Ron et al-
The firmware in the controller sounds likely, but a faulty shorted bypass diode does not. Isn't that what bypass diodes are supposed to do-- turn on and short (bypass) a shaded row of cells?
We use to see this half-panel voltage as a failure mode with the old Kyocera 120's when they were still blue. The solder mask fails in a hot spot and opens, so no current can flow in that row of cells. Then the bypass diode is just doing it's job by bypassing current at lower module voltage, just as it does when half the module is shaded.
If there are other modules in parallel they will push current into the reduced-voltage one until they are also at reduced voltage, which is sensed by the controller. Sounds like a lot of current is being pushed through the damaged module, which will fry the hard-working bypass diode(s) or the solder mask wire in that low module. Best to disconnect the low module or the others will kill it.
I cannot think of any physical way the rest of the solar modules can work at full voltage for awhile without the damaged one, then have the voltage drop suddenly under load, only to be seen at full voltage again when disconnected. Do I have this sequence right?-- This sounds like software (or firmware) attempting to do MPPT in the controller. If it is faulty firmware as Larry C. wrote then it should be upgraded.
So, could the controller be complicit in damaging the low module? Hmmm....
Don Barch
Energy Solar
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