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Encyclopedia > Hydroelectric
Hydroelectric dam diagram
The waters of Llyn Stwlan, the upper reservoir of the Ffestiniog Pumped-Storage Scheme in north Wales, can just be glimpsed on the right. The lower power station has four water turbines which can generate 360 megawatts of electricity within 60 seconds of the need arising.

Hydroelectricity, hydroelectric power, is a form of hydropower (the use of energy released by water falling, flowing downhill, moving tidally, or moving in some other way) to produce electricity. Specifically, the mechanical energy of the moving water is converted to electrical energy by a water turbine driving an generator. Most hydroelectric power is currently generated from water flowing downhill, but a few tidal harnesses exist that draw power from the tide. Hydroelectric power is usually generated at dams or other places where water descends from a height, or coasts with a large tidal swing (such as the Bay of Fundy). Hydroelectricity is a renewable energy source, since the water that flows in rivers has come from precipitation such as rain or snow, and tides are driven by the rotation of the earth.

The energy that may be extracted from water depends not only on the volume but on the difference in height between the water crest (or source) and the water outflow. This height difference is called the head. The amount of potential energy in water is directly proportional to the head. For this reason, it is advantageous to build dams as high as possible to produce the maximum electrical energy.

While many hydroelectric schemes supply public electricity networks, some projects were created for private commercial purposes. For example, aluminium processing requires substantial amounts of electricity, and in Britain's Scottish Highlands there are examples at Kinlochleven and Lochaber, designed and constructed during the early years of the 20th century. Similarly, the 'van Blommestein' lake, dam and power station were constructed in Suriname to provide electricity for the Alcoa aluminium industry.

In many parts of Canada (particularly the provinces of Quebec and to some extent Ontario) 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 two provinces are called "Hydro Quebec" and "Ontario Hydro" (although Ontario uses nuclear power as well).



Hydroelectric power, using the potential energy of rivers, now supplies 20% of world electricity. Norway produces virtually all of its electricity from hydro, while Iceland produces 83% of its (2004). Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it can be readily stored during off hours (in fact, pumped-storage hydroelectric reservoirs are sometimes used to store other electricity for use during peak hours). It is not a major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations.

Advantages and disadvantages

The chief advantage of hydro systems is their capacity to handle seasonal (as well as daily) high peak loads. In practice the utilisation of stored water is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands. Times of drought can cause severe problems, since water replenishment rates may not keep up with desired usage rates.

Concerns have been raised that large hydroelectric projects might be disruptive to the surrounding ecosystem. 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.

The creation of large bodies of water involved with damming rivers for Hydroelectric power is also considered an environmental risk. For example, pine needles that fall in the water can turn the water acidic.

Hydro-electric facts


Largest hydro-electric power stations



These are installed power figures. If rated by annual power production, the order is different.

Countries with the most hydro-electric capacity

  • Canada, 341,312 GWh (66,954 MW installed)
  • USA, 319,484 GWh (79,511 MW installed)
  • Brazil, 285,603 GWh (57,517 MW installed)
  • China, 204,300 GWh (65,000 MW installed)
  • Russia, 160,500 GWh (44,000 MW installed)
  • Norway, 121,824 GWh (27,528 MW installed)
  • Japan, 84,500 GWh (27,229 MW installed)
  • India, 82,237 GWh (22,083 MW installed)
  • France, 77,500 GWh (25,335 MW installed)

These are 1999 figures and include pumped-storage schemes.

See also

  Results from FactBites:
Hydroelectricity (1320 words)
Hydroelectricity is obtained from the ENERGY contained in falling water; it is a renewable, comparatively nonpolluting energy source and Canada's largest source of ELECTRIC-POWER GENERATION.
Early use of hydroelectric generation was limited by the capacity of the generating station, which was governed by the waterpower resource (streamflow and net height of fall), or by the electric-lighting load near the station.
Hydroelectric generation was not developed in Saskatchewan until the early 1960s, when the S Saskatchewan R Development provided control and regulation of the province's major river system.
Hydroelectric generator - Patent 7042113 (3246 words)
A hydroelectric generator having a fixed axle, at least one transmission axle parallel to the fixed axle, and a transmission system configured to rotate the transmission axle about the fixed axle and to apply a force to at least one driven member of a device for generating electricity.
The hydroelectric generator of claim 7, wherein the third mechanical transmission system is configured to drive a first driven member of a device for generating electricity in a first direction and a second driven member of a device for generating electricity in a second direction.
The hydroelectric generator of claim 8, further comprising a device for generating electricity, wherein a first driven member of the device for generating electricity is coupled to a coil of wire and a second driven member of the device for generating electricity is coupled to a magnet.
  More results at FactBites »



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