Flexible solar panel adhesive failure

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.
That seems like a lot: 24 amps / 6 panels = 4 amps/panel in January. Impressive. Are you parked on a slope facing the sun a bit? How much do you get in June then?? I've got room for a sixth panel but was concerned about exceeding the GoPower's 30 amp max capacity for part of the year.

Of course I just have the original GoPower PWM controller, in it's original location, a bit away from the batteries (some voltage drop) and I also understand MPPT controllers will get more out of your panels. According to Victron's web site, you can expect 10-40% more power from the array under certain conditions:
https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/

That said, my numbers are quoted from just one day over a month ago and I can't be certain if my batteries were taking all that the panels could deliver.
 
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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.
That seems like a lot: 24 amps / 6 panels = 4 amps/panel in January. Impressive.

According to Victron's web site, you can expect 10-40% more power from the array under certain conditions:
https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/
Here's an even more helpful explanation of how MPPT controllers work:
https://www.solar-electric.com/mppt-solar-charge-controllers.html

And note how much better they say they work in winter:
You typically get a 20 to 45% power gain in winter and 10-15% in summer.
I think I might replace the stock Go Power PWM controller with a Victron BlueSolar MPPT controller.
 

Graphite Dave

Dave Orton
A simple explanation of the advantage of a MPPT controller:

Watts in = watts out. The controller does not create power.

So panel voltage x panel amperage = charging voltage x charging amperage.

In my case I have a 32 volt panel with maximum output of 9.4 amps.

32 volts x 9.4 amps = 14.1 volts (about) x 21.3 amps

Actual maximum output from the panel is probably around 70% due to flat installation and temperature. So more like 15 amps maximum charging current. I use a 15 amp Morningstar Sunsaver MPPT controller.
 
A simple explanation of the advantage of a MPPT controller:

Watts in = watts out. The controller does not create power.

So panel voltage x panel amperage = charging voltage x charging amperage.

In my case I have a 32 volt panel with maximum output of 9.4 amps.

32 volts x 9.4 amps = 14.1 volts (about) x 21.3 amps

Actual maximum output from the panel is probably around 70% due to flat installation and temperature. So more like 15 amps maximum charging current. I use a 15 amp Morningstar Sunsaver MPPT controller.
Well, what's missing from your explanation and that I thought was so helpful from that detailed article I linked to is an explanation as to how a simpler PWM controller lets the voltage get pulled down to the battery's level so you get less volts at a given amperage which equals less energy/watts overall. The MPPT controller however, does a DC to DC conversion from the higher voltage down to the lower voltage, so you retain most of the watts by getting more amps at the battery's charge voltage:

Your panel puts out 7.4 amps. Your battery is setting at 12 volts under charge: 7.4 amps times 12 volts = 88.8 watts. You lost over 41 watts - but you paid for 130. That 41 watts is not going anywhere, it just is not being produced because there is a poor match between the panel and the battery. With a very low battery, say 10.5 volts, it's even worse - you could be losing as much as 35% (11 volts x 7.4 amps = 81.4 watts. You lost about 48 watts.

Here is where the optimization, or maximum power point tracking comes in. Assume your battery is low, at 12 volts. A MPPT takes that 17.6 volts at 7.4 amps and converts it down, so that what the battery gets is now 10.8 amps at 12 volts. Now you still have almost 130 watts, and everyone is happy.
 
To bring this thread back on topic, I've learned since I first started this thread that it was a mistake to use Sikaflex-221. Despite how others have used the product, Sikaflex-221 is really meant to be used as a weather sealant.

As per the manufacturer's web site:

Sikaflex-221 is a high-quality multi purpose non-sag 1-c polyurethane sealant that cures on exposure to atmospheric humidity to form a durable elastomer.
- See more at: http://usa.sika.com/dms/getredirect.get/us01.webdms.sika.com/977
They do have a number of adhesive products, like SikaFast-3141 or -3131, but Sikaflex-221 is not intended to be used as an adhesive (see also this older thread on the topic) and I shouldn't have followed the lead of others to use it to adhere my panels. They may well be lucking out so far but my panels have a polyethylene backing which made them even less able to bond with this sealant.

