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March 25, 2022

Duration of utility-scale batteries depends on how they’re used

U.S. utility-scale battery storage energy capacity by duration and application
Source: U.S. Energy Information Administration, Annual Electric Generator Report

At the end of 2021, the United States had 4,605 megawatts (MW) of operational utility-scale battery storage power capacity, according to our latest Preliminary Monthly Electric Generator Inventory. Power capacity refers to the greatest amount of energy a battery can discharge in a given moment. Batteries used for grid services have relatively short average durations. A battery's average duration is the amount of time a battery can contribute electricity at its nameplate power capacity until it runs out. Batteries used for electricity load shifting have relatively long durations.

We calculate a battery’s duration by using the ratio of energy capacity (measured in megawatthours [MWh]) to power capacity (in MW). Energy capacity refers to the total amount of energy these batteries can store. Our energy capacity data come from our most recent Annual Electric Generator Report, which contains data through the end of 2020. When fully charged, battery units built through 2020 could produce their rated nameplate power capacity for about 3.0 hours on average before recharging.

Our Annual Electric Generator Report also contains information on how energy storage is used by utilities. Utility-scale battery storage can be used primarily in two ways: serving grid applications and allowing electricity load shifting. Our Battery Storage in the United States: An Update on Market Trends report contains a full description and breakdown of all of the grid service and electricity load shifting applications reported to us.

Battery operators report that more than 40% of the battery storage energy capacity operated in the United States in 2020 could perform both grid services and electricity load shifting applications. About 40% performed only electricity load shifting, and about 20% performed only grid services.

Batteries with a duration of less than two hours are considered short-duration batteries, and almost all can provide grid services that help maintain grid stability. Batteries providing grid services discharge power for short periods of time, sometimes even for only seconds or minutes, which is why it can be economical to deploy short-duration batteries. Most battery capacity installed in the late 2010s was made up of short-duration batteries used for grid services, but that trend has changed over time.

Batteries with a duration between four hours and eight hours are typically cycled once per day and are used to shift electricity from times of relatively low demand to times of high demand. In a region with relatively high solar power capacity, daily-cycling batteries can store solar electricity midday and discharge that electricity during peak electricity consumption hours in the evening when solar power is declining.

According to planned installations compiled in our Preliminary Monthly Electric Generator Inventory, we expect battery storage to increase by 10 gigawatts (GW) by the end of 2023. More than 60% of this battery capacity is intended to be paired with solar power plants. As of 2020, most installed co-located battery storage at solar facilities work to shift electricity loads and have average durations of four hours or more.

Principal contributor: Vikram Linga