Hydroelectricity, orhydroelectric power, iselectricity generated fromhydropower (water power). Hydropower supplies 15% of the world'selectricity, almost 4,210TWh in 2023,[1] which is more than all otherrenewable sources combined and also more thannuclear power.[2] Hydropower can provide large amounts oflow-carbon electricity on demand, making it a key element for creating secure and clean electricity supply systems.[2] A hydroelectric power station that has a dam andreservoir 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. Once a hydroelectric complex is constructed, it produces no direct waste, and almost always emits considerably lessgreenhouse gas thanfossil fuel-powered energy plants.[3] However, when constructed in lowlandrainforest areas, where part of the forest is inundated, substantial amounts of greenhouse gases may be emitted.[4]
Construction of a hydroelectric complex can have significant environmental impact, principally in loss ofarable land and population displacement.[5][6] They also disrupt the natural ecology of the river involved, affecting habitats and ecosystems, and siltation and erosion patterns. While dams can ameliorate the risks of flooding,dam failure can be catastrophic.
In 2021, global installed hydropower electrical capacity reached almost 1,400 GW, the highest among all renewable energy technologies.[7] Hydroelectricity plays a leading role in countries like Brazil, Norway and China.[8] but there are geographical limits and environmental issues.[9]Tidal power can be used in coastal regions.
China added 24 GW in 2022, accounting for nearly three-quarters of global hydropower capacity additions. Europe added 2 GW, the largest amount for the region since 1990. Meanwhile, globally, hydropower generation increased by 70 TWh (up 2%) in 2022 and remains the largest renewable energy source, surpassing all other technologies combined.[10]
Museum Hydroelectric power plant "Under the Town" inUžice,Serbia, built in 1900[11]
Hydropower has been used since ancient times to grind flour and perform other tasks. In the late 18th century hydraulic power provided the energy source needed for the start of theIndustrial Revolution.[12] In the mid-1700s, French engineerBernard Forest de Bélidor publishedArchitecture Hydraulique, which described vertical- and horizontal-axis hydraulic machines, and in 1771Richard Arkwright's combination ofwater power, thewater frame, andcontinuous production played a significant part in the development of the factory system, with modern employment practices.[13] In the 1840s,hydraulic power networks were developed to generate and transmit hydro power to end users.
By the late 19th century, theelectrical generator was developed and could now be coupled with hydraulics.[14] The growing demand arising from theIndustrial Revolution would drive development as well.[15] In 1878, the world's first hydroelectric power scheme was developed atCragside inNorthumberland, England, byWilliam Armstrong. It was used to power a singlearc lamp in his art gallery.[16] The oldSchoelkopf Power Station No. 1, US, nearNiagara Falls, began to produce electricity in 1881. The firstEdison hydroelectric power station, theVulcan Street Plant, began operating September 30, 1882, inAppleton, Wisconsin, with an output of about 12.5 kilowatts.[17] By 1886 there were 45 hydroelectric power stations in the United States and Canada; and by 1889 there were 200 in the United States alone.[14]
TheWarwick Castle water-powered generator house, used for the generation of electricity for the castle from 1894 until 1940
At the beginning of the 20th century, many small hydroelectric power stations were being constructed by commercial companies in mountains near metropolitan areas.Grenoble, France held theInternational Exhibition of Hydropower and Tourism,[18] with over one million visitors 1925. By 1920, when 40% of the power produced in the United States was hydroelectric, theFederal Power Act was enacted into law. The Act created theFederal Power Commission to regulate hydroelectric power stations on federal land and water. As the power stations became larger, their associated dams developed additional purposes, includingflood control,irrigation andnavigation. Federal funding became necessary for large-scale development, and federally owned corporations, such as theTennessee Valley Authority (1933) and theBonneville Power Administration (1937) were created.[15] Additionally, theBureau of Reclamation which had begun a series of western US irrigation projects in the early 20th century, was now constructing large hydroelectric projects such as the 1928Hoover Dam.[19] TheUnited States Army Corps of Engineers was also involved in hydroelectric development, completing theBonneville Dam in 1937 and being recognized by theFlood Control Act of 1936 as the premier federal flood control agency.[20]
Hydroelectric power stations continued to become larger throughout the 20th century. Hydropower was referred to as "white coal".[21]Hoover Dam's initial1,345 MW power station was the world's largest hydroelectric power station in 1936; it was eclipsed by the6,809 MWGrand Coulee Dam in 1942.[22] TheItaipu Dam opened in 1984 in South America as the largest, producing14 GW, but was surpassed in 2008 by theThree Gorges Dam in China at22.5 GW. Hydroelectricity would eventually supply some countries, includingNorway,Democratic Republic of the Congo,Paraguay andBrazil, with over 85% of their electricity.
