PV String failure

tnegun

One of my strings failed a couple of days ago, around midday, during the high heat. There's no voltage from the string where it comes into the roof. I pulled the MC4s from the fireman switch and confirmed it's dead at this point. It's an awkward roof to get onto so I want to be prepared if possible for when I do get up there. Any ideas what I'm possibly looking at? I'm thinking a bad or burnt MC4 connector or is it likely that a panel itself has failed? I put a drone up, and externally, the panels look good at least. Any tips/suggestions before I try get up there? Thanks!

10-10-20

All the panels are in series, so it's most likely to be as you said - a damaged or burnt MC4.

From what I have read and seen photos of, if a panel had a fault on the copper traces you would expect to see a spot where the glass is discoloured. Example off the internet below.

Buffman

Presumably you're out of warranty with your installer or was it DIY?

It would be a very awkward job on your own, hopefully you've a 2nd pair of hands to help, ideally to hold/swivel each panel up a bit while you inspect/test the connection. You never know, might be the first one you check! Maybe do a diagram/list to keep track of what's ok as you move along.

Presumably you have MC4 tool for disconnecting to get a reading.

Ideally I'd have a replacement MC4 and required tools ready to go so if it's a simple fix you can do it there and then.

Worst case it's a dead panel, but the attached cables should be long enough to allow you to bypass it to get the string back up temporarily while you get a replacement sorted.

tnegun

Thanks for the replies. They were installed "professionally" almost 4 years ago, but I wouldn't rate the installer or hold any hope in getting them here promptly. We'd a lot of issues at the beginning that took months to sort and were only sorted as I withheld about 30% of the cost pending completion. The silver lining is that because of the issues and sloppy install, I learned enough to add a second inverter and a 3rd string DIY so I'm confident that if I can get onto the roof I can identify it and possibly sort it.. Thankfully, this is just a 4-panel string, and I have the MC4 tools, the difficult bit will be getting onto the roof safely. I need some repointing done too so I might try get that done and while there's access to the roof, troubleshoot this string.

Buffman

Ye, good idea with the retention, I'd never recommend anyone paying 100% up front.

4 panels makes it a lot easier, 25% chance of picking the issue on 1st go!

If they were that dodgy with the install it might be just a case of a disconnected MC4 that they didn't click in correctly, probably not that simple as they're idiot proof but you never know.

Ye, safe access is a must, and good weather.

tnegun

I made up some multimeter MC4 leads to make testing easier and decided to try them out on the string about 30 mins ago, and there was voltage on the string! I reconnected it to the fireman switch and the inverter sees voltage on that string now! I pulled the voltage logs for that string and am trying to decide if it's a panel or connection issue. THe string hasn't reached the correct voltage since it failed so I'm verging towards a panel issue now? If it was a dodgy connection, the voltage should be ok, but would collapse under load?

graememk

https://www.boards.ie/discussion/comment/123574080#Comment_123574080

Dodgy connection is still high on priority either in isolator (seen one burnt out)

Will likely be non panel connector where wires from the fireman to panels go

tnegun

Still voltage on the string this morning, but it's not reaching the startup voltage. I'll call the original installer and see if they'll check the roof.