Make A Kilowatt-Hour Make Cents

I think most people are aware the primary unit of power is the watt. Even the non-scientifically inclined know that many light bulbs are rated in watts, or at the very least that Marty McFly needed 1.21 gigawatts of power to get back home.

Then why is it that electric companies charge based on kilowatt-hours?  And how can this knowledge be used to reduce your electric bill?

First of all, a watt is actually a very small unit of power in the grand scheme. As we've already shown, a single computer system can use 250 watts or more power. Now consider a typical household with multiple TV's, computers, air conditioning units, lights, clock radios, cell phones charging, clothes dryers, ovens, etc all operating. At any given time well over a thousand watts may be used. Kilo means 1000, so measuring household and commercial power in kilowatts makes sense.

OK, I Understand Kilo...but why Hours?

If I turn on every light in my house for 20 minutes, should I be charged the same amount of money by the electric company as someone running every light in their house for 24 hours a day? Obviously, the answer is no.



Since power usage may occur for a fraction of a second, or hours on end, utility companies have chosen to measure the duration of the usage.

Simply put, a kilowatt-hour (abbreviated KwH) is equivalent to using 1000 watts of power (a kilowatt) for one hour of time. Similarly, it could also be described as using 100 watts of power for 10 hours of time (i.e. 100 * 10 = 1000). And of course, any other combination of hours and watts used that equate to 1000 would be 1 KwH.

Make Your Kilowatt-Hour Make Cents

As mentioned above, most electric companies bill you a rate based on your KwH usage for a month. Use this knowledge to lower your bills!

To help with this, I've created the Home Power Saver Power Savings Calculator, previously discussed. Today I've added an enhancement that will not only show you your money saved, but also the raw KwH used daily, monthly, and annually.

Consider this one simple example. My home has a two car garage and a "swing-in" one car garage. Each garage has two coach lights outside, and my front door also has a light. When I moved in, all five of these fixtures had 60 watt bulbs. On average the lights run for 12 hours per day over the course of a year.

Initial Usage and Cost
Watts	Hours Per Day Used	KwH Per Day	KwH Per Year	Annual Cost
300	12	3.6	1314	$157

Those five lights were costing me $157 a year at my local utility's rate! I ended up replacing all five light bulbs with 12 watt compact fluorescent bulbs (CFLs). Here is the result:

CFL Usage and Cost
Watts	Hours Per Day Used	KwH Per Day	KwH Per Year	Annual Cost
60	12	0.72	263	$33

That's quite a savings! And the beauty of the calculator is that you can play around with all of the variables and see what-if scenarios, such as 'what if I ran the lights only 10 hours per day', etc.

Take your knowledge of KwH and the calculator and make it make 'cents' for you too.