Question: why is kwh used instead of joules?
Answer: While the joule is the SI base unit for energy, when speaking in real-world terms, we often use the kilowatt-hour (kWh) instead. This is due to the fact that a joule is an extremely small amount of energy. To put how small a joule is into perspective, a liter of gasoline has 31,536,000 joules of energy in it.