Submitted by andy.connor.e on 18. April 2019
Everyone needs to understand the difference between the units kilowatt (kW) and kilowatt-hour (kWh)
Kilowatt (kW) is a unit of instantaneous power that is flowing at that very second. Like how you would rate water flow at liters per minute, Kilowatt is thousands of joules per second. So when you refer to electric vehicle power, or a solar installation, the units are in kilowatts, because that is the amount of instantaneous energy they can supply.
Kilowatt-hour (kWh) comes from the amount of kilowatts used over a period of time. The literal translation is 1 kilowatt being used for 1 hour, is 1 kilowatt-hour. Kilowatt-hour is a unit if energy used over a period of time, and not the instantaneous value. So when you refer to battery storage, the units are in kilowatt-hour, because that is the amount of energy it can supply over a given amount of time.
Solar installation of 9kW
Energy storage of 9kWh
The solar panels would generate 9kW for 1 hour to store 9kWh of energy.