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Sustainable energy is energy produced and used in such a way that it "meets the needs of the present without compromising the ability of future generations to meet their own needs."[1][2]

The term "sustainable energy" is often used interchangeably with the term "renewable energy". In general, renewable energy sources such as solar, wind, and hydroelectric energy are widely considered to be sustainable. However, particular renewable energy projects, such as the clearing of forests for the production of biofuels, can lead to similar or even worse environmental damage than using fossil fuel energy. Nuclear power is a safe Sustainable energy is energy produced and used in such a way that it "meets the needs of the present without compromising the ability of future generations to meet their own needs."[1][2]

The term "sustainable energy" is often used interchangeably with the term "renewable energy". In general, renewable energy sources such as solar, wind, and hydroelectric energy are widely considered to be sustainable. However, particular renewable energy projects, such as the clearing of forests for the production of biofuels, can lead to similar or even worse environmental damage than using fossil fuel energy. Nuclear power is a safe zero-emission source, but its sustainability is debated. The concept of sustainable energy is similar to the concepts of green energy and clean energy in its consideration of environmental impacts, however formal definitions of sustainable energy also include economic and socio-cultural impacts.

The energy transition to meet the world's needs for electricity, heating, cooling, and power for transport in a sustainable way is widely considered to be one of the greatest challenges facing humanity in the 21st century. Worldwide, nearly a billion people lack access to electricity, and around 3 billion people rely on smoky fuels such as wood, charcoal or animal dung in order to cook. These and fossil fuels are a major contributor to air pollution, which causes an estimated 7 million deaths per year. Production and consumption of energy emits over 70% of human-caused greenhouse gas emissions.

Proposed pathways for limiting global warming to 1.5 °C describe rapid implementation of low-emission methods of producing electricity and a shift towards more use of electricity in sectors such as transport. The pathways also include measures to reduce energy consumption; and use of carbon-neutral fuels, such as hydrogen produced by renewable electricity or with carbon capture and storage.[3] Achieving these goals will require government policies including carbon pricing, energy-specific policies, and phase-out of fossil fuel subsidies.

Moderate amounts of wind and solar energy, which are intermittent energy sources, can be integrated into the electrical grid without additional infrastructure such as grid energy storage. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly.[4] Costs of wind, solar, and batteries are projected to continue falling due to economies of scale from increased investment.[5]

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.[108]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.[108] Similarly, many households in the developing and developed world suffer from fuel poverty and cannot heat their houses enough.[109] Existing heating practices are often polluting. Alternatives to fossil fuel heating include waste heat, solar thermal, geothermal, electrification (heat pumps, or the less efficient electric heater) and biomass.[110][111][112] The costs of all these technologies strongly depend on location, and uptake of the technology sufficient for deep decarbonisation requires stringent policy interventions.[112]

Transport

There are multiple ways to make transport more sustainable. Public transport usually requires less energy per passenger than

There are multiple ways to make transport more sustainable. Public transport usually requires less energy per passenger than personal vehicles such as cars. In cities, transport can be made cleaner by stimulating nonmotorised transport such as cycling. Energy efficiency of cars has increased significantly, often due to regulation-driven innovation. Electric vehicles use less energy per kilometre, and as electricity is more easily produced sustainably than fuel, also contribute to making transport more sustainable.[113] Hydrogen vehicles may be an alternative for larger vehicles which have not yet been widely electrified, such as long distance lorries.[114]

Carbon capture and storage

Grid energy storage is a collection of methods used for energy storage on a large scale within an electrical power grid. The most commonly used storage method is pumped-storage hydroelectricity, which is feasible only at locations that are next to a large hill or a deep underground mine. Batteries, which store electricity as chemical energy readily reconvertible to electricity, are being deployed widely. Other storage technologies such as power-to-gas have been used in limited situations. Some technologies provide short-term energy storage, while others can keep it for much longer.[125] Further examples include ice storage tanks, which store ice frozen by cheaper energy at night to meet peak daytime demand for cooling.

