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Old 08-11-2020, 03:12 AM   #1
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Default Flex Solar Panels

Any opinions/experience with flexible solar panels? Most of you have newer RVs that don't have the fiberglass turtle shell and have easy provisions for mounting roof racks without drilling through the roof. Flex panels provide an option us turtles without penetrating the fiberglass.

My experience with plastic.......especially here in AZ.....is that it's rapidly degraded by the extreme sun. But I'm not sure about the composite of flex.
I believe early solar panels had a tendency for the plastic to turn yellow over time making them progressively less efficient.

Inspired by Covid, I'm measuring the roof for available real estate.

thx.
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Old 08-11-2020, 06:19 AM   #2
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Our panels are rigid and mounted an inch above the roof. When flexible panels became available we pondered whether we might have 'gone flexible' had such panels been available a couple of years earlier . . . . until . . .

A few weeks ago we borrowed a ladder to inspect our panels (after a vicious hail storm) and to give them a cleaning. Ouch! The panels were blisteringly hot. Way too hot to touch. We could have fried an egg on them. Maybe we shouldn't have been surprised - - the panels are mostly black, after all.

Then we contemplated. Our panels are mounted in 'free air' above the vehicle roof. As such, all sides are exposed to air. Assuming that both flexible and rigid panels absorb a similar amount of the suns energy (for a given area), how do these panels - - comparatively - - dissipate all of this heat?

Our first thoughts were that, at least when in motion, our 'lofted' rigid panels will have airflow over, and under, the panels . . . this has to be a huge benefit in cooling the panels (and it should be remembered that even if the panels can withstand these high temperatures, the efficiency of the panels drops as temperature increases). Second, if one installs flexible panels essentially attached directly to the roof, isn't the absorbed heat energy of these panels directly communicated to the roof and, ultimately, to the vehicle interior? One advantage of our white roof is that it reflects much of the suns energy . . . but if we attached a black 'cover' to the roof (i.e. a flexible black solar panel), aren't we, in essence, converting our reflective white roof into a heat absorbing black roof? (Of course, with the solar panels mounted above the roof . . . it doesn't really matter what color our roof is . . . the sun never reaches it.)

So, we ponder aren't there two significant advantages to mounting a (rigid) panel above the roof? First, top and bottom airflow for panel cooling (and efficiency) and, second, screening/blocking the sun's energy from directly getting to the roof (and heating the inside)?

In conclusion, if we were going to consider flexible panels, we'd want to mount them 'above' the roof . . . allowing for airflow underneath the panels and minimizing the heat conductivity between the panels and roof.
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Old 08-11-2020, 05:45 PM   #3
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The heat gain is a factor that I hadn't considered. That's an excellent point.

Yours is a built on a recent design van, so I'm guessing that drilling into a fiberglass roof was not a concern. I noticed that the newer vans often have existing places where roof rails/racks can be mounted without drilling.

But your comment about heat gain plus the potential for the plastic degrading in the sun (which I noticed Renogy says can happen over time with their panels) is enough to steer me away.

Anyone out there who has put panels or a roof rack on a RV with the fiberglass shell top?
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Old 08-11-2020, 06:44 PM   #4
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On my fiberglass Bigfoot trailer I used large pads with VHB tape sealed around with Dicor lap self levelling sealant. Pads were 4” x 3” four of them for 60W panel. For pads I used aluminum rectangular tube. Panels were mounted to a single screw centered on the pads.

3 critical points:
1. Roof must be free from wax and perfectly clean, see the video. If you had any wax apply acetone first followed isopropyl alcohol.
2. Pads must be freed to conform to roof curvature,
3. VHB should be protected with lap sealant such as self levelling Dicor.

AM solar has VHB mounts https://amsolar.com/rv-solar-panel-k...ng-accessories

For years I am big proponent to mount rigid panels with 1” gap because:
1. Rigid panels outer surface is glass and has longer life than plastic layer on flex panels.
2. Panels serve the function of double / tropic roofs used in tropics. (search tropic roof)
3. Better panel cooling critical for efficiency.

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Old 08-11-2020, 08:37 PM   #5
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If you go the VHB route here is some discussion about VHB type. Note that they also use 3M Adhesion Promoter 111 https://www.3m.com/3M/en_US/company-...2992808&rt=rud.

https://sprinter-source.com/forums/i...threads/88436/

Good luck.
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Old 08-11-2020, 08:51 PM   #6
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I have always wondered about the whole heat thing with flexibles since I put on our glass/aluminum frame panels years ago. Our instructions were very specific about allowing space between them for thermal expansion.


With them being black and running hot because of it they will be somewhat hotter than the roof under them, plus they are plastic vs a steel or fiberglass roof so they likely expand more per degree of temp besides. I would think that the panel itself and/or the adhesive would get stressed quite a bit. We have heard of a few times the leading edges got peeled up in the wind of driving, but not much since many are taped or Dicored on the edge now.



Odd they don't pucker and buckle a bunch.
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Old 08-11-2020, 09:05 PM   #7
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My miniscule 20W flex solar panel is cracked and edges are curling slightly but still working after 8 years screwed directly onto the fiberglass roof. I plan to replace it with a 50W panel but insert a 5/64" ribbed pad beneath for an air gap. They get mighty hot when applied directly to a surface and no telling what my roof looks like under the current panel. I'm wondering if that is part of the reason flex panels fail more often.
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Old 08-11-2020, 09:12 PM   #8
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I'm anticipating a solar cell fabric to load into my awning:


https://www.solarfabric.com/
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Old 08-11-2020, 09:26 PM   #9
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Quote:
Originally Posted by mkguitar View Post
I'm anticipating a solar cell fabric to load into my awning:


https://www.solarfabric.com/

Roadtrek offered a solar awning for a while IIRC. I don't know if they actually shipped any, though, as they have touted other things and never shipped any.
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Old 08-11-2020, 09:43 PM   #10
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touted other things and never shipped any.

yes...


