Pumped hydro storage
Energy storage that pumps water to an upper reservoir when electricity is cheap or abundant and releases it through turbines when power is needed; the largest form of grid storage worldwide.
Pumped storage hydropower (PSH) accounts for most of the world's installed grid storage energy capacity: about 180–190 GW of power capacity (IHA 2024), storing on the order of 9,000 GWh, though batteries are now adding power capacity faster. China, Japan and the United States have the largest fleets.
Stored energy depends on water volume and head:
One million m³ at 400 m head stores about 1,090 MWh before losses. Key parameters:
- Round-trip efficiency: 70–85% for modern plants
- Duration: typically 6–20 hours at full power, with some seasonal schemes far longer
- Response: generating mode in about 1–3 minutes from standstill, seconds from spinning; variable-speed and ternary units can also regulate power while pumping
- Lifetime: 50–100 years for civil works, with electromechanical overhauls every 30–40 years
Most plants use reversible Francis pump-turbines. Large examples include Fengning (China, 3.6 GW), Bath County (US, about 3 GW) and Dinorwig (UK, 1.7 GW, famous for black-start capability).
Constraints are geographical and financial: suitable topography, long build times (5–10 years) and high upfront capital. Closed-loop "off-river" schemes, mapped globally by ANU, avoid river impacts and are gaining interest as long-duration storage for high-renewable grids.
Related terms
All terms →- Hydraulic head
The vertical height difference between the water surface at a hydropower intake and the turbine outlet or tailwater, which together with flow determines available power.
- Francis turbine
A reaction-type hydro turbine with fixed blades in which water enters radially and leaves axially; the most widely installed design, used for medium heads of about 30 to 700 m.
- Round-trip efficiency
The share of energy put into a storage system that can be recovered on discharge, measured at a defined boundary (cell, DC, or AC grid connection).
- Long-duration energy storage (LDES)
Storage able to discharge at rated power for roughly 8 hours or more, covering multi-day lulls and seasonal imbalances that 2–4 hour batteries cannot.
- Black start
The process of restoring a power system after a total or partial blackout using units that can start without power from the grid.
- LCOS (Levelized Cost of Storage)
The average cost per MWh discharged over a storage asset’s lifetime, including investment, operation, charging energy and efficiency losses.