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How Do Pumped-Storage Hydro Plants Work?

1. Upper Reservoir
When power from the plant is needed, water stored in an upper reservoir is released into an underground tunnel.

2. Intake Tunnel
The water rushes down the intake tunnel.

3. Turbines
The force of the water drives huge turbines, which are underground at the base of a dam. The spinning turbines are connected to large generators, which produce the electricity.

4. Discharge Tunnel
The water then flows through a discharge tunnel into a lower reservoir.

5. Recharging
When demand for electricity is low, the turbines spin backward and pump the water back up into the upper reservoir to make it available to generate electricity when it's needed.