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Old 01-03-2017, 05:10 PM   #1
Incredulocious
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Default Flexible solar panel adhesive failure

I recently upgraded my Unity TB's solar charging by adding three 100W GreeSonic flexible solar panels, particularly with help from the posting of others here on the forum.

However, the Sikaflex-221 that's commonly used and recommended as an adhesive for flexible panels on fiberglass roofs failed on me and I found out when one of the panels broke loose and flew off while on the freeway. On inspection, I found the remaining two panels could be easily peeled right off.



While the Sikaflex did bond well with my fiberglass roof, it did not bond at all with the backs of my GreeSonic panels. They're made of aluminum but covered in a thin, lightly textured, semi-permanent plastic film. It did not appear to be meant to be removed. I contacted GreeSonic about this film and for adhesive recommendations but they didn't give a very definitive reply:

Quote:
“The plastic film on the back of the panel can be removed before installation. If you remove the film, the panel may turn out to be yellow after several years because of oxidation by sun and rain, but it still work. So you may just remove the film before installation.

You can use some more adhesive material such as 3M powerful tape to adhesive the panel. Of course, the best way is to use the four eyelets to fasten it.”
I'm going to test Sikaflex-221 to see how it bonds on the bare aluminum (plastic film removed) using the damaged panel and I'll report back. Presumably the "3M powerful tape" they're referring to is 3M VHB tape. I'm not sure how well that would work in this situation but I have some and can at least test to see how it adheres to the back of the damaged panel (with and without the film).

I've got more detail and pictures of my installation and my thoughts on what happened on my web page:
http://crimdom.net/rv-upgrades-and-c...panel-adhesive

I mostly wanted to be sure to warn folks to be careful with their usage of Sikaflex but here's some other questions that perhaps some can help answer here:

1) What adhesive does LTV use on the GoPower Flex100 panels they install?
2) If you installed flexible panels, what kind of backing did they have and what adhesive did you use?
3) Does this purported yellowing of the panels make sense if a film is removed from the aluminum backside?
4) Any other adhesives I should test for bonding abilities with or without that protective film?

Last edited by Incredulocious; 01-03-2017 at 07:59 PM.
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Old 01-03-2017, 05:45 PM   #2
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Default Re: Flexible solar panel adhesive failure

Just about standard to find a plastic film on both sides aluminum sheet stock bought from most sources today. It is there to protect the aluminum from scratching during transport. It is made to easily peel off when you put the aluminum sheet in service. Looks like that is what you have on the back of these panels.
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Old 01-03-2017, 05:59 PM   #3
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Default Re: Flexible solar panel adhesive failure

The plastic film on the back of the aluminum should have been removed before bonding. Moisture cured urethane sealants do not bond well to flexible plastic without proper surface preparation. I'm leery about using moisture cured urethanes (Sikaflex-221 or 3M-5200) for an application like this where a large impervious surface (the aluminum panel) is being bonded to a second impervious surface (the fiberglass roof). There is simply no way for moisture to get more than a few inches into the urethane from the edge to cure it. I'd avoid one-part moisture cured urethanes for this application and go to a two part like my company's Silverthane SA-2100. This will cure without moisture and will bond extremely well and permanently to lightly sanded (120 grit) and solvent wiped aluminum and fiberglass.

I've looked at the photos on your website. If I were using SA-2100 to bond these I'd probably bond the perimeter as you did using a bead such that I could get a half-inch wide glue line when the panel was pressed down. Add a few dabs in the middle and you'll have it. I'd recommend that you tape some small wooden spacers down so as to get a thick enough glue line so that if you ever have to remove the panel you can cut the cured SA-2100 with a saw on edge. About the only way you'll be able to remove the panel is to cut through the adhesive line by abrading it.

Last edited by kernhend; 01-03-2017 at 06:22 PM. Reason: Added bonding recommendations.
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Old 01-03-2017, 06:16 PM   #4
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Default Re: Flexible solar panel adhesive failure

1. Permanent Adhesive. Do NOT use. Semiflexible panels may not last as long glass solar panels, and you'll want ability to remove without destroying not only the panels but the roof.

2. 3M Dual Lock. This is an excellent option. There are several types of Dual Lock with different types of adhesive and different mushroom density (mushrooms interlock). Like Velcro, can remove panels (one side of strip would remain on roof). If necessary, it'd be easier to remove the roof side strip as panel would no longer be covering.

The Dual Lock does have some thickness, so must be careful to create sufficient support so Dual Lock doesn't create ridges on panel. Use around perimeter with gaps to let any moisture to drip out from under panel. Then maybe some more strips in middle area.

3..Backing. Semiflexible panels can be delicate. Polycarbonate panel backing adds rigidity and cooling for better solar output. Would add another layer (could use 3M dual sided tape to adhere panels to polycarbonate, then 3M Dual Lock to adhere polycarbonate to roof.
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Old 01-03-2017, 06:49 PM   #5
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Default Re: Flexible solar panel adhesive failure

I haven't personally seen your flexible panels.

