natural gas and nuclear. Although construction and maintenance costs are higher at sea some analysts forecast that, because the winds are steadier and stronger than on land, with future larger blades offshore wind power will become cheaper than onshore wind in the mid-2030s.

Onshore wind farms, often built in wild or rural areas, have a visual impact on the landscape. The noise and flickering light created by the turbines can be annoying, and restricts the construction near densily populated areas. In terms of wildlife, bat populations may be strongly impacted by collusions. Turbine blades are not fully recyclable yet, and research continues on how to manufacture blades which are easier to recycle. Wind power, in contrast to nuclear and fossil fuel plants, does not consume water to produce power. Little energy is needed for wind turbine construction compared to the energy produced by the wind power plant itself.

Hydropower

Main article: Hydroelectricity

A hydrodam with trees in the background

Hydroelectric plants convert the energy of moving water into electricity. On average, hydropower ranks among the energy sources with the lowest levels of greenhouse gas emissions per unit of energy produced, but levels of emissions vary enormously between projects. In 2019, hydropower supplied 16% of the world's electricity, down from a high of nearly 20% in the mid-to-late 20th century. It produced 60% of electricity in Canada and nearly 80% in Brazil. Reservoir-based hydropower plants provide a highly flexible, dispatchable electricity supply. They can be combined with wind and solar power to provide peak load and to compensate when wind and sun are less available.

In conventional hydropower, a reservoir is created behind a dam. In most cases, the biological matter that becomes submerged in the flooding of the reservoir decomposes, becoming a source of carbon dioxide and methane. These greenhouse gas emissions are particularly large in tropical regions. In turn, deforestation and climate change can reduce energy generation from hydroelectric dams. Depending on location, the implementation of large-scale dams can displace residents and cause significant local environmental damage.

In general, run-of-the-river hydroelectricity facilities have less environmental impact than reservoir-based facilities, but their ability to generate power depends on river flow, which can vary with daily and seasonal weather conditions. They also lack the water regulation features reservoirs provide, including flood control, dispatchable electrical power, and the provision of fresh water for agriculture.

Geothermal

Main articles: Geothermal power and Geothermal heating

Cooling towers at Larderello geothermal power plant

Geothermal energy is produced by tapping into the heat that exists below the earth's crust. Heat can be obtained by drilling into the ground and then carried by a heat-transfer fluid such as water, brine or steam. Geothermal energy can be harnessed for electricity generation and for heating. The use of geothermal energy is concentrated in regions where heat extraction is economical: a combination of heat, flow and high permeability is needed. Worldwide in 2018, geothermal provided 0.6% of heating and cooling final energy demand in buildings.

Geothermal energy is a renewable resource because thermal energy is constantly replenished from neighbouring hotter regions. The greenhouse gas emissions of geothermal electric stations are on average 45 grams of carbon dioxide per kilowatt-hour of electricity, or less than 5 percent of that of conventional coal-fired plants. Geothermal energy carries a risk of inducing earthquakes, needs effective protection to avoid water pollution, and emits toxic emissions which can be captured.

Bioenergy

Main article: Bioenergy

Biogas produced from biomass is a renewable energy source and can provide both heat and light where electricity is not available.

Sugarcane plantation to produce ethanol in Brazil.

Biomass is a versatile and common source of renewable energy. If the production of biomass is well-managed, carbon emissions can be significantly offset by the absorption of carbon dioxide by the plants during their lifespans. Biomass can either be burned to produce heat and to generate electricity or converted to modern biofuels such as biodiesel and ethanol. Biofuels are often produced from corn or sugar cane. They are used to power transport, often blended with liquid fossil fuels.

Use of farmland for growing biomass can result in less land being available for growing food. Since photosynthesis only captures a small fraction of the energy in sunlight, and crops also require significant amounts of energy to harvest, dry, and transport, a lot of land is needed to produce biomass. If biomass is harvested from crops, such as tree plantations, the cultivation of these crops can displace natural ecosystems, degrade soils, and consume water resources and synthetic fertilizers. In some cases, these impacts can actually result in higher overall carbon emissions compared to using petroleum-based fuels.

In the United States, corn-based ethanol has replaced less than 10% of motor gasoline use since 2011, but has consumed around 40% of the annual corn harvest in the country. In Malaysia and Indonesia, the clearing of forests to produce palm oil for biodiesel has led to serious social and environmental effects, as these forests are critical carbon sinks and habitats for endangered species.

