From New World Encyclopedia
The Nagarjuna dam & hydroelectric plant, India.

Hydroelectricity is electricity produced by hydropower—that is, the energy of moving water. It is the world's leading form of renewable energy. In 2005, it accounted for over 63 percent of the total renewable energy.[1] That same year, hydroelectricity supplied about 715,000 megawatts (or 19 percent) of the world's electricity (compared to 16 percent in 2003). Although large hydroelectric installations generate most of the world's hydroelectricity, small hydro schemes are particularly popular in China, which has over 50 percent of the world's small hydro capacity.

On the downside, hydroelectric projects can disrupt ecosystems by reducing access to salmon spawning grounds and damaging habitats of birds. These projects also lead to changes in the downstream river environment, by the scouring of river beds and loss of riverbanks. Large-scale hydroelectric dams, such as the Aswan Dam and the Three Gorges Dam, have created environmental problems both upstream and downstream.

Hydroelectricity is the world's leading renewable energy source.

Electricity generation

Hydraulic turbine and electrical generator.
Hydroelectric dam in cross section.

Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. In this case, the energy 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 the head. The amount of potential energy in water is proportional to the head. To obtain very high head, water for a hydraulic turbine may be run through a large pipe called a penstock.

Pumped storage hydroelectricity produces electricity to supply high peak demands by moving water between reservoirs at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. Pumped storage schemes currently provide the only commercially important means of grid energy storage and improve the daily load factor of the generation system.

Less common types of hydro schemes use water's kinetic energy or undammed sources such as run-of-the-river, waterwheels, and tidal power.

Industrial hydroelectric plants

Many hydroelectric projects supply public electricity networks, but some are created to serve specific industrial enterprises. Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed for aluminium electrolytic plants, for example. In the Scottish Highlands there are examples at Kinlochleven and Lochaber, constructed during the early years of the twentieth century. In Suriname, the "van Blommestein" lake, dam and power station were constructed to provide electricity for the Alcoa aluminium industry. As of 2007 the Kárahnjúkar Hydropower Project in Iceland remains controversial.[2]



The main advantage of hydroelectricity is that it is nearly independent of increases in the cost of fossil fuels such as oil, natural gas, or coal. Fuel is not required, and so it need not be imported. Hydroelectric plants tend to have longer economic lives than fuel-fired generation, with some plants now in service having been built 50 to 100 years ago. Operating labor cost is usually low since plants are automated and have few personnel on site during normal operation.

Where a dam serves multiple purposes, a hydroelectric plant 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 the Three Gorges Dam will cover the construction costs after 5 to 7 years of full generation.[3]

Related activities

Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions in themselves. In some countries, farming fish in the reservoirs is common. Multi-use dams installed for irrigation can support the fish farm with relatively constant water supply. Large hydro dams can control floods, which would otherwise affect people living downstream of the project. When dams create large reservoirs and eliminate rapids, boats may be used to improve transportation.

Greenhouse gas emissions

Since no fossil fuel is consumed, emission of carbon dioxide (a greenhouse gas) from burning fuel is eliminated. While some carbon dioxide is produced during manufacture and construction of the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity generation. However, there may be other sources of emissions as discussed below.


Recreational users must exercise extreme care when near hydroelectric dams, power plant intakes and spillways.[4]

Environmental damage

Hydroelectric projects can be disruptive to surrounding aquatic ecosystems. For instance, studies have shown that dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream, even though most dams in salmon habitat have fish ladders installed. Salmon spawn are also harmed on their migration to sea when they must pass through turbines. This has led to some areas transporting smolt downstream by barge during parts of the year. Turbine and power-plant designs that are easier on aquatic life are an active area of research.

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. Since turbines are often opened intermittently, rapid or even daily fluctuations in river flow are observed. For example, in the Grand Canyon, the daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to erosion of sand bars. Dissolved oxygen content of the water may change from pre-construction conditions. Water exiting from turbines is typically much colder than the pre-dam water, which can change aquatic faunal populations, including endangered species. Some hydroelectric projects also utilize canals, typically to divert a river at a shallower gradient to increase the head of the scheme. In some cases, the entire river may be diverted, leaving a dry riverbed. Examples include the Tekapo and Pukaki Rivers.

