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 during times of low use. It also allows us to keep our coal-fired and nuclear plants running longer and more efficiently.
When 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.