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." It 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 social 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. Production and consumption of energy emits over 70% of human-caused greenhouse gas emissions. Worldwide, nearly a billion people lack access to electricity, and around 3 billion rely on smoky fuels such as wood, charcoal or animal dung to cook. These and fossil fuels are a major contributor to air pollution, which causes an estimated 7 million deaths per year.
In general, renewable energy sources such as solar, wind, and hydroelectric energy are widely considered to be sustainable. However, aspects of some renewable energy projects, such as the clearing of forests for the production of biofuels, can lead to similar worse environmental damage than using fossil fuel energy. Nuclear power is a low-carbon source and has a safety record comparable to wind and solar, but radioactive waste and the risk of major accidents are disadvantages of this technology.
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 and demand-response measures. These sources generated 8.5% of worldwide electricity in 2019, a share that has grown rapidly. Costs of wind, solar, and batteries are projected to continue falling due to innovation and economies of scale from increased investment.
Proposed pathways for limiting global warming to 1.5 °C describe rapid implementation of low-emission methods of producing electricity and heat, 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 low-carbon fuels, such as hydrogen produced by renewable electricity or with carbon capture and storage. Achieving these goals will require government policies including carbon pricing, energy-specific policies, and phase-out of fossil fuel subsidies.
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 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 of sustainable energy:
- 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.
Providing sustainable energy is widely viewed as 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.
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. The lack of electricity exacerbates the coronavirus pandemic, with half of health facilities having no or poor access to electricity in six surveyed countries in Asia and Africa.
In developing countries, over 2.5 billion people rely on traditional cookstoves and open fires to burn biomass or coal for heating and cooking. This practice causes harmful indoor air pollution, resulting in an estimated 3.8 million deaths annually, particularly among young children and women who spend much time near the hearth. 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.
The United Nations Sustainable Development Goal 7 calls for "access to affordable, reliable, sustainable and modern energy for all" by 2030. 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.
Pathways for climate change mitigationEdit
Energy production and consumption are major contributors to climate change, being 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 transportation 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. As of 2015, 80% of the world's primary energy is produced from fossil fuels.
Cost–benefit analysis work has been done by a disparate array of specialists and agencies to determine the best path to decarbonizing the energy supply of the world. The IPCC's 2018 Special Report on Global Warming of 1.5 °C says that for limiting warming to 1.5 °C and avoiding the worst effects of climate change, "global net human-caused emissions of CO
2 would need to fall by about 45% from 2010 levels by 2030, reaching net zero around 2050." As part of this report, the IPCC's working group on climate change mitigation reviewed a variety of previously-published papers that describe pathways (i.e. scenarios and portfolios of mitigation options) to stabilize the climate system through changes in energy, land use, agriculture, and other areas.
The pathways that are consistent with limiting warning to approximately 1.5 °C describe a rapid transition towards producing electricity through lower-emission methods, and increasing use of electricity instead of other fuels in sectors such as transportation. These pathways have the following characteristics (unless otherwise stated, the following values are the median across all pathways):
- Renewable energy: The proportion of primary energy supplied by renewables increases from 15% in 2020 to 60% in 2050. The proportion of primary energy supplied by biomass increases from 10% to 27%, with effective controls on whether land use is changed in the growing of biomass. The proportion from wind and solar increases from 1.8% to 21%.
- Nuclear energy: The proportion of primary energy supplied by nuclear power increases from 2.1% in 2020 to 4% in 2050. Most pathways describe an increase in use of nuclear power, but some describe a decrease. The reason for the wide range of possibilities is that deployment of nuclear energy "can be constrained by societal preferences."
- Coal and oil: Between 2020 and 2050, the proportion of primary energy from coal declines from 26% to 5%, and the proportion from oil declines from 35% to 13%.
- Natural gas: In most pathways, the proportion of primary energy supplied by natural gas decreases, but in some pathways, it increases. Using the median values across all pathways, the proportion of primary energy from natural gas declines from 23% in 2020 to 13% in 2050.
- Carbon capture and storage: Pathways describe more use of carbon capture and storage for bioenergy and fossil fuel energy.
- Electrification: In 2020, around 20% of final energy use is provided by electricity. By 2050, this proportion more than doubles in most pathways.
- Energy conservation: Pathways describe methods to increase energy efficiency and reduce energy demand in all sectors (industry, buildings, and transport). With these measures, pathways show energy usage to remain around the same between 2010 and 2030, and increase slightly by 2050.
