Grid-level storage is energy storage connected to an electricity grid and used to meet utility or power-system needs. It takes in electricity, stores it in another form, and later returns electricity or provides another grid service. It is also commonly called grid-scale energy storage or utility-scale energy storage; for batteries, the term is often grid-scale battery energy storage system (BESS). These names describe a role and deployment scale, not one specific technology or battery chemistry.
How grid-level storage works
A storage system charges with electricity from a generator or the grid, holds that energy, then discharges it when needed. It is therefore a secondary source of electricity, not primary generation: it shifts electricity produced elsewhere from one time to another. Charging and discharging are not perfectly efficient, so the system uses more electricity to charge than it returns as electricity, as the U.S. Energy Information Administration explains in its overview of energy storage for electricity generation.
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Storage can also provide services without simply supplying energy over a long period. Depending on its design and operation, it can respond quickly to changes in the grid, help balance supply and demand, and support voltage or frequency management.
What MW, MWh and duration mean
Power and energy describe different limits of a storage system. The U.S. Department of Energy explains that a megawatt-hour is the unit used to describe how much energy a battery can store in its Solar-Plus-Storage 101 explainer.
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- Power capacity (MW): the maximum rate at which the system can deliver electricity at a given moment.
- Energy capacity (MWh): the amount of energy the system can store.
- Duration: how long it can deliver power at a stated rate, subject to usable energy and operating limits.
For example, the U.S. Department of Energy uses a 60 MW battery with four hours of storage to illustrate a system with 240 MWh of energy capacity. The 60 MW figure alone does not say how long the system can sustain output: the MWh capacity and operating conditions matter too.
Which technologies count as grid storage?
Grid storage is a portfolio of technologies with different response speeds, durations, efficiencies and siting needs. The U.S. Government Accountability Office describes several technologies used on the U.S. grid in its report on utility-scale energy storage.
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- Batteries: can respond quickly and provide short-duration flexibility and grid services. Battery systems may use different chemistries and designs.
- Pumped-storage hydropower: pumps water uphill when electricity is available and releases it through turbines to generate electricity later. It depends on suitable sites and water infrastructure.
- Compressed-air storage: uses electricity to compress air for later use in producing power.
- Flywheels: store energy as rotational motion and can respond rapidly, though their useful discharge duration differs from that of longer-duration systems.
- Thermal storage: stores heat or cold; in some grid-related applications, it is paired with concentrated solar power.
These options are not interchangeable in every project. Choosing among them depends on the required service, discharge duration, response speed, energy losses, site, project lead time, cost and connection to the existing grid. Battery projects also depend on chemistry and cycling needs.
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What grid storage is used for
Storage can move electricity from hours when it is available or less valuable to hours when demand is higher or supply is tighter. The International Energy Agency describes storage as one source of flexibility in its Electricity 2026 report; grid operators and utilities may use systems for several purposes, including:
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- Balancing and frequency regulation: adjusting power quickly to help match supply and demand.
- Shifting renewable energy: storing electricity generated when wind or solar output is high and discharging it later.
- Peak supply and capacity: delivering stored energy during periods of high demand, within the system’s power and energy limits.
- Network support: in some cases, deferring a transmission or distribution upgrade or providing backup capability.
One installation may serve more than one application at different times, depending on grid needs and operating arrangements. The U.S. Energy Information Administration’s battery application data reports overlapping uses, so the categories should not be treated as exclusive shares.
Does a grid need batteries to use renewable energy?
No single amount of battery storage is required for every power system, and batteries are not the only way to manage variable wind and solar output. NREL and Sandia National Laboratories say the need depends on the generation mix, how flexibly other generators can operate, transmission connections to neighboring systems, and the timing of demand and renewable production across hours, days and seasons. Other flexibility resources may be more economical in some systems, as their Grid-Scale Battery Storage FAQ explains.
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Storage can contribute to reliability, but it does not guarantee reliability by itself. Its contribution depends on available stored energy, discharge duration, system conditions and the other resources available when demand is high.
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Battery deployment is growing rapidly, but battery statistics are not totals for every form of grid storage. The International Energy Agency reports that 108 GW of battery capacity was added worldwide in 2025, 40% more than in 2024; around 80% of those new batteries were utility-scale. The IEA also reports that around 90% of 2025 battery deployments used lithium-iron phosphate (LFP), which it describes as typically cheaper and better suited to frequent cycling than more energy-dense chemistries often used in electric vehicles. These are global battery figures for 2025, not measurements of all storage technologies.
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For a historical U.S. reference, the EIA reported that utility-scale battery systems had 8,842 MW of nameplate power capacity and 11,105 MWh of energy capacity at the end of 2022. Those figures describe the U.S. fleet at that date; they should not be read as current or global totals.
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