Hydropower, or hydroelectric power, is one of the oldest and largest sources of renewable energy, which uses the natural flow of moving water to generate electricity. Hydropower currently accounts for 28.7% of total U.S. renewable electricity generation and about 6.2% of total U.S. electricity generation. 

While most people might associate the energy source with the Hoover Dam, a huge facility harnessing the power of an entire river behind its wall, hyropower facilities come in all sizes. Some may be very large, but they can be tiny too, taking advantage of waterflows in municipal water facilities or irrigation ditches. They can even be “damless,” with diversions or run-of-river facilities that channel part of a stream through a powerhouse before the water rejoins the main river. Whatever the method, hydropower is much easier to obtain and more widely used than most people realize. In fact, all but two states (Delaware and Mississippi) use hydropower for electricity, some more than others. For example, in 2020, about 66% of the state of Washington’s electricity came from hydropower. 

In a study led by the National Renewable Energy Laboratory on hydropower flexibility, preliminary analysis found that the firm capacity associated with U.S. hydropower’s flexibility is estimated to be over 24 GW. To replace this capability with storage would require the buildout of 24 GW of 10-hour storage, which is more than all the existing storage in the United States today. Additionally, in terms of integrating wind and solar, the flexibility presented in existing U.S. hydropower facilities could help bring up to 137 gigawatts of new wind and solar online by 2035.


Hydropower technologies generate power by using the elevation difference, created by a dam or diversion structure, of water flowing in on one side and out, far below, on the other. The Department of Energy’s “Hydropower 101” video explains how hydropower works and highlights some of the research and development efforts of the Water Power Technologies Office (WPTO) in this area.


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 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 93% 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.


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

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.