How does pumped hydroelectric storage work?

Pumped hydro stores energy by pumping water to an upper reservoir when electricity is cheap/abundant and releasing it through turbines to generate when needed. Round-trip efficiency is 70-85%. It provides: large-scale storage (GWh capacity), long duration (hours to days), rapid response for grid services, and long asset life (50+ years). Requirements include suitable topography (elevation difference) and water availability. It remains the dominant grid-scale storage technology globally, though new projects face environmental and siting challenges.