Tuesday, August 23, 2011

The #1 Rule of Thumb

The #1 rule of thumb about electric power usage that everyone should know is simply this:

1 Watt = $1 (per year)*

For example, it costs $100 to keep a 100 Watt bulb burning for an entire year. Wow! That's a rule any first grader can grasp. It's precisely true when electricity costs 11.4 cents per kilowatt hour (kWh), and has been a useful rule of thumb over the past decade and at the present here in Texas. 

Adjustments for differing rates
So you want to be a little more precise for different electric rates? A quick adjustment will do:
Electric Rate per kWh 1 Watt all year =
11¢ $1
17¢ $1.50
23¢ $2

The $77 CFL savings
I used to see $7 CFLs (compact fluorescents) that claimed "this bulb save you $77," and thought I should take that claim "with a grain of salt"--until I applied the above simple rule of thumb. Can one CFL "100 Watt equivalent" bulb really save $77?? Absolutely! Most CFL bulbs are rated to last 10,000 hours, a bit more than 1 year (which is 24 hours x 365 = 8,760 hours). The 100-Watt-equivalent CFL uses only 23 Watts, so it costs $23 of electricity over it's lifetime. Meanwhile, it's replacing 100 Watt bulbs (it would take about 4 replacements during the year) which would have burned up $100 of electricity. So the electricity savings is $77 for one bulb! I'd never have believed it till I did the math myself.

At this rate of electricity savings, how much the bulbs cost is of no consequence--especially since good CFLs can be found for around $1.50--barely more than a single incandescent. (More to come on the best CFLs available.)

So what's all the silliness about Joe Barton defending the energy hog incandescent? The rhetoric about personal freedom is misguided at best, and is largely a defense of pure and simple ignorance. The real freedom that's at stake is the energy independence of our country--which in turn contributes to our national security and ultimate personal freedoms!

So get rid of the incandescents in your home and office and bring in the CFLs immediately. It doesn't make any sense to wait until the incandescents burn out. I know of nothing better to do with them than to throw them away. They're simply burning through money every second they're on. 

Changing light bulbs is the main contributor to the 20% reduction in electricity usage at our home over the past year (see the light blue line in the graph below).

More Examples
Here's a few more observations based on the 1W = $1 rule of thumb:
  • A 10-year old 120W computer that's been left on continuously has cost $120 per year, or $1,200 of electricity to-date--more than its original cost.
  • A 3.5W clock radio costs $3.50 per year, or $35 over 10 years--several times its cost.
  • An electric piano with a power cord that uses 4.1W when the piano is "on" but still uses 2.9W when the piano is "off" costs at least $2.90 to leave plugged in all year. Not terrible, but a needless waste of power. There are better ways: unplugging it, using a power strip with a switch, or using a newer power cord that uses 0W when not in use. 
  • An old and inefficient UPS (Uninterruptible Power Supply) used 22W of power continuously. A new green UPS model uses only 2.4W of extra power--a $20 annual savings.
  • A fan running at 30W costs $10 if run constantly for 4 months of the year ($30 x 4/12). But if it's only used 8 hours a day for 3 months, it costs only $3.33.  
So this #1 rule of thumb simply puts energy costs in perspective. It makes energy use concrete and measurable. It's much more meaningful to tell the kids to turn the light off not just because "You're wasting energy," but because "That's $23 you left burning there." You can explain it really costs $23 if they leave that CFL on all year long. They get the message. And for the forgetful kid you can throw in a "$1 fine" (or other realistic amount relative to the size of his allowance) for leaving the light in his closet on. It'll bring a smile to his face (sort of) every time you catch him with the light on!
"Make the most of your opportunities because these are evil days." (Ephesians 4.16)
PS: Remember to recycle your spent CFLs. Both Home Depot and Lowes provide CFL recycle drop boxes just inside the entrance. 

* The specific math is this:
1 Watt x 24 hours/day x 365 days/year / 1000 Watts/kW x $0.114/kWh = $1.00/year


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