kW vs kWh

kW is power (rate of energy use); kWh is energy (amount used over time). A 7kW charger pulling for 1 hour delivers 7kWh.

The kW vs kWh distinction trips up almost everyone. kW (kilowatt) is power — the rate at which energy is used or produced at any given instant. kWh (kilowatt-hour) is energy — power multiplied by time. A 1kW heater running for 1 hour uses 1kWh; running for 24 hours it uses 24kWh.

In renewable energy land:

Heat pumps are sized in kW (e.g. 8kW Vaillant aroTHERM)
Solar arrays are sized in kWp (peak power capacity)
Batteries are sized in kWh (storage capacity) and have separate kW power ratings (charge/discharge speed)
EV chargers are rated in kW (charge rate)
Bills are charged in kWh (energy consumed)

A common error: assuming a 5kW battery means 5 hours of storage. It does not — 5kW is the discharge speed, the storage capacity might be 10kWh or 13.5kWh depending on the model. Always check both numbers. See our battery storage page.