Pumped-Storage Hydroelectricity
Pumped-storage hydroelectricity (PSH) moves water between two reservoirs at different elevations: it pumps water uphill when power is cheap and releases it through reversible turbines to generate when demand peaks. With 70-80% round-trip efficiency and facility lifespans of decades to over a century, it is by far the world's largest grid storage technology, limited mainly by the need for suitable hilly terrain.
Pumped-storage hydroelectricity (PSH) is a form of Grid Energy Storage that holds energy as the gravitational potential of water between two reservoirs at different elevations. When electricity is cheap or abundant, water is pumped from the lower to the upper reservoir; when demand and prices rise, that water flows back down through turbine generators. Many plants use reversible Francis turbine units that act as both pump and generator. The round-trip efficiency of PSH is typically 70 to 80 percent. Despite that being lower than lithium-ion, PSH dominates because of cost and longevity: as of 2020 it accounted for roughly 95 percent of active grid storage worldwide, with installed capacity over 181 GW, growing to around 200 GW and about 9,000 GWh by the mid-2020s. Facilities commonly run for decades and in some cases over a century, three to five times longer than utility-scale batteries, which is why their lifetime cost per kWh is hard to beat. The key constraint is geography: PSH needs hilly country with two reservoir sites near each other at different elevations. Even so, a global greenfield atlas has identified over 800,000 candidate sites, far more than would be needed for a fully renewable grid. The largest plants include Fengning in China (3,600 MW, 40 GWh), Bath County in the United States (about 3,000 MW, 24 GWh), and Ludington (1,872 MW). China leads global capacity by a wide margin. PSH is one of the mechanical storage technologies, alongside Compressed-Air Energy Storage and the Energy Dome CO2 Battery.