Also, remember things fall apart (it's scientific).  Good old el sol breaks down wire insulation, roofing materials dry out and crack and leak, or maybe you're near a golf course and golf balls occasionally end up breaking a panel. I've even seen solar panels ​shorted out because maybe the manufactured messed up, and sometimes there has been installer or roofer error.  Or birds make a nest under those cozy solar panels.  Once I was called to repair a solar hot water panel which had a bullet embedded in the insulation, after it broke the tempered glass, which was presumably after if fell out of the sky, after it was shot from a gun, perhaps on new years, or fourth of July.  Stuff happens, even on boring ol' rooftops.   We can go up there and check it our, or fly our drone up first for a preliminary survey.  Yeah stuff deteriorates over time, with mother nature's help.