Most utility-scale battery systems used for energy storage on the U.S. electric grid use lithium-ion batteries, and they have high-cycle efficiency, quick response times and high energy density, according to the U.S. Energy Information Administration (EIA). Nearly all of the utility-scale battery systems installed in the United States over the past five years use lithium-ion technology.

Batteries are characterized by their power capacity and energy capacity, according to the EIA. Power capacity is the maximum instantaneous power output available and is measured in megawatts. Utility-scale systems have at least 1 megawatt of power capacity. Energy capacity is the maximum energy that can be stored or discharged during one charge-discharge cycle and is measured in megawatt-hours.

By the end of 2018, the United States had 862 megawatts of operating utility-scale battery storage capacity and 1,236 megawatt-hours of battery energy capacity. More than 90% of operating battery capacity used lithium-ion based batteries. Demand has risen for lithium-ion batteries in electronics and vehicles, and the rise has led to continued improvements in performance and cost reductions for the batteries.

The oldest utility-scale battery storage system operating in the United States is the Battery Energy Storage System project in Fairbanks, Alaska. The system started operating in 2003 and uses nickel-based batteries in a system with 40 megawatts of power capacity and 11 megawatt-hours of energy capacity. Nickel-based batteries have higher energy densities but lower cycle lives. Other types of batteries, such as sodium and lead-acid, have been installed in a few systems, but the use of these types of batteries has not been rising.

Newer technologies, such as vanadium flow batteries, are being developed to improve battery capacity and safety and increase cycle life at lower costs. In 2017, two vanadium flow battery systems were installed in the United States, and they have a total of 4.4 megawatts of power capacity and 16 megawatt-hours of energy capacity.

By 2023, total utility-scale battery storage power capacity in the United States is expected to exceed 2,500 megawatts, according to the EIA. This assumes that planned battery systems are completed and no existing operating capacity is retired.

In July, the largest solar array on city-owned land in Arkansas started operating in Fayetteville. The 10-megawatt system includes 24 megawatt-hours of battery storage, and it’s the only one in the state with onsite utility-scale storage. In March, electric utility Entergy Arkansas and NextEra Energy Resources LLC announced plans to build a 100-megwatt solar plant in White County near Searcy. It would be the largest utility-owned solar plant in Arkansas and feature 30 megawatt-hours of battery storage. It’s expected to start operating by 2021.

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