Pumped storage hydropower (PSH) is a type of hydroelectric energy storage. It is a configuration of two water reservoirs at different elevations that can generate power as water moves down from one to the other (discharge), passing through a turbine. The system also requires power as it pumps water back into the upper reservoir (recharge). PSH acts similarly to a giant battery, because it can store power and then release it when needed. The Department of Energy's "Pumped Storage Hydropower" video explains how pumped storage works.

The first known use cases of PSH were found in Italy and Switzerland in the 1890s, and PSH was first used in the United States in 1930. Now, PSH facilities can be found all around the world! According to the 2021 edition of the Hydropower Market Report, PSH currently accounts for 95% of all utility-scale energy storage in the United States. America currently has 43 PSH plants and has the potential to add enough new PSH plants to more than double its current PSH capacity.

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Pumped-storage hydropower is the most dominant form of energy storage on the electric grid today. It also plays an important role in bringing more renewable resources on to the grid.
U.S. Department of Energy

Open-Loop Versus Closed-Loop Pumped Storage Hydropower

PSH can be characterized as open-loop or closed-loop. Open-loop PSH has an ongoing hydrologic connection to a natural body of water. With closed-loop PSH, reservoirs are not connected to an outside body of water.

Illustration showing open-loop and closed-loop pumped storage hydropower, with the elements of the systems labeled.

The Water Power Technologies Office (WPTO) invests in innovative PSH technologies and research to understand and determine the value of the potential benefits of existing and prospective advanced PSH facilities. Through the HydroWIRES Initiative, WPTO is currently working on projects designed to evaluate and expand hydropower and PSH’s contribution to grid resilience and reliability.

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