As solar and other renewable energy resources expand across the U.S. power system, storing electricity has become an increasingly important part of how energy is generated, managed, and delivered.
A battery energy storage system (BESS) allows electricity to be stored when it is available and discharged when it is needed. This capability can help businesses manage energy demand, allow renewable energy projects to shift generation to different times of day, and provide utilities with services that support grid operations.
Battery storage is already expanding rapidly in the United States. According to the U.S. Energy Information Administration (EIA), U.S. utility-scale battery storage reached nearly 52 GW of nameplate capacity by June 2026. That followed average annual expansion of approximately 70% over the previous three years.
Understanding how these systems work, their major components, and their applications can help solar professionals and businesses make better decisions when evaluating energy storage.
Table of Contents
What is a battery energy storage system?
A battery energy storage system is a collection of batteries and supporting electrical equipment designed to store electricity and release it later.
Unlike a power plant that produces electricity from a primary energy source, a battery stores electricity that has already been generated. That electricity may come directly from the power grid or from a generation resource such as a solar installation.
The EIA defines two important measurements for energy storage:
- Power capacity, measured in kilowatts (kW), megawatts (MW), or gigawatts (GW), represents the maximum amount of power the system can supply at a given time.
- Energy capacity, measured in kilowatt-hours (kWh), megawatt-hours (MWh), or gigawatt-hours (GWh), represents the total amount of energy the system can store or discharge.
The distinction is important. A 10 MW/40 MWh battery, for example, could theoretically discharge at its full 10 MW power rating for approximately four hours, although actual operating parameters depend on system design and operating limits.
How does a battery energy storage system work?
At its simplest, BESS operation involves three stages: charging, storage, and discharging.
During charging, electricity from the grid or an associated generation source enters the system and is converted into a form that can be stored electrochemically inside the batteries.
The stored energy remains available until the system is instructed to discharge. During discharge, the process is reversed, and electricity is delivered to the facility or grid.
Behind this relatively straightforward process is a network of equipment responsible for controlling and protecting the system.
A typical BESS may include battery cells assembled into modules and racks, a battery management system (BMS), a power conversion system (PCS), thermal management equipment, monitoring and control systems, electrical protection equipment, and fire detection and suppression systems.
Key components of a BESS
| Component | Primary function |
|---|---|
| Battery cells/modules | Physically store electrical energy |
| Battery management system | Monitors battery conditions and manages safe operation |
| Power conversion system | Converts electricity between AC and DC |
| Energy management system | Controls charging, discharging, and system operation |
| Thermal management | Maintains appropriate battery operating temperatures |
| Electrical protection | Helps isolate faults and protect equipment |
| Monitoring system | Tracks performance, operating conditions, and system status |
| Safety systems | Detect and respond to abnormal conditions |
Browse current solar battery inventory on Sunhub when evaluating equipment for a storage project.
The exact configuration depends on system size, battery chemistry, application, manufacturer, and installation requirements.
Common battery technologies
Lithium-ion batteries currently dominate U.S. utility-scale BESS installations. The EIA notes that the majority of utility-scale systems use lithium-ion technology because characteristics such as fast response and high cycle efficiency make it suitable for grid applications.
Within lithium-ion technology, different chemistries are available.
Lithium iron phosphate (LFP) has become particularly important for stationary energy storage. The National Renewable Energy Laboratory’s utility-scale battery storage modeling identifies LFP as the primary lithium-ion chemistry for stationary storage in recent years.
Other storage technologies are also being developed and commercialized, including flow batteries and alternative electrochemical systems. Technology selection ultimately depends on factors including required duration, cycling frequency, cost, operating environment, expected lifetime, safety requirements, and project application.
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What is a battery energy storage system used for?
One of the biggest advantages of battery storage is versatility. The same installation may perform multiple functions rather than serving only one purpose.
Renewable energy integration
Solar generation varies throughout the day and stops at night. Adding batteries allows some electricity generated during high-production periods to be stored for use later.
The EIA reports that pairing or co-locating battery systems with renewable generation has become increasingly common in the United States, with solar accounting for the overwhelming majority of renewable projects co-located with batteries in its historical data.
Peak shaving
Commercial and industrial electricity customers can experience periods of particularly high demand.
Depending on the utility tariff and system configuration, batteries can discharge during these periods to reduce the amount of electricity drawn from the grid. This strategy is commonly known as peak shaving.
Energy arbitrage
Battery systems can also charge when electricity prices are comparatively low and discharge when electricity becomes more valuable.
