Pumped-storage hydroelectricity

We can use water to save power.

This works with two lakes. One lake is high up on a hill.

When we have extra power, we pump water up. This fills the top lake. We do this when people use less power.

When people need more power, we let the water fall. The falling water turns a wheel. This makes new power for us to use.

This is like a giant battery made of water.

It helps us keep the lights on all day.

These plants can work for many, many years. They are very good at saving energy.

Pumped-storage hydroelectricity is a way to save electric power.

It works like a giant battery made of water. This system uses two reservoirs, which are large pools of water. One pool sits at a high place. The other sits at a low place.

When people do not need much power, we use extra electricity to run pumps. These pumps move water from the low pool to the high pool. This stores power as gravitational potential energy. This is power that comes from the water's height.

When people need more power, we let the water flow down. The moving water turns a turbine. A turbine is a machine with blades that spins when water hits it. This spinning makes electricity. This helps balance the power grid. It can even help use energy from wind and sun.

These plants are very big. They make up about 94% of the world's long-term energy storage. They can last for many decades. Some can even work for over a century. This is much longer than most other types of batteries.

Pumped-storage hydroelectricity is a way to save electric power for later.

It works like a giant battery made of water. This system helps balance the power grid when demand changes. It can save extra energy from wind and solar power. These sources can be intermittent, meaning they do not always work. This technology makes sure we have power when we need it most.

The way it works involves two water reservoirs at different heights.

One reservoir sits at a high elevation. The other sits at a lower elevation. When there is extra electricity, pumps move water to the upper reservoir. This stores energy as gravitational potential energy. When people need more power, the water is released. It flows down through turbines to make electricity. This process can happen in just seconds.

Scientists and engineers have used this method for a long time. One example is the Rance tidal power station in France. It was inaugurated in 1966 and can act as a pumped-storage plant. In 1999, the Yanbaru project in Okinawa showed how seawater could be used. Most plants use fresh water instead of salt water. Using seawater is harder because salt can cause corrosion.

These plants are the largest type of energy storage in the world. They account for about 94% of long-duration energy storage capacity. The global capacity is nearly 200 GW. As of 2020, the total installed storage capacity was over 1.6 TWh. Some projects, like Snowy 2.0 in Australia, are very large. China has also built many systems, reaching 106.9 GW by May 2025.

You can think of these plants as a way to smooth out energy. They help steady the electrical network frequency. This is important when using many different types of power sources. Some plants are "closed loop," meaning they do not use natural rivers. They use two man-made pools to keep things simple. This helps plants like coal or nuclear stay efficient. It also helps us use more renewable energy in the future.

Pumped-storage hydroelectricity, often called PSH, is a vital method for storing electric energy. It functions as a massive mechanical battery for the electrical grid. This technology helps balance the load, which is the amount of electricity being used at any given time.

By storing energy, PSH can manage the needs of a changing society. It is especially useful for handling intermittent energy sources. These are sources like wind and solar that do not produce power constantly.

The mechanism of a PSH system relies on gravitational potential energy. A typical plant consists of two water reservoirs located at different elevations. When there is a surplus of low-cost electricity, the system uses that power to run pumps. These pumps move water from the lower reservoir to the upper reservoir. This process stores the energy in the high position of the water.

When electricity demand rises, the stored water is released. The water flows down through turbines to the lower reservoir. As the water moves, it spins the turbines to generate electricity. Many plants use reversible turbine/generator assemblies, such as Francis turbines. These machines can act as both a pump and a generator.

There are different types of PSH systems based on their water sources. Closed-loop systems are pure pumped-storage plants. They use an upper reservoir that has no natural inflows from rivers or streams. These systems are often built in hilly areas using man-made reservoirs. Other systems are called pump-back plants. These utilize a combination of pumped storage and conventional hydroelectric plants. In these cases, the upper reservoir is replenished by natural inflows from a river.

Some projects also use existing bodies of water, which are known as "bluefield" locations. Others use "brownfield" locations, such as disused mines. This flexibility helps engineers find suitable sites for new projects.

Historically, PSH has been a cornerstone of large-scale energy storage. The Rance tidal power station in France was inaugurated in 1966. It is unique because it can partially work as a pumped-storage station using seawater. In 1999, the Yanbaru project in Okinawa became the first demonstration of seawater pumped storage. While seawater can be used, it presents challenges like saltwater corrosion and barnacle growth. Most global projects prefer freshwater to avoid these issues. The technology has proven to be very durable over long periods. Some plants have a service life of decades or even over a century. This is three to five times longer than many utility-scale chemical batteries.

The scale of PSH is much larger than other storage technologies. It is the world's largest battery technology. PSH accounts for over 94% of the world's long-duration energy storage capacity. The global installed capacity is nearly 200 GW. According to the International Hydropower Association, PSH projects worldwide store up to 9,000 GWh of electricity. As of 2020, the total installed storage capacity was over 1.6 TWh. China is a major player in this field. By May 2025, China's cumulative battery energy storage installations reached 106.9 GW and 240.3 GWh. The 2025 World Hydropower Outlook reports that 600 GW of new projects are currently under development.

Economic efficiency is a major driver for using pumped storage. The round-trip efficiency, or the energy recovered compared to what was used, is between 70% and 80%. While the plant consumes more energy than it produces, it increases revenue. Operators can buy electricity when prices are low or even negative. They then sell that electricity during peak demand when prices are highest. PSH also provides essential ancillary services to the grid. These include frequency regulation and operating reserves. These services help stabilize the electrical network's frequency and voltage.

Finally, PSH connects to broader goals for a sustainable energy future. It allows base-load plants, like coal or nuclear, to operate at peak efficiency. These plants can run continuously while PSH handles the sudden changes in demand. This coordination is crucial when managing many different types of generators. As more renewable energy enters the grid, PSH becomes even more important. It helps balance the fluctuating output of wind and solar power. The global greenfield pumped hydro atlas suggests there are 800,000 potential sites worldwide. These sites could provide 86 million GWh of storage. This is enough to support a massive transition to renewable electricity.