What could cause a string to fail?

[2barry]

I have 42 SolarWorld 250 watt panels with Tigo boxes. The other day my B string failed while the other 3 are still running fine. There are 2 Sunnyboy inverters as well. There appears to be no obvious cabling issues. I tested the gateway, power cycled the inverters and the power modules. I have sent the string failure warning email from Tigo to my installer.

[solarix]

Almost always a bad connection somewhere. Most likely in the home run wiring or intermodule wiring, but potentially inside a panel. With about 10 panels in series there are well over 600 connections involved. Kind of the downside of high-voltage string inverters. I'm not familiar with Tigos but I assume that if a panel fails, the Tigo will allow the string to keep going so hopefully that limits the problem to just the external wiring or the Tigos. One possibility is that not all "MC4" connectors are as compatible as you would think. If your installer used one brand and the panels use a different brand, they might not be making good contact. Even with both connectors being the same brand, there isn't a whole lot of contact length on these connectors. Looking at the connector, you would think that there is contact over the whole length of the 1/2"+ connector snout - but the actual contact length inside is really only 1/4".

Be sure and let us know what the installer finds....

[ACW]

Hi all ,i have had a 3.2kw system for 3 years now,i live in south west UK ,system has worked well and i'm very pleased with return ,only problem i have encountered is i have lost one of the two strings for 24hrs when temperatures are in the low 30's ,1/7/15 and again yesterdayalmost to the year 19/7/16 the knocked out string starts working the day after the extreme heat ,so i have lost half my input for only 2 days out of the 3 years but was wondering if anyone could tell me why this happens in extreme temps ,thanks Andy

[solarix]

Expansion and contraction from extreme temps can cause problems with electrical contacts. Either in a cable connection or worse a bad solder joint...

[EmmaHardy]

Really!?

[SunEagle]

Really!?

Is your comment directed at solarix or someone else that posted.

It is a red flag when someone new to the forum just makes a simple one word post without any other comment.

[littleharbor]

Something fishy about both her posts.

[SunEagle]

Something fishy about both her posts.

Yes. But it could just be someone getting use to posting on an open forum for the first time.

I have no problem giving someone a warning but I also do not want to chase a new comer off.

[inetdog]

Hi all ,i have had a 3.2kw system for 3 years now,i live in south west UK ,system has worked well and i'm very pleased with return ,only problem i have encountered is i have lost one of the two strings for 24hrs when temperatures are in the low 30's ,1/7/15 and again yesterdayalmost to the year 19/7/16 the knocked out string starts working the day after the extreme heat ,so i have lost half my input for only 2 days out of the 3 years but was wondering if anyone could tell me why this happens in extreme temps ,thanks Andy

Another possibility is that the panel voltage increase with low temperature is driving the string voltage above the maximum voltage of the connected equipment, causing it to shut down for protection.

[PistolPete]

I'm going to +1 on the home run failure due to the fact that if it was an optimizer/module (is this a tigo optimizer install??) failure it would be able to bypass the bad component. If you can give more information like where the strings are combined (soladeck??) we could give you some more troubleshooting information. Otherwise if it is in warranty you may be best served by your installer as this seems like an install issue.

[2barry]

Well it turned out to be something fried on a circuit board in one of my inverters. SMA is sending a replacement board. They don't feel it was a lightning or a hit from the grid.

[redheadreed]

This sounds stupid but I can't figure out how to post a question on here.

[redheadreed]

How do I post a question? I can't find the option on this site. Wtf?

[Mike90250]

How do I post a question? I can't find the option on this site. Wtf?

Chose a forum and it's sub-forum. Then, just above the listing of all the active topics, is a button labeled :
+ New Topic

[Qtips]

I have 42 SolarWorld 250 watt panels with Tigo boxes. The other day my B string failed while the other 3 are still running fine. There are 2 Sunnyboy inverters as well. There appears to be no obvious cabling issues. I tested the gateway, power cycled the inverters and the power modules. I have sent the string failure warning email from Tigo to my installer.

I have a Tigo system and can vouch for the fact that if one panel or one optimizer goes bad, the other panels can produce power just fine. During the initial install of my system, one panel with Tigo did not initialize and therefore did not communicate and did not produce any power, but the other panels with built in Tigo optimizers on the same string kept on producing power just fine. Although my Tigo-based system with Trinasmart panels is only four months old, it is, knocking on wood, very reliable so far. One time I even purposely disconnected the Tigo MMU unit to see if the individual optimizers would still function. Yes, it did. Having a bad MMU unit or gateway would not bring down the system system.

I did frequently have lower than ideal insulation values on my Power One Aurora main inverter (10 M-ohms instead of 20, but that's a main inverter or cabling problem; perhaps rodents bit through the cables somewhere), but it's not a Tigo problem.

Based on the fact that your entire B string was down, it seems it was either a cabling or connection issue with your B string or it was a main inverter issue with one branch of your Sunnyboy inverter. In either case, it doesn't sound to me the Tigo optimizers were the source of your problem.