Wintertime solar array troubleshooting

It’s the middle of February in Montana and recently I was troubleshooting an off grid system that suddenly stopped producing amperage from the pole mount to an old C-40 charge controller located 40′ away in a basement.  So what’s the cause the system to fail and how to fix it?  For this array we checked voltage from the battery bank to the C-40 controller, which was good with the controller showing battery voltage and it’s green light on.  Then we tested voltage through the DC output circuits from the charge controller to the combiner at the pole mount and up to the solar modules while the controller was disconnected from the batteries.  Again, we found good open circuit string voltage so we knew our output circuit was still good but maybe something was wrong with a source circuit.  We then went outside and switched out the fuses in the combiner and started to look from the source circuit combiner back to the individual solar modules.  This old array was using Kyocera 120’s which do not have MC4 output cables like we are accustomed to seeing today.  Instead, you have to punch out a knockout on each individual J box and run wire and conduit between the modules.  This is a tedious process since you can’t just put your meter on the end of a pos/neg string wires and see what your voltage is.  Instead you need to open all the J boxes to see if there are any obvious signs of damage inside the boxes or to the wire’s traveling through the flexible conduit as well as to the conduit connections attaching the conduit to the boxes.  If the connection to the J box allows water into the box you can end up with corrosion in the box and overheating to the wires; which is what happened to this system.  What was interesting was that the conduit connections to the boxes looked good for all the modules and the flexible conduit wasn’t running downward from one box to another so it didn’t look like water should have be able to get into the boxes.  But during a winter with a lot of dramatic temperature fluctuations causing strong freeze thaw conditions combined with an old solar array, moisture or water was able to get into the box and cause a failure.  The water that penetrated the box created corrosion inside which caused resistance and overheated the wires inside the junction box, which can be seen in the photo.  The junction box did contain the overheated wires well but was also the cause of the problem.  These types of older boxes are subjected to failure from the repetitive knockout attachments when wiring modules instead of using modern pre-existing MC4 connectors coming out of a sealed J box.

Our solution was to take this modules string out of the system and run on a little less power until a new module can be found.  As soon as we did this amperage started flowing back into the charge controller and batteries.  We now plan on getting the string back up and running with a new module and during the spring when conditions are easier on the ground to work out at the pole mount.  So if you have a system that has been working perfectly and all of a sudden stops producing power during the winter months ice maybe the reason and it might not be easily noticed.


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