Electric energy storage is becoming more important to the energy industry with the growth of intermittent generation technologies, such as wind and solar, according to the U.S. Energy Information Administration (EIA).
The energy storage helps to meet fluctuating demand and is often paired with intermittent generation technologies. Storage technologies include batteries and pumped-storage hydropower, which capture energy and store it for later use.
In 2019, U.S. utility-scale batteries operated at a slightly higher efficiency level than pumped-storage facilities. The efficiency level is based on the percentage of electricity put into storage that is later retrieved. The higher the round-trip efficiency, the less energy is lost in storage. The batteries had an average round-trip efficiency of 82%, while the pumped-storage facilities had an average round-trip efficiency of 79%, according to the EIA.
Pumped-storage facilities account for the largest energy storage resource in the United States. As of November, the facilities comprise 21.9 gigawatts of capacity and 92% of the total energy storage capacity in the United States.
In recent years, utility-scale battery capacity has risen rapidly as battery costs have declined. Batteries are often paired with renewables and have become the second-largest source of electricity storage. As of November, utility-scale battery capacity comprised 1.4 gigawatts of operational capacity. Another 4 gigawatts of battery capacity is set to become operational in 2021, according to the EIA.
Though battery storage has a slightly higher round-trip efficiency than pumped storage, pumped-storage facilities typically operate at use levels that are twice as high as batteries. A rise in the duration use for batteries may lead to battery operations with longer output periods. In 2015, the weighted average battery duration was more than 46 minutes. By 2019, the weighted average battery duration doubled to 1.5 hours. Batteries and their capability to provide high levels of round-trip efficiency might become more important as battery storage continues to come online and intermittent renewables account for a larger share of electricity generation.