According to data from the U.S. Energy Information Administration (EIA), in 2019, the US utility-scale battery fleet operated with an average monthly round-trip efficiency of 82%, and pumped-storage facilities operated with an average monthly round-trip efficiency of 79%.
EIA’s ‘Power plant operation report’ provides data on utility-scale energy storage, including the monthly electricity consumption and gross electric generation of energy storage assets, which can be used to calculate round-trip efficiency. The metrics reviewed in the report use the finalised data from the Power Plant Operations Report for 2019 – the most recent year for which a full set of storage data is available.
Pumped-storage facilities are the largest energy storage resource in the USA. The facilities collectively account for 21.9 GW of capacity and for 92% of the country’s total energy storage capacity as of November 2020.
In recent years, utility-scale battery capacity has grown rapidly as battery costs have decreased. As batteries have been increasingly paired with renewables, they have become the second-largest source of electricity storage. As of November 20, 2020, utility-scale battery capacity had 1.4 GW of operational capacity. Another 4.0 GW of battery capacity is scheduled to come online in 2021, according to EIA’s ‘Preliminary Electric Generator Inventory’.
Although battery storage has slightly higher round-trip efficiency than pumped storage, pumped storage facilities typically operate at utilisation factors that are currently twice as high as batteries. Increasing durations among battery applications could shift battery operations toward services that reward longer output periods. For example, in 2015, the weighted average battery duration was a little more than 46 minutes, but by 2019, weighted average battery durations had doubled to 1.5 hours. The role of batteries and their capability to provide high levels of round-trip efficiency may become more important as batteries continue to be deployed and as the intermittent renewables share of the electricity mix grows.
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