Future potential
In 2021 the International Energy Agency (IEA) said that more efforts are needed to helplimit climate change.[23] Some countries have highly developed their hydropower potential and have very little room for growth: Switzerland produces 88% of its potential and Mexico 80%.[24] In 2022, the IEA released a main-case forecast of 141 GW generated by hydropower over 2022–2027, which is slightly lower than deployment achieved from 2017–2022. Because environmental permitting and construction times are long, they estimate hydropower potential will remain limited, with only an additional 40 GW deemed possible in the accelerated case.[7]
Modernization of existing infrastructure
In 2021 the IEA said that major modernisation refurbishments are required.[2]: 67
Most hydroelectric power comes from thepotential energy ofdammed water driving awater turbine andgenerator. The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called thehead. A large pipe (the "penstock") delivers water from thereservoir to the turbine.[25]
This method produces electricity to supply high peak demands by moving water betweenreservoirs at different elevations. At times of low electrical demand, the excess generation capacity is used to pump water into the higher reservoir, thus providingdemand side response.[2] When the demand becomes greater, water is released back into the lower reservoir through a turbine. In 2021 pumped-storage schemes provided almost 85% of the world's 190 GW ofgrid energy storage[2] and improve the dailycapacity factor of the generation system. Pumped storage is not an energy source, and appears as a negative number in listings.[26]
Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that only the water coming from upstream is available for generation at that moment, and any oversupply must pass unused. A constant supply of water from a lake or existing reservoir upstream is a significant advantage in choosing sites for run-of-the-river.[27]
Atidal power station makes use of the daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also bedispatchable to generate power during high demand periods. Less common types of hydro schemes use water'skinetic energy or undammed sources such as undershotwater wheels. Tidal power is viable in a relatively small number of locations around the world.[28]
Conduit hydroelectricity stations use mechanical energy of water as part of the water delivery system through man-made conduits to generate electricity. Generally, the conduits are existing waterpipelines such as inpublic water supply.[29] Some definitions expand the definition of conduits to be existing tunnels, canals, oraqueducts that are used primarily for other water delivery purposes than electricity generation.[30][31]
Sizes, types and capacities of hydroelectric facilities
The classification of hydropower plants starts with two top-level categories:[32]
The classification of a plant as an SHP or LHP is primarily based on itsnameplate capacity, the threshold varies by the country, but in any case a plant with the capacity of 50 MW or more is considered an LHP.[33] As an example, for China, SHP power is below 25 MW, for India - below 15 MW, most of Europe - below 10 MW.[34]
The SHP and LHP categories are further subdivided into many subcategories that are not mutually exclusive.[33] For example, alow-head hydro power plant withhydrostatic head of few meters to few tens of meters can be classified either as an SHP or an LHP.[35] The other distinction between SHP and LHP is the degree of the water flow regulation: a typical SHP primarily uses the natural water discharge with very little regulation in comparison to an LHP. Therefore, the term SHP is frequently used as a synonym for therun-of-the-river power plant.[33]
The largest power producers in the world are hydroelectric power stations, with some hydroelectric facilities capable of generating more than double the installed capacities of the currentlargest nuclear power stations.
