November through February are pretty dark months in Seattle. Often you’ll leave for work before the sun comes up, and return home after the sun goes down. You might get a sunny week or two in January, but most years February’s got you searching for clinical definitions of Seasonal Affective Disorder.

Because my solar array was installed last fall, I have been paying extra close attention to insolation statistics through this period, the darkest third of the year. I now have data for four full months of operation, which should essentially tell me the worst news I can hear about how my solar array is performing.

Chart showing monthly solar data

February has been the best month so far, with roughly 61% of our electricity needs powered by the solar panels. By contrast, December’s solar output offset only 32% of our electricity. Overall, we are seeing approximately 45% of our demand being supplied by solar power, with an average daily output of about 5 kWh from the renewable energy source.

At some point this summer (July? August?) I bet we’ll see a crossing of those lines on the chart, indicating that solar is providing full coverage of my electricity and then some. That said, this exercise has been a good reminder to me to work on limiting my consumption, at the same time as I cross my fingers for sunny days ahead.

Just a quick entry today, with performance data from the first four weeks of my rooftop solar array. The news is both disappointing and hopeful.

During this time span, we used an average of 12.3 kWh per day, which is more than normal for this household. More on that in a moment. To meet that daily demand, just a tick more than half (6.2 kWh) came from solar power production. 6.1 kWh had to be purchased from the utility.

Over time, I think we’ll see the percentage of my electricity needs offset by solar go way up, from roughly 50% to closer to 100% or more. Here’s what I think happened:

  • Household demand was up due to wrapping up a remodeling project from the summer. Lots of power tools plugged in in the garage, and at one point a high-powered fan blowing 24/7. (Don’t ask…it had to be done.)
  • Solar production was weak for days at a time, as we got soaked with much higher than normal rainfall in October. What I’ve observed so far is that the array is of course highly productive on sunny days, surprisingly productive with the indirect light of partly-cloudy days, but scarcely productive at all on those wall-to-wall rainy days that the Pacific Northwest can sometimes have.

As we head in to the darkest weeks of the year now, it’s possible the array will offset even less of my overall electricity needs. But I knew this going in. Spring and summer of 2015 will be the big test.