Monday, July 09, 2018

Suburban 5-4-and-a-Door Solar: Savings in the First Year

We have now had our solar array for a year's worth of bills. Since our array gives us data for every 15 minutes, that's a lot of data to analyze (a 15MB Excel workbook at the moment). But here's some of the more useful graphs from our experience.

Probably the most asked for - what is your bill with solar compared to without solar. Our total bill for the 12 months ending June 30th was $1541. Compare that to last year at $2064 or to our peak year at $2502 and there's a significant savings. If you want to use average bills over the last four years as a comparison, we've saved about $770.

Average bill isn't the best way to compare, because we were making moves to lower our overall energy use during that time period. We're switching burned out light to LEDs, we're using the clothesline more, etc. You can see that dramatically in the graph of yearly grid use.

From a peak of just about 20,000kWh for the year ending in August, 2015, we've dropped to about 12,000kWh for the year ending in June, 2018. That's a drop of almost 40% over three years, and you can see from the graph that the drop started before we had our panels installed in June, 2017. There is a dramatic drop starting when the panels were installed, as would be expected. from what looked to be a leveling off point. We suspect that the graph will start to level off again now and maybe drop again in a year when we start losing kids to college.

Calculating the actual savings versus what we would have paid over the last year without solar panels is more difficult. Determining exactly what the power company charges for power is surprisingly opaque (see this post for how we tried to estimate what power really costs). Using our best information and the power usage information from our smart meter, we estimate that the bills with and without solar would reflect a somewhat more modest savings.

Using those relatively complicated calculations, we see a yearly savings of about $670. So we tell folks that our actual savings is somewhere between the average bill savings and our calculated savings - $670 to $770.

Our original ROI estimates for a 10-11 year return were $740 savings in year one, so we're pretty close depending on our calculations.

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