Although no official definition exists for the capacity range of large hydroelectric power stations, facilities from over a few hundredmegawatts are generally considered large hydroelectric facilities.[36]
Currently, only seven facilities over10GW (10,000MW) are in operation worldwide, see table below.[37]
Small hydro ishydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies but a generating capacity of up to 10megawatts (MW) is generally accepted as the upper limit. This may be stretched to25 MW and30 MW inCanada and the United States.[39][40]
Small hydro stations may be connected to conventional electrical distribution networks as a source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a grid, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on the balance between stream flow and power production.[41][citation needed]
Micro hydro meanshydroelectric power installations that typically produce up to100kW of power. These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks. There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without purchase of fuel.[42] Micro hydro systems complementphotovoltaic solar energy systems because in many areas water flow, and thus available hydro power, is highest in the winter when solar energy is at a minimum.
Pico hydro ishydroelectric power generation of under5kW. It is useful in small, remote communities that require only a small amount of electricity. For example, the 1.1 kWIntermediate Technology Development Group Pico Hydro Project in Kenya supplies 57 homes with very small electric loads (e.g., a couple of lights and a phone charger, or a small TV/radio).[43] Even smaller turbines of 200–300 W may power a few homes in a developing country with a drop of only 1 m (3 ft). A Pico-hydro setup is typicallyrun-of-the-river, meaning that dams are not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before returning it to the stream.
Anunderground power station is generally used at large facilities and makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake. A tunnel is constructed to take water from the high reservoir to the generating hall built in a cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway.
Efficiency is often higher (that is, closer to 1) with larger and more modern turbines. Annual electric energy production depends on the available water supply. In some installations, the water flow rate can vary by a factor of 10:1 over the course of a year.[44][citation needed]
Hydropower is a flexible source of electricity since stations can be ramped up and down very quickly to adapt to changing energy demands.[37] Hydro turbines have a start-up time of the order of a few minutes.[45] Althoughbattery power is quicker its capacity is tiny compared to hydro.[2] It takes less than 10 minutes to bring most hydro units from cold start-up to full load; this is quicker than nuclear and almost all fossil fuel power.[46] Power generation can also be decreased quickly when there is a surplus power generation.[47] Hence the limited capacity of hydropower units is not generally used to produce base power except for vacating the flood pool or meeting downstream needs.[48] Instead, it can serve as backup for non-hydro generators.[47]
High value power
The major advantage of conventional hydroelectric dams with reservoirs is their ability to store water at low cost fordispatch later as high value clean electricity. In 2021, the IEA estimated that the "reservoirs of all existing conventional hydropower plants combined can store a total of 1,500 terawatt-hours (TWh) of electrical energy in one full cycle" which was "about 170 times more energy than the global fleet of pumped storage hydropower plants".[2] Battery storage capacity is not expected to overtake pumped storage during the 2020s.[2] When used aspeak power to meet demand, hydroelectricity has a higher value thanbaseload power and a much higher value compared tointermittent energy sources such as wind and solar.
Hydroelectric stations have long economic lives, with some plants still in service after 50–100 years.[49] Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation.
Where a dam serves multiple purposes, a hydroelectric station may be added with relatively low construction cost, providing a useful revenue stream to offset the costs of dam operation. It has been calculated that the sale of electricity from theThree Gorges Dam will cover the construction costs after 5 to 8 years of full generation.[50] However, some data shows that in most countries large hydropower dams will be too costly and take too long to build to deliver a positive risk adjusted return, unless appropriate risk management measures are put in place.[51]
Suitability for industrial applications
While many hydroelectric projects supply public electricity networks, some are created to serve specific industrial enterprises. Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed foraluminium electrolytic plants, for example. TheGrand Coulee Dam switched to supportAlcoa aluminium inBellingham, Washington, United States for AmericanWorld War II airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminium power) after the war. InSuriname, theBrokopondo Reservoir was constructed to provide electricity for theAlcoa aluminium industry.New Zealand'sManapouri Power Station was constructed to supply electricity to thealuminiumsmelter atTiwai Point.
