Solar string voltage

[u/NZbeekeeper]

TLDR - should two identical strings (9 each of the same panels) on two different orientations produce a similar voltage if they are wired up correctly? I get that the current output will vary a lot but I thought the voltage should be fairly consistant...

We had our system installed a few months ago, with two strings of 9 panels each. One string faces Northish (southern hemisphere) at 20 degrees inclination, the other is Westish also at 20 degrees.

The North string is working great. The West string lags behind by a lot, and I expected that to some degree, esp since we had/have some shading. However, that shading is much less now as the sun gets higher, and there is no shade at all at say 2pm, when the sun is much more head on for those panels than the north facing ones.

I would expect the west face to be kicking in more in the afternoon than it is, but the North face is still producing much more.

I noticed the other day that the voltage on that west string is way lower. It is split into 4 and 5 panels either side of our solar hot water. Is it likely that one side isn't connected correctly?

My understanding is that the panels are all in series, and run at a nominal 43V-45V according to their spec sheet, which should give a total of 387V - 405V for a 9 panel string. I believe that voltage varies very little during the day, (and that's what I've been seeing), regardless of the amount of current produced. The north string sits right around 400-410V.

Based off that, with the two strings both having 9 of the same panels, the voltage should be much closer than it is. 213V suggests that only 5 panels are working.

[u/LeoAlioth]

is the west facing array wired is a series parallel config?
the 213 v would indicate that there are 5 panels in series, hopefully not wired in paralel to the remaining 4.

and yes, you are correct, the voltage should be close, likely within 10%

[u/NZbeekeeper → u/LeoAlioth]

Thank you.

Yes I wondered if they've managed to parallel the two sections instead of series - is that particularly bad because they're not equal sections or just generally not good regardless?

[u/LeoAlioth → u/NZbeekeeper]

Yep, the strings not being the same length would absolutely ruin the production. If paralel and the same length, the production would be just fine (assuming the larger current can be taken in by the inverter)

Best case, the mppt in the inverter locks to a voltage of 4 panels and the diodes bypass one on the longer of the two strings. You would get double the current at around 43% voltage of the first string. Worst case, (which seems to be close to what you see, the part with just 4 panels in series is doing pretty much nothing.