More sustainable sources of biomass include crops grown on soil unsuitable for food production, algae and waste. If the biomass source is agricultural or municipal waste, burning it or converting it into biogas also provides a way to dispose of this waste. Second-generation biofuels, produced from non-food plants, reduce competition with food production, but may have other negative effects including trade-offs with conservation areas and local air pollution.

According to the UK Climate Change Committee in the long term all uses of biomass must maximise carbon sequestration, for example by using it in conjunction with carbon capture and storage (BECCS) when the biomass is burned, and move "away from using biofuels in surface transport, biomass for heating buildings, or biomass for generating power without CCS". Due to lack of technologically feasible alternatives, aviation biofuel may one of the best uses of biomass, providing that some carbon is captured and stored during manufacture of the fuel.

Marine energy

Main article: Marine energy

Marine energy represents the smallest share of the energy market. It encompasses tidal power, which is approaching maturity, and wave power, which is earlier in its development. Two tidal barrage systems, in France and in Korea, make up 90% of total production. While single devices pose little risk to the environment, the impacts of multi-array devices are less well known.

Non-renewable energy sources

Fossil fuel switching

A woman in rural Rajasthan (India) collects firewood for cooking. Firewood is not regarded as a sustainable or clean energy source as it is labor-intensive and causes harmful outdoor or indoor air pollution.

For a given unit of energy produced, the life-cycle greenhouse-gas emissions of natural gas are around 40 times the emissions of wind or nuclear energy, but much less than that of coal. Natural gas produces around half the emissions of coal when used to generate electricity, and around two-thirds the emissions of coal when used to produce heat. Reducing methane leaks in the process of extracting and transporting natural gas further decreases emissions. Natural gas also produces significantly less air pollution than coal.

Building gas-fired power plants and gas pipelines is promoted as a way to phase out coal and wood burning pollution, and increase energy supply in some African countries with fast growing populations or economies, however this practice is controversial. Developing natural gas infrastructure risks the creation of carbon lock-in and stranded assets. However, switching cooking from dirty fuels such as wood or kerosene to LPG, biogas or electricity quickly provides significant health benefits.

Nuclear power

Main article: Nuclear power debate

Nuclear power plants have been used since the 1950s to produce a steady low-carbon supply of electricity, without creating local air pollution. In 2020, nuclear power plants in over 30 countries generated 10% of global electricity. Nuclear power's lifecycle greenhouse gas emissions (including the mining and processing of uranium), are similar to the emissions from renewable energy sources. Reducing the time to build and cost to operate nuclear power have been goals for decades, but progress has been limited. As of 2020, costs per unit of electricity produced for nuclear are about 4 times as high as for utility-scale solar and onshore wind (not including the costs of energy storage), and about 3 times as high as for base load natural gas.

There is considerable controversy over whether nuclear power can be considered sustainable, with debates revolving around the risk of nuclear accidents, the generation of radioactive nuclear waste, and the potential for nuclear energy to contribute to nuclear proliferation. These concerns spurred the anti-nuclear movement. Public support for nuclear energy is often low as a result of safety concerns, however for each unit of energy produced, nuclear energy is far safer than fossil fuel energy and comparable to renewable sources. The uranium ore used to fuel nuclear fission plants is a non-renewable resource, but sufficient quantities exist to provide a supply for hundreds of years. Pathways consistent with ambitious climate policy typically see an increase in power supply from nuclear, but growth is not strictly necessary.

Concluding a scientific debate around place of nuclear power in European Union's Taxonomy of environmentally sustainable technologies, the European Commission Joint Research Centre (JRC) published a report discussing sustainability and environmental impact of nuclear fission life-cycle greenhouse gas emissions, waste management, radiation, safety and other debated topics, recommending that it is included into the taxonomy as sustainable. In many aspects nuclear power has been found to be comparable to other technologies, including renewable energy, while methods for ensuring long-term safety of the plants and waste exist.

Various new forms of nuclear energy are in development, hoping to address the drawbacks of conventional nuclear. Nuclear power based on thorium, rather than uranium, may be able to provide higher energy security for countries that do not have a large supply of uranium. Small modular reactors may also have several advantages over current large reactors: it should be possible to build them faster, and their modularization would allow for cost reductions via learning-by-doing. Several countries are attempting to develop nuclear fusion reactors, which would generate very small amounts of waste and no risk of explosions.

Sustainable energy systems

Carbon capture and storage

The greenhouse gas emissions of fossil fuel and biomass power plants can be significantly reduced through carbon capture and storage (CCS), however deployment of this technology is still very limited, with only 21 large-scale CCS plants in operation worldwide as of 2020. The CCS process is expensive, with costs depending considerably on the location's proximity to suitable geology for carbon dioxide storage. CCS can be retrofitted to existing power plants, but is more energy-intensive in that case. Most studies use a working assumption that CCS can capture 85–90% of the CO₂ emissions from a power plant. If 90% of emitted CO₂ is captured from a coal-fired power plant, its uncaptured emissions would still be many times greater than the emissions of nuclear, solar, or wind energy per unit of electricity produced.

