kWh vs kW

kWh (kilowatt-hour) measures energy: how much electricity a battery can store, or how much your home uses over a period. kW (kilowatt) measures power: how fast that electricity can be charged or discharged at one moment. A kettle might draw about 3 kW. Running it for 20 minutes uses about 1 kWh.

What it means for a home battery

Capacity in kWh sets how many cheap overnight units you can move into the day. Power in kW sets whether the battery can cover a spike, such as an oven and a kettle together, before the grid makes up the rest. The Energy Saving Trust sizes home batteries in kWh for that reason: storage is an energy question first.

EcoFlow lists the STREAM AC 5000 at 5,024 Wh capacity (about 5 kWh) and up to 2,500 W grid-tied output for a single unit, or 3,000 W with an Expansion Battery, on its UK product page. Habo's offer is an electrician-wired EcoFlow STREAM from £2,499. Join the waitlist. The kWh figure feeds the savings calculator. The kW figure feeds G98 vs G99, because the DNO looks at amps and inverter power, not kWh alone.

When you read a quote, keep the two columns apart. A larger kWh pack stores more energy but does not automatically deliver more power. A higher kW inverter covers bigger loads but does not add storage. Match usable kWh to evening use with what size battery, and match inverter kW to the loads you care about. See also usable vs total capacity and the glossary.

A quick check on any datasheet: capacity and expansion options are in kWh or Wh; charge rate, discharge rate and backup output are in kW or W. If a salesperson quotes only one number, ask for the other before you compare payback claims.

Frequently asked questions