Pumped-storage hydroelectricity

Did You Know?

• Closed-loop pumped hydro storage has the smallest carbon emissions per unit of storage of all candidates for large-scale energy storage.
• The global greenfield pumped hydro atlas lists more than 800,000 potential sites with combined storage of 86 million GWh.
• The first use of pumped storage was in 1907 in Switzerland, at the Engeweiher pumped storage facility near Schaffhausen.

Basic principle

A pumped-storage system uses two water reservoirs at different heights connected by a turbine and pump assembly. During periods of low electricity demand, excess generation capacity drives pumps to move water to the upper reservoir. When demand rises, water flows back down through turbines to generate electricity. Reversible turbine/generator assemblies, often Francis turbine designs, can operate in both pumping and generating modes. Variable speed operation can improve round-trip efficiency.

Economic efficiency

Energy recovery of 70–80% or more is achievable after accounting for conversion and evaporation losses. This technique is currently the most cost-effective means of storing large amounts of electrical energy, though capital costs and suitable geography are critical factors. The low energy density of pumped storage requires either large water flows or significant height differences between reservoirs. Systems may be economical because they flatten load variations on the power grid, allowing base-load thermal power stations to operate at peak efficiency and reducing the need for flexible peaking plants. Capital costs are relatively high but are offset by long service lives of decades, sometimes exceeding a century—three to five times longer than utility-scale batteries. When electricity prices become negative, pumped hydro operators can earn twice: once when buying electricity to pump water at negative spot prices, and again when selling that electricity later at high prices. Pumped storage also helps stabilize electrical network frequency and provides reserve generation, responding to load changes within seconds.

Potential technologies

Pumped storage can operate with seawater, though saltwater corrosion and barnacle growth pose challenges. The 240 MW Rance tidal power station in France, inaugurated in 1966, can partially function as a pumped-storage station by using turbines to pump seawater into its reservoir during off-peak high tides. The 30 MW Yanbaru project in Okinawa (1999) was the first demonstration of seawater pumped storage but has since been decommissioned. A 300 MW seawater-based project has been proposed for Lanai, Hawaii, and projects have been proposed in Ireland. In northern Chile, a pair of proposed projects would use 600 MW of photovoltaic solar together with 300 MW of pumped storage lifting seawater 600 m up a coastal cliff. Freshwater from river floods can be stored in coastal reservoirs, replacing seawater, and then pumped to uplands via embankment canals and pumped storage stations for energy storage, irrigation, and other purposes. Underground reservoirs have been investigated, including projects using abandoned mines; the Callio site in Finland would utilize the deepest base metal mine in Europe with a 1450 m elevation difference. Cost-per-kilowatt estimates for underground projects can be lower than for surface projects if existing mine space is used.

Worldwide use

In 2009, world pumped storage generating capacity was 104 GW, though other sources claim 127 GW. The European Union had 38.3 GW net capacity (36.8% of world capacity) out of 140 GW of hydropower. Japan had 25.5 GW net capacity (24.5% of world capacity). Australia has 15 GW of pumped storage under construction or development, including 14 sites identified in Tasmania with potential for 4.8 GW, and the Snowy 2.0 project linking two dams for 2 GW capacity and 350 GWh storage. A 2022 scheme at Pioneer-Burdekin in Queensland, with potential for 2.5–5 GW / 120 GWh, was cancelled in 2024, after which power price forecasts increased by 60% for 2035. China has the largest capacity and is expanding, adding 7.75 GW in 2024 to reach 58.69 GW total installed PSH capacity. With over 200 GW under construction or approved, China is on track to exceed its 2030 target of 120 GW.