Sunday, February 11, 2007

Electricity use analysis

I took a bit of time to review the electricity use (as per our monthly bills) of our country home and the six little houses of my siblings and their families.

This summer I changed out about 100 normal bulbs with CFL/swirl bulbs, and we installed a solar hot water system. I had hoped we might see a 5% drop in energy use from these changes. For the year we used 2% more electricity in the main house and 8% more for the complex. Sigh! At least it was less than it would have been without these changes.

Since this is a “vacation house” there are a ton of variables that effect electricity use. The biggest variable is how many days (and by how many people) per year the house is used. I do not have a measure for people days/usage, especially not w.r.t. the prior year. I think this measure would have been higher in ‘06 than ’05, but I cannot support this or say by how much. Obviously the weekend/vacation aspect also limits to a certain degree the benefit of the solar water heater, since we have large and fluctuating water usage/load, which is the opposite of what one would like for solar heating (consistent use is best).

Another big variable is degree days (for heating), since we heat the houses with electricity. Last year (2006) was 1% colder than 2005 as measured by degree days.

In trying to tease out some conservation effect, I found that we used 2% less electricity in the June-Sept period of 2006. These are the four months with no need for heating so one might expect to see a more noticeable effect from the more efficient lighting. Also the main house registered the lowest monthly energy use (by 10%) of the past three years in June (which is the month the bulbs were changed, but before the solar water heater was installed). Still, the end result is a bit disappointing. I will see if we continue to have lower summer bills in the future, and try to figure out a way to measure “people days” going forward.


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