Model Answer

The process shows how electricity is generated in a hydroelectric power station. In general, the diagram can be broadly separated into day and night stages with the daylight stages involving the generation of electricity from a river and storage of water in a reservoir. At night the water flows back in the other direction towards an initial reservoir and the river.

The first stage of the process involves channelling the river into a high-level reservoir backed up by a dam. There is an intake area leading to the power station that is open during the day and closes at night. Water flows during the day to generate electricity through the power station turbines and the resulting electricity is sent to a national grid through power lines while the water then continues to a low-level reservoir.

The reversible turbines that operate the generator during the day allow the station to pump the water in the low-level reservoir back into the high-level reservoir for use the next day.