Hydropower in the United States is used extensively for power system flexibility and resilience. In many parts of the country, hydropower provides more frequency regulation and reserves than its share of installed capacity. In nearly every balancing area assessed, hydropower was more extensively utilized for hourly ramping flexibility than any other resource. Hydropower represents less than 6.7% of U.S. electricity generation capacity but provides approximately 40% of black start resources.

U.S. hydropower capacity continues to grow through upgrades to existing plants and other types of innovative new projects. Hydropower capacity has increased by a net of 431 MW since 2017, with total net growth of 1,688 MW from 2010 to 2019, mostly through capacity increases at existing facilities, new hydropower in conduits and canals, and by powering non-powered dams (NPDs). At the end of 2019, an additional 1,490 MW, from 217 projects, were in the U.S. development pipeline, 93% of proposed capacity from powering NPDs and expanding existing facilities.

Pumped Storage Hydropower (PSH) contributes 93% of grid storage in the United States and it is growing nearly as fast as all other storage technologies combined. Forty-three PSH plants with a total power capacity of 21.9 GW and estimated energy storage capacity of 553 GWh accounted for 93% of utility-scale storage power capacity (GW) and more than 99% of electrical energy storage (GWh) in 2019. Almost as much PSH capacity was added from 2010 to 2019 (1,333 MW), mostly from upgrades to existing plants, as the combined installed capacity of all other forms of energy storage in the United States (1,675 MW).

PSH continues to be the preferred least cost technology option for 4–16 hours duration storage. Energy storage cost for 4–16 hours duration is even lower for compressed air energy storage (CAES), but there are only two CAES projects installed worldwide (built in 1978 and 1991) versus more than 150 PSH projects.

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