The battery storage capacity in the US more than tripled to reach 4.6 GW in 2021 (from 1.4 GW in 2020) and increasingly broadened out of ancillary services, according to the American Energy Information Administration (EIA). The amount of battery storage capacity grew 220%, driven by the commissioning of 106 utility-scale systems with 3.2 GW of capacity. About 78% of all storage capacity added 2021 was built in regional transmission organization (RTO) service territories.
Ancillary services such as frequency response and ramping/spinning reserve were the dominant use cases of battery energy storage over the last decade, however, in 2021, batteries were increasingly reported to provide additional services like arbitrage, load management, and response to excess solar and wind generation, reducing power losses from curtailment. Batteries were also paired with solar and wind energy to address intermittent cycles of generation. Over 93% of battery capacity that went online in 2021 was co-located with solar.