Devices that charge or store electricity during periods of high energy supply and low demand and then release that electricity when it is most needed (during periods of low supply and high demand). These systems enable project developers to exploit wind and sunlight when they are available by allowing energy produced by these projects to be stored and used at a later date. These devices address the main criticisms of wind and solar energy sources, their seasonality and intermittency.

BESS can be used to provide back-up capacity to ensure electric grid reliability and resilience. They can also be built on a standalone basis to charge from the power grid or as a co-located system that charges directly from a generator. Most battery storage systems currently installed in the US are lithium-ion batteries, but other battery technologies are being explored and developed.

For more information, see Practice Note, Renewable Energy Project Development Issues: Siting Considerations for Co-Located Energy Storage.