Troubleshooting a new array

[ebenbayer]

Hey All,

Scratching my head a bit after some recent power output changes and looking for some ideas!

Situation:

New (9 mo old) Array using Solaria XT 325 panels (https://www.solaris-shop.com/solaria-powerxt-325r-px-325w-mono-solar-panel/)

21 panels, wired in strings of 3, going to two mid nite classics via a mid nite combiner.

4 strings == ~3.9 KW
3 strings == ~2.9 KW

Set up in Fall, around May of this year the 3.9 KW array power output dropped to match the 2.9 KW array output.

I assume a string or panel in a string must have gone out...

Just checked each strings open circuit Voltage. 7 were at 117.9 (this AM) +/- .5

1 string was at 113.5. I removed this string (took fuse out). And there is basically no change in array output. (e.g both arrays remains balanced).

Does this mean one of those panels is out? I assumed if a string went down (e.g bad panel) that it would pass a voltage. Or I suppose that it would be further clamped down.

my assumption at this stage is at least one panel in that string is out, and next step would be to break the string up and test each panel.

Does this make sense? Anything else to consider? And would a single panel failure on a string of 3 give only a slight change in open circuit voltage?

Thanks for any thoughts or suggestions

E

[ClassicCrazy]

If you wanted to test the output of each panel separately you could disconnect the wires on each panel and then test the voltage for open circuit voltage Voc  and then short the leads and find out what the short circuit current is Isc  . It helps to have a DC clamp meter to test the currents though if you can do it with regular meter as long as you know how to set up the meter in series for the current test.

If you have a DC clamp meter it is also easy to test the current on each string of panels and compare them. There are some inexpensive DC meters if you don't have one.

Larry

[ebenbayer]

Thanks!

Roof is hard to access (45 degree pitch, metal, 20' off ground). Trying to get as much thinking done before going up. (the combiner is inside, so easy to take measurements there).

I think I have a clamp meter, I'll take a look, at the very least I can test the Isc of the string before I get up there.

[Westbranch]

Are both arrays attached to the same battery as well as the hydro?
How charged is the battery, SoC?

[ebenbayer]

Yes,

All attached to one battery via 4 classic charge controllers (3 solar, 1 for hydro). Battery SOC has carried over the past 30 days from 20-100%

the 3.9 KW array dropped its output abruptly (looking at logs of average production, similar shading for the 2.9 and 3.9 as they are on same roof); for instance, today (perfect clear day in upstate NY) both arrays are 6.1 Kwh for the day. prior to the drop off they would have been closer to 6.1 / 7.9 Kwh for day so far (e.g 30% or so more on the larger array).

The power characteristics make me think its a string issue; hopefully shorting the defective string will give me some more insight....

E

[Vic]

ebenbayer said,  "   ...   looking at logs of average production, similar shading for the 2.9 and 3.9   ...".

Speaking of Shading,    any shading,   at all,   can really kill Solar production.

Is there any shading at all on any of the strings,   particularly the one suspect string (if you can easily tell)?

Thanks,  Vic

[ebenbayer]

Hey Vic,

Shading at start and end of day. the smaller (2.9) KW array gets slightly for more shading at end of day; These panels are in a good spot.

I'm mostly looking at peak output (during completely non-shaded times.) and noting that the the arrays now match ( to within a few watts at any given second) compared to start up. Where the larger array had a predictably larger peak + average production. A this point trying to confirm I have a defective panel so I can order that before going on roof... (Or, find another possible solution)...