National Renewable Energy Laboratory

Learning About Renewable Energy

Pumped Hydropower

Pumped hydro facilities use off-peak electricity to pump water from a lower reservoir into one at a higher elevation. When the water stored in the upper reservoir is released, it is passed through hydraulic turbines to generate electricity.

The off-peak electrical energy used to pump the water up hill can be stored indefinitely as gravitational energy in the upper reservoir. Thus, two reservoirs in combination can be used to store electrical energy for a long period of time, and in large quantities.

Switching large coal and nuclear power stations on and off frequently is an inefficient way to run them. Pumped hydro energy storage can be used to smooth out the demand for baseload generation from such plants. It can also be used to provide emergency power injection to the grid when a plant goes offline unexpectedly.