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kilo-watt-hour
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.
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.
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!
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.
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….
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?
Clarence, I dont think anyone is trying to out do anyone else, it’s just a discussion. The answer to your question is yes.
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.
Um… Head Hurts..
I have two lamp 40w and 80w one panasonic fan 80w and one computer if I used 6 hours per day how many kilowatt-hour ?
That’s simple. You multiply the watts by the time. ==> (40 Watt + 80 Watt + 80 Watt ) * 6 hrs = 1200 Wh = 1.2 kWh
I am trying to figure the daily cost of running a 1hp pool pump 12 hrs./day. The label shows 7.1/14.2 amps and 230/115 volts.
Will running the pump at 230 volts use less power or simply require a smaller wire?
Thanks
You are correct that operating @ 230 V would require a smaller wire but it will consume the same amount of electricity ( power equals voltage times current ).
So how do I figure out how much i will pay if i use my 10,000w electric furnace for 2 hours a day for 30 days at .0750 per kwh?
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?
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?
OMG – ouch!! BUT THANKS for helping us make some progress on understanding it! You have to take this info in small increments, then step away and allow any left-eye twitches or cranial conniptions to ebb away… retain a little at a time and one day I might fully grasp this.
Dear All,
I think one usual mistake with the analogy to the speed comes from the way we should normally write the abbreviations and its meaning :
Km/h : kilometres divided by hours (“/”)
kW.h : kilowatts multiplied by hours (“.” usually equivalent to “x”)
So Km/h is a instantaneous measurement, and kW.h a totalized measurement, which confused me also at the beginning.
I came across your discussion, as I am trying to understand the basic of electricity, in order to understand the solar system I have installed for my house…
I just started selling Energy Electric right now and I get so many questions regardind how to read the kilowatt hours.
I would like to link your site here to my webpage if that is possible.
This info will help a lot of us new to this business. I am hiring more brokers and really want them to know the info.
I find this fascinating. I just installed solar for my entire home & pool. I need to understand how all this works…I get so many questions!
[...] detailed analysis (most of them are written by people who don’t know what a Watt is; much less a kWh) but Houston has done an excellent job comparing a LED tube to a Fluorescent tube. It reminds me of [...]
I’m on an oxygen converter 24/7. It says it uses 280 watts. I pay .065 p/kWh. Will it cost $42.00 a month? Thanks
If it uses 280 watts all the time.. .240 kW * 24 hours/day * 30 days/month * .065 $/kWh = $13.10
I’m not sure how you come up with 240 kW but when I take 280 X 24 X 30 and then divide by 1000 I come up with 202. However, when you mulitply that by .065 that gives me the $13.10. I want to thank you because of this I can deduct a part of my yearly electric charge off my federal and state taxes. You’ve been a great help. Jim
Sorry, the 240 should have been 280. How are you able to deduct it from your taxes?
I wrote the IRS last year and they wrote back that “Per Publication 502 you can include in medical expenses amounts you pay for oxygen and oxygen equipment to relieve breathing problems caused by a medical condition.” It then goes into detail of how you must prove the electric use. If you would like more detail you can write to TaxHelp@HAL1.ausc.irs.gov They were very quick in answering my question and sent almost 2 pages of information about it and other sources and phone #’s where you can ask questions. It’s not enough to retire on but every little bit adds up! Again thanks for your help. Jim
Wow, I never knew that, but it makes sense!
Am trying to find out something about electricity that is being metered, but not consumed in my home. I’m told that this might be called either arcing electricity or dumping electricity. Maybe it’s got another name. Am in disagreement with Arizona power company. Was told that one month in 2011 that my electricity usage was 102% higher than the average of 100 homes of similar size within 0.12 miles away from me. Have you ever heard of this?
I havent heard of this. What about a TED 5000? I haven’t heard of dumping electricity though? How many kWh did you use and what month was it? Where did you get the data on the other homes?
[...] The International Cycling Union (UCI) maintains records for the Hour Record, which is an ongoing contest to see who can ride the farthest in one hour. To get a good estimate of the maximum energy a person can produce (these are elite athletes after all), we’ll figure out the average wattage of someone competing for the Hour Record, and since it lasts an hour, this average wattage will be the total energy the rider expended over that hour. Therefore, the energy they expend over the time they compete can be presented in Watt-hours. [...]
Ok, I might be going a little bit on a limb here but hear me out. I’m thinking about going off the grid completely, the whole 72 car batteries in the basement and going solar. I have alot of high energy use equipment in my house, air conditioners, all appliances, and about 10 different computers and a few servers thrown in too… if I just measure up all the wattage of all the devices and multiply buy the hours used I’ll come out with X. Now how do I figure up how many solar panels and how many batteries I need to become fully sustainable? Alot of the mumble jumble on the solar panel is kinda hurting my brain.
Bryan,
First, I would take out your electricity bills from last year and total up the total kWh you used for the whole year. I would then read our post on solar power production by city to figure out how big of a system you would need to power your home for a year.
That’s a very short answer to a semi-complicated question. What you should really do is speak with some solar installers in your area. Get an idea of the cost to install the system and figure out if you can afford it. If you can’t afford one to power your whole home, just power part of it and then add on over time!
[...] unit for electricity usage. If this term is not familiar to you, read Chris’ post on “What is a kilowatt-hour” for a good primer on this topic. In addition to the kWh energy unit, I discovered that [...]