Flexible solar panel adhesive failure

Incredulocious

2016 LTV Unity TB
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:

“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-customizations/#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?
 
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turbopilot

New member
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.
 

kernhend

2017 Unity MB
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.
 
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OldWest

2004 T1N Westfalia
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.
 

Aqua Puttana

Poly - Thread Finder
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/misc/sd900110/index.htm

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

:2cents: vic
 
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Incredulocious

2016 LTV Unity TB
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.
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.

 
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Incredulocious

2016 LTV Unity TB
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.

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!
 
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israndy

2007 LTV Serenity
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
 

Boxster1971

2012 Sprinter 3500 Ext
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/gpelectric/documents/PDF/MANUAL_GP-FLEX-30-100-100E-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.
 

Incredulocious

2016 LTV Unity TB
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/gpelectric/documents/PDF/MANUAL_GP-FLEX-30-100-100E-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:

 

kernhend

2017 Unity MB
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.

I had not seen the plastic film prior to my post. It looks like it is a fiberglass reinforced plastic fabric. Obviously, the failure occurred between this and the adhesive. My guess that the plastic is vinyl. Flame treating vinyl improves adhesion. You Tube "flame treating" and you'll see how this is done. This may be all this takes to get the panels to bond. The cured beads can be removed by using a very sharp chisel held flat using care to not cut into the fiberglass roof. Alternatively, you could clean and dirt off and abrade the surface of these beads. Then apply new adhesive on top of the old beads and press the panel down on the new adhesive until it cures. This will take several days with the Sikaflex 221 or several hours with SilverThane SA-2100.
 

Midwestdrifter

Engineer In Residence
As mentioned this looks like a failure to asses the materials being bonded. When in doubt, you can apply a bead of adhesive as a test beforehand.

Many plastics bond well with polyurethane when treated or scuffed beforehand. Vinyl, polyethylene, and polypropylene are difficult to bond though.

If I was in your shoes, I would be tempted to see if there was a VHB tape that bonded well to the plastic liner. There are several versions of VHB which are designed for low surface energy substrates such as plastics. :idunno:

Alternatively you could put a countersunk bolt through a piece of aluminum bar, then bond the bar to the roof with adhesive. The bolt would protrude upwards, and could be used to secure the corners of the panel.
 

OldWest

2004 T1N Westfalia
1. Fein Multimaster or other oscillating tool. Can use to cut away the leftover adhesive on the roof.

2. Debond. https://www.debondcorporation.com/

Before, during or after using the oscillating tool, could also soften adhesive with Debond.

3. Good chance of scratching and gouging roof during adhesive removal process. May want to repaint.

If solar panels were still in place, would be very difficult to remove panels as oscillating tools would not be able to reach adhesive.
 

OldWest

2004 T1N Westfalia
ABS Brackets. Plastic corners and sides which are glued to roof and solar paneks rest on top. Will want to find ones which are lower profile for semiflexible panels. There are also ones which have a bolt through the corner bracket to hold down solar panel. Here's an example of these brackets:
http://www.bimblesolar.com/solar-abs-mount-kit
 
Curious as to why you used the Greesonic 100W panels instead of the Gopower Flex panel used by LTV? I'm betting that the backside materials are different on the two panels?

You need to identify exactly what polymer is used on the back of your panel then call 3M to chat with one of their adhesive consultants to find out what to use. Got to identify the two polymers that you're trying to bond together first. Good luck...
 
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Incredulocious

2016 LTV Unity TB
Curious as to why you used the Greesonic 100W panels instead of the Gopower Flex panel used by LTV? I'm betting that the backside materials are different on the two panels?

You need to identify exactly what polymer is used on the back of your panel then call 3M to chat with one of their adhesive consultants to find out what to use. Got to identify the two polymers that you're trying to bond together first. Good luck...
As I described in my installation write-up, when I was looking at various available flexible panels, I decided to go with somebody like GreeSonic offering this supposedly better performing top layer of Ethylene tetrafluoroethylene (ETFE vs. PET) while still using SunPower cells. (Extra resilience, some self-healing capacity, non-viscous, dirt resistant, self-cleaning, and less reflective thus potentially better performing.) It sounded like this might address some of the surface degradation issues I had read about with some flexible panels (possibly including GoPower). There's some more info here and from here from other suppliers using ETFE.

