Mounting panels on slightly flexible roof

[buckeyestargazer]

I am preparing to mount rigid panels on my travel trailer roof (Travelite Rove Lite 14BH) using VHB tape and aluminum strut channel. It's a composite roof, although I don't know the technical term for the roof material.

The roof has a little bit of flex to it and I just want to make sure that this will not be a problem for long term stability and use of the panels? I'm guessing that most or all travel trailers have this flex and I know lots of people have used VHB tape without issue, but I just want to confirm.

 

[0truck0]

What is the surface of the roof? Composite does not mean much and it does not matter what is composed of under the top, just the top as far as taping it.
A little give should be fine, your mounting metal will give it strength and the roof there will be as strong as the metal you mount to it. Though, I do not know what roof it is.
I have mounted panels to alumin roof, where the aluminum is barely thicker than cooking foil and it was fine. The roof had cross bars every 20 inches or so under the roof, so that gave some strength and the angle aluminum taped to it gave it more and really sat on the cross bars more than just the roof material. Never had an issue.

 

[buckeyestargazer]

What is the surface of the roof? Composite does not mean much and it does not matter what is composed of under the top, just the top as far as taping it.
A little give should be fine, your mounting metal will give it strength and the roof there will be as strong as the metal you mount to it. Though, I do not know what roof it is.
I have mounted panels to alumin roof, where the aluminum is barely thicker than cooking foil and it was fine. The roof had cross bars every 20 inches or so under the roof, so that gave some strength and the angle aluminum taped to it gave it more and really sat on the cross bars more than just the roof material. Never had an issue.

Thanks for the reply. As mentioned I don't know exactly what the roof is. I just know it's not rubber or aluminum. The give on the roof is between the "rafters" under the roof and I didn't think about the fact that the strut channel will provide some stability between the underlying rafters.

I just want to make sure I'm not doing something stupid before I start applying that tape

 

[0truck0]

It is either rubber (on top of plywood) or aluminum (thin textured, thinner than license plate) or fiberglass (either a thin sheet glued to something or, not in your case, a gel coat molded structure like a boat hull or Scamp camper). Very very rare to see a steel roof on a camper other than a cargo trailer.
I am guessing you have a fiberglass sheet that is glued to your composite material like foam then thin plywood under that, but that would not flex as u say, so you probably have just the fiberglass on top of the roof framework and then insulation below that which is not part of the roof structure. FIberglass can be textured or smooth. Smooth is better to tape on, and textured is fine for tape but you should use more tape.
If you look very close you should be able to see the glass fibers in the fiberglass, if it is fiberglass.
It will not be plastic.

You should be fine. Pics would help. Rubber is the only thing you should not tape to as the rubber will pull away too easy.

 

[Aussieguy]

ou should be fine. Pics would help. Rubber is the only thing you should not tape to as the rubber will pull away too easy.

I got rubber membrane roof and screwed through it.... used lots of sealant

you could remove a fitting ON your roof
see how they constructed it and what they used to screw into the roof

I just used Z brackets for my panels ...
but opted to add an EXTRA bracket down each side because I got bigger 370w panels
8 brackets per panel , 4 down each side .......... screwed into the luan plywood
no leaks and all panels still firmly attached after 4000 miles

Your roof has a lot of holes in it already... no reason more can't be added as long as you follow good practices
if in doubt ... adding more screws is better ........... I put 2 screws per Z bracket = 16 holes per panel

PS do not use a power tools to tighten screws into the roof
tighten the last few turns ... by hand tools to avoid stripping out the holes

 

[buckeyestargazer]

It is either rubber (on top of plywood) or aluminum (thin textured, thinner than license plate) or fiberglass (either a thin sheet glued to something or, not in your case, a gel coat molded structure like a boat hull or Scamp camper). Very very rare to see a steel roof on a camper other than a cargo trailer.
I am guessing you have a fiberglass sheet that is glued to your composite material like foam then thin plywood under that, but that would not flex as u say, so you probably have just the fiberglass on top of the roof framework and then insulation below that which is not part of the roof structure. FIberglass can be textured or smooth. Smooth is better to tape on, and textured is fine for tape but you should use more tape.
If you look very close you should be able to see the glass fibers in the fiberglass, if it is fiberglass.
It will not be plastic.

