Hydroelectricity

Hydroelectricity, or hydroelectric power, is a form of hydropower, (i.e.,the use of energy released by water falling, flowing downhill, moving tidally, or moving in some other way) to produce electricity. Specifically, the kinetic energy of the moving water is converted to electrical energy by a water turbine driving a 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 most 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 Hydro" respectively.

Importance

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 requirements(2004), Austria produces 67 % of all electricity generated in the country from hydro (over 70 % of its requirements). 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-peak hours (in fact, pumped-storage hydroelectric reservoirs are sometimes used to store electricity produced by thermal plants 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 utilization of stored water is sometimes complicated by demand for irrigation which may occur out of phase with peak electricity demand. Times of drought can cause severe problems, since water replenishment rates may not keep up with desired usage rates.

Reservoirs created by hydroelectric schemes often provide excellent leisure facilities for water sports, and become a tourist attraction in themselves.

Concerns have been raised by environmentalists that large hydroelectric projects might 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.

Generation of hydroelectric power can also have an impact on the downstream river environment. First, water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks. Second, since turbines are often opened intermittently, rapid or even diurnal fluctuations in river flow are observed. 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 preceding conditions. Finally, 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 may produce substantial amounts of methane and carbon dioxide. This is due to plant material in newly flooded and re-flooded areas being inundated with water, decaying in an anaerobic environment, allowing for the formation of methane, a very potent greenhouse gas. The methane is released into the atmosphere once the water is discharged from the dam and turns the turbines. In some cases, where the reservoir is large compared to the dam capacity (less than 100 watts per square metre of surface area) and no clearing of the reservoir growth has occured, effectively as much greenhouse gas may be released from a dam for electricity generation as for generating the equivalent amount of energy from burning oil [1].

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.

Hydro-electric facts

Oldest

• 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.

Largest hydro-electric power stations

Operational

• Itaipu, Brazil/Paraguay, completed 1983, 12,600 MW
• Guri, Venezuela, completed 1986, 10,300 MW
• Grand Coulee, USA, completed 1942, expanded in 1980 to 6,900 MW
• Sayano-Shushenk, Russia, completed 1983, 6,400 MW
• Churchill Falls, Canada, completed 1971, 5,428 MW, expandable to 9,252 MW

In Progress

• Three Gorges Dam, China, First power July 2003,Scheduled completion, 2009, 18,200 MW

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.

References

1. New Scientist report on greenhouse gas production by hydroelectric dams.

See also

• Energy directory compiles various energy technologies and issues featured at Wikipedia, with emphasis on clean, renewable energy systems.
• wave power
• tidal power
• List of reservoirs and dams
• Tennessee Valley Authority
• Small hydro
• Pumped-storage hydroelectricity
• Environmental concerns with electricity generation
• Roll on Columbia (song)

External links

• World Commission on Dams report on environmental and social effects of large dams, including discussion of greenhouse gas emissions
• Hydroelectricity – Water potential powered systems, focusing on non-impactive small hydro. (FreeEnergyNews.com)
• River Energy – river turbine systems, not dam. (FreeEnergyNews.com)