Mini-hydro

Small hydro is the development of hydroelectric power on a scale suitable for local community and industry, or to contribute to distributed generation in a regional electricity grid. The definition of a small hydro project varies, but a generating capacity of 1 to 20 megawatts (MW) is common. In contrast many hydroelectric projects are of enormous size, such as the generating plant at the Three Gorges Dam at 22,500 megawatts or the vast multiple projects of the Tennessee Valley Authority.

Small hydro projects may be built in isolated areas that would be uneconomic to serve from a national electricity grid, or in areas where a national grid does not exist.

The use of the term "small hydro" varies considerably around the world, the maximum limit is usually somewhere between 10 and 30 MW. While a minimum limit is not usually set, the US National Hydropower Association specifies a minimum limit of 5 MW. The "small hydro" description may be stretched up to 50 MW in the United States, Canada and China. Small hydro can be further subdivided into mini hydro, usually defined as 100 to 1,000 kilowatts (kW), and micro hydro which is 5 to 100 kW. Micro hydro is usually the application of hydroelectric power sized for smaller communities, single families or small enterprise. The smallest installations are pico hydro, below 5 kW.

Since small hydro projects usually have correspondingly small civil construction work and little or no reservoir, they are seen as having a relatively low environmental impact compared to large hydro.

According to a report by REN21, during 2008 small hydro installations grew by 28% over year 2005 to raise the total world small hydro capacity to 85 gigawatts (GW). Over 70% of this was in China (with 65 GW), followed by Japan (3.5 GW), the United States (3 GW) and India (2 GW).

China planned to electrify a further 10,000 villages between 2005 and 2010 under their China Village Electrification Program, including further investments in small hydro and photovoltaics. By 2010, China had 45,000 small hydro installations, especially in rural areas, producing 160 Twh annually. Over 50% of the world's potential small hydro power was found in Asia however the report noted "It is possible in the future that more small hydropower potential might be identified both on the African and American continents".

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Wikipedia