Pumped-storage hydroelectricity is a method of storing energy by using two water reservoirs at different elevations. During periods of low electricity demand, excess energy is used to pump water from the lower reservoir to the upper one. This process converts electrical energy into potential energy. When electricity demand increases, the stored water is released back down to the lower reservoir, passing through turbines that generate electricity. This system allows for quick adjustments to energy supply, making it a valuable tool for balancing the grid and integrating renewable energy sources like solar and wind.