Bosque Bill said:
My guess, as a retired engineer, is that instead of heat flow from the panel to the roof, you would get heat flow from the large roof area, exposed to the sun, to the panel (plus whatever the panel absorbs from the sun.)
This is exactly where I'm coming from. The corrugated plastic isn't to stream air through the panels while driving. In fact, the direction of the corrugation isn't relevant in my mind - it could be side-to-side rather than front-to-rear. We're obviously not driving 100% of the time and solar, for me, is for not driving and hanging out off grid. The roof transfers heat to the panel when directly mounted. Any medium that prevents heat transfer to the panel will help keep it within its operating range (I think the max temp for the Solar Cynergy panel is something like 180 F). My thought with adding the corrugation is that it's essentially 3 layers of insulation; polycarbonate, air, polycarbonate - with the air gap being the most efficient part of the trio.
There are a coupe good reasons for not mounting the panel directly to the studs. Even with a nut under the panel to create an air gap, the panel is very flexible and would bow in the middle allowing it to come in contact with roof. Also, with wind speeds while driving, the flex in the panel and the gap would create a lot of movement in the panel. I can't imagine that would be good for it. The corrugated polycarbonate is significantly stiffer. Making it one long piece with the panels glued to it adds to its structural integrity. Rather that each panel having 4 to 6 mount points and flex, this one, single reinforced unit it mounted with 16 total studs.Having built and experienced it first hand, this not just theoretical. It really is a lot stronger and I'm not concerned with airflow getting under it like I would have been with a raised panel.
I agree with MarkBC that efficiency isn't a big deal when compared to, say, the angle of the panel, but directly mounting it to the roof isn't just an efficiency issue. People routinely report the cells cupping and warping from the excessive heat. I'm trying to avoid physically damaging and ultimately breaking the panel. I oversized my setup to overcome the efficiency issues. 290 watts of solar can suffer from a number of efficiency issues and still charge me up quickly. Especially with panels wired in series which is desirable for the nice MPPT controller I have. Not to mention a LiFePO4 battery that can charge much faster than conventional lead acid.
I love these conversations, This forum kicks ass.