Readers of my posts will know that I collect quite a bit of data about my solar panels. Once a year I like to take a look at the bigger picture and see how the system is performing over time. First some quick numbers: Overall system efficiency averaged just over 13.1% in 2015, slightly up from 12.5% in 2014. The panels themselves were also a bit more efficient, up to 14.4% from 13.7%. This is a little surprising since they're expected to drop 0.5% per year.
Panel efficiency doesn't seem to correlate terribly strongly with temperature, although there may be a slight downward trend as the temperature goes up.
Similarly there's a small negative relationship between panel efficiency and the amount of solar exposure, likely because sunny days also tend to be warmer. It does seem a little weird, though, that the panels perform better when there's less sun available.
Just for comparison, here's the relationship between solar exposure and average temperature.
Here's how solar exposure varied over the course of the year. It's interesting to see the maximum values tracking very closely to the sinusoid I'd expect. My weather data doesn't include cloud levels, but I'd hazard a guess that the maximums correlate to sunny days.
Panel production was very consistent with the solar exposure (with the exception of a few outliers).
Last but not least, here's my electricity use compared to average temperature. It's interesting to see that it seems to be a curve, with higher use at the (relatively) extreme temperatures. I assume this is because I run a lot of fans when the temperature gets high in the summer, and the heaters (gas heat, but electric fans) in the winter. The high outliers are probably laundry days.