Pumped Storage Hydropower
Water batteries for the renewable energy sector
Pumped storage hydropower (PSH) is a form of clean energy storage that is ideal for electricity grid reliability and stability. PSH complements wind and solar by storing the excess electricity they create and providing the backup for when the wind isn’t blowing, and the sun isn’t shining.
PSH absorbs surplus energy at times of low demand and releases it when demand is high.
How it works
Think of it like a giant battery. When the grid has surplus power—like on a sunny or windy day—the water is pumped up to the higher reservoir (charging the battery). Later, when demand increases and the supply decreases, such as during the evening when people are cooking and the sun has gone down, the water is released to generate power (discharging the battery).
There are also seasonal variations. In winter when the days are shorter and the electricity demand is higher, PSH can again come to the rescue.
The amount of energy a PSH project can store depends on the size and height difference of the two reservoirs it is made up of, while the amount of electricity it can produce at once depends on the size of the turbines.
For example, 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. The Fengning Pumped Storage Power Station is the one of largest of its kind in the world, with twelve 300 MW reversible turbines, 40-60 GWh of energy storage and 11 hours of energy storage, their reservoirs are roughly comparable in size to about 20,000 to 40,000 Olympic swimming pools. The station could power approximately 20 million homes per day in nearby regions, depending on the local household energy usage rates.
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.
World's biggest battery
Pumped storage hydropower is the world's largest battery technology, with a global installed capacity of nearly 200 GW – this accounts for over 94% of the world’s long duration energy storage capacity, well ahead of lithium-ion and other battery types.
Water in a PSH system can be reused multiple times, making it a rechargeable water battery.
PSH systems typically have large capacities and can run for long durations. This is crucial because they can provide reliable power when demand is high. They’re also very flexible, meaning they can quickly increase or decrease the amount of power they generate. As more renewable energy sources like solar and wind power come online, which can be unpredictable, PSH systems help balance out the grid by adjusting to changes in power generation, especially as we electrify more of our energy use.
In the US, the 3 GW Bath County PSH holds 11 hours of energy storage which provides power to 750,000 homes. But many have been built to exceed 11 hours, providing 20+ hours of energy storage.
The International Hydropower Association (IHA) estimates that PSH projects worldwide store up to 9,000 gigawatt hours (GWh) of electricity.
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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 and flexible storage solutions that can operate at utility-scale.
The flexibility pumped storage hydropower provides through its storage and ancillary grid services is seen as increasingly important in securing stable power supplies.
Pumped storage hydropower 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.
PSH excels at long discharge duration and its high-power capacity is crucial in avoiding curtailment, reducing transmission congestion, and reducing overall costs and emissions in the power sector.
In addition, PSH enjoys several distinct advantages over other forms of energy storage due to its long asset life, low-lifetime cost, and independence from raw materials.
Also given its water storage capacity, it is important for flood and drought control. It is mitigation for, and resilient to, climate change.
Future potential
PSH is currently experiencing a renaissance, with world leaders recognising it as a flexible, reliable and renewable long duration energy storage option.
The 2024 World Hydropower Outlook reported that 214 GW of pumped storage hydropower projects are currently at various stages of development. Recent atlases compiled by the Australian National University identify 600,000 identified off-river sites suggesting almost limitless potential for scaling up global PSH capacity.
Retrofitting
There is growing research and evidence for the benefits to retrofitting disused mines, underground caverns, non-powered dams and conventional hydropower plants.
Barriers
The market alone will not deliver all the PSH that is needed to keep on track with net zero pathways. Markets need to be regulated and policies developed to reward flexibility and ensure a return on the initial high capital costs.
The flexibility and storage services provided by pumped storage hydropower are not yet adequately valued in many countries around the world, which has limited private sector investment and is holding back potential new projects. Investors need confidence, which governments can provide through designing electricity markets with flexibility in mind and to ensuring long-term revenue visibility.
International Forum on Pumped Storage Hydropower
The International Forum on Pumped Storage Hydropower was formed in 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. This forum was formed by a coalition of 13 governments led by the U.S. Department of Energy, with former Australian Prime Minister Malcolm Turnbull, the IHA and involving more than 70 multilateral banks, research institutes, NGOs and public and private companies.
In September 2025 the next International Forum on Pumped Storage Hydropower will be held in Paris, France. The Forum will culminate in a two-day global conference on pumped storage hydropower in Paris in 2025, bringing world experts and leaders together to discuss the critical role of pumped storage hydropower in the future energy mix and present recommendations for enabling its uptake. Register your interest.
- International Forum on Pumped Storage Hydropower - Executive Summary - September 2021
- Working Paper on Sustainability of Pumped Storage Hydropower
- Pumped Storage Hydropower Capabilities and Costs
- Pump it up: Recommendations for urgent investment in pumped storage hydropower to back the clean energy transition
- Innovative Pumped Storage Hydropower Configurations and Uses
Further reading
Access the new guidance note here: Enabling new pumped storage hydropower: A guidance note for key decision makers to de-risk pumped storage investments
Latest statistics
Download the World Hydropower Outlook for the latest pumped storage statistics from IHA's hydropower database.
