Hi folks,

Yesterday I noticed my production was 30% down from the usual. I have 3 strings of panels (3x330w each). Each string has the 3 panels in series, to get to around 110V, and then they all connect in parallel to my Axpert Inverter.

After some quick diagnostics, I found out one of the strings was not giving any power to the inverter. (I realized this by disconnecting one by one, and noticing that this one did not make any difference being unplugged or not).

I spent most of my day trying to check the cables (some of them underground), and making sure there was no connectivity issue. I tested connectivity with my multimeter and everything seemed to be ok (I did not want to dig the underground cables...)

I checked the voltage of this particular string, and it was ok at around 110V.

Today I tried something else, and this is when things begin to get weird.

I disconnected completely the 2 good strings. I measured the voltage of the bad string before connecting to fuse box+inverter. 110V as expected.

Once I plug things on, the voltage drops to about 50-60V, and the inverter is not able to "connect" the charge (it does this "click" sounds every couple of seconds).

I'm lost trying to understand what this might be. Please let me know if you have any ideas. I really do miss those precious 30% now in winter time

Edited October 20, 20214 yr by Nuno

31 minutes ago, Nuno said:

I disconnected completely the 2 good strings. I measured the voltage of the bad string before connecting to fuse box+inverter. 110V as expected.

Once I plug things on, the voltage drops to about 50-60V, and the inverter is not able to "connect" the charge (it does this "click" sounds every couple of seconds).

It sounds like you have high resistance somewhere in that string. As soon as there is a load, even just the Solar Charge Controller idling, the voltage collapses.

It could be one of the panels, or the wiring, the connectors, or a fuse or its holder.

If you're handy with electricity, you could load that string with say a jug element, then use a multimeter to find voltage drops during the day. You need to be careful with moderate power DC like that; for example, ordinary AC switches can't interrupt DC properly, you could damage your eyes through UV light from an arc, and so on. Otherwise, you'll need to pay someone to troubleshoot it.

Update!
With only the bad string connected, I took out one of the panels and I think I got lucky right on the first one! I tried to connect the string with 2 panels to the inverter and it began charging! So i guess I found out the culprit.

Is it worth to open the panel's "box" and look into some possible issues I can fix? Or is it good to replace? (its only 2 years old )

You can watch these videos to give you an idea of what could be wrong.

By the way what brand are your panels?

 

thanks. will take a look

I did open the panel's box but found out the whole thing was immersed(for lack of a better word) in some kind of silicone. I guess thats to avoid people messing up with it 😕

They dont really have a brand.. some sort of generic

since I got down from 9 to 8 panels, I wonder if its worth to reconfigure my setup
from: (3x300) + (3x300) + (3x300)
to: (2x300) + (2x300) + (2x300) + (2x300)

I need to get new cables for that and re-do some wiring... is it worth it?

Edited October 20, 20214 yr by Nuno

8 hours ago, Nuno said:

I need to get new cables for that and re-do some wiring... is it worth it?

It could still be something simple like the connectors. Try shorting the panel (in the shade), then put it in the sun and check for current with a DC clamp meter.

It could be that the panel is fine, and you have some sort of intermittent problem.

I would not do the rewire: it's a lot of work and expense. Better to find a replacement panel (if needed), with a Vmp within 5% of the others, and at least the same Imp, it could be higher.

Though certainly 2S4P would work. You could then add a fifth and even sixth string at a later stage, with just 2 panels each time (but more cable, fuses, etc).

A friend sent me this, from a job he was on recently. This MC4 connector was never crimped when the idiot installed it! No wonder the client had issues with the system not performing.

I'm pretty positive its the panels fault. Today I'm getting slightly more power than the 2 previous days. Around 200W more (not a full sun day), so I'm guessing its due to the other 2 panels now being connected and outputting some power. Not sure at what rate are they working now, since the voltage of this string will be always lower than of the other two strings...

Err, you can't put a 2S string in parallel with 3S strings! It's dangerous, there is a risk of fire. The other strings can push power into the shorter string, turning the panels in the shorter string into infra-red LEDs.

My apologies if I have misunderstood what you have done. 

Edited October 21, 20214 yr by Coulomb