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Electricity generation
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Electricity generation is the process of generating electric power from sources of primary energy. For utilities in the electric power industry, it is the stage prior to its delivery (transmission, distribution, etc.) to end users or its storage, using for example, the pumped-storage method.
Consumable electricity is not freely available in nature, so it must be "produced", transforming other forms of energy to electricity. Production is carried out in power stations, also called "power plants". Electricity is most often generated at a power plant by electromechanical generators, primarily driven by heat engines fueled by combustion or nuclear fission, but also by other means such as the kinetic energy of flowing water and wind. Other energy sources include solar photovoltaics and geothermal power. There are exotic and speculative methods to recover energy, such as proposed fusion reactor designs which aim to directly extract energy from intense magnetic fields generated by fast-moving charged particles generated by the fusion reaction (see magnetohydrodynamics).
Phasing out coal-fired power stations and eventually gas-fired power stations,[1] or, if practical, capturing their greenhouse gas emissions, is an important part of the energy transformation required to limit climate change. Vastly more solar power[2] and wind power[3] is forecast to be required, with electricity demand increasing strongly[4] with further electrification of transport, homes and industry.[5] However, in 2023, it was reported that the global electricity supply was approaching peak CO2 emissions thanks to the growth of solar and wind power.[6]
History
[edit]
The fundamental principles of electricity generation were discovered in the 1820s and early 1830s by British scientist Michael Faraday. His method, still used today, is for electricity to be generated by the movement of a loop of wire, or Faraday disc, between the poles of a magnet. Central power stations became economically practical with the development of alternating current (AC) power transmission, using power transformers to transmit power at high voltage and with low loss.
Commercial electricity production started with the coupling of the dynamo to the hydraulic turbine. The mechanical production of electric power began the Second Industrial Revolution and made possible several inventions using electricity, with the major contributors being Thomas Alva Edison and Nikola Tesla. Previously the only way to produce electricity was by chemical reactions or using battery cells, and the only practical use of electricity was for the telegraph.
Electricity generation at central power stations started in 1882, when a steam engine driving a dynamo at Pearl Street Station produced a DC current that powered public lighting on Pearl Street, New York. The new technology was quickly adopted by many cities around the world, which adapted their gas-fueled street lights to electric power. Soon after electric lights would be used in public buildings, in businesses, and to power public transport, such as trams and trains.
The first power plants used water power or coal.[7] Today a variety of energy sources are used, such as coal, nuclear, natural gas, hydroelectric, wind, and oil, as well as solar energy, tidal power, and geothermal sources.
In the 1880s the popularity of electricity grew massively with the introduction of the Incandescent light bulb. Although there are 22 recognised inventors of the light bulb prior to Joseph Swan and Thomas Edison, Edison and Swan's invention became by far the most successful and popular of all. During the early years of the 19th century, massive jumps in electrical sciences were made. And by the later 19th century the advancement of electrical technology and engineering led to electricity being part of everyday life. With the introduction of many electrical inventions and their implementation into everyday life, the demand for electricity within homes grew dramatically. With this increase in demand, the potential for profit was seen by many entrepreneurs who began investing into electrical systems to eventually create the first electricity public utilities. This process in history is often described as electrification.[8]
The earliest distribution of electricity came from companies operating independently of one another. A consumer would purchase electricity from a producer, and the producer would distribute it through their own power grid. As technology improved so did the productivity and efficiency of its generation. Inventions such as the steam turbine had a massive impact on the efficiency of electrical generation but also the economics of generation as well. This conversion of heat energy into mechanical work was similar to that of steam engines, however at a significantly larger scale and far more productively. The improvements of these large-scale generation plants were critical to the process of centralised generation as they would become vital to the entire power system that we now use today.
Throughout the middle of the 20th century many utilities began merging their distribution networks due to economic and efficiency benefits. Along with the invention of long-distance power transmission, the coordination of power plants began to form. This system was then secured by regional system operators to ensure stability and reliability. The electrification of homes began in Northern Europe and in the Northern America in the 1920s in large cities and urban areas. It was not until the 1930s that rural areas saw the large-scale establishment of electrification.[9]
Methods of generation
[edit]2024 world electricity generation by source in terawatt-hours (TWh). Total generation was 30.85 petawatt-hours.[10]
- Coal 10,587 (34.4%)
- Natural gas 6,796 (22.1%)
- Hydro 4,417 (14.4%)
- Nuclear 2,765 (8.99%)
- Wind 2,497 (8.12%)
- Solar 2,130 (6.92%)
- Other 1,569 (5.10%)
Several fundamental methods exist to convert other forms of energy into electrical energy. Utility-scale generation is achieved by rotating electric generators or by photovoltaic systems. A small proportion of electric power distributed by utilities is provided by batteries. Other forms of electricity generation used in niche applications include the triboelectric effect, the piezoelectric effect, the thermoelectric effect, and betavoltaics.
Generators
[edit]
Electric generators transform kinetic energy into electricity. This is the most used form for generating electricity based on Faraday's law. It can be seen experimentally by rotating a magnet within closed loops of conducting material, e.g. copper wire. Almost all commercial electrical generation uses electromagnetic induction, in which mechanical energy forces a generator to rotate.
Electrochemistry
[edit]
Electrochemistry is the direct transformation of chemical energy into electricity, as in a battery. Electrochemical electricity generation is important in portable and mobile applications. Currently, most electrochemical power comes from batteries.[11] Primary cells, such as the common zinc–carbon batteries, act as power sources directly, but secondary cells (i.e. rechargeable batteries) are used for storage systems rather than primary generation systems. Open electrochemical systems, known as fuel cells, can be used to extract power either from natural fuels or from synthesized fuels. Osmotic power is a possibility at places where salt and fresh water merge.
Photovoltaic effect
[edit]The photovoltaic effect is the transformation of light into electrical energy, as in solar cells. Photovoltaic panels convert sunlight directly to DC electricity. Power inverters can then convert that to AC electricity if needed. The photovoltaic industry has undergone spectacular growth since the 1990s.
Economics
[edit]The selection of electricity production modes and their economic viability varies in accordance with demand and region. The economics vary considerably around the world, resulting in widespread residential selling prices. Hydroelectric plants, nuclear power plants, thermal power plants and renewable sources have their own pros and cons, and selection is based upon the local power requirement and the fluctuations in demand.
All power grids have varying loads on them. The daily minimum[12] is the base load, often supplied by plants which run continuously. Nuclear, coal, oil, gas and some hydro plants can supply base load. If well construction costs for natural gas are below $10 per MWh, generating electricity from natural gas is cheaper than generating power by burning coal.[13]
Nuclear power plants can produce a huge amount of power from a single unit. However, nuclear disasters have raised concerns over the safety of nuclear power, and the capital cost of nuclear plants is very high. Hydroelectric power plants are located in areas where the potential energy from falling water can be harnessed for moving turbines and the generation of power. It may not be an economically viable single source of production where the ability to store the flow of water is limited and the load varies too much during the annual production cycle.
Generating equipment
[edit]
Electric generators were known in simple forms from the discovery of electromagnetic induction in the 1830s. In general, some form of prime mover such as an engine or the turbines described above, drives a rotating magnetic field past stationary coils of wire thereby turning mechanical energy into electricity.[14] The only commercial scale forms of electricity production that do not employ a generator are photovoltaic solar and fuel cells.
Turbines
[edit]
Almost all commercial electrical power on Earth is generated with a turbine, driven by wind, water, steam or burning gas. The turbine drives a generator, thus transforming its mechanical energy into electrical energy by electromagnetic induction. There are many different methods of developing mechanical energy, including heat engines, hydro, wind and tidal power. Most electric generation is driven by heat engines.
The combustion of fossil fuels supplies most of the energy to these engines, with a significant fraction from nuclear fission and some from renewable sources. The modern steam turbine, invented by Sir Charles Parsons in 1884, currently generates about 80% of the electric power in the world using a variety of heat sources. Turbine types include:
- Steam
- Water is boiled by coal burned in a thermal power plant. About 41% of all electricity is generated this way.[15]
- Nuclear fission heat created in a nuclear reactor creates steam. Less than 15% of electricity is generated this way.
- Renewable energy. The steam is generated by biomass, solar thermal energy, or geothermal power.
- Natural gas: turbines are driven directly by gases produced by combustion. Combined cycle are driven by both steam and natural gas. They generate power by burning natural gas in a gas turbine and use residual heat to generate steam. At least 20% of the world's electricity is generated by natural gas.
- Water Energy is captured by a water turbine from the movement of water - from falling water, the rise and fall of tides or ocean thermal currents (see ocean thermal energy conversion). Currently, hydroelectric plants provide approximately 16% of the world's electricity.
- The windmill was a very early wind turbine. In 2018 around 5% of the world's electricity was produced from wind
Turbines can also use other heat-transfer liquids than steam. Supercritical carbon dioxide based cycles can provide higher conversion efficiency due to faster heat exchange, higher energy density and simpler power cycle infrastructure. Supercritical carbon dioxide blends, that are currently in development, can further increase efficiency by optimizing its critical pressure and temperature points.
Although turbines are most common in commercial power generation, smaller generators can be powered by gasoline or diesel engines. These may used for backup generation or as a prime source of power within isolated villages.
World production
[edit]
Total world generation in 2024 was 30,850 TWh, including coal (34%), gas (22%), hydro (14%), nuclear (9%), wind (8%), solar (7%), oil and other fossil fuels (3%), biomass (2%).[16]
Production by country
[edit]Environmental concerns
[edit]Variations between countries generating electrical power affect concerns about the environment. In France only 10% of electricity is generated from fossil fuels, the US is higher at 70% and China is at 80%.[17] The cleanliness of electricity depends on its source. Methane leaks (from natural gas to fuel gas-fired power plants)[18] and carbon dioxide emissions from fossil fuel-based electricity generation account for a significant portion of world greenhouse gas emissions.[19] In the United States, fossil fuel combustion for electric power generation is responsible for 65% of all emissions of sulfur dioxide, the main component of acid rain.[20] Electricity generation is the fourth highest combined source of NOx, carbon monoxide, and particulate matter in the US.[21]
According to the International Energy Agency (IEA), low-carbon electricity generation needs to account for 85% of global electrical output by 2040 in order to ward off the worst effects of climate change.[22] Like other organizations including the Energy Impact Center (EIC)[23] and the United Nations Economic Commission for Europe (UNECE),[24] the IEA has called for the expansion of nuclear and renewable energy to meet that objective.[25] Some, like EIC founder Bret Kugelmass, believe that nuclear power is the primary method for decarbonizing electricity generation because it can also power direct air capture that removes existing carbon emissions from the atmosphere.[26] Nuclear power plants can also create district heating and desalination projects, limiting carbon emissions and the need for expanded electrical output.[27]
A fundamental issue regarding centralised generation and the current electrical generation methods in use today is the significant negative environmental effects that many of the generation processes have. Processes such as coal and gas not only release carbon dioxide as they combust, but their extraction from the ground also impacts the environment. Open pit coal mines use large areas of land to extract coal and limit the potential for productive land use after the excavation. Natural gas extraction releases large amounts of methane into the atmosphere when extracted from the ground, which greatly increases global greenhouse gases. Although nuclear power plants do not release carbon dioxide through electricity generation, there are risks associated with nuclear waste and safety concerns associated with the use of nuclear sources.
Per unit of electricity generated coal and gas-fired power life-cycle greenhouse gas emissions are almost always at least ten times that of other generation methods.[28]
Centralised and distributed generation
[edit]Centralised generation is electricity generation by large-scale centralised facilities, sent through transmission lines to consumers. These facilities are usually located far away from consumers and distribute the electricity through high voltage transmission lines to a substation, where it is then distributed to consumers; the basic concept being that multi-megawatt or gigawatt scale large stations create electricity for a large number of people. The vast majority of electricity used is created from centralised generation. Most centralised power generation comes from large power plants run by fossil fuels such as coal or natural gas, though nuclear or large hydroelectricity plants are also commonly used.[29]
Centralised generation is fundamentally the opposite of distributed generation. Distributed generation is the small-scale generation of electricity to smaller groups of consumers. This can also include independently producing electricity by either solar or wind power. In recent years distributed generation as has seen a spark in popularity due to its propensity to use renewable energy generation methods such as rooftop solar.[30]
Technologies
[edit]Centralised energy sources are large power plants that produce huge amounts of electricity to a large number of consumers. Most power plants used in centralised generation are thermal power plants meaning that they use a fuel to heat steam to produce a pressurised gas which in turn spins a turbine and generates electricity. This is the traditional way of producing energy. This process relies on several forms of technology to produce widespread electricity, these being natural coal, gas and nuclear forms of thermal generation. More recently solar and wind have become large scale.
