Mounting Flexible panels to RV Roof.. Heat concern, placement etc?

[CanadianEhh]

I dove into getting a few flexible solar panels for my travel trailer, mostly to maintain batteries and use for the occasional boon docking experience.

On a curved rv roof, is it better ot run the panels along the crest of the curve so the panels themselves have very little curve, or does it matter if you to perpendicular to the crest so the panels will be curved with the roof?

I have been reading that some folks seem to dislike flexible panels taped or glued (dicor) flat to the roof, due to the lack of airflow and buildup of heat, which would reduce the efficiency of the panel. Has anyone tested this if it is a valid concern?

If so, I was curious a solution to the problem. I was thinking of using a super strong double sided 3m tape along with some eternabond to glue down a panel of corrugated polycarbonate Then enternabond the panel directly to the corrugated sheet, which would give a 1/2" space between the roof and the panel for air to move.

Worth While? or waste of time?

[J.P.M.]

Well, the open literature is chock full of confirming and probably exhaustive detail about convective heat transfer from flat surfaces that pretty much positively confirms the reasons for those dislikes you mention.

Your polycarbonate solution will allow perhaps some reduction in panel temps, but not a lot. Panels in direct contact with a roof, depending on the tightness of the thermal bond, panel to roof, will tend to make the roof act like a heat fin and transfer heat to the panel (or from the panel if it's cold out, making the roof cooler than the panel). Best method to keep panels cool(er) for what's probably most situations is to:1) Minimize/eliminate contact with hot things like roofs and 2) Increase the available panel heat transfer area of the panel. #2 is most easily achieved by keeping the panels away from their mounting surface by some healthy distance like 10-15 cm. or so to allow what's probably cooler air to circulate across and behind the panel as well as across and over it. Further on #1, the polycarb stuff will actually act as an insulator behind the panel. That will inhibit heat transfer the backside of a panel. A common use for such material is as a form of insulating glazing. It works fairly well for that purpose when used vertically with the spaces running horizontally.

Overall, I'd scrap the flexible panel idea based on what's probably a shorter service life, lower efficiency than other types of panels, and installation problems for this application.

[CanadianEhh]

Interesting read and you bring up some valid points.

Usually when this product is used as say a greenhouse wall as an insulator, the edges are sealed together. not left open to allow air to move freely down the channels.

What if I used the same idea, but in an aluminum corrugate instead of plastic, so it would act like a heat sink.

[J.P.M.]

Interesting read and you bring up some valid points.

Usually when this product is used as say a greenhouse wall as an insulator, the edges are sealed together. not left open to allow air to move freely down the channels.

What if I used the same idea, but in an aluminum corrugate instead of plastic, so it would act like a heat sink.

You do not want a heat sink. Look, what you want is a way to support solar panels that will provide the safest and most practical mounting while also maximizing heat dissipation from the panels as much as possible and practical. Putting panels on a continuous surface will make the panels run hotter. Rigid panels that require support only at the edges is one answer that has other advantage as well.

BTW, when that polycarbonate material (twinwall, tufftex, thermoclear, other commercial names) is used a glazing, the idea is that the channels are supposed to run horizontally, or perpendicular to gravity. That's how they work to inhibit convection suppression - lots of spaces with a short vertical dimension instead of one big, long vertical dimension that will allow stronger convection currents to set up. Running the channels vertically (as I assume you mean when you write " down the channels..." defeats most of the advantage such products may have over simple(r) dual glazing. And of course, the ends ought to be sealed regardless of orientation if for no other reason than to help keep the interior surfaces clean, but all that has little to do with this application. Upper limits on the poly carbonate service temp. might.

Either or any way, or for any support schemes, putting a continuous surface under a horizontal panel means you are putting a thermal barrier, and also what's probably a better insulator - a "dead" air space between that continuous surface and the underside of the panel - even a very thin one - will both act as an insulating barrier between the underside of a horizontal panel and any air circulating between the underside of the panel and the vehicle (or other) roof, with the inter facial space also being a place to collect stuff/bugs/whatever, is not the best solution..

The idea that a flexible panel in a horizontal orientation needs pretty much continuous support is one of several reasons why I'd not use flexible panels for such an application.

One other option among the plethora of options and as long as you're adamantly convinced of the worth of flexible solar devices, is to consider using something like metal mesh with ~ 1/2" or so square pattern as a panel support.

Take what you want of the above. Scrap the rest.