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Small hydropower plants use falling water to generate electricity.
Water power has been a familiar sight for thousands of years. Most people in the UK probably know an old water mill whether or not it still has its water-wheel that has been converted to another use. But the water that powered a threshing machine or grindstones can be used equally well to generate electricity.
The power available from a hydro-turbine depends on two things: the distance the water falls to the turbine (known as the head) and the amount of water flowing through the turbine.
The combination of these factors means that power can be generated from many types of river, from small but fast-flowing hill streams to large, slow-moving rivers. It also means that hydro-generation equipment has become far more varied than, for example, wind turbines, as developers have tried to abstract power efficiently from a variety of watercourses.
High-head schemes generally use Pelton turbines (named after the American engineer L.A. Pelton). These bear some resemblance to water-wheels, in that the water flows into a series of vessels (known as buckets). They are described as impulse turbines: the impulse is transferred directly from the falling water, turning the turbine and a central shaft that is attached to a generator.
Pelton turbines can range from several centimetres to several metres across, depending on head and flow, but they cannot be used for low-head schemes. Instead, a reaction turbine
