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Low head hydro power applications use tidal flows or rivers with a head of or less to produce energy.〔http://www.expertglossary.com/water/definition/low-head-hydroelectric〕 These applications may not need to dam or retain water to create hydraulic head. Using the drop in a river or tidal flows to create electricity may provide a renewable energy source that will have a minimal impact on the environment. ==Comparison to conventional hydro== Most current hydroelectric projects use a large hydraulic head to power turbines to generate electricity. The hydraulic head either occurs naturally, such as a waterfall, or is created by constructing a dam in a river valley, creating a reservoir. Using a controlled release of water from the reservoir drives the turbines. The costs and environmental impacts of constructing a dam can make traditional hydroelectric projects unpopular in some countries. ''Damless hydro'' captures the kinetic energy of rivers, channels, spillways, irrigation systems, tides and oceans without the use of dams.〔 〕 Construction of a dam and reservoir may have harmful environmental effects. For example, the damming of a river may “block the movement both of fish upstream to spawn and of silt downstream to fertilize fields”.〔 〕 Where sites aren't cleared “the vegetation overwhelmed by the rising water decays to form methane – a far worse greenhouse gas than carbon dioxide”, particularly in the tropics.〔 Since no dam is required, low-head hydro may dramatically reduce the following: * The safety risks (of having a dam), avoiding the risk of a flash flood caused by a breached dam * Environmental and ecological complications * *Need for fish ladders * Regulatory issues * The initial cost of dam engineering and construction * Maintenance * *Removing Silt accumulation. However, low-head units are necessarily much smaller in capacity than conventional large hydro turbines, requiring many more to be built for a given annual energy production, with some of the costs of small turbine/generator units being offset by lower civil construction costs. Just as for large hydro, not every site can be economically and ecologically developed; sites may be too far from customers to be worth installation of a transmission line, or may lie in areas particularly sensitive for wildlife. Another potentially promising type of low head hydro power is dynamic tidal power, a novel and unapplied method to extract power from tidal movements. Although a dam-like structure is required, no area is enclosed, and therefore most of the benefits of 'damless hydro' are retained, while providing for vast amounts of power generation. 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「Low head hydro power」の詳細全文を読む スポンサード リンク
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