The system was initially sized with the intention of completely canceling out our electric bill. Of course, there are a number of factors that can cause actual generation in any given year to vary from projected generation, of which variations in weather is probably the largest.
Overall, we came pretty close to hitting our target; our net electric bill for the year was $100, only about 5% of our actual electrical usage. I'll call that a success.
I knew that we'd get a lot more power generated in the summer than the winter -- longer days, better sun angle (power generation is proportional to the cosine of angle of incidence), clearer skies, and no snow on the roof. But I was surprised by just how big the swing was -- almost a 10x difference between generation in June and generation in December.
Below is a graph of cumulative power generation by month over the past twelve months; the Y axis is kWH.
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