Pumpedhydro

Pumped hydro, or pumped water storage, is a form of hydroelectric energy storage that uses two reservoirs at different elevations to store and release energy. It is one of the most mature and widely deployed methods of grid-scale storage and can provide large-scale power quickly when needed.

The system typically consists of an upper and a lower reservoir connected by a tunnel or pipeline and reversible pump-turbine units. During periods of excess electricity supply, pumps move water from the lower to the upper reservoir, storing energy as gravitational potential energy. When demand rises, water is released back to the lower reservoir through the turbines to generate electricity. Pumped hydro can be implemented in naturally occurring topographies (open-loop) or as a closed-loop system using entirely man-made reservoirs.

Performance characteristics vary by project, but typical round-trip efficiency is in the range of 70% to 85%. Power capacity often ranges from hundreds of megawatts to several gigawatts, with energy storage capacities from tens to hundreds of gigawatt-hours. The technology offers fast response, long cycle life, and relatively low operating costs, making it suitable for load balancing, peak shifting, frequency regulation, and supporting high-renewable electricity systems.

Limitations include geographic and water-resource requirements, high capital costs, and long development timelines. Environmental and ecological impacts, land use, evaporation losses, and potential seismic considerations are also relevant. Despite these factors, pumped hydro remains the dominant form of utility-scale energy storage by installed capacity, with global installations totaling around the low hundreds of gigawatts in recent years.