The economics depend heavily on the electricity market, rate structure, battery efficiency, degradation, and operating strategy.
Grid services
Battery storage can respond extremely quickly to changes in grid conditions, making it useful for applications such as frequency regulation, reserves, voltage support, and load management.
EIA data shows that utility-scale batteries commonly perform multiple roles rather than operating for a single application.
Backup and resilience
Certain BESS configurations can also provide electricity when normal grid supply is interrupted.
However, installing a battery does not automatically mean a facility will have backup power. The system must be specifically designed with the appropriate controls, switching, capacity, and electrical architecture to operate during an outage.
Solar-plus-storage systems
Solar and battery storage are increasingly being developed together.
During periods when a PV system produces more electricity than is immediately required or economically advantageous to export, some of that electricity can be directed into batteries. The stored electricity can then be discharged later.
At utility scale, this can allow project operators to shift solar generation from midday toward periods of higher evening electricity demand.
The scale of this development is significant. In February 2026, the EIA reported that developers planned to add approximately 24 GW of utility-scale battery capacity during the year, alongside 43.4 GW of planned utility-scale solar capacity.
AC-coupled vs. DC-coupled battery storage
Solar-plus-storage projects can use different electrical architectures.
In an AC-coupled system, the solar array and battery generally have separate power conversion equipment and connect on the AC side. This architecture can provide flexibility when adding storage to an existing solar installation.
In a DC-coupled system, the PV array and battery share portions of the DC-side infrastructure before electricity is converted to AC. Depending on the system design, this can reduce some conversion steps and allow energy that might otherwise be clipped by the solar inverter to be captured.
Neither configuration is universally preferable. Project engineers must evaluate system efficiency, existing equipment, interconnection limitations, operating strategy, costs, and project objectives.
What to consider when selecting a BESS
Battery capacity alone does not determine whether a system is appropriate for a project. Buyers, developers, and EPCs should evaluate the complete system and its intended operating profile.
Important considerations include battery chemistry, MW and MWh ratings, discharge duration, round-trip efficiency, expected cycle life, degradation, warranty terms, operating temperature range, BMS and EMS capabilities, inverter compatibility, certifications, safety requirements, installation conditions, service support, and replacement strategy.
System sizing should also begin with the intended application. A battery designed primarily for short-duration grid services may have very different requirements from one intended to shift several hours of solar production.
The growing role of battery storage
Battery storage is quickly becoming a larger part of the U.S. electricity system.
By the end of 2025, operational utility-scale battery capacity had reached 43.6 GW. Another 8.3 GW was added during the first six months of 2026, bringing capacity to nearly 52 GW. Operators reported plans for substantial additional development through the following years.
The expansion reflects the increasing range of roles storage can perform, from supporting renewable generation and managing electricity demand to providing rapid-response grid services.
For solar businesses, developers, EPCs, and commercial energy users, selecting a battery energy storage system therefore requires more than comparing battery capacity or equipment prices. Battery chemistry, power and energy ratings, operating strategy, system architecture, safety, warranties, and long-term performance all contribute to the value of the finished system.
As solar penetration and electricity demand continue to evolve, understanding those factors will become increasingly important when planning energy projects that combine generation, storage, and intelligent energy management.
Frequently asked questions
What does BESS stand for?
BESS stands for battery energy storage system. It describes batteries and the associated equipment used to store electricity and discharge it when required.
What is the difference between MW and MWh in battery storage?
MW measures the battery system’s power output, while MWh measures how much energy it can store. Both values are necessary to understand a BESS’s capabilities.
Can a BESS be connected to solar?
Yes. Battery systems can be paired or co-located with solar installations, allowing solar-generated electricity to be stored and used or exported later.
What batteries are commonly used in BESS projects?
Lithium-ion technology dominates current U.S. utility-scale battery installations, while LFP has become a major chemistry for stationary storage applications.
How long can a battery energy storage system provide power?
It depends on the system’s power and energy capacity. Utility-scale lithium-ion storage is commonly modeled across multiple durations; NREL’s utility-scale battery analysis, for example, considers systems ranging from 2 to 10 hours.
Sources
- U.S. Energy Information Administration, Energy Storage for Electricity Generation
- U.S. Energy Information Administration, Battery Storage in the United States: An Update on Market Trends
- U.S. Energy Information Administration, New U.S. Electric Generating Capacity Expected to Reach a Record High in 2026
- National Renewable Energy Laboratory, Cost Projections for Utility-Scale Battery Storage: 2025 Update
- U.S. Department of Energy, Energy Storage Reports and Data