I've been following up on suggestions made in this thread and looking into various mounting options which I'll summarize here:

1) Liquid Adhesive: This seems to be how many RV manufacturers (including Leisure Travel Vans) install flexible panels. Despite this, some folk recommend against using liquid adhesives given the potential difficulty of ever removing a damaged panel. With these polyethylene-backed Greesonic panels, it's important to find an adhesive that works well with "low energy" surfaces. One manufacturer recommended using their SilverThane SA-2100 adhesive, but the polyethylene-backing would need to be flame-treated in order for this adhesive to be effective on that surface.

2) High Bond Adhesive Tape (3M VHB): This seems to be the most widely-used method of securing flexible panels. It's also how some well-respected installers, like AM Solar, secure the mounting brackets for much heavier, more air drag prominent rigid panels. AM Solar uses 3M's VHB 4950. I contacted 3M to find out which VHB tape they'd recommend for my polyethylene-backed flexible panels (a "low energy" surface) and they recommended VHB 5952. I've done some tests with this VHB tape using my damaged panel and it does seem to hold very well. It took a lot of force with plenty of leverage to get it to release just a 3" x 1" strip. Not surprisingly, the MCD board I was using gave up the bond first when testing against aluminum but the polyethylene gave up the bond first when I tested against that.

3) Dual Lock / Velcro Tape: Somewhat surprisingly, this is actually a reasonable solution. There are a number of industrial strength "hook and loop" or "mushroom cap" tape products that are used in demanding outdoor, mobile applications like securing flexible panels to an RV rooftop and others have found it to work quite well. It has the added advantage of being easier to replace the panels than with simple adhesive tape. The major concern I have here is that there does not seem to be as many options for the adhesive portion of the tape – and I need to bond with a very "low energy" polyethylene surface. Plus this will also create a thicker gap to deal with under the panels.

4) Screwing into the Roof: Like many others, I'm not at all keen to screw into the fiberglass roof of the Unity. It's easy enough to use sealant to prevent any leaks but it's not at all clear just what your screw will be grabbing onto and you'd be concentrating any forces acting on the panel on a few small points of the roof. It's also apparently not how most everyone else installs flexible panels. Lastly, you would end up having to reuse/weaken holes or make new holes if you ever need to remove and replace a panel. Notably, even well-respected installers like AM Solar use VHB with their rigid panel mounts rather than screwing into fiberglass roofs.

5) Countersunk Bolts through Flush Mounting Brackets: This is a tempting suggestion to use thin aluminum bars, metal angle braces, plastic brackets or something similar and then add upward-facing countersunk bolts. The brackets are secured to the roof with adhesive and the flexible panels are secured to the bolts through their corner grommets. This would have the advantage of spreading the load over a wider area than can be achieved with a screw into fiberglass and would allow the panels to be removed and replaced if they ever become damaged. This is similar to what some installers (like AM Solar) do with much heavier, rigid, framed panels: they mount the panels on brackets secured with 3M VHB 4950 tape (rather than screws) and then they cover the brackets in lap sealant. It would be necessary though to prevent galvanic corrosion between dissimilar metals like aluminum bars and steel bolts, perhaps using something like "Ultra Tef-gel".

So.... I'm currently leaning towards either #2 or #5. I'm still waiting for a stretch of warm, dry weather to proceed. I also need to decide between using sealant all the way around the panels to keep out moisture and prevent the panels from getting any lift or leaving a few gaps around the panel to allow moisture to drain. Different folks have chosen to do this differently.

I just wanted to update this thread now to warn folks off of following the "Sikaflex-221 as an adhesive" path.
 
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To bring this thread back on topic, I've learned since I first started this thread that it was a mistake to use Sikaflex-221. Despite how others have used the product, Sikaflex-221 is really meant to be used as a weather sealant.