It would seem future removal should be a consideration in fastening. Mechanical fasteners allow future removal.

They mention "eyelets". I assume they mean for some sort of mechanical fastening?

You might consider something like this product. No penetration needed for attachment to the roof.

http://www.weldmountsystem.com/products-fasteners.php

http://www.duckworksbbs.com/hardware...0110/index.htm

I would consider including a shallow channel to bridge across the top of the leading edge to hold it down.

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Old 01-03-2017, 07:00 PM   #6
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Default Re: Flexible solar panel adhesive failure

Quote:
Originally Posted by turbopilot View Post
Just about standard to find a plastic film on both sides aluminum sheet stock bought from most sources today. It is there to protect the aluminum from scratching during transport. It is made to easily peel off when you put the aluminum sheet in service. Looks like that is what you have on the back of these panels.
Quote:
Originally Posted by kernhend View Post
The plastic film on the back of the aluminum should have been removed before bonding. Moisture cured urethane sealants do not bond well to flexible plastic without proper surface preparation.
To be clear, this is not a temporary, easily-removed film – as per the manufacturer, it was meant to remain in place. Here's a better picture where you can see that it's slightly textured. Before installation, I found that it did not readily peel away. After the damage, I went ahead and tried peeling it and found that it doesn't come off easily and breaks apart as you try to remove it.


Last edited by Incredulocious; 01-03-2017 at 07:11 PM.
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Old 01-03-2017, 07:05 PM   #7
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Default Re: Flexible solar panel adhesive failure

I see various folks recommending not to use permanent adhesive. I'll reconsider this in the days to come, but I want to point out that using some sort of adhesive seems to be the common way of installing flexible panels and is how similar panels (GoPower Flex100) are installed by some manufacturers like Leisure Travel Vans, including the two panels that my Unity came with. Actually, I haven't seen anyone do otherwise yet.

Quote:
Originally Posted by kernhend View Post
I'm leery about using moisture cured urethanes (Sikaflex-221 or 3M-5200) for an application like this where a large impervious surface (the aluminum panel) is being bonded to a second impervious surface (the fiberglass roof). There is simply no way for moisture to get more than a few inches into the urethane from the edge to cure it.
I'm curious about this comment as it seems the Sikaflex-221 did bond very well with the fiberglass roof (and will probably be a pain to remove). It seems more of an issue with bonding to the panel surface (at least that thin plastic layer).

And thanks for the many other suggestions and comments so far, I'll be investigating. Further comments very welcome!

Last edited by Incredulocious; 01-03-2017 at 07:17 PM.
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Old 01-03-2017, 07:27 PM   #8
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Default Re: Flexible solar panel adhesive failure

Mine have stayed in place for the last 3 years since my initial install and I just used 3M Super 77 spray mount. I protected the paint using that spray film that can be pealed off the paint, protecting from road damage like bugs and pits. I sprayed on the film on the location the panels were going. When that cured I sprayed adhesive on the roof and on the back of the panels plastic backing. When they got tacky I pushed them together. They do pull up a little and I lost one panel that was on the AC shroud but the others are still hanging on. I have the advantage that I have a skylight directly in front of them, it takes the wind blast.

-Randy
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Old 01-03-2017, 07:31 PM   #9
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Default Re: Flexible solar panel adhesive failure

The problem was caused by not removing that protective film from back side of panels.

There is nothing wrong with Sikaflex 221 and note that it stuck to your roof just fine. It fact, as you said, it will be a big job to remove those beads of Sikaflex left on your roof. Did LTV also use screws to fasten the GoPower panels they installed? That is the GoPower recommended method.
http://gpelectric.com/files/gpelectr...0-100E-200.pdf

This site from Australia also has some good tips on installing flexible solar panels, like sealing the entire edge perimeter.
https://www.solar4rvs.com.au/installation.html

Good luck on the fix.
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Old 01-03-2017, 07:41 PM   #10
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Default Re: Flexible solar panel adhesive failure

Quote:
Originally Posted by Boxster1971 View Post
There is nothing wrong with Sikaflex 221 and note that it stuck to your roof just fine. It fact, as you said, it will be a big job to remove those beads of Sikaflex left on your roof. Did LTV also use screws to fasten the GoPower panels they installed? That is the GoPower recommended method.
http://gpelectric.com/files/gpelectr...0-100E-200.pdf
Yes, I had seen that: "Use the screws and washers provided in the kit to secure the solar panel to the RV. Or an adhesive sealant can be used to attach the panels to the RV roof. Please contact your RV manufacturer for specifications on an appropriate sealant."

But no, LTV does not screw them down. Some sort of adhesive was used:

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