BESS (Battery Energy Storage System)
A complete grid- or site-connected battery installation, including cells, battery management, power conversion, thermal management and controls.
A BESS combines battery racks (usually LFP today) with a battery management system, bidirectional inverters (power conversion system, PCS), transformers, HVAC or liquid cooling, fire suppression and an energy management system that decides when to charge and discharge. Utility systems are typically packaged in 20-foot containers holding 3.5–6 MWh each.
Duration (h) = energy (MWh) / power (MW)
AC round-trip efficiency: about 85–90%
Revenue streams include energy arbitrage, frequency response and other ancillary services, capacity markets, congestion relief and reducing solar curtailment. Early markets were dominated by 1-hour systems for frequency services; as those saturated, 2–4 hour systems for daily shifting became standard.
Global installed grid-scale battery capacity grew from under 20 GW in 2020 to well over 150 GW by 2024 (IEA), led by China and the United States (California, Texas). Turnkey 4-hour system costs fell to roughly 200–300 USD/kWh in 2024 outside China and lower inside it. Behind-the-meter systems serve homes and businesses; see behind-the-meter.
Related terms
All terms →- Lithium-ion battery
A rechargeable battery in which lithium ions shuttle between a graphite anode and a metal-oxide or phosphate cathode; the dominant chemistry for EVs and grid storage.
- LFP (Lithium Iron Phosphate)
A lithium-ion cathode chemistry (LiFePO4) prized for safety, long cycle life and low cost, at the expense of lower energy density than nickel-based cells.
- Round-trip efficiency
The share of energy put into a storage system that can be recovered on discharge, measured at a defined boundary (cell, DC, or AC grid connection).
- LCOS (Levelized Cost of Storage)
The average cost per MWh discharged over a storage asset’s lifetime, including investment, operation, charging energy and efficiency losses.
- Ancillary services
Services beyond bulk energy that system operators procure to keep the grid stable and secure, such as frequency reserves, voltage control and black start.
- Behind-the-meter
Equipment located on the customer's side of the utility meter, such as rooftop solar, home batteries or EV chargers, which primarily serves on-site load.