Solar
[edit]
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system (PV system) designed for the supply of merchant power. They are different from most building-mounted and other decentralized solar power because they supply power at the utility level, rather than to a local user or users. Utility-scale solar is sometimes used to describe this type of project.
This approach differs from concentrated solar power, the other major large-scale solar generation technology, which uses heat to drive a variety of conventional generator systems. Both approaches have their own advantages and disadvantages, but to date, for a variety of reasons, photovoltaic technology has seen much wider use. As of 2019[update], about 97% of utility-scale solar power capacity was PV.[31][32]
In some countries, the nameplate capacity of photovoltaic power stations is rated in megawatt-peak (MWp), which refers to the solar array's theoretical maximum DC power output. In other countries, the manufacturer states the surface and the efficiency. However, Canada, Japan, Spain, and the United States often specify using the converted lower nominal power output in MWAC, a measure more directly comparable to other forms of power generation. Most solar parks are developed at a scale of at least 1 MWp. As of 2018, the world's largest operating photovoltaic power stations surpassed 1 gigawatt. At the end of 2019, about 9,000 solar farms were larger than 4 MWAC (utility scale), with a combined capacity of over 220 GWAC.[31]
Most of the existing large-scale photovoltaic power stations are owned and operated by independent power producers, but the involvement of community and utility-owned projects is increasing.[33] Previously, almost all were supported at least in part by regulatory incentives such as feed-in tariffs or tax credits, but as levelized costs fell significantly in the 2010s and grid parity has been reached in most markets, external incentives are usually not needed.Hydroelectricity
[edit]
Hydroelectricity is electricity generated from hydropower (water power). Hydropower supplies 15% of the world's electricity, almost 4,210 TWh in 2023, which is more than all other renewable sources combined and also more than nuclear power. Hydropower can provide large amounts of low-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems. A hydroelectric power station that has a dam and reservoir is a flexible source, since the amount of electricity produced can be increased or decreased in seconds or minutes in response to varying electricity demand.
Wind
[edit]
A wind farm, also called a wind park or wind power plant,[34] is a group of wind turbines in the same location used to produce electricity. Wind farms vary in size from a small number of turbines to several hundred wind turbines covering an extensive area. Wind farms can be either onshore or offshore.
Many of the largest operational onshore wind farms are located in China, India, and the United States. For example, the largest wind farm in the world, Gansu Wind Farm in China had a capacity of over 6,000 MW by 2012,[35] with a goal of 20,000 MW[36] by 2020.[37] As of December 2020, the 1218 MW Hornsea Wind Farm in the UK is the largest offshore wind farm in the world.[38] Individual wind turbine designs continue to increase in power, resulting in fewer turbines being needed for the same total output.
Because they require no fuel, wind farms have less impact on the environment than many other forms of power generation and are often referred to as a good source of green energy. Wind farms have, however, been criticised for their visual impact and impact on the landscape. 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", habitat loss, and a drop in tourism. Some critics claim that wind farms have adverse health effects, but most researchers consider these claims to be pseudoscience (see wind turbine syndrome). Wind farms can interfere with radar, although in most cases, according to the US Department of Energy, "siting and other mitigations have resolved conflicts and allowed wind projects to co-exist effectively with radar".[39]Coal
[edit]
A coal-fired power station or coal power plant is a thermal power station which burns coal to generate electricity. Worldwide there are about 2,500 coal-fired power stations,[40] on average capable of generating a gigawatt each.[41][a] They generate about a third of the world's electricity,[42] but cause many illnesses and the most early deaths per unit of energy produced,[43] mainly from air pollution.[44][45] World installed capacity doubled from 2000 to 2023 and increased 2% in 2023.[46]
A coal-fired power station is a type of fossil fuel power station. The coal is usually pulverized and then burned in a pulverized coal-fired boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines that turn generators. Thus chemical energy stored in coal is converted successively into thermal energy, mechanical energy and, finally, electrical energy.
Coal-fired power stations are the largest single contributor to climate change,[47] releasing approximately 12 billion tonnes of carbon dioxide annually,[41] about one-fifth of global greenhouse gas emissions.[48] China accounts for over half of global coal-fired electricity generation.[49] While the total number of operational coal plants began declining in 2020,[50][51] due to retirements in Europe[52] and the Americas,[53] construction continues in Asia, primarily in China.[54] The profitability of some plants is maintained by externalities, as the health and environmental costs of coal production and use are not fully reflected in electricity prices.[55][56] However, newer plants face the risk of becoming stranded assets.[57] The UN Secretary General has called for OECD nations to phase out coal-fired generation by 2030, and the rest of the world by 2040.[58]Natural gas
[edit]Natural gas is ignited to create pressurised gas which is used to spin turbines to generate electricity. Natural gas plants use a gas turbine where natural gas is added along with oxygen which in turn combusts and expands through the turbine to force a generator to spin.
Natural gas power plants are more efficient than coal power generation, they however contribute to climate change, but not as highly as coal generation. Not only do they produce carbon dioxide from the ignition of natural gas, the extraction of gas when mined releases a significant amount of methane into the atmosphere.[59]
Nuclear
[edit]Nuclear power plants create electricity through steam turbines where the heat input is from the process of nuclear fission. Currently, nuclear power produces 11% of all electricity in the world. Most nuclear reactors use uranium as a source of fuel. In a process called nuclear fission, energy, in the form of heat, is released when nuclear atoms are split. Electricity is created through the use of a nuclear reactor where heat produced by nuclear fission is used to produce steam which in turn spins turbines and powers the generators. Although there are several types of nuclear reactors, all fundamentally use this process.[60]
Normal emissions due to nuclear power plants are primarily waste heat and radioactive spent fuel. In a reactor accident, significant amounts of radioisotopes can be released to the environment, posing a long term hazard to life. This hazard has been a continuing concern of environmentalists. Accidents such as the Three Mile Island accident, Chernobyl disaster and the Fukushima nuclear disaster illustrate this problem.[61]
Electricity generation capacity by country
[edit]The table lists 45 countries with their total electricity capacities. The data is from 2022. According to the Energy Information Administration, the total global electricity capacity in 2022 was nearly 8.9 terawatt (TW), more than four times the total global electricity capacity in 1981. The global average per-capita electricity capacity was about 1,120 watts in 2022, nearly two and a half times the global average per-capita electricity capacity in 1981.
Iceland has the highest installed capacity per capita in the world, at about 8,990 watts. All developed countries have an average per-capita electricity capacity above the global average per-capita electricity capacity, with the United Kingdom having the lowest average per-capita electricity capacity of all other developed countries.
| Country | Total capacity (GW) |
Average per capita capacity (watts) |
|---|---|---|
| World | 8,890 | 1,120 |
 China |
2,510 | 1,740 |
 United States |
1,330 | 3,940 |
 European Union |
1,080 | 2,420 |
 India |
556 | 397 |
 Japan |
370 | 2,940 |
 Russia |
296 | 2,030 |
 Germany |
267 | 3,220 |
 Brazil |
222 | 1,030 |
 Canada |
167 | 4,460 |
 South Korea |
160 | 3,130 |
 France |
148 | 2,280 |
 Italy |
133 | 2,230 |
 Spain |
119 | 2,580 |
 United Kingdom |
111 | 1,640 |
 Turkey |
107 | 1,240 |
 Mexico |
104 | 792 |
 Australia |
95.8 | 3,680 |
 Saudi Arabia |
85.3 | 2,380 |
 Iran |
83.3 | 977 |
 Vietnam |
72.2 | 721 |
 South Africa |
66.7 | 1,100 |
 Poland |
64 | 1,690 |
 Thailand |
63 | 901 |
 Ukraine |
62.2 | 1,440 |
 Egypt |
61.1 | 582 |
 Taiwan |
58 | 2,440 |
 Netherlands |
53.3 | 3,010 |
 Sweden |
52.1 | 5,100 |
 Argentina |
51.9 | 1,130 |
 Pakistan |
42.7 | 192 |
 Norway |
41.7 | 7,530 |
 United Arab Emirates |
40.7 | 4,010 |
 Malaysia |
37.9 | 1,110 |
 Chile |
37 | 1,930 |
 Venezuela |
34.1 | 1,210 |
 Kazakhstan |
29.6 | 1,600 |
 Switzerland |
27.8 | 2,960 |
 Austria |
26.7 | 2,890 |
 Algeria |
25.9 | 590 |
 Greece |
24.4 | 2,400 |
 Israel |
23.7 | 2,520 |
 Finland |
22.2 | 3,980 |
 Denmark |
21.3 | 3,710 |
 Ireland |
13.3 | 2,420 |
 New Zealand |
11.6 | 2,320 |
 Iceland |
3.24 | 8,990 |
See also
[edit]
- Glossary of power generation
- Cogeneration: the use of a heat engine or power station to generate electricity and useful heat at the same time.
- Cost of electricity by source
- Diesel generator
- Engine–generator
- Generation expansion planning
- Steam–electric power station
- World energy supply and consumption
Notes
[edit]- ^ the number 7120 in the cite is actually the number of units - as explained by Global Energy Monitor plants may have more than one unit
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- ^ Cropper, Maureen; Cui, Ryna; Guttikunda, Sarath; Hultman, Nate; Jawahar, Puja; Park, Yongjoon; Yao, Xinlu; Song, Xiao-Peng (February 2, 2021). "The mortality impacts of current and planned coal-fired power plants in India". Proceedings of the National Academy of Sciences. 118 (5). Bibcode:2021PNAS..11817936C. doi:10.1073/pnas.2017936118. ISSN 0027-8424. PMC 7865184. PMID 33495332.
- ^ "Killed by coal: Air pollution deaths in Jakarta 'may double' by 2030". The Jakarta Post. Retrieved April 8, 2022.
- ^ Boom and Bust Coal 2024 (PDF) (Report). San Francisco, California: Global Energy Monitor. April 2024. p. 7, 21. Retrieved April 11, 2024.
2% annual increase in the global operating coal fleet, which currently stands at 2,130 GW […] Figure 16: Global coal power capacity continues steady growth despite Paris Agreement, with a 2% uptick in 2023
- ^ "It's critical to tackle coal emissions – Analysis". International Energy Agency. October 8, 2021. Retrieved October 9, 2021.
Coal power plants produce a fifth of global greenhouse gas emissions – more than any other single source.
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- ^ "China generated over half world's coal-fired power in 2020: study". Reuters. March 28, 2021. Retrieved September 14, 2021.
China generated 53% of the world's total coal-fired power in 2020, nine percentage points more that five years earlier
- ^ Morton, Adam (August 3, 2020). "More coal power generation closed than opened around the world this year, research finds". The Guardian. ISSN 0261-3077. Retrieved August 4, 2020.
- ^ "The dirtiest fossil fuel is on the back foot". The Economist. December 3, 2020. ISSN 0013-0613. Retrieved December 12, 2020.
- ^ Piven, Ben. "EU power sector emissions drop as coal collapses across Europe". Al Jazeera. Retrieved March 21, 2020.
- ^ Roberts, David (March 14, 2020). "4 astonishing signs of coal's declining economic viability". Vox. Retrieved March 21, 2020.
- ^ "China pledges to stop building new coal energy plants abroad". BBC News. September 22, 2021. Retrieved September 22, 2021.
- ^ Borenstein, Severin; Bushnell, James B. (November 1, 2022). "Do Two Electricity Pricing Wrongs Make a Right? Cost Recovery, Externalities, and Efficiency" (PDF). American Economic Journal: Economic Policy. 14 (4): 80–110. doi:10.1257/pol.20190758. Retrieved November 11, 2022.
- ^ Davis, Lucas (September 21, 2020). "Time to Vote Out Coal". Energy Institute Blog. Retrieved September 27, 2020.
- ^ Harrabin, Roger (March 12, 2020). "Coal power developers 'risk wasting billions'". BBC News.
- ^ "The dirtiest fossil fuel is on the back foot". The Economist. December 3, 2020. ISSN 0013-0613.
- ^ "Natural gas power plant". Energy Education. Archived from the original on June 8, 2019. Retrieved June 8, 2019.
- ^ "Nuclear power". Energy Education. Archived from the original on June 8, 2019. Retrieved June 8, 2019.
- ^ "Nuclear Power and the Environment – Energy Explained". Energy Information Administration. Archived from the original on May 27, 2019. Retrieved June 8, 2019.
