Hydroelectric power 2011

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We have used running water as an energy source for thousands of years, mainly to grind corn.The first house in the world to be lit by hydroelectricity was Cragside House, in Northumberland, England, in 1878. In 1882 on the Fox river, in the USA, hydroelectricity produced enough power to light two paper mills and a house.

Nowadays there are many hydro-electric power stations, providing around 20% of the world'selectricity. The name comes from "hydro", the Greek word for water

A dam is built to trap water,usually in a valley where there is an existing lake. Water is allowed to flowthrough tunnels in the dam, to turn turbines andthus drive generators. Notice that the dam is much thicker at the bottom thanat the top, because the pressure of the water increases withdepth.Hydro-electric power stations can produce a great deal of power verycheaply.

Although there are many suitablesites around the world, hydro-electric dams are very expensive to build.However, once the station is built, the water comes free of charge, and thereis no waste or pollution. Gravitational potential energy isstored in the water above the dam. Because of the great height of thewater, it will arrive at the turbines athigh pressure, which means that we can extract a great deal of energy from it.The water then flows away downriver as normal. In mountainous countries such asSwitzerland and New Zealand, hydro-electric power provides more than half ofthe country's energy needs. An alternative is to build the station next to afast-flowing river. However with this arrangement the flow of the water cannotbe controlled, and water cannot be stored for later use. Advantage Once the dam is built, the energy is virtually free. No waste or pollution produced.Much more reliable than wind, solar or wave power. Water can be stored above the dam ready to cope with peaks in demand.Hydro-electric power stations can increase to full power very quickly, unlike other power stations. Electricity can be generated constantly.

Disadvantges The dams are very expensive to build.

    However, many dams are also used for flood control or irrigation, so     building costs can be shared. Building a     large dam will flood a very large area upstream, causing problems for animals     that used to live there. Finding a     suitable site can be difficult - the impact on residents and the     environment may be unacceptable. Water     quality and quantity downstream can be affected, which can have an impact     on plant life.