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.
Increasing energy efficiency is one of the most important ways to reduce energy-related pollution while also delivering economic and social benefits. For some countries, efficiency can improve energy security by reducing dependence on fossil fuel imports, The International Energy Agency estimates that 40% of greenhouse gas emission reductions needed for the Paris agreement can be achieved by increasing energy efficiency.
Between 2015 in 2018, each year saw less improvements 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 ambition level for energy efficiency policy over this period either. Policies to improve efficiency include building codes, performance standards, and carbon pricing. Efficiency slows down energy demand growth so that rising clean energy supplies can make deep cuts in fossil fuel use.
The second aspect of energy conservation are behavioural changes. The International Energy Agency estimates that reaching net zero emissions in 2050 will depend on significant behavioural changes. Their net-zero scenario gives an illustration of the type of changes needed: about half of the energy-saving behavioural change derives from transport. Some business flights are replaced by videoconferencing, cycling and walking increase in popularity, as more people use public transport.
Renewable energy sourcesEdit
The terms "sustainable energy" and "renewable energy" are often used interchangeably, however particular 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.
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. Generally warranted for 25 years, a solar panel will usually generate for longer, although at reduced efficiency, and almost all of it can be recycled. 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.[needs update]
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 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 competitive with, or in some places cheaper than, existing coal plants.
Onshore wind farms have an impact on the landscape, as typically they need to be spread over more land than other power stations and need to be built in wild and rural areas, which can lead to "industrialization of the countryside" and habitat loss. Offshore wind power has less visual impact. After about 20 years wind turbine blades need replacing with larger blades, and research continues on how best to recycle them and how to manufacture blades which are easier to recycle. 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 will become cheaper than onshore wind in the mid-2030s.
Hydroelectric plants convert the energy of moving water into electricity. On average, hydroelectricity is one of the energy sources that emits the lowest levels of greenhouse gas emissions per unit of energy produced, however levels of emissions vary enormously between projects.
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.
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.
Geothermal energy is produced by tapping into the thermal energy created and stored within the earth. It arises from the radioactive decay of an isotope of potassium and other elements found in the Earth's crust. Geothermal energy is considered renewable and sustainable because that thermal energy is constantly replenished.
Geothermal energy can be harnessed to 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.
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 can be obtained by drilling into the ground, very similar to oil exploration, and then it is carried by a heat-transfer fluid (e.g. water, brine or steam). Within these liquid-dominated systems, there are possible concerns of subsidence and contamination of ground-water resources. Therefore, protection of ground-water resources is necessary in these systems.
Biomass is a versatile and common source of renewable energy. It is available in many countries, which makes it attractive for reducing dependence on imported fossil fuels. 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 is inherently inefficient, and crops also require significant amounts of energy to harvest, dry, and transport, the amount of energy produced per unit of land area is very small, in the range of 0.25 W/m2 to 1.2 W/m2. 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. Cellulosic ethanol has many benefits over traditional corn based-ethanol. It does not take away or directly conflict with the food supply because it is produced from wood, grasses, or non-edible parts of plants. However, as of 2020, there have been few commercial plants of cellulosic ethanol, mostly concentrated in Europe.
According to the UK Committee on Climate Change 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 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 system, 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 sourcesEdit
Nuclear power plants have been used since the 1950s to produce a zero emission, steady supply of electricity, without creating local air pollution. In 2019, nuclear power plants in over 30 countries generated 10% of global electricity. Nuclear power is a low-carbon energy source, with lifecycle greenhouse gas emissions (including the mining and processing of uranium), similar to the emissions from renewable energy sources. As of 2020 nuclear power provides half of European Union low-carbon electricity and a quarter of the bloc's total generation.
There is considerable controversy over whether nuclear power can be considered sustainable, with debates revolving around the risk of nuclear accidents, the cost and construction time needed to build new plants, 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.
Thorium is a fissionable material used in thorium-based nuclear power. The thorium fuel cycle claims several potential advantages over a uranium fuel cycle, including greater abundance, superior physical and nuclear properties, better resistance to nuclear weapons proliferation and reduced plutonium production. Therefore, it is sometimes referred as sustainable.
A prospective energy source is nuclear fusion (as opposed to nuclear fission used today). It is the reaction that exists in stars, including the Sun. Fusion reactors currently in construction are expected to be inherently safe due to lack of chain reaction and do not produce long-lived nuclear waste. The fuels for nuclear fusion reactors are widely available deuterium, lithium and tritium.
