What Is Pumped Hydro Storage, and How Does It Work?

While utility-scale batteries are growing in numbers, pumped hydro storage is the most used form of energy storage on the grid today. There are 22 gigawatts of pumped hydro energy storage in the US today, which represents 96% of all energy storage in the US.

Source: The C Three Group's North American Electric Generation Project Database

What Is Pumped Hydro Storage? 

First used in the US nearly a century ago, pumped hydro storage is a means of storing power, and it’s the only commercially viable method of long-term storage. 

Commonly, these facilities store 10 hours of power, compared to typically two to six hours of power for batteries. (See how grid-scale batteries work.)

How Does Pumped Hydro Storage Work? 

Pumped hydro storage moves water from an upper reservoir through a turbine to a lower reservoir. This generates electricity for the grid. Generally, pumped hydro storage moves water to the upper reservoir during times when electricity is in low demand or is cheap and stores it there for times when electricity is in high demand or is expensive. 

There are two main types of pumped hydro storage: open loop and closed loop. An open loop system is connected to a natural water source, and a closed loop system is not.

How Efficient Is Pumped Hydro Storage? 

Pumped hydro storage is 80% efficient, which means that 20% of its power is lost during a cycle.

A facility with two reservoirs roughly the size of two Olympic swimming pools with a 1,640-foot height difference could store up to 3.5 megawatt hours of electricity. 

What Are the Challenges of Pumped Hydro Storage? 

Firstly, not every area is ideal for pumped hydro storage. To build pumped hydro storage, you need two reservoirs at two different elevations. In addition, some locations that are ideal for this method of storing energy aren’t near large urban areas, making the transmission of the electricity it generates a challenge. 

Secondly, installations of pumped hydro storage can be expensive and face lengthy regulatory processes. This is partly why there haven’t been as many installations of pumped hydro storage in the US recently. (America currently has 43 pumped storage hydropower facilities.)

Source: The C Three Group, a part of Yes Energy

*2023 capacity is still being confirmed due to a lag in reporting from our data sources

Thirdly, there is a human and environmental cost, because while it doesn’t generate carbon emissions, pumped hydro storage can flood. Dams bottling up water in the reservoirs can also affect fish, but there are technologies in the works to help fish pass through turbines safely. 

What Are the Advantages of Pumped Hydro Storage? 

Pumped hydro storage is a flexible resource that can consume power during times of low grid demand and when excess generation is available at lower costs.

Plus, closed-loop pumped hydro storage systems generate electricity with the least amount of greenhouse gases, according to the National Renewable Energy Laboratory.

Conclusion

While there are challenges in integrating pumped hydro storage in the grid, it can assist in supplying power to the grid in times when renewable energy isn’t available. 

Yes Energy provides power grid data to companies working to create solutions and services to make the grid more efficient, reliable, and sustainable. Browse our list of partners and see the work they are doing to build solutions for power markets. 

If you’d like to understand more about where current hydro plants are located or are being built, explore our New Build Dataset or contact us.