ElectrificationGrid energy storage is a collection of methods used for energy storage on a large scale within an electrical power grid. The most commonly used storage method is pumped-storage hydroelectricity, which is feasible only at locations that are next to a large hill or a deep underground mine. Batteries, which store electricity as chemical energy readily reconvertible to electricity, are being deployed widely. Other storage technologies such as power-to-gas have been used in limited situations. Some technologies provide short-term energy storage, while others can keep it for much longer.[125] Further examples include ice storage tanks, which store ice frozen by cheaper energy at night to meet peak daytime demand for cooling.

ElectrificationElectrification is a key part of using energy sustainably, as many mainstream sustainable energy technologies are electrically powered, in contrast to the technologies they replace.[129] Specifically, massive electrification in the heat and transport sector may be needed to make these sectors sustainable, with heat pumps and electric vehicles playing an important role.[130]

860 million people are estimated to have no electricity as of 2018, of whom 600 million are in sub-Saharan Africa.[131]860 million people are estimated to have no electricity as of 2018, of whom 600 million are in sub-Saharan Africa.[131] 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.[103] But the report says this can be vastly improved, in part by accelerating electrification.[103]

Hydrogen is fuel that is zero-emission at the point of combustion. The overall lifecycle emissions of hydrogen depend on how it is produced:

  • As of 2018, very little of the world's supply of hydrogen is created from sustainable sources. Nearly all hydrogen is produced from fossil fuels, which results in high greenhouse gas emissions.
  • Hydrogen fuel 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. 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.
  • With carbon capture and storage technologies, 90% of the carbon dioxide emitted during the production of hydrogen could be removed.[132] Some academics say that CCS is needed in the short term because not enough electrolysis will be available in time.[133]

Producing steel, cement, glass, and chemicals requires more high temperature heat than electrification could supply: but hydrogen can do so.[133] Also using hydrogen instead of Producing steel, cement, glass, and chemicals requires more high temperature heat than electrification could supply: but hydrogen can do so.[133] Also using hydrogen instead of coking coal as the reducing agent makes direct reduced iron, which can then be made into steel in an electric arc furnace. Therefore steelmaking is considered to be the use of hydrogen which would be most effective in limiting GHG emissions in the short-term.[133]

Twenty per cent hydrogen can be mixed into a natural gas grid without changing pipelines or appliances,[134] but as hydrogen is less energy-dense this would only save 7% of emissions.[135] As of 2020 trials are underway on how to convert a natural gas grid to 100% hydrogen, in order to reduce or eliminate emissions from residential and industrial natural gas heating.[132] Hydrogen fuel cells can be used to power heavy road vehicles.[136] As it has a low energy to volume content, it is easier to use in hydrogen-powered ships[137

Twenty per cent hydrogen can be mixed into a natural gas grid without changing pipelines or appliances,[134] but as hydrogen is less energy-dense this would only save 7% of emissions.[135] As of 2020 trials are underway on how to convert a natural gas grid to 100% hydrogen, in order to reduce or eliminate emissions from residential and industrial natural gas heating.[132] Hydrogen fuel cells can be used to power heavy road vehicles.[136] As it has a low energy to volume content, it is easier to use in hydrogen-powered ships[137] than in cars. Use in airplanes is being researched, but despite emitting no carbon dioxide such flights would still impact the climate.[138]

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.[140]

Energy-specific programs and regulations have historically been the mainstay 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 in the United States which conserved billions of barrels of oil.[141] 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.[142][140] Fossil fuel subsidies remain a key barrier to a transition to a clean energy system.[143]

Carbon taxes are an effective way to encourage movement towards a low-carbon economy, while providing a source of revenue that can be used to lower other taxesfuel efficiency standards in the United States which conserved billions of barrels of oil.[141] 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.[142][140] Fossil fuel subsidies remain a key barrier to a transition to a clean energy system.[143]

Carbon taxes are an effective way to encourage movement towards a low-carbon economy, while providing a source of revenue that can be used to lower other taxes[144] or to help lower-income households afford higher energy costs.[145] Carbon taxes have encountered strong political pushback in some jurisdictions, whereas energy-specific policies tend to be politically safer.[141] According to the OECD climate change cannot be curbed without carbon taxes on energy, but 70% of energy-related CO
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emissions were not taxed at all in 2018.[146]