What is a BESS?
A battery energy storage system (BESS) stores electricity in batteries so it can be used later. It charges when power is cheap or abundant, often during peak renewable generation, and discharges when power is needed, balancing supply and demand on the grid or at a single site.
In plain terms: a BESS is a large rechargeable battery that sits between where electricity is generated and where it is consumed, smoothing out the mismatch between the two. As grids take on more wind and solar, which generate when the weather allows rather than when demand peaks, that smoothing function has gone from useful to essential.
How does a BESS work?
A BESS charges by converting grid AC electricity into DC and storing it in battery cells, then discharges by converting that DC back into AC. Software decides the timing, and a management layer keeps the cells safe.
Four things happen inside a working system. The power conversion system (PCS) handles the AC-to-DC and DC-to-AC conversion. The cells store and release the energy. The battery management system (BMS) watches voltage, temperature and state of charge on every cell to keep them balanced and safe. The energy management system (EMS) is the brain, deciding when to charge and discharge based on electricity prices, demand and signals from the grid operator.
What are the main components of a BESS?
A BESS is more than its batteries. The core components are the cells, the power conversion system, the management software, and the thermal and safety systems that keep it running.
- Battery modules, usually lithium-ion, predominantly LFP chemistry for stationary storage because it is safe, durable and cheap.
- Power conversion system (PCS), converts between the grid's AC and the battery's DC; modern units offer grid-forming capability.
- Battery management system (BMS), monitors and protects every cell.
- Thermal management, often HVAC-based, keeping cells in their safe operating range.
- Fire detection and suppression, certified safety systems, increasingly regulated.
- Energy management system (EMS), the optimisation software that decides operation in real time.
Utility-scale systems package all of this into shipping-container-sized units. A single modern container can hold several megawatt-hours of capacity.
What is a BESS used for?
BESS does several jobs at once: balancing the grid, storing surplus renewable energy, replacing fossil-fuel peaker plants, providing backup, and earning revenue through energy arbitrage.
Grid services (frequency regulation and balancing) are the largest single use. Storing surplus solar and wind for later shifts clean energy from when it is generated to when it is needed. Energy arbitrage means charging when power is cheap and discharging when it is expensive. And behind-the-meter systems back up industrial sites, increasingly including the data centres whose power demand is growing fast.
Why is the BESS market growing so fast?
BESS is one of the fastest-growing parts of the energy system because renewables need storage to be useful, and because storage has become cheaper than building new fossil-fuel peaking plants.
The numbers tell the story. Global BESS additions are forecast above 450 GWh in 2026, up from around 315 GWh in 2025, roughly 50% year-on-year growth. The market was worth about $81 billion in 2026 and is projected to reach nearly $195 billion by 2036. In 2025, global installed BESS capacity passed 250 GW and overtook pumped hydro for the first time. China, the US, the UK, Australia and Germany lead deployment, with emerging markets like Saudi Arabia and Chile rising fast.
BESS vs other energy storage
BESS is not the only way to store energy, but it has become the default for new capacity because it is fast to deploy, fast to respond, and increasingly cheap.
Pumped hydro stores more energy per project but needs specific geography and years to build. Other technologies (flow batteries, thermal, hydrogen) play niche or longer-duration roles. Lithium-ion BESS won the near-term market because it can be sited almost anywhere, installed in months, and responds in milliseconds, which is exactly what a renewable-heavy grid needs.
Informational and educational content only. Not professional, financial, legal, or engineering advice.