Winter Solstice: Solar Power vs. Day Length

The winter solstice at the end of December is a tough time for solar power. It's the shortest day of the year and is prone to cloudy, rainy weather that inhibits good energy generation. I like to take a more positive view and be glad that after today generation will be improving every day. Now that I've got a year of data under my belt I thought it would be interesting to compare my production with the length of the day. The chart below shows my daily solar production (in kWh) in blue and the length of the day (in hours) in red.

Click to enlarge

There's a pretty clear correlation between the two, though the solar production numbers are highly variable (thanks, weather!). Production drops off noticeably in late July and August, some of which can be attributed to the two panels (of 14) that were out of service during that time. Solar power is great, but this goes to show how important it is to have a diversity of energy sources that aren't dependent on weather and the length of the day.