Quote:
Originally Posted by You Need a Thneed
Let's do a quick calculation. Let's figure that there's a light bulb that's on for an average of 8 hours a day, every day. That's 240 hours per month, assuming 30 days in a month on average.
An incandescent bulb uses 60 watts, the replacement CFL uses 13 watts. Therefore, a CFL bulb saves 47 watt/hours every hour.
47x 240 = 11,280 watt hours per month = 11.28 kWh per month.
Now lets assume an average power price of 10 cents per kWh, which means that for every incandescent bulb that you replace with a CFL, you save $1.28 PER MONTH. Obviously, not every bulb is on for 8 hours a day, but replacing every bulb in your house will significantly cut down your power bill.
That's more than a few pennies a month in savings.
Like I said though, everyone should go for LED bulbs, but hopefully they come down in price a lot in the next couple of years. |
I can do a back of the napkin calculation for the defrayed heating costs too:
11.28 kWh/month that wouldn't shed be heat = 11.28 kWh/month that needs to be heated by a furnace
There are nine months a year in Calgary where the average temperature is below 18 degrees Celsius. This means that the furnace needs to replace missing heat equivalent to an average of at least:
11.28*9/12=8.46kWh/month
1GJ=277.8kWh
so
8.46kWh = 0.0354 GJ
A typical furnace is about 80% efficient so that works out to an average of:
0.0354/.8 = 0.04425 GJ
Natural Gas costs about $6/GJ (currently - it's been as high as $14) so the incandescent bulb saves:
0.04425*6 = .2655 = $.27 per month.
If you were somewhere that used home heating oil (~$28/GJ right now in Newfoundland with equivalent electricity prices) the bulb would "save":
0.04425*28 = $1.23/month, meaning the $1.28/month savings for the bulb is a wash. When the price of Oil was half again what it is right now, those CF bulbs would certainly have been more expensive and it would have made economic sense to have had incandescent bulbs and to have left the lights on in the winter.
I know that it's a fairly silly point to make but given a high enough fuel cost and a low enough electricity cost, there is a crossover point where CF bulbs cost more to run than incandescents, despite the propaganda to the contrary.