What is a BESS and why are grid operators buying so many?
A battery energy storage system is a field of shipping-container batteries wired to the grid. It absorbs power when there is too much and returns it when there is too little.
A grid has to match supply and demand every second. For a century that job was done by power plants speeding up and slowing down. Batteries now do part of it, and they react in a fraction of a second.
A grid-scale battery earns money in a few ways. It can charge when electricity is cheap, usually at midday when solar output peaks, and discharge in the evening. It can sell fast frequency response to the grid operator. And it can stand by as reserve capacity in case a plant or a line fails.
Most new systems use lithium iron phosphate cells, the same family found in many electric cars, packed into containers with cooling and fire suppression. Other chemistries such as zinc-bromine and sodium-ion are being tested for longer storage times.
- Typical duration
- Two to four hours at full output
- Dominant chemistry
- Lithium iron phosphate (LFP)
Explainers describe how things generally work. They are not advice for a specific project or country. See our editorial policy.