Why are Watt Hours not Watts per Hour? Are they the same thing?
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A watt is a measure of power, which is defined as energy per unit of time: e/t . So, a watt-hour (or, more typically, a “kilowatt-hour”) is a measurement of energy: e/t * t.
There’s also “watt-seconds,” which have another name: Joules. So, a watt-hour is 3600 watt-seconds, or 3600 joules.
So, why do we use watt-hour, or kilowatt-hours? Mainly because it’s more useful: a A 100 watt light bulb uses 100 watt-hours of energy every hour. Leave it on for 10 hours, and you have one kilowatt-hour. If you measured that in joules, then it would be 3.6M joules over that same 10 hour period.
Watt-hours and watts-per-hour are not the same thing. It’s the difference between saying that “a job consumes 10 man-hours” v. saying “it consumes 10 men per hour.” (I dunno, maybe it’s a job with a really high fatality rate.)
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