Funky facts about your solar PV

... otherwise known as stupid questions I asked a real expert and got answers to

Q. My generation is a bit low even though it's sunny. Has one of my panels died?

A. The panels are generally wired up in series as "strings". You'll probably have two strings if you've got an even number of panels. If one panel dies, it will usually knock out a whole string so the generation will go down by 50% rather than 10% (which is what I had had and which started me asking silly questions).

Q. Why isn't my peak generation as high now as it was in January even though it seems sunnier now?

A. Solar PV works best when it's cold and bright. You lose about 0.3% generation per degree centigrade the temperature goes up.

Q. Why isn't the highest generation at noon? This really bugged me as I studied astronomy at University and I just know I did the calculations right.

A. Several factors:

  • First, noon GMT is the theoretical highest sunlight at Greenwich.

  • Second, Devon is 4 degrees west of Greenwich so the sun is highest at about 12:15pm GMT.

  • Third, because of the temperature, the maximum is a bit earlier (the temperature is higher in the afternoon so generation gets pushed down, lower in the morning so it is a bit higher that you'd expect)

Q. Why isn't the generation graph symmetrical for each day?

A. See above. Even though the start and end of generation are about the same time before and after 12:15pm, the temperature makes afternoon generation lower and morning generation higher.

Q. Why does my generation go up after it rains or if it is windy?

A. Temperature again. The wind and rain cool the panels down.

Andy Chapman