Pumped Storage Hydropower

A flexible, dynamic way to store and generate energy

A flexible, dynamic, efficient, and green way to store and deliver large quantities of electricity, 

pumped-storage hydro plants store and generate energy by moving water between two 

reservoirs at different elevations. During times of low electricity demand, such as at night or on weekends, excess energy is used to pump water to an upper reservoir. The turbine acts as a pump, moving water back uphill. During periods of high electricity demand, the stored water is released through turbines. A pumped-storage plant works much like a conventional hydroelectric station, 

except the same water can be used repeatedly. Waterpower uses no fuel in the generation of 

electricity, making for very low operating costs.

Why use pumped-storage plants?

Electricity itself cannot be stored, but the potential to create electricity can (e.g., in a battery). 

Pumped-storage plants provide a way to store the potential energy of water. This enables companies 

to meet their customers’ future needs by taking advantage of surplus electricity when not all the electricity is being used. When does a utility company use pumped-storage plants?

Pumped-storage plants are peaking plants, designed to be used primarily (but not exclusively) during the peak periods – the hottest parts of the summer and the coldest parts of the winter.

Peak periods are the times when customers’ use of electricity is at its greatest, and they are critical times for utility companies and their customers. These plants are designed to produce significant amounts of electricity at just the times when it’s needed most.

How is a pumped-storage plant different from a conventional hydroelectric

plant?

A pumped-storage plant is designed with two reservoirs – upper and lower. Like every other hydroelectric plant, a pumped-storage plant generates electricity by allowing water to fall through a turbine generator. But unlike conventional hydroelectric plants, once the pumped-storage plant generates electricity, it can then pump that water from its lower reservoir back to the upper reservoir. This is done during the off-peak hours, using electricity from another source to run the plant’s pumps, in effect, “storing” that off-peak electricity.

During high demand periods – the hottest parts of the summer and the coldest parts of the winter – alternating generation and pumping cycles can cause significant water level fluctuations in both the upper and lower reservoirs. If the reservoirs are used for recreation, boaters are advised to be aware

of changes in water depth along shorelines and other shallow areas.

Did you know?

- Pumped-storage plants typically generate power during times of peak electric demand.

- Used strategically, pumped storage can be one of the most economical forms of electric power generation.