Pumped-Storage Hydro Plants

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 over and over again. Water power uses no fuel in the generation of electricity, making for very low operating costs.

Duke Energy operates two pumped-storage plants – Jocassee and Bad Creek. Pumped storage can be employed to capture unused electricity, like that from non-dispatchable renewables like solar, during times of low use. This ability to capture unused electricity, then use that stored energy, helps us minimize carbon emissions created by other forms of generation that may have otherwise been used during times of high energy demand. It also allows us to keep our coal-fired and nuclear plants running longer and more efficiently.

Learn more about Duke Energy's proposed Bad Creek expansion.

Upper reservoir

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

Intake tunnel

The water rushes down the intake tunnel.

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.

Discharge tunnel

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

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.

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.