What panels really need is reverse polarity diodes protecting groups of cells in long series runs. The weakest cells will be driven to reverse polarity by the strongest cells without those diodes. I tried driving a cracked solar cell with reverse polarity and it hit about 40V at 6A for a total of 240W.
One of many installation issues is that Tesla installers used thermal cameras to find hot cells in panels and then marked them with tape to indicate a need for replacement. They were never replaced. Now those slightly defective cells are completely defective because they have tape blocking their light. The rest is unknown but I imagine solder or insulation cooked off hot cells until it arced. A 500VDC @ 6A has a really hot, robust arc.
It's all a mess. Cells shouldn't be failing unless the panels were abused or untested. Panels should have built-in protection diodes around groups of cells to prevent high reverse voltages. The controller should alert if there's a ground fault. Permit inspectors were paid to have noticed these things.
My own solar installation experience (not Tesla) is that messes are very likely. Outsourced construction work is no better than outsourced software work.
Biting the hand that feeds IT
