Why are Watt Hours not Watts per Hour? Are they the same thing?
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It seems like some of the top comments are missing a piece of low hanging fruit:
Joule is a measure of energy.
Watt is a measure of power.
Power = energy/time (Watts or Joules/second, same thing)
So a Watt hour is (energy/time) x time. As you can see this returns back something that is just a unit of energy.
The reason we talk about energy in terms of Watt hours is because it’s something we’re familiar with. Notice how all of our electronics and appliances are rated for power consumption in terms of Watts (or kiloWatts [kW]).
My microwave draws 1000 Watts when it’s operating, so if I run it for the course of an hour I’ve used 1000 Watt hours or 1 kWh. This is relatable and I have context when I read my utility bill. Even though Joule is the proper unit of energy, I have very little conceptual idea how much a Joule is in terms of everyday life.
Last thing I’ll say is that there are some other instances when we talk about a quantity in terms of the product of two units. For example, you may have a car that can produce a certain amount of torque. We typically measure torque in terms of foot pounds. This one is a little bit quirkier, but it’s done for the same reason.
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