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Old 07-07-2020, 10:20 AM   #1
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Attaching solar panels

Hey all,
I'm looking to add a couple solar panel to the roof of my 2003 Adventurer. The panels are 24" x 50" and weigh about 32 pounds each.

I really like the idea of not putting screw holes in my fiberglass roof.
Each panel will have 8 mounts, and each mount is about 1" x 1.5" of roof surface area. That gives about 12 square inches of surface area per panel. 3M VHB 5952 tape says it has 90 pounds of direct adhesion, and 80 pounds of shear strength per square inch.

The math is telling me that tape is many times stronger than the weight and wind resistance of the panels.

Is it OK to just use 3M VHB 5952 tape to hold the solar panels down?
Should I also use screws?

Any real world examples of what people are doing?

Thanks
Jim Streit
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Old 07-07-2020, 11:38 AM   #2
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I have used thickened epoxy (West System cartridges) on fiberglass roofs with no screws and they held up fine.

David
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Old 07-07-2020, 11:52 AM   #3
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I've got 8 160W panels with 4 mounts each put on with 3M VHB double sided tape and sealed with Dicor. This is the long-used process by AM Solar. 5 years now without issue ...
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Old 07-07-2020, 12:01 PM   #4
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Quote:
Originally Posted by Lv2Roam2 View Post
I've got 8 160W panels with 4 mounts each put on with 3M VHB double sided tape and sealed with Dicor. This is the long-used process by AM Solar. 5 years now without issue ...
Lv2Roam2 ... that is good to hear. How much surface area against the roof are your mounts?

Thanks.
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Old 07-07-2020, 01:27 PM   #5
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I would watch this video before doing anything. Thomas knows what he's doing.

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Old 07-07-2020, 01:31 PM   #6
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I screwed down my panels. The screws just hold the mounts with small screws that simply go though the super thin "fiberglass" and Luan panelling the make up the roof. I'm sure the caulking/adhesive does most of the holding. But I'm not at all worried about the 12 small holes in my roof. I plan to add a 4th panel this summer and I'll screw that one down, too.

Should I remove the panels... not likely... they'd be super easy to fill and cover with more sealant.

Many people use VHB tape or simple adhesive without problem so I doubt that's a concern. But I feel better with mine screwed down AND sealed when I'm driving 60 mph into a headwind.
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Old 07-07-2020, 01:40 PM   #7
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I haven't mounted mine yet but I can tell that the fiberglass on my 2002 Suncruiser isn't fully adhered to the luan substrate any more. Therefore, my plan is to use both VHB and screws. Better safe than sorry.
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Old 07-07-2020, 01:46 PM   #8
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Originally Posted by gurroz View Post
I would watch this video before doing anything. Thomas knows what he's doing.
"He knows what he is doing" right???? Well I watched his video until after 4 minutes he confessed that his whole mounting plan was out the window because he didn't take into consideration the convex shape of his RV's roof and had to screw a mounting board to the roof. That is exactly what this thread is trying to avoid.

So use 8 our so L shaped mounting brackets that you can bolt to the panel with slots so you can adjust the height to maintain contact with the roof across its span. Whether you want to use 3M tape is up to you if you feel you have enough contact area. Otherwise use thickened epoxy. I know that will work. It has maybe 100 times the shear/tensile strength of the tape.

I acknowledge that for some Winnie roofs the thin fiberglass isn't attached to the underlying plywood. After taping or epoxying it down, try lifting the panels. If they budge significantly, then a few screws are probably in order.

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Old 07-07-2020, 04:44 PM   #9
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Quote:
Originally Posted by BobC View Post
I haven't mounted mine yet but I can tell that the fiberglass on my 2002 Suncruiser isn't fully adhered to the luan substrate any more. Therefore, my plan is to use both VHB and screws. Better safe than sorry.
Thats what I want to avoid as well. The forces on the fiberglass pulling it away from the luan.
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Old 07-07-2020, 04:48 PM   #10
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Originally Posted by DavidM View Post

I acknowledge that for some Winnie roofs the thin fiberglass isn't attached to the underlying plywood. After taping or epoxying it down, try lifting the panels. If they budge significantly, then a few screws are probably in order.

David
That's a great suggestion. Not sure why I didn't think of this. I'll start with the tape and if I'm not happy with the curve of the roof or things move around too much, then I'll add some short screws.

Thanks.
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Old 07-07-2020, 05:23 PM   #11
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Any real world examples of what people are doing?

I used Z brackets, butyl tape, and #12 stainless steel hex head screws. Then I seal the heads with self leveling Dicor. I also put an extra little gob of butyl tape on the screw threads to ensure that the screw head to bracket is sealed.
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Old 07-07-2020, 08:37 PM   #12
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I used Z brackets, butyl tape, and #12 stainless steel hex head screws. Then I seal the heads with self leveling Dicor. I also put an extra little gob of butyl tape on the screw threads to ensure that the screw head to bracket is sealed.
Thanks for sharing your setup SLOweather.
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Old 07-07-2020, 08:51 PM   #13
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Jim
I estimate each mount is ~ 1 1/2 X 2 1/2" ... you might find a better measurement on AM Solar's website...

http://amsolar.com
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Old 07-12-2020, 04:18 PM   #14
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For my panel(s) I bolted the mounts to long flat aluminum extrusion (each piece 2" wide by the length of the panel), one piece along each long side of the panel. the aluminum extrusion is VHB'd to the roof. The long pieces of extrusion gave me a lot more surface area for adhesion than just the mounts and the mounts themselves are screwed to the extrusion. I also sealed the edges of the extrusion against the roof with Eternabond...but that might be my OCD showing .

Given the thin-ness of the fiberglass roof and the unknown wood or other support under the roof I thought screws through the roof might not have much to hold onto....apart from leak issues down the road.
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Old 07-12-2020, 04:37 PM   #15
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Eternabond will protect the exposed edges of the VHB but will add little or know adhesive strength.
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Old 07-12-2020, 04:57 PM   #16
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yep...figured keeping the elements off the VHB couldn't hurt.
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Old 07-12-2020, 06:03 PM   #17
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I'm running one year on my four 100 Watt panels with tilt brackets using VHB tape. Still solidly held on. I do check periodically. Large surface area on the mounting brackets.
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Old 07-12-2020, 06:47 PM   #18
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Thanks for all the examples. I ended up using both tape and screwed in. Then ran some self-leveling Dicor around the edges and over the screw tops. I went with both because I've got an older rig and didn't want to worry about the fiberglass pulling away from the wood. Thank you all.
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Old 07-13-2020, 06:10 AM   #19
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I have used this tape to attach a sunpower solar panel(4 lbs) without a problem. This tape is very strong. There are a number of videos on y tube concerning this using the heavier, rigid solar panels.
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Old 07-13-2020, 08:58 AM   #20
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Adhesives are notorious for deteriorating. And do you know the aerodynamic load on the panel when you are passing a semi truck? Then you need to consider differential thermal expansion of the panel versus the roof to compute the shear loads on the mounting points.

If you are driving down the road, and it comes off, it could easily kill somebody behind you or oncoming traffic.
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