Large-scale hydroelectric dams, such as the Aswan Dam and the Three Gorges Dam, have created environmental problems both upstream and downstream.

A further concern is the impact of major schemes on birds. Since damming and redirecting the waters of the Platte River in Nebraska for agricultural and energy use, many native and migratory birds such as the Piping Plover and Sandhill Crane have become increasingly endangered.

Greenhouse gas emissions

The reservoirs of hydroelectric power plants in tropical regions may produce substantial amounts of methane and carbon dioxide. This is due to plant material in flooded areas decaying in an anaerobic environment, and forming methane, a very potent greenhouse gas. According to the World Commission on Dams report, where the reservoir is large compared to the generating capacity (less than 100 watts per square meter 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.[5]

In boreal reservoirs of Canada and Northern Europe, however, greenhouse gas emissions are typically only 2 to 8 percent of any kind of conventional thermal generation. A new class of underwater logging operation that targets drowned forests can mitigate the effect of forest decay.[6]

Population relocation

Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned. In many cases, no amount of compensation can replace ancestral and cultural attachments to places that have spiritual value to the displaced population. Additionally, historically and culturally important sites can be flooded and lost. Such problems have arisen at the Three Gorges Dam project in China, the Clyde Dam in New Zealand, and the Ilısu Dam in Southeastern Turkey.

Dam failures

Failures of large dams, while rare, are potentially serious—the Banqiao Dam failure in China resulted in the deaths of 171,000 people and left millions homeless, more than some estimates of the death toll from the Chernobyl disaster. Dams may be subject to enemy bombardment during wartime, sabotage, and terrorism. Smaller dams and micro hydro facilities are less vulnerable to these threats.

The creation of a dam in a geologically inappropriate location may cause disasters like the one of the Vajont Dam in Italy, where almost 2000 people died, in 1963.

Comparison with other methods of power generation

Hydroelectricity eliminates the flue gas emissions from fossil fuel combustion, including pollutants such as sulfur dioxide, nitric oxide, carbon monoxide, dust, and mercury in the coal.

Compared to the nuclear power plant, hydroelectricity generates no nuclear waste, nor nuclear leaks. Unlike uranium, hydroelectricity is also a renewable energy source.

Compared to wind farms, hydroelectricity power plants have a more predictable load factor. If the project has a storage reservoir, it can be dispatched to generate power when needed. Hydroelectric plants can be easily regulated to follow variations in power demand.

Unlike fossil-fueled combustion turbines, construction of a hydroelectric plant requires a long lead-time for site studies, hydrological studies, and environmental impact assessment. Hydrological data up to 50 years or more is usually required to determine the best sites and operating regimes for a large hydroelectric plant. Unlike plants operated by fuel, such as fossil or nuclear energy, the number of sites that can be economically developed for hydroelectric production is limited; in many areas the most cost effective sites have already been exploited. New hydro sites tend to be far from population centers and require extensive transmission lines. Hydroelectric generation depends on rainfall in the watershed, and may be significantly reduced in years of low rainfall or snowmelt. Utilities that primarily use hydroelectric power may spend additional capital to build extra capacity to ensure sufficient power is available in low water years.

Hydroelectric facts

Hydroelectric Reservoir Vianden, Luxembourg

In parts of Canada (the provinces of British Columbia, Manitoba, Ontario, Quebec, and Newfoundland and Labrador) hydroelectricity is used so extensively that the word "hydro" is used to refer to any electricity delivered by a power utility. The government-run power utilities in these provinces are called BC Hydro, Manitoba Hydro, Hydro One (formerly "Ontario Hydro"), Hydro-Québec, and Newfoundland and Labrador Hydro respectively. Hydro-Québec is the world's largest hydroelectric generating company, with a total installed capacity (2005) of 31,512 megawatts (MW).

