Three years of solar power from my panels.

We have now had PV panels for more than three years and I have been taking readings (fairly) regularly - here is a short analysis showing mean daily yield by month, and for comparison I also have mean daily sunshine from the University of Cambridge weather station by month. Three years is not a large dataset but it is lot better than two.


The electricity generated is fairly consistent between years, although it has varied more in March/April  than in the latter part of the year.

Sunshine is more variable than the PV yield. This is for two reasons: firstly solar panels perform fairly well under hazy skies and secondly they become less efficient if they get too hot - so long hot sunny days in summer don't help as much as you might expect: July 2013 was very sunny but the PV yield was only a bit better than average. This probably explains why there is more variation in spring, since even when it is very sunny it doesn't usually get too hot.

In all three years the actual yield has exceeded the original estimate which was 1223 kWh/year. (We have a 1.67 kWp array with some shading issues). The worst year was 2012 when we only got 1311 kWh - still 7% more than the estimate. The best year was 2011 when we got 1359 kWh - just 4% more than the worst.