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Electricity generation
View on Grokipediafrom Grokipedia
Electricity generation is the conversion of mechanical, chemical, or other forms of energy into electrical energy, primarily through electromechanical generators that produce alternating current via electromagnetic induction as conductors rotate within magnetic fields.[1]
This process, which began commercializing in the late 19th century with early dynamo-based stations, now supplies the foundational power for global industry, transportation, and daily life, with total output exceeding 30,000 terawatt-hours annually as of 2024.[2][3]
Key methods include thermal power from combustion of fossil fuels or nuclear fission to drive steam turbines, hydroelectric generation via water flow, and emerging renewables like wind and solar photovoltaics that directly harness kinetic or radiant energy.[4]
Despite rapid expansion in low-carbon sources—accounting for 80% of the 1,200 terawatt-hours growth in 2024—fossil fuels such as coal and natural gas continue to dominate, comprising around 60% of global generation due to their dispatchable reliability and established infrastructure amid surging demand from electrification and data centers.[5][6]
Notable achievements include the scaling of massive facilities like the Three Gorges Dam, which exemplifies hydroelectric capacity, and nuclear reactors providing baseload power, though controversies persist over intermittency in solar and wind outputs requiring grid-scale storage solutions, environmental impacts of large-scale hydro and mining for battery materials, and the economic viability of subsidies-driven renewable deployments versus proven thermal efficiencies.[7]
These dynamics underscore ongoing debates in energy policy, where empirical assessments of levelized costs, land use, and lifecycle emissions reveal trade-offs in transitioning from high-density fuels to diffuse renewables without compromising supply security.[8]
Data compiled from IEA and Ember reports; renewables exclude hydropower in some historical baselines but include it here for consistency.[2][120]
Projections indicate renewables could surpass coal as the largest source category by 2026, with solar and wind driving over 80% of new renewable capacity, though fossil fuels are expected to retain a majority share through 2030 absent accelerated phase-outs.[8] This shift correlates with falling costs for unsubsidized solar and wind (now competitive with new coal in many regions) but hinges on supply chain expansions for critical minerals and grid upgrades, as intermittent sources require complementary dispatchable capacity to meet peak demand.[154] In contrast, coal and gas expansions in non-OECD nations underscore persistent energy security priorities over emissions reductions in high-growth contexts.[153]
Data sourced from aggregated international statistics.[155] [6]
Installed electricity generation capacity in 2023 was led by China at over 2,600 GW, more than double that of the United States at approximately 1,200 GW, reflecting China's aggressive buildout of coal, hydro, and renewables to meet peak demand.[156] India's capacity reached about 430 GW, with significant additions in solar and coal to support industrialization.[157] Russia maintained around 250 GW, emphasizing gas and nuclear for baseload stability, while Japan's 350 GW included a mix constrained by geographic and seismic factors.[158]
The table below outlines installed capacity for leading countries as of 2023 estimates:
Capacities include all sources (fossil, nuclear, renewables); China's dominance stems from state-directed investments yielding high utilization in dispatchable thermal plants, whereas the U.S. features diverse but aging infrastructure.[154] [156] Global capacity exceeded 8,000 GW, with non-OECD countries like China and India contributing over half of additions, often prioritizing affordable fossil expansion over intermittent renewables without adequate storage.[157]
Globally, patterns align but vary by region and year; for instance, nuclear capacity factors have averaged above 80% since 2000, while coal hovers around 50% in major producers like China and India.[164] Hydropower's global average dipped below historical norms in 2023 due to droughts, reaching approximately 40%, exacerbating supply shortfalls in water-stressed areas.[165] Onshore wind for newly commissioned projects improved to 36% weighted average, driven by turbine advancements and site selection, though offshore wind can exceed 45%.[166] Solar PV remains lowest at 15-25% globally, with improvements from tracking systems and higher-efficiency panels, yet still necessitating overbuilding to match firm generation. Trends show modest gains for renewables through technological refinements, but fundamental constraints persist, as evidenced by persistent gaps relative to thermal sources. Capacity factors also inform levelized costs, as low utilization spreads fixed investments over fewer output hours, though subsidies can mask this in policy analyses.[167] Utilization rates, sometimes distinguished as the proportion of time a plant is operational excluding forced outages, closely track capacity factors for most technologies but highlight maintenance impacts in aging fleets like coal.[159]
Data reflect midpoint assumptions including 60% debt financing at 8% interest and 40% equity at 12%; ranges account for site variability and exclude subsidies, transmission, or externalities.[149]
LCOE calculations carry inherent limitations, particularly in overlooking intermittency and system-level integration costs for variable renewables like solar and wind, which require backup generation, storage, or overbuilding to achieve dispatchability—potentially elevating effective system LCOE by 50–100% at high penetration levels without capturing reliability premiums for baseload sources. Standalone LCOE treats all MWh as equivalent, undervaluing firm capacity from nuclear or hydro that avoids curtailment or ramping expenses, and excludes externalities such as grid upgrades (e.g., $10–$50/kW for remote wind farms) or policy-driven distortions. Analyses incorporating full-system costs, including storage pairings (adding $30–$100/MWh to renewables), reveal tighter competitiveness among dispatchable options in grids demanding 24/7 reliability.[170][171]
Overall, while renewables dominate investment flows and enable quick scaling, achieving terawatt-scale reliable generation necessitates complementary dispatchable sources like nuclear or gas, as intermittent technologies alone cannot meet baseload demands without massive storage investments, which remain underdeveloped at grid scale.[189][190]
Criteria pollutants from fossil plants contribute to acid rain, smog, and respiratory issues; U.S. coal plants historically accounted for over 90% of power sector SO2 emissions before scrubbers reduced them by up to 98% in modern facilities, though NOx and PM reductions reach 83% and vary by plant age.[219][220] Biomass combustion adds PM, NOx, and volatile organic compounds, often exceeding coal per energy unit without advanced controls.[221] Nuclear, wind, solar, and run-of-river hydro produce negligible operational air emissions, though upstream fuel cycles for nuclear (e.g., mining) and rare earths in some wind turbines involve trace releases mitigated by regulation.
Water use in electricity generation encompasses withdrawal (total drawn from sources) and consumption (not returned, e.g., via evaporation). Thermoelectric plants dominate U.S. withdrawals, using once-through or cooling tower systems; in 2021, coal averaged 19,185 gallons per megawatt-hour (gal/MWh), far exceeding natural gas combined-cycle at 2,803 gal/MWh, due to higher heat rates and older infrastructure.[222] Consumption is lower overall, at about 0.47 gallons per kilowatt-hour (gal/kWh) for U.S. thermoelectric plants, with nuclear at 2.3–3.0 gal/MWh evaporated versus coal's 1.6 gal/MWh.[223] Reservoir hydropower consumes significantly through reservoir evaporation, up to 20–50 m³/MWh in arid regions, while photovoltaics, onshore wind, and concentrated solar power without wet cooling use near-zero operational water.[224] Globally, energy sector water consumption projected to rise 20% by 2030 under current policies, stressing basins shared with agriculture.[225]
Pollution beyond air and water use includes solid wastes and mining effluents. Coal generates fly ash and bottom ash, totaling over 100 million tons annually in the U.S., with risks of heavy metal leaching (e.g., arsenic, mercury) into groundwater if unlined.[226][227] Coal mining disturbs land, releasing selenium and sulfates into waterways, as seen in Appalachian stream contamination.[228] Nuclear produces high-level waste volumes under 1 m³ per reactor-year but requires geologic isolation due to radioactivity, with no verified environmental releases from commercial operations in decades.[226] Renewable mining for solar panels (silicon, silver) and wind (steel, copper) generates tailings, though per-kWh impacts are lower than fossil fuels; lithium and cobalt for associated storage pose localized risks in extraction regions like the Democratic Republic of Congo.[229] Overall, fossil sources account for the bulk of generation-linked pollution, with controls and phase-outs reducing but not eliminating exposures.[230]
Coal dominates due to air pollution causing millions of premature deaths annually, per WHO estimates integrated into the data; hydro's rate spikes from rare dam failures like Banqiao (1975, ~171,000 deaths).[98] Nuclear's low rate incorporates Chernobyl (433 deaths) and Fukushima (2,314, including evacuation stress), divided across 96,876 TWh generated globally, with UNSCEAR confirming negligible routine radiation risks.[98] Solar and wind rates derive from rooftop falls and turbine maintenance accidents, respectively, but exclude unverified bird/bat impacts or supply chain mining deaths, which peer-reviewed updates suggest remain low.[98] These metrics underscore nuclear's safety parity with renewables, countering perceptions amplified by media focus on rare events over statistical baselines.[98]
Waste management assesses volume, toxicity, and containment efficacy per TWh. Nuclear generates ~2.8 tonnes of high-level waste (spent fuel) per TWh, compact and vitrified for interim dry-cask storage or eventual geological repositories like Finland's Onkalo (operational 2025), with zero historical public exposures from managed waste.[240][241] Coal produces ~89,000 tonnes of ash per TWh, including fly ash laced with heavy metals (arsenic, mercury) and natural radionuclides exceeding nuclear waste concentrations; spills like Kingston (2008, 4 million m³) have contaminated waterways, with ongoing leaching risks from unlined ponds.[242][243][244]
Solar photovoltaic systems yield ~200–300 times more toxic waste per unit energy than nuclear, primarily from end-of-life panels containing lead, cadmium (in thin-film variants), and encapsulants; U.S. projections estimate 1 million tonnes cumulative by 2030, with <10% recycled due to economic barriers, leading to landfill leaching potentials.[245][246] Wind turbines generate ~40–50 tonnes of non-recyclable composite blade waste per MW installed (equivalent to ~1,000–2,000 tonnes per TWh at 30–40% capacity factors), often landfilled or incinerated, with global blade waste forecasted at 47 million tonnes by 2050 absent scalable chemical recycling.[243][247] Nuclear's contained, retrievable waste contrasts with dispersed fossil/renewable residues, enabling fuel reprocessing to reduce volumes by 90% in advanced cycles, though political delays hinder deep disposal.[241] Overall, fossil wastes dwarf others in scale and unmanaged hazards, while renewables' growing discards challenge circular claims without policy-mandated recovery.[243]
Persistent myths include claims of inevitable "meltdowns" causing mass casualties, unmanageable waste, and inevitable proliferation, often propagated by advocacy groups despite evidence to the contrary. Nuclear waste volumes are compact—global annual output equivalent to a few shipping containers per reactor—and contained in stable forms for millennia without environmental release, contrasting with diffuse fossil fuel emissions killing millions annually via particulates and toxins.[255] Proliferation risks pertain more to enrichment facilities than power plants, with international safeguards like IAEA inspections mitigating diversions in civilian programs.[256] Radiation fears invoke the linear no-threshold model, which assumes any exposure is harmful, but epidemiological data from Hiroshima survivors and reactor workers show no elevated cancer risks at occupational levels, challenging low-dose extrapolations from high-exposure events.[257]
Opposition endures due to cognitive biases toward rare catastrophic risks over statistical safety, amplified by media sensationalism and institutional skepticism in academia and environmental NGOs, where ideological commitments to decentralized renewables prevail over dispatchable nuclear despite the latter's proven reliability.[258] These sources, often critiqued for left-leaning biases favoring anti-corporate narratives, downplay nuclear's empirical safety while overlooking intermittency deaths from fossil backups in renewable-heavy grids.[248] Regulatory overreactions post-accidents, such as Germany's 2023 phase-out correlating with increased coal reliance and emissions, illustrate policy distortions prioritizing perception over data-driven risk assessment.[259]
History
Early discoveries and experiments
