Those crazy numbers on your electric bill
February 8th, 2008 by Kishore
A question came up at the solar talk on Tuesday…there is confusion on standard power conversions. What does it mean when a power plant is 15 MW? How about my PG&E bill that rates everything in kw h?
In science class, energy is generally labeled in Joules (sometime kilojoules - KJ or megajoules - MJ). Energy is time independent…it’s just energy.
But we never hear about Joules in normal life. We always hear about Watts (sometimes kW - kilowatt, MW - megawatt).
1 Watts = 1 Joule/second.
So when you hear about a 100 W bulb, that means it ’s using 100 Joules of energy per second. A 15 MW plant (that number represents peak output) can produce 15 million joules per second.
Now to your electric bill. You get billed on a kw*h (kilowatt hour) basis.
1 kw* h= 1000 watts hour= 1000 (Joules/second) * hour = 1000J/sec * 60 sec/1 min * 60 min/hour = 3,600,000 Joules.
So your electric bill actual does state how much energy is being used. Just with a bastardized unit of measure.
This entry was posted on Friday, February 8th, 2008 at 6:17 pm and is filed under Solar. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
February 28th, 2008 at 8:24 am
Hej Kishore,
Thanks for the info. I guess I asked the wrong question because I was more interested in how to get from kw/h to chosing a sufficient size solar panels (or even urban wind turbine). I’m afraid your joules explaination only made it more confusing.
I’ve been scanning a TH forum and am starting to get an idea but if you have a summary that gets directly to the point please let me know.
Here’s lhe link:
http://forums.treehugger.com/viewtopic.php?t=1600
Regards.