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Small hydro is the development of hydroelectric power on a scale serving a small community or industrial plant. The definition of a small hydro project varies, but a generating capacity of 1 to 20 megawatts (MW) is generally accepted, which aligns to the concept of distributed generation. The "small hydro" description may be stretched up to in the United States, Canada and China. In contrast many hydroelectric projects are of enormous size, such as the generating plant at the Hoover Dam of 2,074 MW or the vast multiple projects of the Tennessee Valley Authority. 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. Small hydro plants may be connected to conventional electrical distribution networks as a source of low-cost renewable energy. Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a network, or in areas where there is no national electrical distribution network. Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro. This decreased environmental impact depends strongly on the balance between stream flow and power production. One tool that helps evaluate this issue is the Flow Duration Curve or FDC. The FDC is a Pareto curve of a stream's daily flow rate vs. frequency. Reductions of diversion help the river's ecosystem, but reduce the hydro system's Return on Investment (ROI). The hydro system designer and site developer must strike a balance to maintain both the health of the stream and the economics. Plants with reservoir, i.e. small storage and small pumped-storage hydropower plants, can contribute to distributed energy storage and decentralized peak and balancing electricity. Such plants can be built to integrate at the regional level intermittent renewable energy sources. ==Growth== 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).〔(Renewables Global Status Report 2006 Update ), ''REN21'', published 2006, accessed 2007-05-16〕 China plans to electrify a further 10,000 villages by 2010 under their China Village Electrification Program using renewable energy, including further investments in small hydro and photovoltaics.〔 A 2013 report by the International Center on Small Hydro Power and UNIDO found that installed small hydro power around the globe was estimated at 75 GW and potential small hydro power was approximately 173 GW. China has made small hydro a priority and in 2010 had 45,000 installations, especially in rural areas, producing 160 Twh annually.〔https://www.irena.org/DocumentDownloads/Publications/RE_Technologies_Cost_Analysis-HYDROPOWER.pdf pg12〕 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".〔(【引用サイトリンク】title=World Small Hydro Power Development Report 2016 )〕〔(【引用サイトリンク】title=UNIDO, ICSHP Launch Small Hydropower Knowledge Sharing Portal )〕〔(【引用サイトリンク】title=Small Hydropower, a promising technology for rural electrification )〕 In the mountains and rain forests of British Columbia, Canada there are a great many sites suitable for hydro development. However environmental concerns towards large reservoirs has halted large dam construction since the late 1980s. The solution was to offer guaranteed contracts to independent companies who have built 100 run of the river projects under 50MW. Power production without reservoirs varies dramatically though the year, but allows large dams to retain water and average out capacity. In 2014 they produced 18,000 GWh from 4,500 MW of capacity.〔https://www.bchydro.com/energy-in-bc/acquiring_power/meeting_energy_needs/how_power_is_acquired.html〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Small hydro」の詳細全文を読む スポンサード リンク
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