What is the difference between kW (Kilowatts) and kWh (Kilowatt-hours)?

Kilowatts (kW) measures the amount of power required by a device to the work it is employed for. If you have a rack of servers in data centre with a total power requirement of 5kW then this is the amount of power that must be supplied from your electrical supply to support the load.

Kilowatt-hours (kWh) mesaures the amount of energy used by a device within 1hour. Energy storage is typically measured in kWh. In our example, if you have a 10kWh hour energy storage system this would provide 2hours of power backup for our 5kW load i.e. 10kWh / 5kW = 2hours. If the load of 5kW is reduced to 2.5kW through for example, load-shedding, then the result becomes 4 hours i.e. 10kWh / 2.5kW = 4hours.

Kilowatts can be converted to Kilowatt-hours using the formula:
Load Power requirements (kW) x the time the load is to run for (hours) = answer in kW.h