Kilowatt-Hour (kWh) vs. Kilowatt (kW)
Kilowatt-hours (kWh) measure total energy capacity volume, while Kilowatts (kW) measure instantaneous power output or speed.
Understanding the distinction between kilowatt-hours (kWh) and kilowatts (kW) is fundamental to sizing a home battery backup system correctly.
Kilowatt-hours (kWh) represent total energy capacity—the size of your battery's 'fuel tank'. For example, a 13.5 kWh battery holds enough total energy to run a 1,000-Watt (1 kW) load for 13.5 continuous hours.
Kilowatts (kW) represent power output rate—the width of your battery's 'fuel pipe'. Continuous kW output dictates how many appliances (e.g. air conditioners, refrigerators, sump pumps) can run simultaneously without overloading the inverter.
Why it matters
A battery with high kWh but low kW will drain slowly but struggle to start heavy motors; a battery with high kW but low kWh will power heavy loads but drain quickly.
Example
A 10 kWh battery with a 5 kW inverter can run a 2 kW air conditioner for 5 hours, or a 5 kW total load for 2 hours.