Oldest hydroelectric power stations

  • Cragside, Rothbury, England, completed 1870.
  • Appleton, Wisconsin, U.S., completed 1882. A waterwheel on the Fox river supplied the first commercial hydroelectric power for lighting to two paper mills and a house, two years after Thomas Edison demonstrated incandescent lighting to the public. Within a matter of weeks of this installation, a power plant was also put into commercial service at Minneapolis.
  • Duck Reach, Launceston, Tasmania. Completed 1895. The first publicly owned hydroelectric plant in the Southern Hemisphere. Supplied power to the city of Launceston for street lighting.
  • Decew Falls 1, St. Catharines, Ontario, Canada, completed August 25, 1898. Owned by Ontario Power Generation. Four units are still operational. Recognized as an IEEE Milestone in Electrical Engineering & Computing by the IEEE Executive Committee in 2002.
  • It is believed that the oldest Hydro Power site in the United States is located on Claverack Creek, in Stottville, New York. The turbine, a Morgan Smith, was constructed in 1869, and installed 2 years later. It is one of the earliest water wheel installations in the United States and also generated electricity. It is owned today by Edison Hydro.
  • The oldest continuously operated commercial hydroelectric plant in the United States is built on the Hudson River at Mechanicville, New York. The seven 750 kW units at this station initially supplied power at a frequency of 38 Hz, but later were increased in speed to 40 Hz. It went into commercial service July 22,1898. It is now being restored to its original condition and remains in commercial operation. [7]

Countries with the most hydroelectric capacity

The ranking of hydroelectric capacity is either by actual annual energy production or by installed capacity power rating. A hydroelectric plant rarely operates at its full power rating over a full year; the ratio between annual average power and installed capacity rating is the load factor. The installed capacity is the sum of all generator nameplate power ratings.

Country Annual Hydroelectric Energy Production Installed Capacity Load Factor
People's Republic of China 416,700 Gigawatt hours (GWh) 128,570 MW 0,37
Canada 356,930 GWh 68,974 MW 0,59
Brazil 336,800 GWh 69,080 MW 0,56
USA 289,980 GWh 79,511 MW 0,42
Russia 167,000 GWh 45,000 MW 0,42
India 125,126 GWh 33,600 MW 0,43
Norway 119,000 GWh 27,528 MW 0,49
Japan 88,500 GWh 27,229 MW 0,37
France 56,100 GWh 25,335 MW 0,25

Country, annual hydroelectricity production, installed capacity (2006 data including pumped storage schemes)

Largest hydroelectric power stations

The La Grande Complex in Quebec, Canada, is the world's largest hydroelectric generating system. The eight generating stations of the complex have a total generating capacity of 16,021 MW. The Robert Bourassa station alone has a capacity of 5,616 MW. A ninth station (Eastmain-1) is currently under construction and will add 480 MW to the total. Construction on an additional project on the Rupert River was started on January 11, 2007. It will add two stations with a combined capacity of 888 MW.

