Flat roof mounting solar panels.

Solar panel power output is reduced as temperature rises

See here http://greenliving.nationalgeographic.com/effects-temperature-solar-panel-power-production-20500.html

if you mounted flat on the roof
i can guarantee that some dirt and water would get under and NOT come out, not quickly or easily

elevate them at least 1 inch, two inches is better

wind resistance is not a problem

you are dealing with an 'edge' cutting through the air , not a sail mounted vertically to catch wind

Another advantage to mounting spaced is that you minimize shadows from roof sun blockers like the AC and vents. The higher you can safely mount it, the smaller part of the day those items will cast shadows on your photovoltaics.

Jim

doughere wrote:
just thought tight would cause less wind resistance, and / or wind noise.

No. Allow for airflow. Heat is a concern.

I mounted mine in full 1 1/2" aluminum rails on all four sides. The two running the length of the coach are mounted directly to the roof & properly sealed, where the two cross rails are mounted to the leading and trailing edges of the panel. Using 10mm stainless bolts and hard rubber spacers, I mounted the cross rails to the parallel rails.
The spacers hold the panels up about 5/8" off the roof so the breeze can blow through underneath while underway, and I can rinse the area underneath the panels when cleaning the roof.

This helps with cooling as well.

My panels put out more when cool, can I prove it, no, do I have measurements, no. Just seat of pants. I installed mine ~ 1" off of the roof on one side of the panel, ~1.5" on the other side. I did this based on my experience with panels holding dirt & water on them. With the slight tilt they are "kind of" self cleaning. I have an excess of solar output so any minuscule loss of output is no heartburn for me.