Hydroelectricity is electricity obtained from hydropower. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator, although less common variations use water's kinetic energy or dammed sources, such as tidal power. Hydroelectricity is a renewable energy source.
The energy extracted from water depends not only on the volume but 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.
While many supply public electricity networks, some hydroelectric projects were created for private commercial purposes. For example, aluminium processing requires substantial amounts of electricity, and often dedicated hydroelectric projects are built to serve aluminium electrolytic plants. In the Scottish Highlands there are examples at Kinlochleven and Lochaber, constructed during the early years of the 20th century. In Suriname, the 'van Blommestein' lake, dam and power station were constructed to provide electricity for the Alcoa aluminum industry.
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 MW.
The major advantage of hydro systems is elimination of the cost of fuel. Hydroelectric plants are immune to price increases for fossil fuels such as oil, natural gas or coal, and do not require imported fuel. Hydroelectric plants tend to have longer 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.
Pumped storage plants currently provide the only commercially important means for energy storage on a scale useful for a utility. Low-value generation in off-peak times occurs because fossil-fuel and nuclear plants cannot be entirely shut down on a daily basis. This energy is used to store water that can be released during high load daily peaks. Operation of pumped-storage plants improves the daily load factor of the generation system.
Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions in themselves. Multi-use dams installed for irrigation, flood control, or recreation, may have a hydroelectric plant added with relatively low construction cost, providing a useful revenue stream to offset the cost of dam operation.
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 smolt are also harmed on their migration to sea when they must pass through turbines. This has led to some areas barging smolt downstream during parts of the year. Turbine and power-plant designs that are easier on aquatic life are an active area of research.
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. Large-scale hydroelectric dams, such as the Aswan Dam and the Three Gorges Dam, have created environmental problems both upstream and downstream.
Generation of hydroelectric power impacts on 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.
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 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. In boreal reservoirs of Canada and Northern Europe, however, greenhouse gas emissions are typically only 2 to 8% of any kind of conventional thermal generation. The contributive effect of forest decay can be mitigated by a new class of underwater logging operation targeting drowned forests.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.
The Dnieper Hydroelectric Station (1927-32) was the centerpiece of Lenin's GOELRO plan.
Recreational users of the reservoir or downstream areas are exposed to hazards due to changing water levels, and must be wary of power plant intakes and spillway operation. Ontario Power Generation's brochure 'Stay Clear, Stay Safe' can be downloaded at www.opg.com/power/hydro/ The brochure describes why people need to exercise extreme care when near hydroelectric dams, stations, and surrounding waterways.
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.
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. 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. Though the dams can be built stronger, at greater cost, they are still prone to sabotage and terrorism. Smaller dams and micro hydro facilities are less vulnerable to these threats.
Oldest hydro-electric power stations:
Cragside, Rothbury, England completed 1870.
Appleton, Wisconsin, USA 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 hydro-electric plant in the Southern Hemisphere. Supplied power to the city of Launceston for street lighting.
Decew Falls 1, St. Catharines, Ontario, Canada completed 25 August 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.
Largest hydro-electric 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.
Countries with the most hydro-electric capacity
Country, total annual hydroelectricity production, total capacity installed
People's Republic of China, 416,700 GWh (128,570 MW installed)(2006)
Canada, 396,700 GWh (68,974 MW installed)
Brazil, 285,603 GWh (57,517 MW installed)(1999)
USA, 260,400 GWh (79,511 MW installed)
Russia, 169,700 GWh (46,100 MW installed)(1999)
India, 125,126 GWh (33,600 MW installed)(2006)
Norway, 119,000 GWh (27,528 MW installed)
Japan, 88,500 GWh (27,229 MW installed)
France, 56,100 GWh (25,335 MW installed)