Thursday, October 2, 2008

Bright Idea

My wife sent me to CVS in Harvard Square last night to buy a few things for home. As I was wandering the store I noticed a stack of compact fluorescent light bulbs on sale for 49 cents each. I immediately filled my basket with as many as I could handle. 10 CFL bulbs for under $5.00 is too good to pass by. Predictably I got the "What did you buy?" when I got home.

I explained I was going to give the bulbs to students in my Environmental Science class. Students are working on a project to reduce electricity consumption in the residential houses for the month of October. One group wanted to encourage the use of CFLs but found the cost of CFL bulbs to be prohibitive. They were working on finding a business willing to donate or sell at a reduced cost. With my purchases last night, this group can get CFLs in the residential houses and start educating students about electricity consumption.

I wish the Environmental Sustainability Committee had a budget. I would buy 500 bulbs and give one to every first year student. Let me play with the numbers a bit and show how justified this purchase would be for Lasell College. 500 bulbs would cost $245. Assume each student replaces a 75 watt bulb in their dorm room with the CFL. Also assume the light is on for 3 hours a day and the bulb lasts all four years of college. How does this add up?

Lasell College pays about 12 cents per kWh of electricity. Running a 75 watt bulb for 3 hours uses 0.225 kWh of electricity. Assume the student is on campus for 200 days a year, this one light uses 45 kWh of electricity. The cost to the college for the 1 light is $5.40 in electricity. Multiply this by 500 and the cost is $2700. Now, assume the 75 watt bulb is replaced by a 20 watt CFL that gives off the equivalent amount of light but uses less energy. This bulb will use 0.060 kWh per day which is almost 75% less. The cost of electricity to run this bulb for 3 hours a day is $1.44 per year. Multiply by the 500 I want to buy and this is equal to $720.

By investing $245, Lasell College could reduce electricity costs from $2700 down to $720. The college would save $1980 dollars per year for a $245 investment. The savings get better because we are assuming the bulb is in use at Lasell for four years. Now the $225 investment would save the college $7920. More importantly, the investment would reduce our electricity consumption annually from 22,500 kWh per year to 6000 kWh per year. A good step to reducing our carbon footprint.

I recognize I had to make many assumptions. To break even, only 144 of the 500 students have to utilize the bulbs. This seems like a reasonable risk to me. I don't really know if students each use a bulb for three hours a day though. Many students may only rely on the overhead lighting already installed.

How much of an impact will implementing CFLs have for students doing the project in my Environmental Science Class? A house with 18 students may use about 1500 kWh per month. Assume all 18 switch 1 bulb. The potential monthly savings in electricity is about 100 kWh. A 6.5% reduction is not bad at all!

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