If you want to “go green” for environmental reasons, that’s great. If you want to do it for financial reasons, that’s great too, but what I’ve discovered is that it might be difficult to quantify exactly how much you are saving.

I’ve been waiting since last year to calculate the savings from our solar water heater. I put together a spreadsheet comparing electricity and natural gas usage over the 12-month period before the installation, and the the 12-month period after. What I can say is that our monthly electricity usage increased an average of 20% over that time, but our natural gas usage decreased by 31% — almost a third!

Those numbers are encouraging, however, it is difficult to put actual dollar amounts on them, and determine the cost savings overall. Since utility rates fluctuate in general, and have changed dramatically in the last two years in particular, it is hard to say whether a change in our monthly bill (either up or down) is a result of the system’s performance, or just arbitrary rate changes. The calculations are further complicated by the fact that we’ve chosen to lower our thermostat slightly from last summer so our air conditioner has been running more this year than last. So the “green vs green” challenge remains unsettled, but I will continue to monitor it and report whatever I find.