Pumped hydro

Water batteries for solar and wind power

Pumped storage hydropower is a form of clean energy storage that is ideal for electricity grids reliant on solar and wind power.

The technology absorbs surplus energy at times of low demand and releases it when demand is high.

How it works

Pumped hydropower storage uses the force of gravity to generate electricity using water that has been previously pumped from a lower source to an upper reservoir. 

The water is pumped to the higher reservoir at times of low demand and low electricity prices. At times of high demand - and higher prices - the water is then released to drive a turbine in a powerhouse and supply electricity to the grid.

The energy storage capacity of a pumped hydro facility depends on the size of its two reservoirs, while the amount of power generated is linked to the size of the turbine.

A facility with two reservoirs roughly the size of two Olympic swimming pools, and a 500 metre height difference between them, could provide a capacity of 3 megawatts (MW) and store up to 3.5 megawatt hours (MWh) of electricity.

There are two main types of pumped hydro:

·      Open-loop: with either an upper or lower reservoir that is continuously connected to a naturally flowing water source such as a river.

·      Closed-loop: an ‘off-river’ site that produces power from water pumped to an upper reservoir without a significant natural inflow.

Figure: A closed loop or 'off-river' pumped storage hydropower project


World's biggest battery

Pumped storage hydropower is the world's largest battery technology, accounting for over 94 per cent of installed global energy storage capacity, well ahead of lithium-ion and other battery types.

The International Hydropower Association (IHA) estimates that pumped hydro projects worldwide store up to 9,000 gigawatt hours (GWh) of electricity.

Recent studies suggest there is significant potential for scaling up global pumped hydro capacity, including from more than 600,000 identified off-river sites.

Gravity storage, grid-scale

The rapid growth in variable renewable energy (VRE) sources such as solar and wind is increasing the need for stable, reliable storage solutions that can operate at utility-scale.

The flexibility pumped hydro provides through its storage and ancillary grid services is seen as increasingly important in securing stable power supplies.

Pumped hydro offers services such as system inertia, frequency control, voltage regulation, storage and reserve power with rapid mode changes, and black-start capability. All of these are vital to support the ever-growing proportion of variable renewables.

Pumped hydro excels at long discharge duration and its high power capacity will be crucial in avoiding curtailment, reducing transmission congestion, and reducing overall costs and emissions in the power sector.

In addition, pumped hydro enjoys several distinct advantages over other forms of energy storage due to its long asset life, low-lifetime cost and independence from raw materials.

Future potential

According to IHA's Hydropower Status Report, total installed pumped storage hydropower capacity was estimated at 158 GW in 2019.

Multiple studies have identified vast potential for pumped storage sites worldwide and there is growing research on possibilities for retrofitting disused mines, underground caverns, non-powered dams and conventional hydro plants.

As a result of a resurgence of interest in the technology, with more than 100 projects in the pipeline, IHA estimates that pumped hydropower storage capacity is expected to increase by almost 50 per cent – to about 240 GW by 2030.

Obstacles to pumped storage hydropower include existing market regulations and policy frameworks which fail to incentivise new developments.

The flexibility and storage services provided by pumped storage hydropower are not yet adequately valued in many countries around the world, reducing private sector investment and holding back potential new projects.

Tracking projects

IHA's Pumped Storage Tracking Tool maps the locations and vital statistics for existing and planned pumped storage projects. It is the most comprehensive online resource on the world's 'water batteries'.

The tool shows the status of a pumped storage project, its installed generating and pumping capacity, and its actual or planned date of commissioning.

Policy recommendations

Unless the world scales up investment in pumped hydro to support fast-growing solar and wind power, policy-makers may need to get used to blackouts or risk reverting to fossil fuels.

This was the conclusion of the International Forum on Pumped Storage Hydropower, a coalition of 13 governments led by the U.S. Department of Energy, with former Australian Prime Minister Malcolm Turnbull, the International Hydropower Association (IHA) and involving more than 70 multilateral banks, research institutes, NGOs and public and private companies.

The forum was formed in November 2020 to research practical recommendations for governments and markets aimed at addressing the urgent need for green, long-duration energy storage in the clean energy transition. Its recommendations were launched in September 2021 during the World Hydropower Congress Learn more.

Further reading

Read IHA's working paper, The World’s Water Battery: Pumped Hydropower Storage and the Clean Energy Transition.

The paper shows that pumped hydro needs to secure new sources of reliable and long term revenue to attract investment, particularly in liberalised energy markets.

Latest statistics

Download the World Hydropower Outlook for latest pumped storage statistics from IHA's hydropower database.

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