Most of the utility-scale battery systems used for energy storage on the U.S. electric grid use lithium-ion (Li-ion) batteries, which are known for their high-cycle efficiency, fast response times, and high energy density. Nearly all of the utility-scale battery systems installed in the United States in the past five years use lithium-ion technology.

Unlike most power plants, which are characterized by their power capacity alone, batteries are characterized by their power capacity and energy capacity. Power capacity is the maximum instantaneous power output available, measured in megawatts (MW). Utility-scale systems have at least one megawatt of power capacity. Energy capacity is the maximum energy that can be stored or discharged during one charge-discharge cycle, measured in megawatthours (MWh).

At the end of 2018, the United States had 862 MW of operating utility-scale battery storage power capacity and 1,236 MWh of battery energy capacity. By either measure, more than 90% of operating battery capacity used lithium-ion based batteries. Increased demand for lithium-ion batteries in electronics and vehicles has led to continued performance improvements and cost reductions for those batteries.

The oldest utility-scale battery storage system operating in the United States is the Battery Energy Storage System project in Fairbanks, Alaska. This project, which came online in 2003, uses nickel-based batteries in a system with 40 MW of power capacity and 11 MWh of energy capacity. Nickel-based batteries tend to have higher energy densities but lower cycle lives. Other battery chemistries, such as sodium and lead-acid, have been installed in a few applications, but these chemistries have not shown significant or sustained growth.

Newer battery technologies, such as vanadium flow batteries, continue to be developed to achieve higher capacities, improve safety, and increase cycle life at lower costs. In 2017, two vanadium flow battery systems were installed in the United States, totaling 4.4 MW of power capacity and 16 MWh of energy capacity.

Assuming currently planned battery system additions are completed and no current operating capacity is retired, total utility-scale battery storage power capacity in the United States could exceed 2,500 MW by 2023.

Principal contributor: Vikram Linga