Due to the quality of the pic that I see, and the smoke pattern. it looks like maybe the panel was flat mounted, and was smacked by a baseball? I can't tell if the glass is shattered or just dirty.
I don't know of any way a "bad controller" could burn a panel. I don't know if that was a single panel or part of an array, Heck, the classic almost had a snow melt mode, where applied battery voltage to the panels to melt the snow off them. So the correct polarity of DC won't burn a panel (parallel panel strings proves that) so it was either a baseball or a reverse bias with no charge controller. Or some intentional short through the backsheet to the tab wires.
I agree that looking at the front of the panel it looks like a "shatter" pattern on the third column of cells radiating out from the burnt area that could be glass fracture. I also noticed the terminal box on the back looks to be stuck on using a clear tape so I don't know if it was moved or the tape was added.
Sorry couldn't get back to all, had to go out of town for a couple of days
I did check the diodes and they check out good so that leaves that theory out. Now remember that controller was fried and the plus terminal was totally melted going to the battery but I didn't know that until I got on the roof and took the panel down saw the burnt spot. I'm thinking that the controller was the problem and Sunking was right and max out the amps but if that was true it must of had to pass the diodes to do that and they are good. OH WELL!
Now remember that controller was fried and the plus terminal was totally melted going to the battery
Put it to you this way, a cop hears a shot in a room with only one door, the cop enters the room and sees you with a smoking gun in your hand and standing over a dead body with blood pooling on the floor.
No question about it, the battery is the only thing that has that kind of energy,. Your Controller is the smoking gun.