As per the manufacturer's web site:



They do have a number of adhesive products, like SikaFast-3141 or -3131, but Sikaflex-221 is not intended to be used as an adhesive (see also this older thread on the topic) and I shouldn't have followed the lead of others to use it to adhere my panels. They may well be lucking out so far but my panels have a polyethylene backing which made them even less able to bond with this sealant.

I've been following up on suggestions made in this thread and looking into various mounting options which I'll summarize here:

1) Liquid Adhesive: This seems to be how many RV manufacturers (including Leisure Travel Vans) install flexible panels. Despite this, some folk recommend against using liquid adhesives given the potential difficulty of ever removing a damaged panel. With these polyethylene-backed Greesonic panels, it's important to find an adhesive that works well with "low energy" surfaces. One manufacturer recommended using their SilverThane SA-2100 adhesive, but the polyethylene-backing would need to be flame-treated in order for this adhesive to be effective on that surface.

2) High Bond Adhesive Tape (3M VHB): This seems to be the most widely-used method of securing flexible panels. It's also how some well-respected installers, like AM Solar, secure the mounting brackets for much heavier, more air drag prominent rigid panels. AM Solar uses 3M's VHB 4950. I contacted 3M to find out which VHB tape they'd recommend for my polyethylene-backed flexible panels (a "low energy" surface) and they recommended VHB 5952. I've done some tests with this VHB tape using my damaged panel and it does seem to hold very well. It took a lot of force with plenty of leverage to get it to release just a 3" x 1" strip. Not surprisingly, the MCD board I was using gave up the bond first when testing against aluminum but the polyethylene gave up the bond first when I tested against that.

3) Dual Lock / Velcro Tape: Somewhat surprisingly, this is actually a reasonable solution. There are a number of industrial strength "hook and loop" or "mushroom cap" tape products that are used in demanding outdoor, mobile applications like securing flexible panels to an RV rooftop and others have found it to work quite well. It has the added advantage of being easier to replace the panels than with simple adhesive tape. The major concern I have here is that there does not seem to be as many options for the adhesive portion of the tape – and I need to bond with a very "low energy" polyethylene surface. Plus this will also create a thicker gap to deal with under the panels.

4) Screwing into the Roof: Like many others, I'm not at all keen to screw into the fiberglass roof of the Unity. It's easy enough to use sealant to prevent any leaks but it's not at all clear just what your screw will be grabbing onto and you'd be concentrating any forces acting on the panel on a few small points of the roof. It's also apparently not how most everyone else installs flexible panels. Lastly, you would end up having to reuse/weaken holes or make new holes if you ever need to remove and replace a panel. Notably, even well-respected installers like AM Solar use VHB with their rigid panel mounts rather than screwing into fiberglass roofs.

5) Countersunk Bolts through Flush Mounting Brackets: This is a tempting suggestion to use thin aluminum bars, metal angle braces, plastic brackets or something similar and then add upward-facing countersunk bolts. The brackets are secured to the roof with adhesive and the flexible panels are secured to the bolts through their corner grommets. This would have the advantage of spreading the load over a wider area than can be achieved with a screw into fiberglass and would allow the panels to be removed and replaced if they ever become damaged. This is similar to what some installers (like AM Solar) do with much heavier, rigid, framed panels: they mount the panels on brackets secured with 3M VHB 4950 tape (rather than screws) and then they cover the brackets in lap sealant. It would be necessary though to prevent galvanic corrosion between dissimilar metals like aluminum bars and steel bolts, perhaps using something like "Ultra Tef-gel".

So.... I'm currently leaning towards either #2 or #5. I'm still waiting for a stretch of warm, dry weather to proceed. I also need to decide between using sealant all the way around the panels to keep out moisture and prevent the panels from getting any lift or leaving a few gaps around the panel to allow moisture to drain. Different folks have chosen to do this differently.

