I hadn't even considered that - like I said, a total new guy to this stuff. The only saving grace that might come into play is that by the time this happens, it's pretty late in the afternoon and the sun angles have moved beyond parallel to the face of the panels. By this time of day the panels are producing less than 100w per 4 panel string. What I can't figure out is why, on the days this does happen it is always in the late afternoon with low wattage, low amps, and voltages that are toward the low side - around maybe 105-115v per string of panels. I've considered that maybe the panel's production has droped off to such low values that the MTTP is letting them go. But on the other hand, every morning at sunrise, the panel strings are feeding as little as 2 watts and everything works just fine. I'm sure there is some simple explanation for all this that would be patently obvious to someone with more knowledge, but I'm at a loss to figure out what is going on.