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# Some basic compact flurescent math

by Owyn / March 1, 2007 12:12 PM PST

Cost of 100w incandescent equivalent CF approx = \$1.00
Power consumption of CF bulb = 23W
Cost per kilowatt hour (local) = \$.055
Hours of use to save 1 KW = 1000 / (100 - 23) = 13.0 hours
KWh to save \$1 = 1.00 / .055 = 18.2

Hours to break even (recover cost of CF bulb) = 18.2 * 13.0 = 236.6

Assuming a bulb was used 4 hours per day then

Days to recover cost of CF = 236.6 / 4 = 59 days (i.e. approx 2 months)

Mileage may vary based on local rates, but, not enough to make a difference. In fact, I would guess that in many cases the break even period would be even lower.

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word.
by thriftyT / March 1, 2007 9:05 PM PST

money saved per 1 hour (by using a 23 W CFL vs. a 100W conventional):

(77 W) (1 hr) (1 kW / 1000 W) (0.055 dollars / KWh) = 0.00423 dollars

Therefore, as you said, it would take ~236 hours to save one dollar.

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CO2 savings.
by R. Proffitt Forum moderator / March 2, 2007 12:30 AM PST
http://www.google.com/search?hl=en&q=co2+per+kilowatt+hour gives us from 1.5 to 2.3 pounds of CO2 per KWH.

Over your dollar break even analysis of 236 hours lets figure out the CO2 savings.

For the 100W bulb that's 23600 WH or 23.6 KWH or 34.5 pounds of CO2.
For the CFL @ 23W that's 5428 WH or 5.428 KWH or 8.1375 pounds of CO2.

If CO2 is really a concern, then this is a solution.

Bob
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Yep. CFL may not be perfect but...
by Owyn / March 2, 2007 5:36 AM PST

Lot's of reasons to switch to them where possible today. Lower cooling costs in the summer can be another factor.

Another way to save is to switch to higher efficiency, lower noise, better reliability computer power supplies. Anyone purchasing a new system should specify a premium supply. Spending an extra \$50 can easily reduce consumption by 100W for a typical new system.

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Annual cost of always on 100W load
by Owyn / March 2, 2007 5:47 AM PST

Power used = 365 days * 24 hours/day * 100W / 1000W/KWh = 876KWh
Cost of power = 876 * .055 = \$48.18

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by Pinkmaltese1 / March 3, 2007 3:26 AM PST

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