When CCS is used to capture emissions from burning biomass in a process known as bioenergy with carbon capture and storage (BECCS), the overall process can result in net carbon dioxide removal from the atmosphere. The BECCS process can also result in net positive emissions depending on how the biomass material is grown, harvested, and transported. As of 2014, the lowest-cost mitigation pathways for meeting the 2 °C target typically describe massive deployment of BECCS. However, using BECCS at the scale described in these pathways would require more resources than are currently available worldwide. For example, to capture 10 billion tons of CO₂ per year would require biomass from 40 percent of the world's current cropland.

Managing variable energy sources

Solar and wind are variable renewable energy sources that supply electricity intermittently depending on the weather and the time of day. Most electrical grids were constructed for non-intermittent energy sources such as coal-fired power plants. As larger amounts of solar and wind energy are integrated into the grid, changes have to be made to the energy system to ensure that the supply of electricity is matched to demand. In 2019, these sources generated 8.5% of worldwide electricity, a share that has grown rapidly.

Various sources of flexibility are available. Often, wind and solar production is complementary on a daily and season scale: in many places there is more wind during the night and in winter, when solar energy production is low. Linking different geographical regions through long-distance transmission lines allows for further cancelling out of variability. Energy demand can be shifted in time through energy demand management and the use of smart grids, matching the times when variable energy production is highest. With storage, energy produced in excess can be released when needed. The final mismatch may be covered via overproduction of variable energy (and curtailing further excess), and by using dispatchable energy, such as hydro, bioenergy, natural gas, or nuclear plants.

Energy storage

Main article: Energy storage

Construction of salt tanks to store thermal energy

Energy storage helps overcome barriers for intermittent renewable energy, and is therefore an important aspect of a sustainable energy system. The most commonly used storage method is pumped-storage hydroelectricity, which requires locations with large differences in height and access to water. Battery storage power stations and home energy storage are being deployed widely. Some lithium-ion batteries contain cobalt, now largely mined in Congo some unsustainably. Responsible sourcing of cobalt and more diverse geographical sourcing may ensure a more stable supply-chain. Environmental impacts can be reduced by downcycling and recycling. Batteries typically have capacity to store enough electricity to last for short periods; research is ongoing into technology with sufficient capacity to last through seasons. Pumped hydro storage and power-to-gas with capacity for multi-month usage has been implemented in some locations.

As of 2018, thermal energy storage is typically not as convenient as burning fossil fuels. High upfront costs form a barrier for implementation. Seasonal thermal energy storage requires large capacity; it has been implemented in some high-latitude regions for household heat.

Hydrogen

Main articles: Hydrogen economy, Hydrogen fuel, and Hydrogen storage

Hydrogen can be burned to produce heat or can power fuel cells to generate electricity, with zero emissions at the point of usage. The overall lifecycle emissions of hydrogen depend on how it is produced. Very little of the world's current supply of hydrogen is currently created from sustainable sources. Nearly all of it is produced from fossil fuels, which results in high greenhouse gas emissions. With carbon capture and storage technologies, a large fraction of these emissions could be removed.

Hydrogen can be produced through electrolysis, by using electricity to split water molecules into hydrogen and oxygen, and if the electricity is generated sustainably, the resultant fuel will also be sustainable. This process is currently more expensive than creating hydrogen from fossil fuels, and the efficiency of energy conversion is inherently low. Hydrogen can be produced when there is a surplus of intermittent renewable electricity, then stored and used to generate heat or to re-generate electricity. Further conversion to ammonia allows the energy to be more easily stored at room temperature in liquid form.

There is potential for hydrogen to play a significant role in decarbonising energy systems because in certain sectors, replacing fossil fuels with direct use of electricity would be very difficult. Hydrogen fuel can produce the intense heat required for industrial production of steel, cement, glass, and chemicals. Steelmaking is considered to be the use of hydrogen which would be most effective in limiting greenhouse gas emissions in the short-term.

Transitions across sectors

Emissions produced by different economic sectors, including emissions generated by electricity and heat production used by the sectors, according to the 2014 IPCC Fifth Assessment Report.