Mike
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Old 08-11-2020, 10:18 PM   #11
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Quote:
Originally Posted by GeorgeRa View Post
On my fiberglass Bigfoot trailer I used large pads with VHB tape sealed around with Dicor lap self levelling sealant. Pads were 4” x 3” four of them for 60W panel. For pads I used aluminum...
Thanks for your detailed response! Very appreciated. The tape looks like a good option for mounting in my situation. I've never used the Dicor. Is it thick or do you build up some sort of dam around it when you apply?
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Old 08-11-2020, 10:38 PM   #12
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Quote:
Originally Posted by GallenH View Post
Thanks for your detailed response! Very appreciated. The tape looks like a good option for mounting in my situation. I've never used the Dicor. Is it thick or do you build up some sort of dam around it when you apply?
No dam needed, if you would put a blob on a surface it will mostly retain the contour but it will level itself.
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Old 08-11-2020, 10:44 PM   #13
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Quote:
Originally Posted by mkguitar View Post
I'm anticipating a solar cell fabric to load into my awning:
https://www.solarfabric.com/

Wearer of solar fabric gloves to Doctor
: "Doc, my hands hurt. What are those blisters?"


Doc: "Second degree burns."
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Old 08-16-2020, 05:01 PM   #14
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We mounted our flexible panel to the roof using VHB tape and 1/4 inch spacers. This allows air-flow under the panel. The Lensun panel we used has a fiberglass back sheet and ETFE top sheet which is touted to be better than PET.
Jim
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Old 08-16-2020, 05:07 PM   #15
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In case you need something to read this morning check out https://amsolar.com/diy-rv-solar-ins.../edsolarpanels AM Solar tells you a lot about solar panels.
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Old 08-16-2020, 05:09 PM   #16
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AM Solar was a great help in my setup, sold me parts, and helped with the install.

I put 180 watts of panels on my 2007 Serenity's roof in 2012, there were not any American flex panels for sale back then, so I used Alibaba for the first time. Bank of America freaked out, twice, but my money finally made it to China. The panels have been great. I didn't wanna tap into the fiberglass so I put a paint protection film on the roof and then used spray adhesive to adhere the panels to the film. If I ever remove them the paint underneath should be in great shape.

I had a little panel that I screwed to the cover of the AC unit that snapped the plastic where the screws were and the panel disappeared, but the other two have maintained the battery all these years. Finally, put a whole new AC on the roof after a compressor failure so the cover is complete again.
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Old 08-16-2020, 06:56 PM   #17
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How good is 3M VHB tape really, over time? I like the idea. But roofs are exposed to every temperature extreme, wind/dirt/ice, etc. I just keep thinking that anything adhesive will sooner or later, give up either by deterioration due to the persistence of nature. Bolting down anything on the exterior surfaces of vehicles doing highway speeds just seems the only way to go. And even then, the use of the right hardware with proper tightening has to be in play.

I want to resist looking at Marketing material from a manufacturer when there are plenty of people with real world experience over time with 3M VHB or other products. To that end, I would sure want to know for sure if I purchased the 3M product that it is not an off shore counterfeit. While GRAINGER for example, would be a more expensive source than say, AMAZON, I'd pay the extra and shipping from GRAINGER in this case. A dice roll no matter where these days.

If any of you have years of experience with 3M VHB, I sure would like your comments and I think would be helpful to many of us on this forum.

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Old 08-16-2020, 07:21 PM   #18
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Quote:
Originally Posted by Storysrvwego View Post
How good is 3M VHB tape really, over time? I like the idea. But roofs are exposed to every temperature extreme, wind/dirt/ice, etc. I just keep thinking that anything adhesive will sooner or later, give up either by deterioration due to the persistence of nature. Bolting down anything on the exterior surfaces of vehicles doing highway speeds just seems the only way to go. And even then, the use of the right hardware with proper tightening has to be in play.

I want to resist looking at Marketing material from a manufacturer when there are plenty of people with real world experience over time with 3M VHB or other products. To that end, I would sure want to know for sure if I purchased the 3M product that it is not an off shore counterfeit. While GRAINGER for example, would be a more expensive source than say, AMAZON, I'd pay the extra and shipping from GRAINGER in this case. A dice roll no matter where these days.

If any of you have years of experience with 3M VHB, I sure would like your comments and I think would be helpful to many of us on this forum.

StorysRVwego
I would suggest to trust extensive 3M product information often written by engineers, they are liable for accurate information. To feel at piece study various application 3M is recommending using VHB in the automotive, marine and construction fields.

1. Clean the surface with appropriate cleaners.
2. Protect the edges of the adhesive.
3. Use right VHB, there are many for various applications.
4. Buy VHB from reliable source, VHB has limited a shelf life.
5. Stay within recommended application temperatures
6. Let it cure as 3M literature suggests.
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Old 08-16-2020, 08:02 PM   #19
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Sprinter Vans already have ribs on the roof for structural integrity. Run a bead of silkaflex on the rib where the flex panel contacts the rib and press the panel lightly into it. My Galleria had one already installed by the factory. I added 2 more for 300 watts which deliver almost 16 amps here in central PA.
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Old 08-16-2020, 08:06 PM   #20
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Quote:
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Sprinter Vans already have ribs on the roof for structural integrity. Run a bead of silkaflex on the rib where the flex panel contacts the rib and press the panel lightly into it. My Galleria had one already installed by the factory. I added 2 more for 300 watts which deliver almost 16 amps here in central PA.
Is Coachman using Sikaflex?, that is rather permanent mount.
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