I just wanted to update this thread now to warn folks off of following the "Sikaflex-221 as an adhesive" path.
Excellent line of reasoning! Talk about doing your homework! I also like options #2 and #5 the best but lean toward #2. First of all, by far #2 is the easiest and least expensive. And, as much as it makes me nervous to use adhesives I have to face the facts that plane wings are at least partially glued together in many instances. I've been involved with some of the engineers and scientists at 3M over the years and it is simply amazing what they do with chemistry. If they have a solution for your problem and you follow their guidelines for proper application I suspect that you have little to worry about. Having said all of that, If I have the option to use a nice, strong steel fastener I will usually go that way and use the next bigger bolt and use twice as many of them just to be safe! ;-) That is of course because I'm not a trained Mechanical Engineer so I work from experience, some material science knowledge and instinct. If you really wanted to use mechanical fasteners I would only consider that after a thorough discussion with the folks in Winkler who I suspect will tell you to glue those panels down! ;-) Best of luck!
 

israndy

2007 LTV Serenity
I didn't see mention of the 3M Super 77 that I used. It has been working well for almost 5 years... Is that considered liquid adhesive? Not held down too strongly but across the entire panel it's enough to keep them from blowing away at highway speeds...

-Randy
 
I didn't see mention of the 3M Super 77 that I used. It has been working well for almost 5 years... Is that considered liquid adhesive? Not held down too strongly but across the entire panel it's enough to keep them from blowing away at highway speeds...
Sorry I didn't mention 3M Super 77 outright, but yeah, I would consider that a liquid adhesive (as opposed to tape). However, I wouldn't recommend using it for panels. Here's how 3M describes the product:

Securely bonds many lightweight materials such as attaching foils, carpeting, lightweight paper, cardboard, felt, and cloth to painted or unpainted metals, wood.
A high tack, high coverage fast drying, transparent adhesive for permanently attaching foils, carpeting, many lightweight foams, paper, cardboard, felt and cloth to painted or unpainted metals, wood, hardboard and other base materials.
I'm glad that your panels are doing okay so far, but it doesn't sound to me like it's a safe or recommended use of 3M's spray adhesive.
 
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joeframer44

2014 Unity MB/U-lounge
Sorry I didn't mention 3M Super 77 outright, but yeah, I would consider that a liquid adhesive (as opposed to tape). However, I wouldn't recommend using it for panels. Here's how 3M describes the product:



I'm glad that your panels are doing okay so far, but it doesn't sound to me like it's a safe or recommended use of 3M's spray adhesive.
I would echo the concern for using 77 spray for long term adhesion. We were in the custom picture framing business for 40 years (just retired and planning longer trips in our Unity) and used 77 spray for certain mounting applications. It is effective for mounting inexpensive posters, fabric covered mats and and making mounts for shadowboxes, etc. However, when disassembling items for reframing after some time we would find that the adhesive was dried out and one could easily peel off the fabric, etc without much effort.

For the application of adhering the flex solar panels, I would worry that the air passing around the panels would accelerate drying out the adhesive and cause the panels to start lifting.

I think I would vote for the VHB tape, around the four edges and maybe an X pattern from corner to corner.

Joe K.
2014 Unity MB
 

israndy

2007 LTV Serenity
Good input, thanks. As my flex panels were some of the first installed I am almost looking forward to them blowing away and buying some traditional glass panels, my panels plastic has been deteriorating and probably will not provide as good a charge as they once did. Somehow they are still on their like the day I put them down, but this is my only experience with the spray adhesive.

-Randy
 
Since lvuman posted about their solar install using Eternabond (thanks!), I've been meaning to update this thread and my previous post (and my web page) where I listed various mounting options for flexible panels. So here's #6:

#6 Eternabond Sealant Tape

This is an interesting method that someone has already tried and described in this discussion thread. While it is a sealant (as opposed to an adhesive), it has several potential advantages over using an adhesive tape like VHB. This sealant tape would be installed over the edges of the flexible panel rather than underneath so it would not have the requirement of holding down the panel against potential lift from air currents. I would expect it would be easier to use because you could just lay down the panel where you want it to go and then apply the tape over the panel edges. With adhesive tape underneath, you’d need to be pretty careful how you turn over and lay down the panel so you don’t end up gluing it down in the wrong place. This sealant tape would also eliminate any extra step of sealing around the edges of the panel. Lastly, it would seem you could just cut the panel free from the sealant tape if you ever had a failure and needed to replace it. Here's the company's description of how to replace or simply seal over Eternabond tape. One minor downside with using Eternabond is that you need to leave a little more room around the panel for the tape to bond and it isn’t quite as clean a look as adhesive underneath the panel.
So…. I’m currently leaning towards either #2 or #6. I’m still waiting for a stretch of warm, dry weather to proceed. This Eternabond option is very tempting even though I already bought the VHB tape. I now have a roll of some Eternabond too and I'm going to try using it to repair a gutter on my home and see what it's like to work with before deciding whether to use it for the panels.
 