Observations of electrical phenomena date back to around 600 BC, when the Greek philosopher Thales of Miletus noted that amber, when rubbed with fur, attracted lightweight objects such as feathers and dust, marking the earliest recorded recognition of static electricity.[9] This triboelectric effect, arising from the transfer of electrons between materials, represented the initial empirical encounter with electrical attraction, though without understanding of underlying mechanisms.[10] In 1600, English physician William Gilbert published De Magnete, systematically distinguishing electricity—coined from the Greek elektron for amber—from magnetism through experiments rubbing various substances, including amber, glass, and sealing wax, to produce attractive forces.[11] Gilbert's work established electricity as a distinct phenomenon, identifying that only certain "electrics" like amber and glass exhibited this property when electrified by friction, laying foundational distinctions for later research.[12] Advancing mechanical generation, Otto von Guericke invented the first electrostatic generator around 1663, a device featuring a rotating sulfur globe rubbed by hand to produce static electricity, capable of generating sparks and demonstrating electrical repulsion and attraction.[13] This friction-based machine enabled sustained production of high-voltage static charges, facilitating experiments that revealed electricity's luminous and audible effects, though limited to intermittent discharges rather than continuous current.[14] The breakthrough to continuous electric current occurred in 1800 with Alessandro Volta's invention of the voltaic pile, a stack of alternating zinc and copper disks separated by brine-soaked cardboard, which chemically generated a steady electromotive force through oxidation-reduction reactions.[15] This electrochemical cell, producing about 1 volt per cell, powered early electrolytic decompositions and electrolytic cells, proving electricity could be generated on demand without friction.[16] Electromagnetic generation emerged in 1831 when Michael Faraday discovered induction, observing that a changing magnetic field—via a moving permanent magnet near a coil—induced an electric current in a closed circuit, quantified by the rate of magnetic flux change.[17] Faraday's experiments, using iron rings and coils, demonstrated both motional and transformer induction, establishing the principle that relative motion between conductors and magnetic fields converts mechanical energy to electrical energy.[18] Applying this, Hippolyte Pixii constructed the first practical dynamo in 1832, a hand-cranked device with a rotating permanent magnet inducing alternating current in stationary coils, later rectified to direct current via a commutator.[19] Pixii's magneto-electric machine generated measurable currents for electromagnets, bridging experimental induction to rudimentary power production, though inefficient and low-output compared to modern standards.[20]Commercialization in the 19th and early 20th centuries
The commercialization of electricity generation began in the 1870s with the development of practical dynamo machines capable of producing continuous direct current on an industrial scale. In 1871, Belgian inventor Zénobe Gramme created the Gramme dynamo, featuring a ring-shaped armature that generated smoother and higher voltages than prior designs, enabling applications in electroplating and electric arc lighting.[21] This machine marked the first generator suitable for commercial power production, with demonstrations at the 1873 Vienna Exposition revealing its reversibility as a motor when connected to another dynamo.[22] The first central power station opened on September 4, 1882, as Thomas Edison's Pearl Street Station in New York City, a coal-fired direct current (DC) facility with six dynamos initially serving 59 customers and about 400 incandescent lamps across a one-square-mile area.[23] Operating until a fire destroyed it in 1890, the station demonstrated centralized generation's viability, powering the financial district with steam engines driving the dynamos and underground distribution networks.[23] Edison's system emphasized local DC distribution due to its stability for lighting, but limitations in long-distance transmission spurred competition. This rivalry, known as the War of the Currents, pitted Edison's DC against alternating current (AC) systems promoted by George Westinghouse and Nikola Tesla, whose polyphase AC patents enabled efficient high-voltage transmission over distances.[24] AC's adoption accelerated after Westinghouse secured the contract for the Niagara Falls hydroelectric project in 1893, with generators operational by 1896, transmitting power 20 miles to Buffalo and proving AC's superiority for large-scale generation.[25] By the late 1890s, AC dominated new installations, facilitating the growth of interconnected grids. Into the early 20th century, electricity generation expanded rapidly, driven by hydroelectric and coal-fired plants. The first commercial hydroelectric station began operation in Grand Rapids, Michigan, in 1880, but large-scale hydro development surged post-1900, with coal remaining dominant for baseload power in urban areas.[26] In 1903, Chicago's Fisk Street Station opened as the world's first all-turbine power plant, using steam turbines for higher efficiency over reciprocating engines.[27] By 1920, U.S. installed capacity reached about 20,000 megawatts, primarily from coal and hydro sources, supporting urban electrification and industrial growth through regional utility networks.[28]Post-World War II expansion and electrification
Following World War II, global electricity generation experienced accelerated expansion driven by postwar economic reconstruction, population growth, and rising demand from household appliances, industrialization, and urbanization. In the 1950s and 1960s, annual global electricity consumption increased by approximately 6% per year, outpacing growth in other energy forms like oil and gas, as utilities scaled up capacity through larger coal-fired thermal plants, hydroelectric dams, and early interconnections of regional grids.[29] This period marked a shift toward centralized, high-voltage transmission systems to distribute power over wider areas, enabling economies of scale in generation.[30] In the United States, electricity demand surged due to suburban expansion, widespread adoption of air conditioning, and consumer goods like refrigerators and televisions, prompting a construction boom in power infrastructure. The U.S. Bureau of Reclamation and other agencies built numerous hydroelectric projects post-1945 to meet this demand, with generating capacity expanding significantly alongside fossil fuel plants.[31] Rural electrification, initiated earlier via the 1936 Rural Electrification Act, reached near completion by the mid-1950s, with over 90% of farms connected by 1953, transforming agricultural productivity through powered machinery and irrigation.[32] Urban and suburban areas achieved virtually universal access, supported by federal oversight from the Federal Power Commission promoting grid interconnections for reliability.[33] Europe's reconstruction under the Marshall Plan prioritized energy infrastructure, with power-generating capacity rapidly enlarged despite wartime damage, focusing on coal and hydro resources to fuel industrial recovery.[34] In the Soviet Union, state-directed plans built massive hydroelectric and thermal facilities, propelling it to become the world's second-largest electricity producer by the 1950s, behind only the United States, through projects like Volga River dams that emphasized heavy industry and centralized planning.[35] These efforts reflected a broader global trend where government investment and technological advances in turbine efficiency enabled electrification to underpin economic growth, though access remained limited in developing regions until later decades.[36]Late 20th and early 21st century shifts
In the late 20th century, electricity markets underwent significant restructuring, particularly in the United States and parts of Europe, with deregulation efforts beginning in the 1990s aimed at introducing competition to reduce costs and spur efficiency.[37] This shift from vertically integrated monopolies to wholesale markets facilitated new investments but also led to volatility, as seen in events like the 2000-2001 California energy crisis, where deregulated markets contributed to price spikes and supply shortages.[38] Globally, similar liberalizations occurred, though outcomes varied, with some regions experiencing innovation in generation technologies while others faced challenges in maintaining reliability.[39] Nuclear power construction stagnated following the 1986 Chernobyl accident, which heightened public and regulatory concerns over safety, resulting in fewer new reactors worldwide. Prior to Chernobyl, 409 reactors were commissioned over 32 years, compared to only 194 in the subsequent three decades through 2016, despite nuclear energy's empirical safety record comparable to or better than renewables when accounting for deaths per terawatt-hour.[40] This slowdown persisted into the early 21st century, with global nuclear generation share peaking around 1996 at 17.6% before declining to about 10% by 2020, even as total electricity demand grew.[41] A major shift was the rapid expansion of natural gas-fired combined cycle gas turbine (CCGT) plants, leveraging advancements in gas turbine efficiency that reached up to 60% in modern designs, surpassing traditional coal plants. In the United States, nearly 237 gigawatts of natural gas capacity were added between 2000 and 2010, accounting for 81% of new generation capacity during that period, driven by abundant shale gas supplies and lower emissions relative to coal.[42] Globally, natural gas electricity generation more than doubled from 2,745 terawatt-hours (TWh) in 2000 to 6,634 TWh in 2023, displacing some coal use while providing flexible baseload and peaking power.[6] The early 21st century saw the accelerated deployment of renewable sources, particularly wind and solar photovoltaic (PV), enabled by falling costs and policy incentives like feed-in tariffs and renewable portfolio standards. Wind and solar generation grew from negligible shares in 2000 (0.2% combined) to 13.4% of global electricity by 2023, with renewables overall rising from 19% to over 30% of the mix, though hydropower remained the dominant renewable at around 15%.[43] This expansion, totaling over 90% growth in renewable electricity from 2023 levels projected by 2030, introduced challenges with intermittency, necessitating increased grid flexibility and backup capacity, often from natural gas.[44] Coal generation, meanwhile, nearly doubled globally from 2000 to 2023 to 10,434 TWh, sustaining dominance in Asia amid rising demand, underscoring uneven transitions across regions.[6]Fundamental Principles
Electromagnetic induction and generators
Electromagnetic induction refers to the generation of an electromotive force (EMF) in a conductor exposed to a time-varying magnetic field.[45] This phenomenon was discovered by Michael Faraday in August 1831 during experiments where he observed transient currents in coils upon inserting or withdrawing a magnet, and continuous currents when a copper disc rotated between poles of an electromagnet.[45] [46] Faraday's law quantifies this effect, stating that the magnitude of the induced EMF is proportional to the rate of change of magnetic flux through the circuit, expressed as , where is the number of turns, is the magnetic flux, and the negative sign reflects Lenz's law, which dictates that the induced current opposes the change in flux./23:_Electromagnetic_Induction_AC_Circuits_and_Electrical_Technologies/23.05:_Faradays_Law_of_Induction-_Lenzs_Law) [47] In electric generators, electromagnetic induction converts mechanical energy into electrical energy by exploiting relative motion between conductors and magnetic fields.[48] A prime mover, such as a turbine or engine, rotates a rotor—typically containing field windings or permanent magnets—to produce a rotating magnetic field that cuts across stationary stator windings, inducing sinusoidal AC voltage in the latter.[49] Alternatively, the armature (conductor coils) may rotate within a stationary field, but modern large-scale generators favor rotor field excitation for efficient high-voltage output via step-up transformers.[49] The frequency of the generated AC is determined by the rotation speed and number of magnetic poles, following , where is the number of poles and is revolutions per minute in standard 60 Hz systems.[49] Alternating current (AC) generators, also known as alternators, produce output that reverses direction periodically, suitable for efficient long-distance transmission.[50] Direct current (DC) generators, or dynamos, achieve unidirectional current through a commutator—a split-ring device that reverses connections to the external circuit every half-cycle, rectifying the AC induced in the armature.[50] [51] While DC generators were common in early applications like Edison's systems in the 1880s, AC generators predominate today due to simpler construction, higher efficiency at scale, and compatibility with transformers for voltage adjustment.[50] Lenz's law ensures energy conservation, as the opposing force requires mechanical input to sustain rotation, manifesting as torque load on the prime mover./23:_Electromagnetic_Induction_AC_Circuits_and_Electrical_Technologies/23.05:_Faradays_Law_of_Induction-_Lenzs_Law)Thermodynamic cycles and energy conversion
Thermodynamic cycles form the basis for converting thermal energy from fuels or heat sources into mechanical work in most conventional power plants, with the resulting shaft power driving electrical generators. These cycles operate on principles of heat addition at high temperatures, expansion to produce work, heat rejection at lower temperatures, and fluid return to the initial state, constrained by the second law of thermodynamics.[52] The Rankine cycle, a wet vapor cycle, is prevalent in steam-driven systems such as coal-fired, nuclear, and geothermal plants, involving boiling water to steam in a boiler, expansion through a turbine, condensation in a cooler, and pumping to repeat the process. Practical Rankine cycle efficiencies in subcritical steam plants typically range from 33% to 38%, limited by turbine inlet temperatures around 540°C due to material constraints, though supercritical variants approach 45% with higher pressures and temperatures.[53] The Brayton cycle governs open or closed gas turbine operations in natural gas and some biofuel plants, featuring isentropic compression of air, constant-pressure combustion for heat addition, isentropic expansion in the turbine, and exhaust heat rejection.[54] Modern simple-cycle gas turbines achieve thermal efficiencies of about 40%, enabled by advanced blade cooling allowing combustion temperatures up to 1800 K and pressure ratios of 15-20.[53] Combined-cycle plants enhance performance by recovering Brayton exhaust heat in a heat recovery steam generator to drive a Rankine bottoming cycle, attaining net efficiencies over 64% in commercial units, as heat rejection from the gas turbine occurs at temperatures suitable for steam production (around 500-600°C).[55][56] All such cycles fall short of the Carnot limit, the theoretical maximum efficiency η = 1 - (T_cold / T_hot) in Kelvin, due to irreversibilities like pressure drops, heat transfer losses, and incomplete expansion; for example, a steam cycle with T_hot = 823 K and T_cold = 300 K yields a Carnot η of 64%, but real values are halved by these factors.[57] Reciprocating internal combustion engines employ Otto or Diesel cycles for smaller-scale generation, with Diesel efficiencies up to 44% from higher compression ratios, but these are less dominant in utility-scale electricity production. The mechanical work output from these prime movers is converted to electricity in synchronous generators, where rotor motion in a magnetic field induces alternating current via electromagnetic induction, with conversion efficiencies exceeding 98% but not altering the overall thermal efficiency dominated by the cycle.[52]Efficiency limits and losses
