Many people make the mistake of confusing a Kilowatt (a unit of power) and a Kilowatt-hour (A unit of energy). The same could be said about Watts and Watt-hours, but the Kilowatt is much more commonly applied.

A kilowatt is power. Think of it as a rate of consumption. This is how fast you are gobbling up electrons from the grid.

A kilowatt-hour is energy. This represents the amount of electrons you have gobbled from the grid since your last utility bill, for example. (not really electrons, but you get the picture)

To put it another way, think of a Kilowatt as how fast you are going in your car. Think of Kilowatt-hours as how many miles you have gone. I know, your gonna say “But Alan, how fast I’m going is miles per hour right? Those units sound a lot like Kilowatt-hours!”. And you would be wrong. These are very important distinctions. When I see an industry article saying “We saved 4 million Kilowatts in 2013” I cringe. A 4 million kW reduction in load would be pretty epic, and would actually be (4,000,000*8760= 35,040,000,000 kWH). But they really meant to say 4 million kWH, which is about an average of 450 kW reduction in load. Not the same AT ALL. I know it’s easy to slip up the two, and I know a journalist writing about an engineering topic might not get the importance of the difference, but I hope the way I broke it down helps. If you want to know this stuff for real, check out your local wikipedia page on power and energy.

To get real with it, power is work over time. A Joule is the unit of work (lifting an apple 1 meter requires about 1 Joule of work). Watts are Joules per second and are a unit of power (lifting 1 apple 1 meter every second would require 1 watt of power). Watt-hours are a unit of energy, energy and work are basically the same if that doesn’t trip you out, (lifting apples at a rate of 1 apple a meter every second for an hour would require a watt-hour of energy).

Just to bring the circular logic full circular logic around again one more time, 1 joule =
2.77777778 × 10-7 kilowatt hours

A watt is a joule per second, and a watt-hour is watts times time, time cancels out and leaves you back at joules!


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