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OldWest

2004 T1N Westfalia
Eternabond adhesive is thick, gray, and a bit oozy.

Can see the thick gray adhesive, which then collects dirt along the edges.

Also, the vinyl/plastic tape can peel away in part from the gray adhesive, which then looks quite unattractive.

Very messy to clean-up.

Eternabond has its uses but I think there are better alternatives for semiflexible solar panel installation.
 

OldWest

2004 T1N Westfalia
Think some tips on Eternabond is to put in fridge before use (so gray adhesive is not as oozy and messy).

I used Eternabond to seal the screws and the flange.of a Fantastic Fan. The rear edge of the Fantastic Fan abuts the curved portion of roof, and the Eternabond on the curved portion separated between the gray adhesive and the white vinyl/plastic tape part.

I used 3M Dual Lock around the perimeters of two semiflexible panels on the front curved roof (Airstream Westfalia). In addition, added a bead of Lexel along the leading edge of the solar panels to prevent any wind lift.

Would use again, BUT would add more strips spaced closer together to provide an air gap under panels and to account for thickness on the perimeter. Or could use any other material the thickness of the 3M. Without additional strips (not needed for adhesion but for spacing support), the semiflexible panels sagged in the center portion and touched roof.

If doing installation on a flat surface, would use THIN 3M tape to adhere semiflexible panels to polycarbonate panels. That tape is thin enough not to create an air gap. The polycarbonate panels would add stiffness and air ventilation to cool.

Then would use 3M Dual Lock between the polycarbonate panels and roof, so could remove panels easily.
 

OldWest

2004 T1N Westfalia
If you go with option 2 and use 3M tape, will need to figure out a way on how to remove solar panels in future. If use just on perimeters of panels, then could use an oscillating tool to break adhesive. But tool cannot reach beyond two or so inches so any tape in center of panek would be difficult to reach. If use 3M just on brackets, then not really an issue.

The use of polycarbonate panels as backing to semiflexible panels might be worthwhile to consider. A bit more work but may reduce repair and removal work in future. Also, may get better solar output from cooler panels.
 
Eternabond adhesive is thick, gray, and a bit oozy. Can see the thick gray adhesive, which then collects dirt along the edges. Also, the vinyl/plastic tape can peel away in part from the gray adhesive, which then looks quite unattractive. Very messy to clean-up.

Eternabond has its uses but I think there are better alternatives for semiflexible solar panel installation.
Funny that, I just finished installing my four flexible panels with Eternabond tape only minutes ago! The tape wasn't messy at all and in fact, I was so impressed with how easy it was to fix a four foot crack in a gutter yesterday that I decided to give it a go with the panels today. (Pictures and such to come later. Now I need to do the MPPT controller install because I intend to wire up the six panels in three parallel sets of serial pairs.)

As I mentioned earlier, I don't think it looks as neat and trim as using adhesive under the panels, but it was very easy and it takes care of sealing out any possible air lift (or moisture) all in one step. And yes, I can imagine dirt collecting on the gray edges, much as dirt collects around the various other fixtures sealed with the usual lap sealant. Hopefully the white vinyl/plastic tape won't peel away though. For what it's worth, ivumon mentioned previous success using Eternabond and I found other success stories on the web too.

Think some tips on Eternabond is to put in fridge before use (so gray adhesive is not as oozy and messy).
I didn't have any oozy/messy troubles at all, though I did keep the roll of tape in the shade while working.

