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 reservoirWhen power from the plant is needed, water stored in an upper reservoir is released into an underground tunnel.
The water rushes down the intake tunnel.
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.
The water then flows through a discharge tunnel into a lower reservoir.
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.
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.
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.