(Fossil) fuel switchingEdit
On average for a given unit of energy produced, the greenhouse gas emissions of natural gas are around half the emissions of coal when used to generate electricity, and around two-thirds the emissions of coal when used to produce heat: however reducing methane leaks is imperative. Natural gas also produces significantly less air pollution than coal. Building gas-fired power plants and gas pipelines is therefore 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. Opponents argue that developing natural gas infrastructure will create decades of carbon lock-in and stranded assets, and that renewables create far less emissions at comparable costs. The life-cycle greenhouse-gas emissions of natural gas are around 40 times the emissions of wind and nuclear energy. Switching cooking from dirty fuels such as wood or kerosene to LPG has been criticised and biogas or electricity has been suggested as an alternative.
Sustainable energy systemsEdit
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.
Heating and coolingEdit
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 waste heat, solar thermal, geothermal, electrification (heat pumps, or the less efficient electric heater) and biomass. The costs of all these technologies strongly depend on location, and uptake of the technology sufficient for deep decarbonisation requires stringent policy interventions.
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. Hydrogen vehicles may be an alternative 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 aviations are still in early in their development.
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 penetration, where renewables 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 elimanate greenhouse gas emissions.
Carbon capture and storageEdit
In theory, the greenhouse gas emissions of fossil fuel and biomass power plants can be significantly reduced through carbon capture and storage (CCS), although this process is expensive. To compare the costs of wind and solar power with that from natural gas with CCS it is necessary to estimate not just the levelized cost of energy but the whole system cost. These will depend considerably on the location due to differences in carbon prices, grid enhancements needed for flexibility, and availability of suitable geology for carbon dioxide storage.
When CCS is used to capture emissions from burning biomass in a process known as bioenergy with carbon capture and sequestration (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.[needs update] 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 (GtCO2/y) would require biomass from 40 percent of the world's current cropland.
Managing intermittent energy sourcesEdit
Solar and wind are variable renewable energy sources that supply electricity intermittently depending on the weather and the time of day. Most electric 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, it becomes necessary to make changes to the overall system to ensure that the supply of electricity is matched to demand. These changes can include the following:
- Using dispatchable renewables, natural gas plants or nuclear plants to produce flexible power
- Using grid energy storage to store excess solar and wind energy and release it as needed
- Linking different variable renewable resources, and linking different geographical regions through long-distance transmission lines
- Reducing demand for electricity at certain times through energy demand management and use of smart grids.
- Energy market, or more specifically electricity market, changes so that power supply flexibility is better paid
As of 2019, the cost and logistics of energy storage for large population centers is a significant challenge, although the cost of battery systems has plunged dramatically. For instance, a 2019 study found that for solar and wind energy to replace all fossil fuel generation for a week of extreme cold in the eastern and midwest United States, energy storage capacity would have to increase from the 11 GW in place at that time to between 230 GW and 280 GW, depending on how much nuclear power is retired.
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; lithium iron phosphate batteries are becoming more popular and flow batteries are flexible. Environmental impacts can be reduced by downcycling and recycling. Other storage technologies such as power-to-gas have been used in limited situations. Current battery technology is able to store quantities of electricity that can power a community for days; research is ongoing into technology that have the capacity to last through multiple weeks of low wind and solar electricity generation.
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 is common in high latitudes providing heat.
Electrification is a key part of using energy sustainably, as many mainstream sustainable energy technologies are electrically powered, in contrast to the technologies they replace. 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.
Hydrogen is an alternative to fossil fuels that is zero-emission at the point of combustion. The overall lifecycle emissions of hydrogen depend on how it is produced. Very little of the world's current supply of hydrogen is 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, 90% of the carbon dioxide emitted during the production of hydrogen could be removed. Some academics say that CCS is needed in the short term because not enough electrolysis will be available in time.
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, 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.
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 GHG emissions in the short-term.
Twenty per cent hydrogen can be mixed into a natural gas grid without changing pipelines or appliances, but as hydrogen is less energy-dense this would only save 7% of emissions. As of 2020[update] 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. Hydrogen fuel cells can be used to power heavy road vehicles. As it has a low energy to volume content, it is easier to use in hydrogen-powered ships than in cars. Use in airplanes is being researched, but despite emitting no carbon dioxide such flights would still impact the climate.
Government energy policiesEdit
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 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. 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. Fossil fuel subsidies remain a key barrier to a transition to a clean energy system.
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 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 CO
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