The maximum theoretical efficiency of heat engines used in thermal electricity generation is governed by the Carnot theorem, which states that no engine operating between a hot reservoir at temperature and a cold reservoir at (both in Kelvin) can exceed .[58] For typical steam power plants with boiler temperatures around 800 K and ambient cooling at 300 K, this yields a Carnot limit of approximately 62.5%.[59] However, real-world cycles such as the Rankine (for steam turbines) or Brayton (for gas turbines) achieve far lower efficiencies due to irreversibilities including friction, heat transfer losses, and non-ideal gas behavior, typically 30-60% depending on design.[53] In practice, average thermal efficiencies for U.S. fossil fuel plants were around 33% in 2023, calculated from heat rates of about 10,500 Btu/kWh, while advanced combined-cycle natural gas plants reach up to 60% by recovering waste heat.[60] These figures reflect primary losses in the prime mover, such as incomplete combustion (5-10% fuel energy unburned), boiler stack losses (10-20% as exhaust heat), and condenser rejection (over 50% of input heat in simple cycles). Nuclear plants, limited by lower steam temperatures (around 550 K) to avoid material degradation, average 33-37% efficiency, constrained further by the second law's prohibition on surpassing Carnot bounds without exotic mechanisms. For non-thermal methods like hydropower or wind, efficiency limits stem primarily from mechanical-to-electrical conversion rather than thermodynamics, with prime movers approaching 90-95% (e.g., hydroelectric turbines) but overall system efficiencies reduced by site-specific factors like head loss or Betz limit (59.3% maximum for wind extractable power).[61] Electrical generators themselves exhibit high efficiency, often 98-99% for large synchronous machines, due to minimized copper losses (I²R heating in windings, ~1-2%), core losses (hysteresis and eddy currents, ~1%), and mechanical losses (friction and windage, <1%). [62] Stray and auxiliary losses, including station service power (5-8% of gross output), further degrade net plant efficiency to 20-50% across generation types.[63] These losses underscore causal realities: entropy generation in irreversible processes dictates that full energy conversion is impossible, with empirical data confirming global average generation efficiency below 40% when accounting for fuel-to-grid pathways.[60] Advances like supercritical steam cycles or quantum-inspired harvesters aim to approach limits but remain bounded by fundamental physics.[64]Generating Equipment
Electrical generators and alternators
Electrical generators convert mechanical energy into electrical energy through electromagnetic induction, where a conductor moves relative to a magnetic field to induce an electromotive force.[1] In large-scale electricity generation, synchronous alternators predominate, operating by rotating a magnetic field within stationary windings to produce alternating current at a frequency synchronized with the power grid.[65] These machines consist of a rotor, typically excited by direct current to create the magnetic field, and a stator with windings that generate the output voltage.[66] Synchronous generators maintain constant speed determined by the grid frequency and number of poles, enabling stable power delivery; for a 60 Hz grid, a two-pole rotor spins at 3600 RPM.[67] Asynchronous generators, or induction machines, operate by slipping relative to synchronous speed and require grid connection or capacitors for excitation, finding use in variable-speed applications like certain wind turbines but less common in utility-scale plants due to control complexities.[68] [69] In thermal, hydro, and nuclear power plants, hydrogen-cooled turbo-alternators handle outputs from hundreds of megawatts to over 1,000 MW per unit, with efficiencies exceeding 98% under optimal load, minimizing conversion losses through advanced materials like high-conductivity copper windings and superconducting options in research prototypes. Excitation systems, often brushless with automatic voltage regulators, ensure stable output amid load variations, while protective relays mitigate faults like loss of synchronism.[66] Direct current generators, reliant on commutators for rectification, persist in niche high-voltage DC applications but have largely been supplanted by AC systems with conversion electronics for their simplicity and efficiency in transmission.[70]Prime movers: Turbines, engines, and other mechanisms
Prime movers are machines that convert various forms of energy, such as thermal, hydraulic, or kinetic, into mechanical rotational energy to drive electrical generators in power production.[71] These devices, including turbines and engines, account for the vast majority of global electricity generation through kinetic energy transfer to electromagnetic generators.[1] Turbines represent the dominant class of prime movers, exploiting fluid dynamics to produce torque. Steam turbines, prevalent in coal, nuclear, and geothermal plants, expand high-pressure steam through blades to rotate a shaft, achieving electrical efficiencies up to 45% in large-scale configurations on a higher heating value basis.[72] Gas turbines, often fueled by natural gas, operate on the Brayton cycle by compressing air, combusting fuel, and expanding hot gases; in combined-cycle plants, exhaust heat generates additional steam for a secondary turbine, yielding overall efficiencies around 60%.[73] Hydropower turbines convert water's potential and kinetic energy: Pelton wheels suit high-head sites with impulse jets striking buckets, Francis turbines handle medium heads via mixed-flow reaction, and Kaplan propellers optimize low-head, high-flow with adjustable blades.[74] Wind turbines harness aerodynamic lift on rotor blades to spin a low-speed shaft geared to a generator, serving as prime movers in variable renewable setups.[75] Reciprocating internal combustion engines, including diesel and spark-ignition types, provide flexible alternatives for distributed or backup generation, with capacities from 10 kW to over 18 MW.[76] These engines burn fuel in cylinders to reciprocate pistons, converting linear motion to rotation via crankshafts, offering rapid startup (under 10 minutes) and high reliability for grid support or remote applications.[77] Natural gas or dual-fuel variants predominate for baseload or peaking, with diesel for rugged, off-grid use.[78] Other mechanisms, such as organic Rankine cycle expanders for low-temperature heat sources or microturbines for small-scale cogeneration, supplement primary types but contribute modestly to total output.[79] Selection of prime movers depends on fuel availability, site conditions, and efficiency requirements, with turbines favored for large centralized plants due to scalability and lower maintenance relative to reciprocating engines.[80]Thermal Generation Methods
Fossil fuel combustion
Fossil fuel combustion generates electricity by burning coal, natural gas, or oil to produce heat, which boils water into steam that drives turbines connected to electrical generators.[81] Coal dominates among solid fuels, pulverized and burned in boilers for steam generation, while natural gas often powers combustion turbines directly or in combined cycles utilizing exhaust heat for additional steam.[82] Oil, though less common due to higher costs, follows similar steam-based processes in residual fuel oil-fired plants.[83] In 2023, fossil fuels accounted for 61% of global electricity production, with coal contributing 35% or 10,434 terawatt-hours.[6] Typical efficiencies for coal-fired plants average 33%, limited by thermodynamic constraints and historical plant ages, though advanced supercritical designs reach up to 45%.[61] Natural gas combined-cycle plants achieve higher efficiencies of 50-64%, recovering waste heat from gas turbines to power steam turbines, making them more competitive for flexible generation.[61] [84] Combustion emits carbon dioxide at rates varying by fuel: approximately 820 grams per kilowatt-hour for coal and 490 grams for natural gas, excluding capture technologies.[85] These plants provide dispatchable baseload power with high capacity factors, often exceeding 50% for coal, supporting grid stability amid variable renewables.[86] Technologies like circulating fluidized beds reduce sulfur emissions through limestone injection, but overall, fossil combustion remains the primary source despite efficiency gains and emission controls.[87] Global trends show coal's share declining in advanced economies due to regulations, yet rising demand in Asia sustains its role, with natural gas filling gaps for peaking and transition.[6] Integrated gasification combined cycle (IGCC) processes gasify coal for turbine use, potentially enabling carbon capture, though deployment lags due to costs.[88] Fossil plants' reliability stems from fuel storability and rapid startup in gas configurations, contrasting intermittent alternatives.[89]Nuclear fission
Nuclear fission for electricity generation involves the controlled splitting of heavy atomic nuclei, primarily uranium-235 or plutonium-239, in a reactor core, releasing heat through a chain reaction moderated and sustained by control rods and neutron absorbers. This heat is transferred via a coolant—typically water—to produce steam, which drives turbines connected to electrical generators, converting thermal energy into electricity through electromagnetic induction. The process operates on the principle that fission of a uranium-235 nucleus by a neutron yields two lighter fission products, additional neutrons to propagate the reaction, and approximately 200 MeV of energy per fission event, predominantly as kinetic energy of fragments that thermalizes in the coolant. The first nuclear power plant connected to an electrical grid was the AM-1 reactor at Obninsk in the Soviet Union, achieving criticality on June 27, 1954, and generating 5 MWe for civilian use alongside experimental purposes. The world's first fully commercial nuclear power station, Calder Hall in the United Kingdom, began operation on October 17, 1956, with a capacity of 180 MWe using Magnox reactors fueled by natural uranium. In the United States, the Shippingport Atomic Power Station commenced commercial electricity production on December 2, 1957, as the first full-scale PWR, marking the start of widespread adoption in the West. By 2024, approximately 440 operable reactors in 31 countries provided about 9% of global electricity, with a record annual output of 2,667 TWh.[90][91] Most commercial reactors are light-water reactors (LWRs), divided into pressurized water reactors (PWRs), which comprise about two-thirds of the fleet and maintain coolant above boiling point under pressure to separate steam generation in a secondary loop, and boiling water reactors (BWRs), where steam is produced directly in the core for turbine use. Other types include pressurized heavy-water reactors (PHWRs) like CANDU designs using unenriched uranium and heavy water moderator, gas-cooled reactors such as advanced gas-cooled reactors (AGRs) in the UK, and older Soviet RBMK graphite-moderated designs, though the latter have been phased out due to instability demonstrated at Chernobyl. Emerging advanced reactors, including small modular reactors (SMRs) and Generation IV designs like molten salt or fast reactors, aim for enhanced safety, fuel efficiency, and waste reduction but remain largely pre-commercial as of 2025.[92][93] The nuclear fuel cycle begins with uranium mining and milling to produce yellowcake, followed by conversion to UF6 gas, enrichment to increase U-235 content to 3-5% for LWR fuel, fabrication into pellets and rods, irradiation in reactors for 3-6 years producing about 40 GWd/t burnup, and spent fuel management. Used fuel consists of 94% unused uranium and U-236, 3% fission products, and 1% plutonium; reprocessing in countries like France recovers uranium and plutonium for recycling, reducing waste volume, while the U.S. stores spent fuel dry or in pools pending geological disposal. Cumulative global spent fuel arisings total about 400,000 tonnes as of 2023, with high-level waste volumes equivalent to a few hundred cubic meters annually for the entire industry, far smaller per TWh than fossil fuel ash or mining tailings.[94][95][96] Nuclear plants exhibit high reliability, with a global average capacity factor of 83% in 2024, meaning reactors operated at 83% of maximum possible output over the year, outperforming coal (around 50%) and far exceeding wind or solar intermittency-limited factors of 25-35%. Safety records show nuclear causing 0.03 deaths per TWh lifetime, including Chernobyl (about 50 direct radiation deaths) and Fukushima (zero radiation deaths), compared to coal's 24.6 or oil's 18.4, accounting for air pollution, accidents, and full lifecycle impacts; this low rate stems from multiple redundant barriers, rigorous regulation, and low-probability core damage frequencies below 10^-4 per reactor-year in modern designs.[97][98][99] Despite challenges like high upfront capital costs, long construction times (often 5-10 years for large plants), and regulatory hurdles, nuclear power emits near-zero greenhouse gases during operation—under 12 g CO2eq/kWh lifecycle versus 490 for gas—and supports baseload grid stability amid rising demand from electrification. As of 2025, trends include reactor restarts (e.g., Palisades in the U.S.), 63 units under construction (71 GW, half in China), and upward-revised IAEA projections to 992 GW capacity by 2050 in high scenarios, driven by energy security needs and small modular reactor deployments for faster build times and factory fabrication.[100][101]Geothermal and biomass
