kW vs kWh: What Is the Difference in Energy Storage?

When evaluating a battery energy storage system, two numbers appear everywhere: kW and kWh. They are not the same.
kW means power. It tells you how much electrical power the system can deliver at one moment.
For example, if a factory needs to reduce a 100 kW peak load, the BESS needs enough power capacity to support that reduction.
kWh means energy. It tells you how much electricity the battery can store and supply over time.
If that same 100 kW peak needs to be reduced for two hours, the required usable energy is approximately 200 kWh.
In simple terms: kW answers “how much power?” and kWh answers “for how long?”
Correct BESS sizing starts with the site load curve, tariff structure, and the operational goal—such as peak shaving, solar self-consumption, or backup power.