The concept of Watt-hours was messing me up. I think I get it now.

• Energy is the potential to do some work, measured in Joules.
• Power is the rate at which work is done and is measured in Joules per seconds, i.e., Watts.
• If you want to know how much energy something “uses”, multiply it’s power by how long it has been running.
  • e.g., something with a power of 100 J/s (i.e., 100 Watts) running for 10 s will use 1,000 Joules of energy.
• For household use, Joules is not a very convenient unit, so we use Watt-hours (W•h) or kW•h, which is the number of Watts an appliance uses times the number of hours it runs. Watt-hours and Joules are both units of energy.
  • Watt-hours is not Watts-per-hour, i.e., it is not a rate. It means Watts-times-hours. If we break it down, we can convert back to Joules: W•h = (3600s•J) / s = 3600J.

I hope I summarized it properly and didn’t make any math mistakes!