Geothermal electricity generation harnesses heat from the Earth's subsurface, typically from hot water or steam reservoirs, to drive turbines connected to generators. The process involves extracting geothermal fluids through production wells, passing them through heat exchangers or directly to turbines, and reinjecting cooled fluids to sustain reservoir pressure. Common plant types include dry steam plants, which use steam directly from the ground; flash steam plants, which vaporize high-pressure hot water; and binary cycle plants, which use lower-temperature resources to heat a secondary working fluid with a low boiling point. Globally, installed geothermal capacity reached approximately 15.4 GW by the end of 2024, primarily concentrated in geologically active regions such as the Ring of Fire.[102] The United States leads with the largest share, followed by Indonesia, Turkey, New Zealand, and Iceland, where high capacity factors of 70-90% enable baseload power with minimal intermittency.[103] [104] Efficiency in geothermal power plants typically ranges from 10% to 23%, limited by the relatively low temperatures (100-300°C) of most accessible resources compared to fossil or nuclear fuels, though binary cycle systems can achieve higher utilization of heat. Advantages include near-zero operational greenhouse gas emissions (0.5-1 g CO2/kWh, far below coal's 800-1000 g/kWh) and reliability independent of weather, making it suitable for grid stability. However, deployment is geographically constrained to areas with sufficient subsurface heat flux, high upfront drilling costs (often $5-10 million per well), and risks such as induced seismicity from fluid injection or gradual reservoir cooling over decades without enhanced geothermal systems (EGS). Emerging EGS technologies, which fracture hot dry rock to create artificial reservoirs, aim to expand viability but remain commercially nascent as of 2025, with pilot projects demonstrating potential but facing scalability challenges.[105] [106] [107] Biomass electricity generation combusts organic materials—such as wood chips, agricultural residues, municipal solid waste, or energy crops—to produce steam that drives turbines, often in dedicated plants or co-fired with coal. Other methods include anaerobic digestion of waste to produce biogas for combustion or gasification to syngas for combined-cycle systems, enabling higher efficiencies up to 40-50% in advanced setups. Worldwide biopower capacity stood at about 150 GW in 2023, with growth slowing to 3% annually amid competition from cheaper solar and wind; production contributes roughly 2-5% of electricity in many countries, totaling around 600-700 TWh globally. Major producers include the United States, Brazil, and parts of Europe, where wood pellets and forestry residues dominate feedstocks.[108] [109] [110] While proponents claim carbon neutrality due to CO2 absorption during plant regrowth, empirical data reveals net emissions often exceed those of natural gas (biomass: 230-1200 g CO2/kWh equivalent vs. gas: 400-500 g), particularly for wood-based systems where harvest, transport, and combustion release stored carbon faster than ecosystems recover, leading to 20-50 year delays in neutrality. Direct combustion emits particulate matter, NOx, and SOx comparable to or higher than coal per unit energy, necessitating scrubbers and contributing to air quality issues; sustainability hinges on sourcing, with waste-derived biomass preferable to whole-tree harvesting, which risks deforestation and biodiversity loss if subsidies incentivize overexploitation. Biomass provides dispatchable power with capacity factors of 50-80%, aiding grid flexibility, but economic viability erodes without mandates, as levelized costs ($80-150/MWh) surpass unsubsidized renewables.[111] [112] [113]Kinetic and Photovoltaic Methods
Hydropower
Hydropower generates electricity by harnessing the potential energy of water elevated above a lower level, converting it to kinetic energy as the water flows through turbines linked to electrical generators.[114] This process relies on the water cycle, where precipitation accumulates in reservoirs or rivers, providing a renewable source driven by gravity and solar-evaporated water. Modern turbines achieve efficiencies up to 90%, surpassing fossil fuel plants at around 50%.[115] The primary types include impoundment systems using dams to store water in reservoirs for controlled release; run-of-river facilities that divert natural river flow without large storage; and pumped-storage hydropower, which pumps water uphill during low-demand periods for later generation, functioning as grid-scale energy storage.[116] [114] Turbine designs vary by head height and flow: impulse turbines like Pelton wheels suit high-head sites, while reaction turbines such as Francis or Kaplan handle lower heads with higher flows.[74] In 2023, hydropower produced approximately 4,500 terawatt-hours, accounting for 14% of global electricity generation, with total installed capacity reaching 1,443 gigawatts by 2024, including 1,253 gigawatts of conventional hydropower.[117] [118] Capacity additions slowed to 13 gigawatts in 2023, 50% below the prior five-year average, primarily due to construction delays and environmental opposition in regions like Europe and the Americas, while China accounted for most new builds.[119] Output rebounded in 2024 by 182 terawatt-hours after 2023 droughts, highlighting vulnerability to precipitation variability.[120] The Three Gorges Dam in China, operational since 2012, holds the record as the largest facility at 22.5 gigawatts, capable of supplying power to millions while providing flood control, though its construction displaced over 1.3 million people and submerged archaeological sites.[121] Other major sites include the Grand Coulee Dam in the United States at 6.8 gigawatts and Itaipu on the Brazil-Paraguay border at 14 gigawatts.[122] Large dams fragment river ecosystems, altering flow regimes, water temperatures, and sediment transport, which disrupts fish migration and aquatic habitats; for instance, salmon populations in the Pacific Northwest have declined due to hydropower infrastructure blocking spawning routes.[123] Reservoirs can emit methane from decaying organic matter, particularly in tropical areas, contributing to greenhouse gases comparable to some fossil sources per unit energy in certain cases.[124] Social costs include displacement of communities and loss of farmland, as seen in projects like Three Gorges, though benefits encompass reliable baseload power, low marginal costs post-construction, and ancillary services like frequency regulation.[125] Despite these trade-offs, hydropower remains a cornerstone of low-carbon generation, supplying over half of global renewable electricity.[126]Wind power
Wind power produces electricity by harnessing the kinetic energy of wind through turbines that drive electrical generators. The standard horizontal-axis wind turbine features two or three airfoil-shaped blades attached to a rotor hub, which connects to a low-speed shaft in the nacelle; wind impinging on the blades generates lift and torque, rotating the rotor to turn the generator via a gearbox that steps up speed for efficient electricity production. Towers elevate the rotor to access stronger, less turbulent winds, typically reaching 80 to 140 meters in height for modern utility-scale units with capacities of 2 to 5 megawatts onshore and up to 15 megawatts offshore.[75][127] Global installed wind capacity surpassed 1,174 gigawatts by the end of 2024, following the addition of a record 117 gigawatts that year, including 109 gigawatts onshore and 8 gigawatts offshore. China dominates with 522 gigawatts, accounting for over 44% of the total, while the United States follows with 153 gigawatts. Wind electricity generation grew by 216 terawatt-hours in 2023, contributing approximately 7-8% to worldwide electricity supply amid renewables' expansion.[128][129][130] Capacity factors, measuring actual output against maximum potential, average 34-38% for onshore wind and 40-50% for offshore installations, influenced by wind resource variability, turbine design, and site conditions. This intermittency poses integration challenges, as output fluctuates unpredictably, requiring system operators to balance supply with demand through reserves, curtailment during oversupply, or complementary dispatchable sources.[131][132][133] Operation emits negligible greenhouse gases, with lifecycle emissions of 0.02-0.04 pounds of CO2 equivalent per kilowatt-hour, far below fossil fuels. However, turbines can cause bird and bat mortality via collisions, estimated at thousands annually per gigawatt in some regions, alongside habitat fragmentation, noise, and visual impacts. Construction disturbs local ecosystems, and end-of-life blade disposal burdens landfills due to non-recyclable fiberglass composites, though advances in recycling are emerging. Offshore deployments risk marine life entanglement and habitat alteration from foundations and cabling.[134][135][136]Solar power
Solar power generates electricity primarily through photovoltaic (PV) systems, which convert sunlight directly into electrical current using semiconductor materials such as silicon, exploiting the photovoltaic effect where photons excite electrons across a p-n junction to produce direct current.[137] A smaller portion comes from concentrated solar power (CSP) plants, which use mirrors or lenses to focus sunlight onto a receiver, heating a transfer fluid to generate steam that drives conventional turbines.[138] PV dominates globally, accounting for nearly all new solar capacity additions due to lower costs and simpler deployment compared to CSP, which requires direct normal irradiance and has higher water and land needs.[139] By the end of 2024, global cumulative PV capacity exceeded 2.2 terawatts (TW), with over 600 gigawatts (GW) added that year alone, driven largely by installations in China, the United States, and Europe.[140] Solar PV generation reached approximately 2,000 terawatt-hours (TWh) in 2024, comprising about 7% of worldwide electricity production, though this share varies by region with higher penetration in sunny areas like California or Australia.[141] CSP capacity remains under 10 GW globally, limited by higher upfront costs and geographic constraints, though it offers potential for thermal storage to extend output beyond daylight hours.[142] Capacity factors for solar PV average 15-25% worldwide, reflecting dependence on diurnal and seasonal sunlight availability, cloud cover, and latitude, far below dispatchable sources like nuclear (over 90%) or coal (50-60%).[143] CSP can achieve 30-40% with storage but constitutes a negligible fraction of solar output.[144] This intermittency necessitates grid-scale balancing via overbuild, backup generation, or batteries, increasing system-level costs; without such measures, solar displaces less reliable fossil peaker plants but struggles for baseload reliability.[145] Lifecycle greenhouse gas emissions for PV systems range from 40-50 grams CO2-equivalent per kilowatt-hour (g CO2eq/kWh), primarily from manufacturing and materials extraction like polysilicon production, which is energy-intensive and concentrated in coal-reliant regions such as China.[146] These emissions are lower than natural gas (400-500 g CO2eq/kWh) but comparable to wind or hydro, with end-of-life panel recycling challenges adding hazardous waste from cadmium or lead in thin-film variants.[147] Land use for utility-scale arrays can disrupt ecosystems, requiring 5-10 acres per megawatt, though rooftop PV mitigates this.[148] Levelized cost of electricity (LCOE) for unsubsidized utility-scale PV fell to around $30-50 per megawatt-hour (MWh) in 2024 in optimal locations, benefiting from module price drops below $0.20/watt, but this excludes integration costs like transmission upgrades or storage, which can double effective system expenses.[149] [150] Subsidies, including tax credits under policies like the U.S. Inflation Reduction Act, have accelerated deployment but distort markets by underpricing intermittency risks, with critics noting that true all-in costs exceed fossil alternatives when accounting for capacity value.[151] Despite rapid scaling, solar's variability limits its role without fossil or nuclear backups, as evidenced by grid curtailments in high-penetration regions like Germany.[152]Global Production and Capacity
Worldwide generation by source and trends
In 2024, fossil fuels generated approximately 59% of the world's electricity, with coal contributing 34.4%, natural gas 22%, and other fossil sources 2.8%.[120] Renewables accounted for about 33% of global generation, led by hydropower at 14%, wind at 8%, and solar photovoltaics at 7%, alongside smaller contributions from bioenergy and geothermal.[2] Nuclear fission provided roughly 9%, maintaining a stable but modest role amid limited new capacity additions.[2] Total global electricity production reached an estimated 30,000 terawatt-hours (TWh), reflecting a 3-4% annual demand growth driven by electrification in developing economies and data centers.[153] The share of renewables in global electricity has risen from 21% in 2010 to 33% in 2024, propelled by a 50% increase in capacity additions in 2023 alone (507 gigawatts, GW) and continued policy-driven expansions, particularly in solar PV and wind.[154] Coal's dominance has eroded from 41% in 2010 to 34% in 2024, though its absolute output grew by 1-2% annually in Asia due to rising demand in China and India offsetting declines elsewhere.[120] Natural gas shares have held steady or slightly increased to support grid flexibility, while nuclear generation has stagnated at 2,500-2,800 TWh per year since 2010, constrained by high capital costs, regulatory hurdles, and aging reactors in OECD countries.[2]| Source | Share in 2010 (%) | Share in 2024 (%) | Annual Growth Rate (2010-2024, approx.) |
|---|---|---|---|
| Coal | 41 | 34 | +1% (absolute), -1% (share) |
| Natural Gas | 21 | 22 | +2% |
| Renewables | 21 | 33 | +6% |
| Nuclear | 13 | 9 | 0% |
| Other Fossils | 4 | 3 | -1% |
Production and capacity by country
China produced 9,456 TWh of electricity in 2023, representing over 30% of the global total of approximately 29,500 TWh, driven primarily by coal-fired plants supplemented by hydropower and rapidly expanding solar and wind installations.[6] The United States generated 4,249 TWh, relying heavily on natural gas (about 43%), nuclear (19%), and coal (16%).[155] India followed with 1,968 TWh, where coal accounted for over 70% of output amid surging demand from economic growth.[155] Russia produced 1,177 TWh, with natural gas dominating at around 45% and nuclear at 20%, while Japan generated 1,014 TWh, increasingly dependent on fossil fuels post-Fukushima due to limited nuclear restarts.[155] The following table summarizes electricity generation for the top five countries in 2023:| Country | Generation (TWh) | Share of Global (%) |
|---|---|---|
| China | 9,456 | 32.1 |
| United States | 4,249 | 14.4 |
| India | 1,968 | 6.7 |
| Russia | 1,177 | 4.0 |
