Need help diagnosing solar system


New Member
Sep 25, 2021
I have an older 26 panel 5.6KW system. I believe they are Mitsubishi panels 215w each connected to a Fronius IG Plus inverter. There are two strings of panels. I recently had the panels removed for a roof replacement.

Just to shorten the story, I hired a contractor that was impersonating another company. They did a horrible job with the installation. After they were done with the install, the system was only putting out 50% capacity and they came out did some work for an hour and then it was producing full power. The guy didn't seem to know how he fixed it. He said he tapped either the inverter or the j box and then it just started working. It was a very iffy response but his English was bad. A month goes by and a ground fault fuse blows in the inverter. The system is leased and Tesla came out. Tesla said it was such a shitty install that they wouldn't touch the system. They recommended I have the system pulled and reinstalled.

Fast forward a month and I found a contractor who has ran into the first guy I hired in the past and told me that he has been scamming people for a long time. In exchange for making sure I contact the ROC and file a complaint, he agrees to pull the panels and reinstall the system for a agreed upon price. The second contractor then used a couple of guys that didn't seem to know what they were doing with one of them being his son.

So this is what they did:

They pulled the panels and checked them. These were checked by the contractor himself and not his guys. I was told the panels were good (He would later tell me he only checked for voltage and that he wasn't really sure if they were good or not).

They leveled the rails the best they could as everything was crooked. They took the panels off the roof to do this.

They slowly reinstalled the panels. One was dropped from ladder height while lifting it back to the roof but it appeared OK. I was told that some of the MC4 connectors were on backwards and they rewired them.

On the last day I found out that the contractors son connected one string of the panels backwards. They thought they blew the fuse in the inverter. They didn't know that it was already blown. They lifted approx 8 panels before they found the one that was backwards.

The contractor basically had his son contacting me at this point. He kept trying to locate a fuse for the panel. Telsa took the fuse when they came out so the contractor didn't have anything to go on. After waiting a week and the contractor son coming out with the wrong fuse, I found what fuse the system took simply by calling Fronius and had it in my hands the next day.

Fuse installed and the system is fired back up. It is only putting out 50% power. I notified the contractor and he blames it on the panels not being installed correctly the first time by the other contractor. I said that can't be possible because he (the new contractor) checked the panels after pulling them and he verbally told me that "Well, good news, all the panels tested OK".

I think there is still a wiring issue with how the panels are ran. They are basically refusing to come out at this point saying the panels were bad from the last guys install (They found at least one panel mounted with a loose mounting bolt on the rail pushing up in the middle of the panel bowing it). I only saw one but now they are claiming there were at least 10 like that and that ruined the panels and now they don't have full capacity which is why my system is putting out such a low output. They said that after testing the panels, because they were bowed, the panels eventually relaxed back to their normal shape and now were bad. This excuse sounded like complete BS to me. Even if 10 of the panels were 100% failed, it would still have more capacity than what the system was putting out. I honestly think the guy is lying to me at this point because he is just done working on my system. It ended up being a money loser for him because they were so unorganized and his work truck was stolen in the middle of the job with a lot of his supplies and tools. He is located over an hour away and every time they forgot something they would have to pack up and come again another day.

Any advice on what I should do? Can the panels be checked without pulling them again? Could it be an inverter issue? Could they have fried a string of panels by wiring it backwards which is why I am down to 50% output? Is there anyway to check that? I also paid the new contractor partially by check and by credit card. Does this sound like a case where I should initiate a charge back with the credit card?

I have a 15 year lease with Solar City (Now Tesla) that was completely paid off by the homes previous owner. There are only 3 years left on the system. I've already spent more than what the system would have saved me through the end of the lease. I don't know if I should just live with the reduced output until the lease is over or spend any more money on this thing and hope it is left in place once the lease is up. Anyway, I'm seeing what trouble shooting steps I can take myself at this point.


Works in theory! Practice? That's something else
Sep 20, 2019
Key Largo
Wow! What a nightmare!

My first question would be is how safe do you feel working around high voltages on the roof. If not, then don't do it.

I didn't see your 215W panels listed in the CA GO database, but the two close matches were about 29.3V and 7.4 amps, so a string of 13 is probably around 380V and 7.4 amps around solar noon.

Next would be if you happen to have or have a friend/relative with Flir? If so, you might get a hint with it, see

I have microinverters with per-panel diagnostics so no real experience diagnosing string problems. Hopefully, more knowledgeable people can give you better advice.

But with a good DC voltage/clamp meter you can get the current from both strings and it's relatively safe to do. You're at 50% power, so it might be as simple as one string not producing and there's a tripped breaker. If they both have some reading it would be useful to know the power in each and time of day the reading was taking (typically voltage is fairly constant through the day and current varies based on the amount of sunshine). Possibly your inverter has diagnostics or something you can share?

A panel can also be tested individually with the open-circuit voltage and short-circuit current from each. If you want to give that a whirl but aren't sure how just say so.

...completely paid off by the homes previous owner. There are only 3 years left on the system. I've already spent more than what the system would have saved me through the end of the lease....

The system will still keep producing after 3 years. It's not like a light bulb that burns out, they dont always die, just produce less power over time. But if it's at half power now and you want to replace it in 3 years anyway, then you're right it might not be worth doing anything with it now.

Possibly some of the professionals like @HomeEcGuy or @Supervstech can let you know if there are actions/recourse you can take with your idiot vendors. Hope that helps and wish you the best of luck!


Staff member
Sep 21, 2019
Wow indeed!
My first step would be to contact a solar qualified electrician. Not a solar installer, not a handyman, a vetted, recommended insured and bonded electrician. And have them inspect the wiring, and each and every connection…
You don’t want uncontrolled solar outputting DC high voltage into bad connections taking down the house.

I would also report the second contractor to the same authorities you reported the first one to.

Keep us posted.