If you go with option 2 and use 3M tape, will need to figure out a way on how to remove solar panels in future. If use just on perimeters of panels, then could use an oscillating tool to break adhesive.
Yeah, my intention was to just use it around the perimeter, but I had not decided whether to go all the way around or not. From my earlier testing, I believed I would be able to remove the panels if I wanted. Anyway, moot now as I went with Eternabond tape.
 

israndy

2007 LTV Serenity
Eternabond is designed to NEVER be removed. Even if you remove the backing, the micro sealant will live on your roof. OK if you are planning to re-install, but I have seen pictures of people trying to get it off and it's a b i t c h

I put my panels on four years ago and they started to deteriorate, all this summer when I hosed the RV off I would find plastic shards, flakes, all over and I though it was my clear coat! Eventually discovered that it was my flexible panels from China. I will be needing to replace them during the RVs Lifetime and I am stoked that I put them on with just spray adhesive.

-Randy
 
Eternabond is designed to NEVER be removed. Even if you remove the backing, the micro sealant will live on your roof. OK if you are planning to re-install, but I have seen pictures of people trying to get it off and it's a b i t c h

I put my panels on four years ago and they started to deteriorate, all this summer when I hosed the RV off I would find plastic shards, flakes, all over and I though it was my clear coat! Eventually discovered that it was my flexible panels from China. I will be needing to replace them during the RVs Lifetime and I am stoked that I put them on with just spray adhesive.
Not so terrible to remove:
http://www.eternabond.com/articles.asp?id=165

And the corresponding video:
https://youtu.be/AGiKusd5r8A

Of course, the most likely reason to do a removal would be to replace a damaged panel, and then it should be easy to cut the panel free and it won't be important to remove all the residue.

You should post the source of your flexible panels that started to deteriote, for others to avoid. Also, it should be interesting to see how your spray adhesive held up when you remove the panels.
 
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woundedpig

2018 Unity MB
There is a larger experience with Eternabond in the Class A world and trailers. When you go and read about removal, whether at the company's site or on forums, it is clearly not impossible. It may not be a 5 minute job but it is doable.
It is not quite permanent, in the sense that if a panel failed, you could use a fresh bladed utility knife around the edge of the panel to cut the panel off and re-install a panel over the thin strip of tape remaining with another strip of Eternabond - or you could remove the tape with a heat gun/razor knife. It doesn't seem mandatory to remove all of the adhesive residue. The old adhesive residue remaining could be left and would "melt" into the new tape adhesive. To me, this seems easier than trying to unseat adhesive that is under the panels. Unless you have the worst of luck or "chose poorly," thinking of the old Indiana Jones movie where Indie has to choose the right chalice, you'll only have to remove one panel.

https://www.eternabond.com/articles.asp?id=165

https://www.youtube.com/watch?v=AGiKusd5r8A

Oh, that music......

I'm considering using Eternabond, and also selecting flex solar panels with ETFE film coating and aluminum backing, hoping they'll be more durable. More expensive, yes, but the coating has more durability, texture and friction that the typical PET coating, making them safer to walk on. I could see myself sliding off the roof if the slick flex panels were wet. At the same time, having 5-6 rigid framed panels on a roof the size of the Unity, I could see myself stepping through one of them when tiptoeing around them. I have bad ballet moves.

David
 

israndy

2007 LTV Serenity
You should post the source of your flexible panels that started to deteriote, for others to avoid. Also, it should be interesting to see how your spray adhesive held up when you remove the panels.
It was in the early days of alibaba. Now they have AliExpress. Much nicer, but at the time AliBaba saved me a bunch and let me do business with a group in china without worry that my money would disappear. Although I had to convince BofA that I seriously wanted to send $800 to China, they locked me out of my account for fraud, twice, in one night. No warranty, but I was able to get SunPower cells made to my custom sizes, that was nice, except their durability.

Still think eternabond is a horrible thing to do to your RV unless this is it, like the roof seams are a great use for it. While 3M vhb tape is so strong, but can be rolled away with your thumb or a plastic implement and it's gone.

-Randy
 

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