| Japan | 1,014 | 3.4 |
| Country | Capacity (GW) |
|---|---|
| China | 2,600 |
| United States | 1,200 |
| India | 430 |
| Japan | 350 |
| Russia | 250 |
Capacity factors and utilization rates
The capacity factor measures the actual electrical energy output of a generating facility over a given period relative to the maximum possible output if it operated continuously at full rated capacity during that time, typically expressed as a percentage.[159] This metric reflects operational efficiency, resource availability, and dispatchability, with higher values indicating more consistent production. For dispatchable sources such as nuclear and fossil fuel plants, capacity factors are influenced by demand, maintenance schedules, and economic dispatch decisions, often exceeding 50% when actively utilized. In contrast, variable renewables like wind and solar exhibit inherently lower factors due to intermittency tied to weather patterns, diurnal cycles, and geographic variability, typically ranging from 20-40% globally.[160][161] In the United States, 2023 data from the Energy Information Administration illustrate these differences across major sources. Nuclear plants achieved an average capacity factor of 92.1%, reflecting their baseload design and minimal downtime beyond refueling outages. Coal-fired plants averaged 40.5%, constrained by competition from cheaper natural gas and regulatory retirements. Combined-cycle natural gas plants reached 56.2%, benefiting from flexible ramping capabilities. Conventional hydropower averaged 37.2%, affected by seasonal water flows and droughts. Onshore wind turbines operated at 35.4%, while utility-scale solar photovoltaic systems yielded 24.6%, limited by nighttime and cloud cover.[162][163] These figures underscore that renewables require substantially more installed capacity—often 2-4 times that of dispatchables—to deliver equivalent annual energy, amplifying requirements for land, materials, and grid infrastructure.[161]| Energy Source | Average Capacity Factor (US, 2023) |
|---|---|
| Nuclear | 92.1% |
| Natural Gas (Combined Cycle) | 56.2% |
| Coal | 40.5% |
| Hydropower | 37.2% |
| Wind (Onshore) | 35.4% |
| Solar PV (Utility-Scale) | 24.6% |
Economic Considerations
Cost components and levelized cost of electricity
The costs of electricity generation encompass several key components: capital costs for plant construction and equipment, operations and maintenance (O&M) expenses (fixed costs independent of output, such as routine upkeep, and variable costs scaling with generation, like consumables), fuel expenditures (prominent in fossil fuel and biomass systems but absent in renewables, nuclear, and hydro), financing charges reflecting debt and equity returns, and decommissioning or waste management at end-of-life. Capital costs dominate for technologies with high upfront investments, such as nuclear plants (often exceeding $6,000/kW overnight cost) and utility-scale solar photovoltaic (PV) systems ($850–$1,400/kW), while fuel accounts for up to 60–70% of lifetime costs in natural gas combined-cycle plants at assumed prices of $3.45/MMBtu. Fixed O&M typically ranges from $10–$20/kW-year for renewables to $100+/kW-year for nuclear, with variable O&M adding $2–$5/MWh for most dispatchable sources. These components vary by technology maturity, site-specific factors, and regional labor/fuel markets, with total O&M comprising about two-thirds of non-capital operating expenses in nuclear facilities.[149][168][169] The levelized cost of electricity (LCOE) standardizes these components into a single metric, computed as the present value of total lifetime costs (capital, O&M, fuel, etc.) divided by the present value of expected electricity output over the plant's operational life, typically using a discount rate of 6–8% and technology-specific capacity factors (e.g., 89–92% for nuclear, 15–30% for solar PV, 30–55% for onshore wind). This yields unsubsidized LCOE estimates in $/MWh, enabling cross-technology comparisons under consistent assumptions like U.S. market conditions, 20–30-year lifetimes for renewables, and 60–80 years for nuclear. As of June 2024, utility-scale solar PV and onshore wind exhibit the lowest ranges due to declining capital costs and zero fuel expenses, while nuclear's high capital intensity results in elevated figures despite superior capacity factors and longevity. Gas combined-cycle benefits from low capital ($1,000–$1,200/kW) and flexible dispatch, yielding competitive LCOE amid low fuel prices.| Technology | Unsubsidized LCOE Range ($/MWh, 2024) |
|---|---|
| Solar PV (Utility) | 29–92 |
| Wind (Onshore) | 27–73 |
| Wind (Offshore) | 74–139 |
| Gas Combined Cycle | 45–108 |
| Coal | 69–168 |
| Nuclear | 142–222 |
| Geothermal | 64–106 |
| Hydro | 27–136 |
Subsidies, incentives, and market distortions
Governments worldwide provide subsidies to electricity generation sources through mechanisms such as production tax credits (PTCs), investment tax credits (ITCs), feed-in tariffs, loan guarantees, and direct payments, aiming to reduce costs, promote deployment, or internalize externalities. In the United States, federal subsidies for renewables totaled $15.6 billion in fiscal year 2022, more than double the $7.4 billion in 2016, primarily via PTCs for wind (approximately 2.6 cents per kWh) and ITCs offering up to 30% of capital costs for solar.[172] By contrast, fossil fuel production subsidies were about $3.2 billion in the same period, with nuclear receiving far less on a per-unit basis—solar generation subsidized over 76 times more per dollar of output than nuclear.[173] In 2023, U.S. wind produced 425 TWh while receiving $4.3 billion in federal support, and solar generated 238 TWh with $4.4 billion, yielding subsidies exceeding 10 dollars per MWh for each—rates far above those for coal or natural gas per unit energy.[174] Globally, explicit fossil fuel production and consumption subsidies reached $620 billion in 2023 per IEA estimates, concentrated in underpricing fuel for end-users in developing economies, though broader IMF calculations including unpriced externalities like pollution tally $7 trillion— a figure contested for conflating policy with market failures rather than direct fiscal transfers.[175] Renewable subsidies, while smaller in aggregate, disproportionately favor intermittent sources in OECD countries; for instance, Europe's feed-in tariffs and contracts for difference have driven wind and solar capacity additions despite their low capacity factors (20-30% vs. 80-90% for nuclear or coal).[176] These incentives lower apparent upfront costs but exclude system-level expenses like backup generation and grid upgrades, distorting levelized cost of electricity (LCOE) comparisons and channeling investment toward technologies requiring subsidies to compete on dispatchability.[177] Renewable portfolio standards (RPS), mandating utilities to source a percentage of electricity from renewables, function as implicit subsidies by imposing compliance costs passed to consumers, estimated at $2-48 per MWh of renewable output across U.S. states.[178] Such policies elevate wholesale and retail prices—states with stringent RPS saw electricity rates 20-30% higher than non-RPS peers from 2000-2015—while prioritizing subsidized intermittent generation over baseload alternatives, leading to inefficient resource allocation and reduced incentives for storage or demand response innovations.[179] Market distortions manifest in overcapacity during subsidized peaks (e.g., midday solar curtailment) and underinvestment in reliable capacity, exacerbating reliability risks as seen in Texas' 2021 freeze, where RPS-driven wind and solar underperformance amid fossil/gas constraints contributed to blackouts despite ample subsidized intermittent assets.[180] Empirical analyses indicate RPS and similar mandates raise system costs by 10-20% without proportional emissions reductions, as displaced fossil plants often operate more efficiently when not preempted by priority dispatch rules favoring subsidized renewables.[181]Investment trends and scalability
Global investment in clean energy technologies reached approximately $2 trillion in 2024, marking the first time it exceeded this threshold and comprising about two-thirds of total energy sector investments exceeding $3 trillion.[182][183] Within the power sector, solar photovoltaic investments alone surpassed $500 billion in 2024, outpacing combined spending on all other generation technologies including wind, nuclear, and fossil fuels.[182] This surge reflects declining capital costs for renewables and policy incentives, though growth in clean energy investments slowed slightly in 2024 compared to prior years amid higher interest rates.[184] Investments in fossil fuel-based generation, particularly coal, have declined as retirements accelerate; the U.S. electric power sector anticipates retiring 4% of existing coal capacity by end-2025, driven by economic uncompetitiveness and regulatory pressures.[185] Nuclear power investments remain subdued globally, constrained by lengthy permitting processes and construction overruns, with nuclear comprising a small fraction of new capacity funding despite its role in providing about 10% of electricity.[186] In contrast, wind and solar deployments have scaled rapidly, contributing to renewables and nuclear together accounting for 40% of global electricity generation in 2024 for the first time.[2] Scalability varies markedly by source due to technological modularity, resource availability, and infrastructural demands. Solar and wind exhibit high scalability through distributed, modular installations that can deploy in months rather than years, enabling rapid capacity additions—solar PV capacity grew by over 20% annually in recent years—but require extensive land, rare earth materials, and grid upgrades to handle intermittency.[187] Fossil fuels offer dispatchable scalability via established supply chains but face constraints from depleting reserves, emissions regulations, and investor divestment, limiting long-term expansion.[184] Nuclear power provides dense, reliable energy with potential for gigawatt-scale plants but scales slowly, often taking 10-15 years per project due to safety regulations and financing risks, resulting in fewer new builds despite proven capacity factors exceeding 90%.[186]| Generation Source | Key Scalability Factors | Recent Capacity Growth Example (2023-2024) |
|---|---|---|
| Solar PV | Modular, low upfront per MW, weather-dependent | +27% global generation increase[188] |
| Wind | Site-specific, offshore potential, supply chain bottlenecks | +19% global generation increase[188] |
| Nuclear | High energy density, long lead times, regulatory hurdles | Stable, minor growth amid few new reactors[2] |
| Coal/Fossil | Dispatchable, aging infrastructure, phase-out policies | Broadly stable or declining generation[188] |
Reliability and Grid Stability
Baseload, dispatchable, and intermittent sources
Baseload power refers to electricity generation sources that operate continuously at a steady output to meet the minimum, irreducible demand on the grid, typically achieving high capacity factors above 80%.[191] These plants are designed for long-term, efficient operation with minimal ramping, as frequent startups increase wear and fuel inefficiency; examples include nuclear reactors, which averaged a U.S. capacity factor of 92.7% in 2023, coal-fired plants at around 50%, and geothermal facilities nearing 70-80%.[162] Baseload sources ensure grid stability by providing predictable, firm power without reliance on external variables, though transitioning them offline for maintenance requires coordinated planning to avoid shortfalls.[192] Dispatchable sources, in contrast, offer flexibility by allowing operators to start, stop, or adjust output in response to fluctuating demand or to balance other generation, often with ramp rates enabling changes within minutes to hours.[193] Common examples encompass combined-cycle natural gas turbines, with capacity factors of 50-60% in baseload roles but lower for peaking, hydroelectric dams (excluding run-of-river types), and biomass combustion plants.[162] These resources are essential for peak demand periods and as backups, yet their dispatchability depends on fuel availability and infrastructure; for instance, gas plants can reach full load in under 30 minutes, supporting grid responsiveness.[194] Over-reliance on dispatchable fossil fuels for frequent cycling, however, elevates operational costs and emissions compared to steady baseload operation. Intermittent sources generate power variably based on uncontrollable factors like weather or time of day, lacking inherent dispatchability and requiring external balancing to maintain supply reliability.[195] Solar photovoltaic systems, for example, exhibit global capacity factors of 10-25% due to diurnal cycles and cloud cover, while onshore wind averages 30-40%, with outputs dropping to zero during lulls lasting days.[167] [162] This variability necessitates overbuild capacity, storage, or curtailment to avoid mismatches; in high-penetration scenarios, such as California's 2023 grid events, intermittency contributed to reliability risks without sufficient firm backups, underscoring the need for hybrid systems.[196] [197] Empirical data from grids like Germany's Energiewende reveal that intermittent integration correlates with increased dispatchable fossil fuel cycling, potentially offsetting emissions reductions unless paired with scalable storage or baseload alternatives.[198]Intermittency, variability, and backup requirements
