Pumped-storage hydropower (PSH) is a type of hydroelectric energy storage. It is used to balance the supply from intermittent renewable energy sources like solar and wind. Excess electricity generated during periods of low demand or high supply is used to pump water from a lower reservoir to an upper reservoir. When electricity demand is high, the water is released from the upper reservoir back to the lower reservoir, passing through turbines to generate electricity. This system is particularly effective for long-duration energy storage needs.