How to swap strings to test if Inverter is faulty

[Sandy67]

HI, One of my two strings did not work today and generated 49V and 0W. Its string one and should have generated at least 1800W on this sunny day. I was told it could be a faulty panel, but the system is temperamental and both strings work and some days only one string will work. I think it's the Inverter but I need to be sure as I have been told to swap the strings around to test, but not sure how and when I should do this.

Any idea on the above? I have Tigo's on all but Tigo data is not available today due to some upgrading, so hope they can send me data s I should be getting a warning if the string is faulty at least.

Appreciate any support

 

[chrisski]

My strings are connected through a Combiner Box and I could shut individual strings off. I am set up 4S6P.

I would swap mine at the combiner box. There'd be a bit more to shutting it down prior to the actual swap.

Are your strings connected through a combiner box or are they connectoed directly to your AIO/MPPT/etc.?

 

[Sandy67]

I dont speak Solar, so not sure what Combiner is, but MPPT is more likely here in UK as the norm and it was a standard installation.

 

[wildbillpdx]

Combiner box is used to attach multiple PV strings to your system:

 

[Hedges]

May be bad connections, or damaged panels. If they every put out part power, use IR thermometer or camera to look for hot spot.

Whether part power or no power, try probing for voltage.

Screw terminals holding a wire can loosen. Best with power off and PV array unplugged, you can pull/wiggle connectors. I wiggle while snugging screws, because stranded wires settle.

But if bad connection in MC4 connectors, not accessible. Mix-n-match MC4 connectors are a known failure point, sometimes causing fires. Do you have any mixed brands? You could wiggle while watching voltage reading or inverter power.

If you have a suitably DC rated switch to handle string Voc and Isc, you can short the string to measure current. Series through a DMM can be done if current not too high, but DC clamp ammeter is easiest.

By disconnecting individual panels, they can each be tested. I found a couple degraded ones that way.

I also connected individual panels in series with electric heaters (radiator type, 120V in my case, couple in parallel for 6 ohms which would be near Vmp/Imp. Switch left on and thermostat turned all the way up, because those can't switch DC.) I found a couple more degraded panels that seemed ok for Voc & Isc, but they weren't for V(load) and I(load).