You can see a visible difference in the top layer in these photos – shiny & smooth is GoPower; matte & textured is GreeSonic:



GoPower says their backsheet is "laminated TPT". So yes, I believe both the top and bottom layer materials are different between the GreeSonic and the GoPower Flex panels.

I have another message out to GreeSonic to try to find out what the backing is since whoever responded the first time wasn't able to provide a lot of info about appropriate adhesives. Perhaps the bottom layer will turn out to be the same ETFE polymer. (That seems possible given how the guy mentioned yellowing if it were removed – reading from his own marketing material for the top layer.)

For what it's worth, GoPower is also unwilling to suggest adhesives and recommends contacting the RV manufacturer... which also misses the point of determining what adhesive bonds with the back of their panels.
 
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Mikemxo

New member
I'd like to put additional solar panels on my 2016 Unity IB. I've been told the flexible solar panels don't produce much (my 2 200 amps are only supply say 50 amps or so) and not effective. In fact, there has been a recall on most of those brands. My question---a qualified solar vendor says the rigid panels are best, but I'm concerned about attaching into the beautiful roof of my new Unity. Can this be done safely?
 

Boxster1971

2012 Sprinter 3500 Ext
I'd like to put additional solar panels on my 2016 Unity IB. I've been told the flexible solar panels don't produce much (my 2 200 amps are only supply say 50 amps or so) and not effective. In fact, there has been a recall on most of those brands. My question---a qualified solar vendor says the rigid panels are best, but I'm concerned about attaching into the beautiful roof of my new Unity. Can this be done safely?
Sure can. Check out AM Solar.
http://amsolar.com/diy-rv-solar-instructions/edmounts/
 

Incredulocious

2016 LTV Unity TB
I'd like to put additional solar panels on my 2016 Unity IB. I've been told the flexible solar panels don't produce much (my 2 200 amps are only supply say 50 amps or so) and not effective. In fact, there has been a recall on most of those brands. My question---a qualified solar vendor says the rigid panels are best, but I'm concerned about attaching into the beautiful roof of my new Unity. Can this be done safely?
Your panels are 200 watts (not amps) but you're not going to see a lot of watts (or amps) out of any panels (rigid or semi-flexible) with the sun so low in the sky right now and your panels pointing straight up. For comparison, in December, with the sun at a low angle of about 31 degrees, I was seeing 11-13 amps with my five 100-watt panels (two of which were the original GoPower panels). I may be seeing about twice that later in the year. Pointed directly at the sun, the GreeSonic panels I added are rated to produce about 5.7 amps each at 77 degrees Fahrenheit.

Here's someone testing another brand of flexible panels (Lensun) and seeing amps comparable to their Renogy rigid panels:
http://www.loveyourrv.com/lensun-flexible-solar-panel-review/

I, for one, would not be too quick to write off all "semi-flexible" panels and I would investigate those rumors of "a recall on most of those brands". Not all panels are created equal (even those that use the same solar cells) and plenty of people enjoy the power they get out of these very lightweight designs (3 lbs versus 20+ lbs for rigid panels). I definitely prefer the idea of putting less weight up high on our vehicles. But yes, you can certainly safely attach rigid panels to our Unity roofs as well.

I'm still working on exploring the options for adding additional flexible panels to my Unity after discovering the hard way that Sikaflex-221 is not an adhesive (it's a sealant!), despite how some have used and recommended it as such. I'll be providing more info and thoughts on installation options here but I've been held back by the extended wet and cold weather here.

More info and pictures on my install here:
http://crimdom.net/rv-upgrades-and-customizations/#solar
 
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ablock

Member
For comparison, in December, with the sun at a low angle of about 31 degrees, I was seeing 11-13 amps with my five 100-watt panels (two of which were the original GoPower panels). I may be seeing about twice that later in the year.
That's interesting. Right now in Northern California I am seeing peak power of 300-340W (23-25A) from our six 100W panels (two GoPower + four AM Solar SP100s). Since our days have actually been rather cloudy the more typical numbers are around 200W midday.

I should mention that we are using the Victron MPPT controller, which supposedly does somewhat better at getting watts out of the panels than PWM controllers like the stock GoPower.
 

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