Renewable energy sources such as solar photovoltaic (PV) and wind exhibit inherent intermittency, meaning their output is unpredictable and non-dispatchable, ceasing entirely during periods without sunlight or sufficient wind, which can last hours to days.[199] Solar generation drops to zero at night and is further reduced by cloud cover or seasonal variations, with empirical data from aggregated solar farms showing variability influenced by geographic dispersion but persistent daily cycles.[200] Wind power similarly fluctuates with wind speeds, experiencing calm periods where output falls below 10% of rated capacity for extended durations, as observed in European and U.S. grids where wind intermittency correlates with supply-demand imbalances requiring rapid adjustments.[201] These characteristics contrast with dispatchable sources like natural gas or nuclear, which maintain steady output regardless of weather. Variability compounds intermittency through rapid output changes, or "ramping," which challenges grid operators to balance supply and demand in real time. For instance, in regions with high solar penetration, midday peaks can lead to overgeneration and curtailment, followed by evening ramps down exceeding 10 GW/hour in California, necessitating flexible backup to prevent frequency deviations.[202] Wind variability in Germany has exported instability to neighboring grids, with sudden drops prompting emergency imports or fossil fuel ramp-ups, as documented in 2015-2017 analyses of cross-border flows.[203] Global capacity factors underscore this: onshore wind averaged 36% for new installations in 2023, solar PV around 20-25%, compared to nuclear's 81.5%, indicating renewables produce far below nameplate capacity due to these factors.[166][204] Addressing intermittency requires backup capacity, typically from gas-fired peaker plants or hydro, sized to cover full system demand during low-renewable periods, often approaching a 1:1 ratio with installed renewable capacity to maintain reliability.[205] In practice, U.S. grids with rising renewables rely on natural gas for 43% of generation in 2023, serving as flexible backup despite renewables' growth, as batteries provide only short-duration storage (hours) insufficient for multi-day lulls.[206][207] High-penetration scenarios in California and Germany illustrate elevated backup needs, with costs for overbuilding capacity and grid reinforcements adding 20-50% to system expenses, per engineering assessments, without which blackouts risk increases due to unmatched variability.[208][202] Empirical models confirm that without adequate firm backup, renewable-heavy systems face higher unserved energy risks, emphasizing the causal need for complementary dispatchable generation to achieve causal reliability in electricity supply.[209]Grid integration challenges and blackouts
Integrating large shares of intermittent renewable sources, such as wind and solar, into electricity grids poses technical challenges related to system inertia, frequency control, and voltage stability, primarily because these sources use inverter-based resources (IBRs) that lack the physical rotating mass of traditional synchronous generators. Synchronous machines inherently provide rotational inertia, which slows the rate of frequency decline following a sudden loss of generation or load, allowing operators time to respond; in contrast, IBRs connected via power electronics contribute minimal or no inherent inertia, leading to steeper nadir frequencies and higher risks of under-frequency load shedding during disturbances.[210] This low-inertia condition has been documented in systems with high renewable penetration, such as those exceeding 50% instantaneous IBR levels, where frequency response must rely on synthetic inertia from batteries or advanced inverter controls to emulate traditional behavior.[211] Voltage regulation and reactive power management present additional hurdles, as IBRs typically operate in grid-following mode, which assumes a strong grid voltage reference and can exacerbate instability during faults or weak grid conditions by failing to provide sufficient reactive support. Grid-forming inverters, capable of establishing voltage and frequency autonomously, are emerging as a solution but remain limited in deployment, with ongoing research emphasizing the need for standardized performance requirements to ensure stability in IBR-dominated systems.[212][213] The rapid variability of renewable output—driven by weather patterns—further strains ramping capabilities of dispatchable plants, necessitating overprovision of backup capacity, curtailment during oversupply, and enhanced forecasting accuracy; for instance, the "duck curve" in California illustrates evening net load ramps exceeding 10 GW per hour due to solar drop-off, increasing reliance on fast-start gas peakers or imports.[214][215] These challenges have contributed to blackouts in specific cases, though primary triggers often involve compounded factors like extreme weather. In South Australia on September 28, 2016, a statewide blackout affected 1.7 million people after severe storms damaged transmission lines, with multiple wind farms disconnecting due to inadequate fault ride-through capabilities and protection settings calibrated for weaker grid conditions, halting 456 MW of wind generation amid 40% renewable penetration.[216] California's August 2020 rolling blackouts, impacting over 800,000 customers for up to two hours, stemmed from heatwave-driven demand peaks coinciding with reduced hydroelectric output and solar variability, exposing shortfalls in flexible capacity despite mandates for 60% renewable energy by 2030; post-event analysis highlighted insufficient evening ramping resources and over-dependence on variable generation without adequate storage.[215] In Texas during the February 2021 winter storm, while frozen natural gas infrastructure caused the bulk of the 34 GW generation shortfall leading to blackouts for 4.5 million customers, the event underscored broader vulnerabilities in grids with rising renewables, as iced turbine blades offline reduced wind output by about 4 GW, amplifying the need for weather-resilient dispatchable backups.[217][218] NERC assessments indicate elevated reliability risks in regions pursuing rapid decarbonization, with the 2024 Long-Term Reliability Assessment projecting potential shortfalls in 79 GW of capacity by 2033 in the U.S. if retirements outpace additions of firm resources, urging enhanced interconnection standards for IBRs to mitigate low-inertia effects. Mitigation strategies include deploying grid-forming technologies, utility-scale batteries for fast frequency response (e.g., providing 100-200 ms synthetic inertia), and transmission expansions, though these add costs estimated at 20-50% premiums for high-renewable scenarios without sufficient overbuild or storage.[210] Despite scapegoating narratives, empirical data from NERC and NREL emphasize that while renewables do not inherently cause most blackouts, unaddressed integration gaps—such as delayed adoption of advanced controls—heighten cascading failure probabilities in low-inertia environments.[218]Environmental and Health Impacts
Air emissions, water use, and pollution
Fossil fuel combustion in electricity generation is the primary source of anthropogenic air emissions, including greenhouse gases (GHGs) and criteria pollutants such as sulfur dioxide (SO2), nitrogen oxides (NOx), and particulate matter (PM). Coal-fired plants emit the highest levels, with lifecycle GHG emissions averaging 820–1,000 grams of CO2 equivalent per kilowatt-hour (g CO2eq/kWh), driven by mining, transport, and combustion. Natural gas combined-cycle plants produce about 490 g CO2eq/kWh, primarily from methane leakage and fuel processing. In contrast, nuclear power's lifecycle emissions are around 12 g CO2eq/kWh, mainly from uranium enrichment and construction, while wind (11 g CO2eq/kWh) and solar photovoltaic (41–48 g CO2eq/kWh) derive most from manufacturing supply chains.| Generation Source | Median Lifecycle GHG Emissions (g CO2eq/kWh) |
|---|---|
| Coal | 820–1,000 |
| Natural Gas (CC) | 490 |
| Nuclear | 12 |
| Wind | 11 |
| Solar PV | 41–48 |
Land use, mining, and resource extraction
Electricity generation sources differ markedly in their land use requirements, encompassing both direct infrastructure (e.g., power plants, farms, or dams) and indirect uses (e.g., fuel extraction and processing). Land use intensity is typically measured in square kilometers per terawatt-hour (km²/TWh) of electricity produced over the system's lifecycle. A 2022 analysis of 268 real-world electricity generation sites found nuclear power to have the lowest median land use intensity at 7.1 hectares per TWh (equivalent to 0.071 km²/TWh), followed by onshore wind at approximately 0.36 km²/TWh when accounting for turbine spacing and associated infrastructure.[231][232] Solar photovoltaic installations exhibited higher intensities, around 4-5 km²/TWh due to panel arrays and spacing needs, while coal plants, including mining, required about 0.4-1 km²/TWh depending on extraction methods.[233][231] Hydropower reservoirs often inundate vast areas, with large dams like China's Three Gorges displacing over 600 km² of land and affecting 1.3 million people through flooding and relocation.[233] Fossil fuel-based generation, particularly coal, imposes substantial land disturbance through continuous mining operations. In the United States, surface coal mining disturbs approximately 10-15 acres per million short tons extracted, with annual production exceeding 500 million tons supporting electricity output that equates to land use intensities higher than nuclear by factors of 10-50 when including spoil piles and reclamation challenges.[233][234] Natural gas extraction via fracking fragments habitats across thousands of well pads, contributing to 0.1-0.5 km²/TWh including pipelines and processing.[233] In contrast, nuclear fuel extraction disturbs far less land due to uranium's high energy density; a typical 1 gigawatt nuclear plant requires mining roughly 200-300 tons of uranium ore annually (yielding about 27 tons of fuel), compared to 2-3 million tons of coal for an equivalent coal plant, resulting in mining footprints orders of magnitude smaller—often less than 0.01 km²/TWh lifecycle-wide.[233] Resource extraction for renewables involves mining metals like copper, steel inputs, and for wind turbines, rare earth elements such as neodymium and dysprosium for permanent magnets in generators—each multi-megawatt turbine requiring 200-600 kg of rare earths.[235] Solar panels demand silicon, silver, and aluminum but minimal rare earths, though scaling to terawatt-hours necessitates vast material volumes, with global PV deployment in 2023 requiring over 20,000 tons of silver alone.[236] Overall, however, lifecycle mining mass for low-carbon sources like nuclear, wind, and solar is 500-1,000 times lower per unit energy than for fossil fuels, as fossil plants consume millions of tons of bulk fuel annually versus grams to kilograms of enriched materials for nuclear or components for renewables.[237] Extraction impacts include habitat loss and pollution; rare earth mining, often in China (producing 60-70% of global supply), generates toxic tailings affecting water sources, while coal mining releases heavy metals and acid drainage across disturbed sites.[238][239] Nuclear uranium mining employs in-situ leaching in many cases, minimizing surface disturbance compared to open-pit coal operations, though legacy sites require remediation.| Electricity Source | Median Land Use Intensity (km²/TWh) | Key Extraction Notes |
|---|---|---|
| Nuclear | 0.071 | ~27 tons U fuel/GW-year; small mining footprint due to energy density.[232] |
| Onshore Wind | 0.36 | Rare earths (200-600 kg/turbine); copper/steel mining.[231] |
| Solar PV | ~4 | Silicon/silver/aluminum; no rare earths, but high material throughput.[233][236] |
| Coal | 0.4-1 | Millions tons fuel/GW-year; large surface/underground disturbance.[233][234] |
| Hydropower | Variable (high for reservoirs) | No fuel mining; land flooding (e.g., 600+ km² for large dams). |
Safety metrics: Deaths per terawatt-hour and waste management
Safety in electricity generation is quantified by deaths per terawatt-hour (TWh), a metric aggregating fatalities from accidents (occupational, construction, transport), and air pollution effects over the lifecycle.[98] This includes chronic respiratory diseases from particulate matter, sulfur dioxide, and nitrogen oxides for fossil fuels, drawn from epidemiological studies like those in The Lancet.[98] Renewables and nuclear incur primarily accident-related risks, with data from meta-analyses of incident reports (e.g., Sovacool et al., 2016).[98] Figures reflect global production from 1965–2021, excluding indirect wars or undercounted pollution in developing regions.[98]| Energy Source | Deaths per TWh |
|---|---|
| Coal | 24.62 |
| Oil | 18.43 |
| Natural Gas | 2.82 |
| Hydro | 1.3 |
| Wind | 0.04 |
| Solar | 0.02 |
| Nuclear | 0.03 |
Policy Debates and Controversies
Nuclear power opposition and safety myths
Opposition to nuclear power emerged prominently in the 1960s and 1970s, driven by environmental organizations and anti-nuclear activists concerned with reactor safety, radioactive waste disposal, and potential links to weapons proliferation.[248] Groups such as Greenpeace and Sierra Club campaigned against new plants, citing risks amplified by Cold War-era associations with atomic bombs, leading to widespread protests and policy delays in countries like the United States and Germany.[249] This movement influenced green political parties, which often prioritized opposition to both nuclear power and weapons, framing nuclear energy as inherently incompatible with environmentalism despite its low-carbon profile.[250] Major accidents have fueled opposition, yet empirical assessments reveal limited direct impacts relative to exaggerated narratives. The 1979 Three Mile Island partial meltdown in Pennsylvania released minimal radiation, resulting in no immediate deaths or detectable health effects beyond stress-related cases among evacuees.[251] Chernobyl's 1986 explosion in the Soviet Union, caused by design flaws and operator errors in an outdated RBMK reactor, killed 30 workers and firefighters from acute radiation syndrome, with subsequent thyroid cancer cases in children estimated at around 5,000 but largely treatable; long-term cancer attributions remain contested and far below initial activist projections of millions.[252] Fukushima Daiichi's 2011 failures, triggered by a magnitude 9.0 earthquake and tsunami exceeding design bases, produced no deaths from radiation exposure, though evacuation measures contributed to approximately 2,300 indirect fatalities among the elderly and infirm.[99] These events, while highlighting needs for improved safety standards, occurred in unique contexts—Soviet secrecy, inadequate containment, and natural disasters—and do not reflect modern reactor designs with passive safety features. Safety metrics underscore nuclear power's record: it causes fewer fatalities per unit of electricity generated than fossil fuels or even some renewables when accounting for lifecycle risks including accidents and air pollution. A comprehensive analysis attributes 0.03 deaths per terawatt-hour (TWh) to nuclear, compared to 24.6 for coal, 18.4 for oil, 2.8 for natural gas, and 1.3 for hydropower; wind and solar register 0.04 and 0.02, respectively, but exclude rare rooftop installation fatalities that elevate solar's rate in some datasets.[253]| Energy Source | Deaths per TWh |
|---|---|
| Coal | 24.6 |
| Oil | 18.4 |
| Natural Gas | 2.8 |
| Hydropower | 1.3 |
| Wind | 0.04 |
| Solar | 0.02 |
| Nuclear | 0.03 |