What is a kiloWatt-hour a.k.a kWh? (part 1)

kilo-watt-hour

We have a new and improved page on "What is kWh?"

This is one of the most important articles for people just starting out understanding their electricity bill! While I am proud of my famous What's a Watt blog, this one is just as important.

The bill you get from your power company gives you your electricity consumption in kilowatt-hours (kWh). The price you pay for that electricity is in cents per kWh. In Georgia, I pay around 9 cents/kWh, up North they pay round 17 cents/kWh, and in Hawaii they pay almost 30 cents/kWh! Thanks Nebraska for this handy chart.

To get your final bill amount, you simply multiply your usage (total kWh/month) times the amount you pay per kWh (your rate). Unfortunately, you also have to pay some flat rate fees your utility charges. Pretty simple right?

This is very obvious, but your goal is to reduce the kWh you consume each month! So how do you achieve this? The best targets are the big power (remember power = watt) users that are on for the longest amount of time (energy (kWh) = power (watt) * time).

When I was working at a Nuclear power plant (no, I don't glow) I remember being confused by Watts and kilo-Watt hours (I was an intern ok!) and I remember reading Michael Bluejay's great write up on the Watt/kWh . Here is another good article from Appropedia.

I am going to go into much more detail in part 2 of What is a kWh. I dont want to turn too many readers away at the technical stuff by writing too much at once. It is important, so PLEASE don't blow it off. Ignorance is not bliss when it comes to saving money and helping the environment.

Use the kilowatt hour calculator below to see how much it costs you to run an appliance. Look at the cord or on the appliance to see how many watts the appliance uses and fill in how long you keep the appliance on per day. If minutes, divide by 60 to get the units in hours. You'll have to know how much your utility charges you per kwh. If you don't know your rate, you can find the average rate in your state by looking at the first image on the Electricity Graphics page.

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Learn more about the kilo-Watt-hour in part 2!

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Comments

Anonymous (not verified) Tue, 03/16/2010 - 00:50

If my company has a Power Plant and can produce 100Megawatts of power and sold it at a wholesale price of .13 cents per Kilowatt. How would you figure out the total wholesale price?

Anonymous (not verified) Tue, 03/16/2010 - 07:03

First, you would be selling it at .13 cent per Kiolwatt-HOUR. Determining the wholesale price is complicated and takes into account the fixed costs of building your power plant, the variable costs of the energy course you use for power, and then any financing costs associated with initial construction. All of this is combined, then the life of the power plant is considered, and the price per kWh is figured out from the total costs divided by the life of the plant + some other stuff. This isn't meant to be an explanation, I'm trying to show that it is fairly complicated. Can anyone else be of more help?

Anonymous (not verified) Thu, 09/10/2009 - 14:40

none of your answers is clear. Quit trying to out do each other with conversions and math. If you have a gerneator that produces 1kWh per hour then haven't I produced 24 kWh in one day?

Anonymous (not verified) Sun, 12/19/2010 - 14:45

no. you are producing 1000w. you can not "store" electricity. it is a use/lose technology (less you have a battery bank, but now we are talking inversion/conversion) basically, if you shut off your generator after 24 hours, off goes the electricity. it is not stored for later if you did not use it all up.

Anonymous (not verified) Thu, 09/10/2009 - 21:35

Clarence, I dont think anyone is trying to out do anyone else, it's just a discussion. The answer to your question is yes.

Anonymous (not verified) Mon, 03/16/2009 - 12:39

All valid points. I will concede the fact that my analogy was pretty bad! In my analogy MPH would be equivalent to Watts, where "total miles" would be equivalent to kWh. But yes, you are correct, but I will make one point. Instead of saying "multiply by the hours" I would say "multiply by the time on". For example, if you are trying to measure how much it costs to run your toaster, you would figure out how much power it consumes in Watts (probably on the cord) and then multiply by the total time it is on each morning, either seconds or minutes. You then have to convert those seconds or minutes into hours first. Some people might be confused if you just refer to "time on" as hours, but this is a technicality....

Anonymous (not verified) Mon, 03/16/2009 - 08:35

If people are going to embrace the subject in any serious quantity it has to be simpler. The MPH analogy only makes it worse...(I think). MPH is instantaneous, KWH isnt. But I am not sure the distinction is important. Basically, you get watts or kilawatts and multiply by the hours used to get your "amount" used. If starting with KWH, divide by one hour to get average KW used (amount). The rest in my view is jargon, and, valid technical but confusing, data.

Anonymous (not verified) Sun, 03/15/2009 - 18:06

Mark, I agree it can be a very confusing subject! Think of power as an instantaneous view of an appliance's situation. While energy is a "totalized" value. For example, if you are in your car and you look down at your speedometer you may be going 50 miles/hr. But that is just an instantaneous view of your current situation. If you need to know the distance you've gone over a period of time (totalized value) you would have to multiply your average speed (miles/hr) by the length of time you were traveling (hours). This will give you your total distance, just like multiplying watts (instantaneous view) by total time will give you the totalized energy. I'll work on a better explanation in part 2!

Anonymous (not verified) Sun, 03/15/2009 - 15:10

Ok, this makes my head hurt. If I measure something with my kill -a- watt I get watts. I multiply that by 1000 to get kilowatts. .004 kw. That however isn't power use over time, KWH is, and it's the same as KW if it's on for exactly one hour. .004 kilowatt hours. For most everything we need you just get watts and or killowatts. Multiply that by hours used and call it KWH. The fridge and air conditioner is where it gets tricky because you probably want usage over time that will vary considerably from the initial measurement in KW. So then you need to get the KWH and work back to an average KW. The energy vs power thing just confuses me.

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