Compact fluorescent lamps (CFLs) have become more popular in recent years, but d
ID: 2778796 • Letter: C
Question
Compact fluorescent lamps (CFLs) have become more popular in recent years, but do they make financial sense? Suppose a typical 60-watt incandescent lightbulb costs $0.54 and lasts for 1,000 hours. A 15-watt CFL, which provides the same light, costs $3.85 and lasts for 12,000 hours. A kilowatt-hour is 1,000 watts for 1 hour. Suppose you have a residence with a lot of incandescent bulbs that are used on average 500 hours a year. The average bulb will be about halfway through its life, so it will have 500 hours remaining (and you can’t tell which bulbs are older or newer).
If you require a 10 percent return, at what cost per kilowatt-hour does it make sense to replace your incandescent bulbs today? (Negative amount should be indicated by a minus sign. Do not round intermediate calculations and round your final answer to 6 decimal places. (e.g., 32.161616)).
Break-even cost = ?
Compact fluorescent lamps (CFLs) have become more popular in recent years, but do they make financial sense? Suppose a typical 60-watt incandescent lightbulb costs $0.54 and lasts for 1,000 hours. A 15-watt CFL, which provides the same light, costs $3.85 and lasts for 12,000 hours. A kilowatt-hour is 1,000 watts for 1 hour. Suppose you have a residence with a lot of incandescent bulbs that are used on average 500 hours a year. The average bulb will be about halfway through its life, so it will have 500 hours remaining (and you can’t tell which bulbs are older or newer).
If you require a 10 percent return, at what cost per kilowatt-hour does it make sense to replace your incandescent bulbs today? (Negative amount should be indicated by a minus sign. Do not round intermediate calculations and round your final answer to 6 decimal places. (e.g., 32.161616)).
Break-even cost = ?
Explanation / Answer
OK so if you're using the fixture for 500 hours per year, an IL would last about 2 years and a CFL would last 24 years
over the life of the bulb, the IL would use 1000*60=60 kWH
the CFL would use 12000*15=180 kWH
to match the life of the CFL, you would need 12 IL which would burn 720 kWH
12 ILs would cost $6.00
1 CFL would cost $3.65
The weird thing is if you are looking at less than 7 years, the ILs are always cheaper (the cost of the bulb is the deciding factor) and if you go more than 12 years, the CFLs are always cheaper (the fact that you are using more IL bulbs becomes an issue)
If you look at 7 years, the break-even point (where the IL costs more than the CFL) would be $0.051667
8 years, 0.020833
9 years, 0.015556
10 years, 0.005417
11 years, 0.002333
12 years, 0.000278
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