Low head hydro power

Low head hydropower applications use tidal flows or rivers with a head of 20 metres (66 ft) or less to produce energy. 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.

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:

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.

A "Hydrokinetic" turbine is an integrated turbine generator to produce electricity in a free flow environment. It does not need a dam or diversion. Instream Energy Systems has coined the phrase Instream Energy Generation Technology or IEGT places turbines in rivers, man made channels, tidal waters, or ocean currents. These turbines use the flow of water to turn them, thus generating electricity for the power grid on nearby land. In effect, IEGT is like planting windmills in the water and is environmentally friendly. While hydrokinetic includes generation from ocean tides, currents and waves, many researchers believe its most practical application in the near term is likely to be in rivers and streams.

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Wikipedia