You should be fine. Pics would help. Rubber is the only thing you should not tape to as the rubber will pull away too easy.

The roof is a seamless poured resin fiberglass, and is smooth.
How much VHB tape should be used? I'm installing a 200w panel that weighs about 30lbs on aluminum strut channel. The strut channel is 5ft long. I have enough tape to run it the full length on each channel.

 

[0truck0]

Interesting, I have not seen a roof like that.
You do not need as much tape as you think. I have a scary small amount of tape on two panels yet have driven thousands of miles and in some extremem cross winds with no issues. By small amt I mean one square inch at one corner.
I typically use aluminum angle iron at the short ends, and tape them almost all the way across using 1 inch wide vhb tape. This is overkill. The sides are open, so that is the short sides are front and back and the long sides are side to side on roof.
8 square inches of vhb tape would hold a 100w panel, but you likely will use more so will be fine. Be sure to clean both surfaces well. Can use rubbing alcohol. Mounting to dirty surface will be a fail.
The higher off the roof your panels are them more force they will see. A panel with a 1 inch gap, or two, will not see any forces of note. I have seen guys mount them 8 inches over the roof and that would require scientist to figure how much force is pulling on them at speed.

 

[Aussieguy]

wind loading is a real issue with solar and any other roof component
be real careful small panels you might get away with it

increase in panel size.... the wind load increases a LOT

please do not drive in front of me!

 

[ToddG]

Does anyone know of a documented case where a panel flew off at speed? RV's have the aerodynamics of a brick and would think only panels placed near the very front would be subject to wind. Angle those down towards the front to lessen the effects...

 

[HarryN]

Does anyone know of a documented case where a panel flew off at speed? RV's have the aerodynamics of a brick and would think only panels placed near the very front would be subject to wind. Angle those down towards the front to lessen the effects...

I am not sure if you want to call this documented or not, but here is the story.

About 10 year ago when I was doing van electrical stuff, I put some solar panels on a customer's sprinter van. She was a traveling nurse at the time and lived in it part time when on the road. I went to some bother to make sure that they would not come off, and she commented that it seemed a bit excessive.

She took her van on a trip from WA near the Canada border to I think Montana and hit a pretty windy area. She called me a few hours later and thanked me for being a bit over the top, as there were quite a few solar panels on the side of the road as she drove there - from other RVs and vans.

The largest panel that I would ever put on a vehicle is ~ 26 x 60 inch.

Added - my default is to use 8020 style, 1515 rails and L brackets to attach to the roof and bottom of solar panels.

 

[HRTKD]

I strongly recommend against using VHB with a rubber RV roof. I'm not real comfortable with VHB on other roof materials either. In your case, if the external (top) layer of the roof is glued down to the substrate, the VHB could lift that layer and then you're in for a lot of trouble.

If you're putting down strut you have the option to put fasteners in every roof joist.

Be careful about using low profile strut. Before buying it, make sure that the PV fasteners can slid along the strut if there are fasteners holding the strut to the roof. I used low profile aluminum and my PV fasteners could not slide past the roof fasteners. If I were doing it again, I would find full profile aluminum strut.

 

[0truck0]

Does anyone know of a documented case where a panel flew off at speed? RV's have the aerodynamics of a brick and would think only panels placed near the very front would be subject to wind. Angle those down towards the front to lessen the effects...

Sadly, the leaves wont even blow off my roof around the panels, I have to blast it with a water hose to get it clean, even driving across the country is not enough of a wind situation to blow leaves off the roof.
There are a lot of knee jerk comments that the sky is falling.

Nobody suggest using tape on a rubber roof. That is when you have to use screws, and hope the wood doesnt rot eventually from the screw hole

 

[occuplus]

I have camper CTP used VHB. 18 monthş ago added aluminium rail and pv panels. Each rail is 8cm wide and 280cm length. No problems yet.