We got about 3 inches of fresh snow on my test panels last night.
It is clear that even the tiny ridge where the panel frame is higher than the panel surface is a big obstacle to the snow just sliding off. As the snow melts, the moisture sinks down to the base of the snow, right on the panel, and slush develops. The slush gets caught on the small lip, and will not allow the snow to slide off at my rather shallow slope. No doubt this would be a much smaller problem at steeper pitches, and the slush would be more slippery if things were just a bit higher in temp.
The gap between panels seems to be the major catching area, as the snow/slush flowing from the top panel just falls into the gap and gets more and more saturated, as well as filling the gap deeper and deeper.It was in the 20s today, so the slush was just at the freezing point. The snow above because of the shallow slope does not have enough force to break off at the gap and just slide off, so the snow will remain until the slug in the gap breaks off or melts.
First thoughts are that covering the gap with aluminum tape, and maybe running an icedam heating strip between the panels horizontally would prevent this?
Will modify the test setup and be ready for the next storm.