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

, 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

in a

reservoir

. At night, the

water

flows back in the opposite direction towards an initial

reservoir

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

water

behind it in the upper

reservoir

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

water

to flow through. As the

water

moves downhill to the lower

reservoir

, it passes through the turbines and generates mechanical energy

then

the generator turns mechanical energy into electricity, which is

subsequently

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

water

from the lower

reservoir

back to the upper

reservoir

for reuse.