Reduced CO2 emissions
Since hydroelectric dams do not use fuel, power generation does not producecarbon dioxide. While carbon dioxide is initially produced during construction of the project, and some methane is given off annually by reservoirs, hydro has one of the lowestlifecycle greenhouse gas emissions for electricity generation.[52] The lowgreenhouse gas impact of hydroelectricity is found especially intemperate climates. Greater greenhouse gas emission impacts are found in the tropical regions because the reservoirs of power stations in tropical regions produce a larger amount ofmethane than those in temperate areas.[53]
Like other non-fossil fuel sources, hydropower also has no emissions of sulfur dioxide, nitrogen oxides, or other particulates.
Other uses of the reservoir
Reservoirs created by hydroelectric schemes often provide facilities forwater sports, and become tourist attractions themselves. In some countries,aquaculture in reservoirs is common. Multi-use dams installed forirrigation supportagriculture with a relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project.[54] Managing dams which are also used for other purposes, such asirrigation, is complicated.[2]
In 2021 the IEA called for "robust sustainability standards for all hydropower development with streamlined rules and regulations".[2]
Ecosystem damage and loss of land
Merowe Dam inSudan. Hydroelectric power stations that usedams submerge large areas of land due to the requirement of areservoir. These changes to land color oralbedo, alongside certain projects that concurrently submerge rainforests, can in these specific cases result in the global warming impact, or equivalentlife-cycle greenhouse gases of hydroelectricity projects, to potentially exceed that of coal power stations.
Large reservoirs associated with traditional hydroelectric power stations result in submersion of extensive areas upstream of the dams, sometimes destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands. Damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife.[37] The loss of land is often exacerbated byhabitat fragmentation of surrounding areas caused by the reservoir.[55]
Hydroelectric projects can be disruptive to surrounding aquaticecosystems both upstream and downstream of the plant site. Generation of hydroelectric power changes the downstream river environment. Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks.[56] The turbines also will kill large portions of the fauna passing through, for instance 70% of the eel passing a turbine will perish immediately.[57][58][59] Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed.[60]
Drought and water loss by evaporation
Drought and seasonal changes in rainfall can severely limit hydropower.[2] Water may also be lost by evaporation.[61]
Siltation and flow shortage
When water flows it has the ability to transport particles heavier than itself downstream. This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation.Siltation can fill a reservoir and reduce its capacity to control floods along with causing additional horizontal pressure on the upstream portion of the dam. Eventually, some reservoirs can become full of sediment and useless or over-top during a flood and fail.[62][63]
Changes in the amount of river flow will correlate with the amount of energy produced by a dam. Lower river flows will reduce the amount of live storage in a reservoir therefore reducing the amount of water that can be used for hydroelectricity. The result of diminished river flow can be power shortages in areas that depend heavily on hydroelectric power. The risk of flow shortage may increase as a result ofclimate change.[64] One study from theColorado River in the United States suggest that modest climate changes, such as an increase in temperature in 2 degree Celsius resulting in a 10% decline in precipitation, might reduce river run-off by up to 40%.[64]Brazil in particular is vulnerable due to its heavy reliance on hydroelectricity, as increasing temperatures, lower water flow and alterations in the rainfall regime, could reduce total energy production by 7% annually by the end of the century.[64]
Methane emissions (from reservoirs)
TheHoover Dam in the United States is a large conventional dammed-hydro facility, with an installed capacity of2,080MW.
Lower positive impacts are found in the tropical regions. In lowlandrainforest areas, where inundation of a part of the forest is necessary, it has been noted that the reservoirs of power plants produce substantial amounts ofmethane.[65] This is due to plant material in flooded areas decaying in ananaerobic environment and forming methane, agreenhouse gas. According to theWorld Commission on Dams report,[66] where the reservoir is large compared to the generating capacity (less than 100 watts per square metre of surface area) and no clearing of the forests in the area was undertaken prior to impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant.[67]
Inboreal reservoirs of Canada and Northern Europe, however,greenhouse gas emissions are typically only 2% to 8% of any kind of conventional fossil-fuel thermal generation. A new class of underwater logging operation that targets drowned forests can mitigate the effect of forest decay.[68]
Relocation
Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In 2000, the World Commission on Dams estimated that dams had physically displaced 40–80 million people worldwide.[69]
Because large conventional dammed-hydro facilities hold back large volumes of water, a failure due to poor construction, natural disasters or sabotage can be catastrophic to downriver settlements and infrastructure.
