What is a kilowatt-hour?

A kilowatt-hour is a measure of power over a usage hour. Electric appliances are rated in watts of electricity – a 50W light bulb will consume 50W of electricity at any given point that it is turned on. If one were to keep the light on for one hour the light bulb would have consumed 50Wh of electricity. If you were to keep the same 50W bulb on for 100 hours, you would have consumed 5,000Wh of electricity or 5kWh of electricity.