Update: I am actually searching for really simple, intuitive ways to explain it. I have a background in engineering, but am struggling to explain why we “pay for kwh”, and not kw (on our electricity bill) to someone who doesn’t. I have tried in many ways but maybe I’m not giving the right examples or making the right comparisons. I am really searchig for a way to ELI5.
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The standard unit of energy is the Joule. Joules could be used to describe the energy stored in a battery, in a gallon of gasoline, in food (Calories are also a unit of energy), and so on. Energy being transferred over time is such a commonly used concept, that we gave the unit its own name: the Watt. 1 Watt = 1 Joule per second.
1 Watt is actually a small amount, so often we use kilowatts (kW) instead. 1 kW = 1000 W = 1000 J/s.
A kilowatt-hour is the amount of energy needed to transfer energy at 1000 Watts for an hour. There are 3600 seconds/hour, so 1 kWh =1 kJ/s * 1 hour = 1 kJ/s * 3600 seconds = 3600 kJ = 3.6 MJ.
We often use kWh instead of megajoules because we want to answer questions like “how many hours will my battery last?” and not “how many seconds will my battery last?”. They’re technically equivalent, but kWh is more convenient.
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