DuringTyphoon Nina in 1975Banqiao Dam in Southern China failed when more than a year's worth of rain fell within 24 hours (see1975 Banqiao Dam failure). The resulting flood resulted in the deaths of 26,000 people, and another 145,000 from epidemics. Millions were left homeless.[70]
The creation of a dam in a geologically inappropriate location may cause disasters such as 1963 disaster atVajont Dam in Italy, where almost 2,000 people died.[71]
TheMalpasset Dam failure inFréjus on theFrench Riviera (Côte d'Azur), southern France, collapsed on December 2, 1959, killing 423 people in the resulting flood.[72]
Smaller dams andmicro hydro facilities create less risk, but can form continuing hazards even after being decommissioned. For example, the small earthen embankmentKelly Barnes Dam failed in 1977, twenty years after its power station was decommissioned, causing 39 deaths.[73]
Comparison and interactions with other methods of power generation
This section needs to beupdated. The reason given is: solar panels on reservoirs, also Tasmania link. Please help update this article to reflect recent events or newly available information.(January 2022)
Nuclear power is relatively inflexible; although it can reduce its output reasonably quickly. Since the cost of nuclear power is dominated by its high infrastructure costs, the cost per unit energy goes up significantly with low production. Because of this, nuclear power is mostly used forbaseload. By way of contrast, hydroelectricity can supply peak power at much lower cost. Hydroelectricity is thus often used to complement nuclear or other sources forload following. Country examples where they are paired in a close to 50/50 share includethe electric grid in Switzerland, theElectricity sector in Sweden and to a lesser extent,Ukraine and theElectricity sector in Finland.[74]
Wind power
Wind power goes through predictablevariation by season, but isintermittent on a daily basis. Maximum wind generation has little relationship to peak daily electricity consumption, the wind may peak at night when power is not needed or be still during the day when electrical demand is highest. Occasionally weather patterns can result in low wind for days or weeks at a time, a hydroelectric reservoir capable of storing weeks of output is useful to balance generation on the grid. Peak wind power can be offset by minimum hydropower and minimum wind can be offset with maximum hydropower. In this way the easily regulated character of hydroelectricity is used to compensate for the intermittent nature of wind power. Conversely, in some cases wind power can be used to spare water for later use in dry seasons.
An example of this isNorway's trading with Sweden, Denmark, the Netherlands, Germany and the UK.[75][76] Norway is 98% hydropower, while its flatland neighbors have wind power. In areas that do not have hydropower,pumped storage serves a similar role, but at a much higher cost and 20% lower efficiency.[77][citation needed]
Hydro power by country
Yearly hydro generation by continent[78] Hydro generation by country, 2021[78]
In 2022, hydro generated 4,289 TWh, 15% of total electricity and half of renewables. Of the world total,China (30%) produced the most, followed byBrazil (10%),Canada (9.2%), theUnited States (5.8%) andRussia (4.6%).[79]
Paraguay produces nearly all of its electricity from hydro and exports far more than it uses.[80] Larger plants tend to be built and operated by national governments, so most capacity (70%) is publicly owned, despite the fact that most plants (nearly 70%) are owned and operated by the private sector, as of 2021.[2]
The following table lists these data for each country:
Data are sourced fromEmber dating to the year 2023 unless otherwise specified.[78] Only includes countries with more than 1 TWh of generation. Links for each location go to the relevant hydro power page, when available.
^Șentürk, Fuat (1994).Hydraulics of dams and reservoirs (reference. ed.). Highlands Ranch, Colo.: Water Resources Publications. p. 375.ISBN0-918334-80-2.
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