Electricity generation

As of 2018, about a quarter of all electricity generation came from modern renewable sources (excluding the traditional use of biomass). The growth of renewable energy usage has been significantly faster in this sector than in heating and transport. Those sectors rely more heavily on fossil fuels, gas for heating and oil for transport, and there are fewer alternatives for those compared to power, where nuclear, wind, solar and hydro all provide low-carbon energy.

Electrification is a key part of using energy sustainably. Many options exist to produce electricity sustainably, but sustainably producing fuels or heat at large scales is relatively difficult. Specifically, massive electrification in the heat and transport sector may be needed to make these sectors sustainable, with heat pumps and electric vehicles playing important roles. Ambitious climate policy would see a doubling of energy consumed as electricity by 2050, from 20% in 2020.

Heating and cooling

Further information: Renewable heat

A large fraction of the world population cannot afford sufficient cooling or live in poorly designed houses. In addition to air conditioning, which requires electrification and additional power demand, passive building design and urban planning will be needed to ensure cooling needs are met in a sustainable way. Similarly, many households in the developing and developed world suffer from fuel poverty and cannot heat their houses enough. Existing heating practices are often polluting. Alternatives to fossil fuel heating include electrification (heat pumps, or the less efficient electric heater), geothermal, biomass, solar thermal, and waste heat. The costs of all these technologies strongly depend on location, and uptake of the technology sufficient for deep decarbonisation requires stringent policy interventions.

Transport

Main article: Sustainable transport

Cycling is a sustainable method of transport.

There are multiple ways to make transport more sustainable. Public transport frequently emits less per passenger than personal vehicles such as cars, especially with high occupancy. Transport can be made cleaner and healthier by stimulating nonmotorised transport such as cycling, particularly in cities. The energy efficiency of cars has increased as a consequence of technological progress.

It is easier to sustainably produce electricity than it is to sustainably produce liquid fuels. Therefore, adoption of electric vehicles is a way to make transport more sustainable; Hydrogen vehicles may be an option for larger vehicles which have not yet been widely electrified, such as long distance lorries. Many of the techniques needed to lower emissions from shipping and aviation are still in early in their development.

Industry

Of final energy demand, over one third is used by industry. Most of that energy is deployed in thermal processes: generating steam, drying and refrigeration. The share of renewable energy in industry was 14.5% in 2017, which mostly include low-temperature heat supplied by bioenergy and electricity. The more energy intensive part of industry have the lowest shares of renewable energy, as they face limitations to meet heat demand over 200 °C. For some industrial processes, such as steel production, commercialization of technologies that have not yet been built or operated at full scale is needed to eliminate greenhouse gas emissions. The production of plastic, cement and fertilizers also requires significant amounts of energy, with limited possibilities available to decarbonise.

Government policies

Main article: Energy policy

Climate

Main article: Climate change mitigation

Internationally, the main vehicle for climate policy is the Paris Agreement, which encourages countries to pursue efforts to keep global warming under 1.5 °C (2.7 °F). According to the IPCC, both explicit carbon pricing and complementary energy-specific policies are necessary mechanisms to limit global warming to 1.5 °C. Some studies estimate that combining a carbon tax with energy-specific policies would be more cost-effective than a carbon tax alone.

Energy-specific programs and regulations have historically been the mainstays of efforts to reduce fossil fuel emissions. Successful cases include the building of nuclear reactors in France in the 1970s and 1980s, and fuel efficiency standards for cars and light trucks in the United States which conserved billions of barrels of oil. Other examples of energy-specific policies include energy-efficiency requirements in building codes, banning new coal-fired electricity plants, performance standards for electrical appliances, and support for electric vehicle use.

Carbon taxes provide a source of revenue that can be used to lower other taxes or to help lower-income households afford higher energy costs. Carbon taxes have encountered strong political pushback in some jurisdictions, whereas energy-specific policies tend to be politically safer. According to the OECD, climate change cannot be curbed without carbon taxes on energy, but 70% of energy-related CO₂ emissions were not taxed at all in 2018. Fossil fuel subsidies form a significant barrier to the energy transition.

In 2020, the International Energy Agency warned that the economic turmoil caused by the coronavirus outbreak may prevent or delay companies from investing in green energy. The outbreak could potentially spell a slowdown in the world's clean energy transition if no action is undertaken, but also offers possibilities for a green recovery.

Energy security

Energy security is another major policy goal. Historically, energy independence has been the focus of energy security policy, with countries wanting to become less dependent on oil exporters. With the integration of variable renewables, countries are increasingly considering the benefits of interdependence to compensate for intermittency. The market for metals and minerals required for sustainable energy is sometimes dominated by a small group of countries or companies, raising geopolitical concerns.

See also

• Life-cycle greenhouse gas emissions of energy sources

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