Name Country Year of completion Total Capacity Max annual electricity production
Itaipú Brazil/Paraguay 1984/1991/2003 14,000 MW 93.4 TeraWatt (TW)-hours
Three Gorges Dam China 2004* 11,200 MW (July 2007); 22,500 MW (when complete) 84.7 TW-hours
Guri Venezuela 1986 10,200 MW 46 TW-hours
Grand Coulee United States 1942/1980 6,809 MW 22.6 TW-hours
Sayano Shushenskaya Russia 1983 6,721 MW 23.6 TW-hours
Krasnoyarskaya Russia 1972 6,000 MW 20.4 TW-hours
Robert-Bourassa Canada 1981 5,616 MW
Churchill Falls Canada 1971 5,429 MW 35 TW-hours
Bratskaya Russia 1967 4,500 MW 22.6 TW-hours
Ust Ilimskaya Russia 1980 4,320 MW 21.7 TW-hours
Tucurui Brazil 1984 4,240 MW
Yaciretá Argentina/Paraguay 1998 4,050 MW 19.2 TW-hours
Ertan Dam China 1999 3,300 MW (550MW×6) 17.0 TW-hours
Gezhouba Dam China 1988 3,115 MW 17.01 TW-hours
Nurek Dam Tajikistan 1979/1988 3,000 MW
La Grande-4 Canada 1986 2,779 MW
W. A. C. Bennett Dam Canada 1968 2,730 MW
Chief Joseph Dam United States 1958/73/79 2,620 MW
Volzhskaya (Volgogradskaya) Russia 1961 2,541 MW 12.3 TW-hours
La Grande-3 Canada 1984 2,418 MW
Atatürk Dam Turkey 1990 2,400 MW
Zhiguliovskaya (Samarskaya) Russia 1957 2,300 MW 10.5 TW-hours
Iron Gates Romania/Serbia 1970 2,280 MW 11.3 TW-hours
John Day Dam United States 1971 2,160 MW
La Grande-2-A Canada 1992 2,106 MW
Aswan Egypt 1970 2,100 MW
Tarbela Dam Pakistan 1976 2,100 MW
Hoover Dam United States 1936/1961 2,080 MW
Cahora Bassa Mozambique 1975 2,075 MW
Karun III Dam Iran 2007 2,000 MW 4.1 TW-hours

* Powered first 14 water turbogenerators

Major schemes in progress

Name Maximum Capacity Country Construction started Scheduled completion Comments
Three Gorges Dam 22,400 MW China December 14 1994 2009 Largest power plant in the world. First power in July 2003, with 10,500MW installed by June 2007.
Xiluodu Dam 12,600 MW China December 26 2005 2015
Baihetan Dam 12,000 MW China 2009 2015 Still in planning
Wudongde Dam 7,000 MW China 2009 2015 Still in planning
Longtan Dam 6,300 MW China July 1 2001 December 2009
Xiangjiaba Dam 6,000 MW China November 26 2006 2009
Jinping 2 Hydropower Station 4,800 MW China January 30 2007 2014 To build this dam, only 23 families and 129 local residents need to be moved. It works with Jinping 1 Hydropower Station as a group.
Laxiwa Dam 4,200 MW China April 18 2006 2010
Xiaowan Dam 4,200 MW China January 1 2002 December 2012
Jinping 1 Hydropower Station 3,600 MW China November 11 2005 2014
Pubugou Dam 3,300 MW China March 30 2004 2010
Goupitan Dam 3,000 MW China November 8 2003 2011
Boguchan Dam 3,000 MW Russia 1980 2012
Son la Dam 2,400 MW Vietnam 2005
Bureya Dam 2,010 MW Russia 1978 2009
Ilısu Dam 1,200 MW Turkey August 5 2006 2013 one of the Southeastern Anatolia Project Dams in Turkey

Those 10 dams in China will have total generating capacity of 70,400 MW (70.2 gigawatt (GW)) when completed. For comparison purposes, in 1999, the total capacity of hydroelectric generators in Brazil, the third country by hydroelectric capacity, was 57.52 GW.


  1. REN21, Renewables Global Status Report 2006 Update. Retrieved July 23, 2007.
  2. Saving Iceland, Summer of International dissent against Heavy Industry. Retrieved July 23, 2007.
  3. International Water Power and Dam Construction, Beyond Three Gorges in China. Retrieved July 23, 2007.
  4. Ontario Power Generation, Stay Clear, Stay Safe. Retrieved July 23, 2007.
  5. Duncan Graham-Rowe, Hydroelectric power's dirty secret revealed, New Scientist. Retrieved July 23, 2007.
  6. Inhabitant, “REDISCOVERED” WOOD & THE TRITON SAWFISH. Retrieved July 23, 2007.
  7. IEEE Industry Applications Magazine, "The Historic Mechanicville Hydroelectric Station Part 1: The Early Days," Jan/Feb. 2007.

ISBN links support NWE through referral fees

External links

All links retrieved January 22, 2018.


New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

The history of this article since it was imported to New World Encyclopedia:

Note: Some restrictions may apply to use of individual images which are separately licensed.