Solar Panel Issue

[Dr._Prof_ECECS]

I have an Eco-worthy 24V AIO inverter system with 2S-2P batteries and 2S-2P solar panels (4 panels in all; bought used, buy one get one deal! Each panel rated 30.8V Op. voltage and 8A ==> 240W or a total of 960W generating like 720 to 800Watts. I had it in ground mount in a rental house for a year and moved them to another rental home. After the move the unit worked well for a week, but suddenly the output has halved. I traced the issue to one pair of solar panels (I used the individual fuse for the two parallel connections to operate one at a time). For 10 minutes (my app records every 5 minutes) I had like 1) 54.6V, 5.6A 2) 53.7V, 6.0A, then it went 1) 24V, 0 A. 2) 0, 0, 3) 0,0, 4) 24V, 0A, and drifted slowly to 22V, 0A in an hour.
I connected the other parallel 2 solar panel alone and they were the ones giving me the half power at approximately 40V, 8 A. or 320W.
Can anyone figure out what is happening to those 2 panels where the open circuit voltage is only 20V and getting zero current. I thought of testing each panel (OC Voltage) but I am a 75 old senior citizen and thought I will ask first if there is anyway to check further without physically yanking the MC4 (or whatever) connectors as it is a PITA in the Tucson hot sun. I have the knowledge (see my screen name) to test further if given any hardware suggestion like opening the electronic box under the panel to test voltage etc.
Thanks.
Here is a snapshot when both were working. Peak like 720W with both working at 45V, 8A, I suppose.

 

[Dr._Prof_ECECS]

 

[Glock24]

Well of they hace no shade on them and they were working just fine before I think the problem might be a bad connection, so you would have to check all connections.

 

[42OhmsPA]

What's the min and max VOC of your MPPT?
I'm wondering if 2S isn't enough to hit the minimum to "wake it up".

 

[DVD]

I suspect you’re going to have to dig deeper and tackle those MC4s to get to the culprit. Tucson temps notwithstanding, 75 is still a pretty decent number to be digging deep into this stuff.

 

[Dr._Prof_ECECS]

Thank you all for responding.
Yes, I went ahead and pulled out the MC4 connectors for testing. The individual OC voltage came about 36V, around the spec. I checked the short circuit currents in both of them. Came out to be 6.4A (as opposed to spec of 8A), again not bad given it is old.
In a hurry, I put it back but it is not adding any power.
I realized I should have checked the diodes. Especially since the 2S panels start with op voltage of 40 and soon go down to 24V. Perhaps this indicates one is getting shorted after some 10 minutes.
@42OhmsPA -- This is a system that has been operational for 1 1/2 years. The MPPT op voltage range 30Vdc to 80Vdc. In fact, in the initial install, testing, I found it would not work as 1S4P (as the op voltage for the individual panels is also 30.x Vdc when brand new). That is why I went for 2S2P config. As you can see the picture I added / the numbers I gave, I am seeing, for the one 2S panel working, 40V, 8A. The defective 2S config is giving just 24V op. voltage. Let me add another power image where the defective pair was connected for 2 hours (9 to 11 AM) and I switched to good pair after that. You can see that the defective pair generated power (300W as expected) for 10 minutes and went silent after that. So, one panel is doing something that 1) the voltage is not going to the open circuit 36V (stays at 24 which is higher than the op voltage of a single one of 20V) 2) but no power getting extracted (24 not enough for MPPT).
@Glock24 If connection is a problem, how did they work for some 10 minutes? Heating? of what. the diode?
Thanks.

 

[MisterSandals]

Please change your color scheme if you are going to be posting these without warning...

 

[Dr._Prof_ECECS]

@DVD @42OhmsPA @Glock24
Thank you guys, the problem solved.
Weekend, I removed the MC4 connectors, tested for diode issue -- I(infinity) in one direction and some 560 in my cheapy multimeter. What number that represents?
Then I tested each wire for continuity and found one connection at the combiner box has become loose and showed OC. I pulled out the whole unit and bundled the wires haphazardly when I moved and might have loosened the connection. I tightened it and the system is working good now producing like 180 watts per panel (720 total) at peak, good enough to keep my window AC running during the peak rate hours 3 to 7 PM during summer .

 

[Glock24]

Glad you could solve your problem and that everything's working fine now. Enjoy the cool air.

 

[Backyard]

@DVD @42OhmsPA @Glock24
Thank you guys, the problem solved.
Weekend, I removed the MC4 connectors, tested for diode issue -- I(infinity) in one direction and some 560 in my cheapy multimeter. What number that represents?
Then I tested each wire for continuity and found one connection at the combiner box has become loose and showed OC. I pulled out the whole unit and bundled the wires haphazardly when I moved and might have loosened the connection. I tightened it and the system is working good now producing like 180 watts per panel (720 total) at peak, good enough to keep my window AC running during the peak rate hours 3 to 7 PM during summer .

That 560 your meter showed on the diode test is the voltage drop across the diode (0.56V). From your description, it's working fine