The chart below shows the value of one country’s exports in various categories during 2015 and 2016. The table shows the percentage change in each category of exports in 2016 compared with 2015.

The illustrations depict how hydroelectric power stations generate

electricity

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.

Overall

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, the flow chart illustrates that the process is cyclical, showing how

water

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is stored in a

reservoir

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, used to produce

electricity

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during the day, and

then

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recycled back to the original

reservoir

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at night.

To begin

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with, river

water

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is collected in a high-level

reservoir

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impounded by the dam. During the day, the intake is opened, allowing

water

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to flow into the power station. As it passes through reversible turbines, the

water

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drives a generator, which produces

electricity

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. The

electricity

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is transmitted via power lines and supplied to the national grid,

while

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the used

water

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is released into a lower-level

reservoir

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. In the subsequent stages, at night,

water

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stored in the lower

reservoir

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is pumped back into the upper

reservoir

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for reuse.

This

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is achieved by reversing the turbines, which operate as pumps to lift the

water

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back to the high-level

reservoir

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.