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Wednesday, April 4, 2012

Better than expected!

by Tom Ferrio

Regular readers of Progressive Charlestown will recall that I described the installation of a solar electric system at our home in January.

I received a surprise with our bill for mid-February through mid-March.

My earlier reports on the installation and cost of the solar system can be seen here.

Here is the bottom line from my March 2011 bill, last year before the solar system

And here is the bill I received a few days ago

If you heard a loud "wow" echoing across Charlestown that was me (and sorry about the noise).

Of course the weather was considerably warmer in 2012 but we don't see much change in electric use with temperature. We heat with wood quite a bit. The billing cycle was also one day longer in 2011 but that should only account for a couple dollars.

Even if this continues, it still doesn't make this an incredible investment. But we love being green and believing that we are doing our part to reduce natural gas consumption.

For the technically inclined here is a bar graph of daily use and generation for that electric bill (click on the image to enlarge). The turquoise lines are the solar electric generation, the pinkish lines are our usage and the dark blue are our net purchase of power for National Grid. A few days were negative for the entire day, meaning National Grid paid us on those days.


  1. I wonder if your gain is, in part, a portion of the warm winter?

    1. I have been thinking about that but cannot give a good explanation for a large change because of low temperature. We did use about twice as much propane last winter and I could see how that might result in a half-dollar/day or so to run the furnace fan and pumps more.

      A big thing would be if we used the electric clothes dryer a lot more but that isn't obvious.

      I might still be missing something related to temp...

    2. Wow, wicked cool. Wish my house was tilted the right way and that my trees were shorter so it would've been worth it for us to do it. I imagine the fact we had so many sunny days this winter where you didn't need electric light as much also helped.

    3. Yes, I bet the amount of sun is part of it. Less lights and more solar than would normally be expected for that time of year. The mathematical model says I should get 1.5 times the solar in July versus February. If that were true I would end up negative for the month but I somehow doubt that will happen...


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