Why is PEAK output for solar less in winter?

DIY
1

Yes I mean PEAK not the total, the latter which is obvious due to less sunlight hours in the day but it is not immediately apparent to me why peak will be lower.

Is the sun just further away from the earth in winter, producing less useable energy? EDIT: I just looked it up and apparently the sun is closer in winter in the northern hemisphere not farther away! So there goes that theory!

I installed my new string towards the end of autumn and for the first week or two the MPPT would consistently be clipping at maximum output at near 40A.

As the sun got lower and lower so has the maximum output of the panels and I cannot recall the output breaking over 30A current lately. Maximum is high 20s for short periods, weather permitting.

I tried compensating for the lower curve by angling the panels to near vertical. This may have increased it but too many variable mixed clouds to say for certain, which causes the output to jump around all over the place anyway. It does seem to have made a difference during sunrise and sunset, with higher starts for each.

I also moved the panels up the hill to clear the trees which were blocking due to lower sun trajectory and this still hasn’t allowed them to reach their previous output.

So is it expected to just be less overall due to winter? If so what is the reason?

2

One factor is the “Air Mass” → AM. As the sun is getting lower the way the sun rays needs to get to the panel through the atmosphere is longer. AM for STC is 1,5 (48,2° Angle). In winter time AM rises to 2 or 3 - depends on the exact global position of the panel ….. and this lowers the peak output (even if the panel is pointing perfectly to the sun)

Hope it helps

Jens

3 Likes
3

That, and sunhours per day

4

WELL with the sun being lower in the sky my neighbours TWO ENORMOUS PINE TREES are right in line with my roof mounted panels and the sun in the sky from about 12:00 till about 15:00. So here was I wondering what the problem was when I saw a massive dip in my solar output UNTIL I went out into the garden and saw what the problem was :frowning: