FAQs Pumped-Storage Hydro

Electricity itself cannot be stored, but the potential to create electricity can (e.g., in a battery). Pumped-storage plants provide a way for Duke Energy to store the potential energy of water. This enables us to meet our customers’ future needs by taking advantage of surplus electricity when not all of our electricity is being used.

These plants are vital to Duke Energy’s ability to quickly deliver low-cost electricity in the Carolinas.

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

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.

Duke Energy’s first pumped-storage plant, Jocassee Hydroelectric Station, was completed in 1975. This was followed by Bad Creek Hydroelectric Station, which began commercial operation in 1991.