A year ago yesterday I was toasting the completion of the solar array installation at my house. At the time, I knew that if I wasn’t at the cutting edge of the residential renewable energy movement, I was at least in a very small minority of homeowners who had actually purchased rooftop solar.

Now we finally have a large enough sample size to look at the data and draw conclusions about the effectiveness of the installation and how it fits into the context of this home’s energy use.

Production from the panels: 15.1 kWh per day

Electricity use in our home: 11.3 kWh per day

The sunlight hitting the surface of the 20 solar panels on my roof for a full year produced 5.5 megawatts of electricity, which is exactly what was forecast by the company that installed the system. So the system performed as expected, factoring in the location and orientation of the roof, the number and wattage rating of the SolarWorld panels, expected shading from backyard trees, and so on. I’m very appreciative to Northwest Electric and Solar, as well as Solarize Bellevue, for their honesty and accuracy in setting expectations for how the array would perform.
Some notable details on the production side:

  • The system averaged 15.1 kWh per day. Over time, it’s normal to see slight decreases in production, so it will be interesting to track, year-over-year, whether the system will continue to generate close to this level of production.
  • Production was highly dependent on season, even more so than I had anticipated. For example, December was unable even to crack 4 kWh per day. June, on the other hand, soared to just over 30 kWh per day. The best six-month span (what I like to call the baseball months, April through September) produced nearly 85 percent of the total for the year.
  • Cleaning the panels had little to no impact on production. I cleaned them myself one morning, and although I could see a difference in the appearance of the panels, I was disappointed to find no difference in the “before-and-after” numbers. However, I will likely have the array professionally cleaned just to confirm.

Probably the first question any homeowner considering solar has is, “Can the panels take care of all my electricity needs, and spin my meter backwards?”

The data bears out that this was definitely the case at our house. But it should be noted that our electricity consumption is significantly less than the average American household. The house itself is relatively small (fewer than 1400 square feet), there are only two of us living here, and we try to make energy-efficient choices in lighting, appliances, and so on. So the medium-sized array on the roof easily handled our electricity needs over the year.

Earlier this year, I purchased an electric vehicle. Right now, because of a promotional perk, I’m charging it free at fast-charge stations outside the house. But eventually I will use the charger I had installed in my garage. That will most likely use up the surplus electricity from my panels, putting us back at approximately net-zero. We could always add more panels to the roof, so that production continues to stay ahead of usage. At the moment, I can’t see doing that, but it is a good reminder that solar scales at least as far as your rooftop allows!