The diagram below shows how electricity is generated in hydroelectric power station. Summarise the information by selecting and reporting the main features, and make comparisons where relevant.

The diagram describes the way in which electricity is produced in a hydroelectric power station.

Overall

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, the production of hydroelectricity is cyclical and the process is broadly distributed into day and night stages. The daylight stages involve electricity production from a river and storage of

water

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in a

reservoir

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. At night, the

water

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flows back in the opposite direction towards an initial

reservoir

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and the river. First of all, the dam stores river

water

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behind it in the upper

reservoir

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that has an intake at the bottom. During the day, the intake is open and it allows

water

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to flow through. As the

water

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moves downhill to the lower

reservoir

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, it passes through the turbines and generates mechanical energy

then

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the generator turns mechanical energy into electricity, which is

subsequently

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delivered to the national grid through power lines. During the night, the turbines act as pumps that pump

water

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from the lower

reservoir

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back to the upper

reservoir

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for reuse.