Solar panel junction box connections

[FiveNines]

I have two 100W panels from the same manufacturer with the same part # that are wired differently in the panel’s junction box. Panels were purchased about one year apart.

Panel B has the center connection connected to a trace on the panel whereas panel A does not. Panel A does not have a similar trace. (All of the panels I own from other manufacturers are similar to panel B.)

I noticed this past summer that panel A’s output reduced. After examining connections and other system components, I concluded that the bypass diodes might be damaged on panel A, so I replaced them a few weeks ago with exact replacements. There was no change in the output. Unfortunately during the summer I did not document the reduction, but when I swap the panels, panel B is working as it should. (My point is that panel A may not have worked properly from the day of installation.)

IMO, panel A does not need two diodes as the center connection is not connected to anything.

It’s been cloudy where I live the past six days, so I have not had a chance to experiment.

I looking for guidance on this issue.

 

[Samsonite801]

Did you look at the spec sheet for lifecycle / output chart they usually provide with panels? Check to see what they should put out after a year's worth of use vs new panel and see if the difference matches what you're seeing (since you indicated one is a year older than the other).

Assuming the panels are mounted parallel (on same angle to the Sun) in the same position and no areas of the panels are shaded. It might just be a manufacturing difference/defect, or based on difference in their life use between the two, or perhaps you can contact the manufacturer if you are seeing a significant difference in output between the 2 panels, and ask them if the difference is within their normal tolerance for QC.

 

[FiveNines]

I contacted the manufacturer about the difference in junction box wiring. Their response was a design change. I can understand that, but having 2 diodes installed on panel A serves no purpose as only one is required to shut down the panel. Having the center connection allows the panel (B) to continue working if only half of the panel is operational (the panel is electrically split vertically.) This is all per my understanding of panel construction…

I conducted more tests a few days ago during a sunny WI day. Panel A produces about 20 VOC, but the charge controller states 0. I tested all wiring for resistance and used different controllers from different manufacturers. Apparently the controller’s algorithms determine there is a problem.

Panels one year apart should not have any degradation. For most of each panel’s life in my ownership, they remained in their boxes.

My suspicion is that the panel is damaged, yet I have carefully inspected it and do not see any physical damage. I am, therefore, concluding the damage is to the electrical traces, either during manufacturing or transient electricity from a thunderstorm.

I asked the panel manufacturer for a troubleshooting guide. So far I have not received anything.

 

[Samsonite801]

I am guessing it is outside of warranty then?

 

[12VoltInstalls]

having 2 diodes installed on panel A serves no purpose as only one is required to shut down the panel. Having the center connection allows the panel (B) to continue working if only half of the panel is operational (the panel is electrically split vertically.) This is all per my understanding of panel construction…

I’m not sure about this exactly in a combiner box; but you do need two diodes because they are there for the individual panel as they are for other panels. The idea is to not wind up heating a panel that happens to have a lesser electrical value than the intended path to the SCC or back-feeding volts.

 

[Rogermija]

The manufacturer saved money by not providing a center tap and thus two strings per panel. If any part of the panel is shaded the whole panel is bypassed...they win, you lose, too bad.