Mounting solar panel using AM Solar's rocker feet

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BillTheHiker

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I bought the 100 watt panel kit with self-adhesive rocker feet so I would not need to put screws into the roof. The claim the VHB tape makes a very strong connection.

One concern I have is the painted aluminum roof. AM Solar has a video demonstrating the installation and the narrator states that if the roof is painted aluminum that you better know the paint is very well adhered to the aluminum.

So if anyone has used this installation and put a bunch of miles on it, that would be comforting to know. And which sealant was used.

AM Solar told me that for an aluminum roof use the Sikaflex 221 sealant to cover the feet because it contains an adhesive unlike others such as Dicor.
 
I used a similar mounting method as outlined in "Flexible Solar Panel Installation." I attached my homemade mounts with VHB tape, and then went around the mounts with Sikaflex 221. The Sikaflex protects the VHB tape, and also adds a bit of adhesive to the mount. This method bonded the mount VERY well to the painted aluminum roof, and has remained for over a year now. It shows no signs of coming off - in fact it would be a major task to remove the mounts from the roof, though very possible with a lot of patience.
 
Having worked for 3M for 20+ years and tested a number of their adhesives, I have two comments:
1. The bond is only as good as the strength of what it is attached to. If the roof paint has a solid attachment to the aluminum (it should), then:
2. Preparation is critical. Follow the manufacturers instructions EXACTLY. VHB adhesives do not do well when attached to wax, dirt, road grime, oxidIzed paint, . . .

And obviously, the larger the contact surface the stronger the connection.

As to whether the bond is as strong as screws; I've not seen anyone test to failure, so can't say. A number of installs have used VHB tape with no failures I have seen. MDOT is gluing together a highway bridge across the St. Croix river in Stillwater, MN.

YMMV
 
I posted a reply on VHB awhile back so I will add my knowledge of it again if it helps. Back in the 80's, I worked for a distributor of 3M and they came out with VHB tape. Being in Silicon Valley back then, it did not take long for people to start coming up with ideas of how or where to use it. One of the first things we did to show customers its strength was to attach the 10 mil thick (not double sided foam tape type) double sided "tape" between 2 pieces of 4 inch long aluminum (cleaned and prepped) I-Beam. In less than 10 seconds, no one could pull it apart and you could get a very good hand grip on each I-beam. That piece sat on top of our will-call desk for months and we would challenge anyone to attempt to break the adhesive bond. The most burly guys tried but no one could. Finally, after many, many tries, the aluminum on one of the I-beams broke. I will add that we tried the 5 mil thick and it would not hold long at all. We found that the best use for this new stuff was attaching name or serial number plates to parts or equipment. The only way you could remove one of these was to use a razor blade or a very nasty solvent. Water did not seem to faze it at all.
 
The windows in the tallest building in the world - the Burj Khalifa in Dubai - are all held in place with 3M adhesive similar to VHB. So far as I know, they have not lost any.
 
If I were concerned with attaching the tape to painted aluminum, I would cut some pieces of sheet aluminum, say 6"x6" and tape one to the roof at each point the panel foot was going to go. That way, the panel would be attached to bare aluminum, and the 6"x6" piece of sheet aluminum would have many more square inches of tape holding it to the painted aluminum roof, thus spreading out the forces.
 
Another trick for improving adhesion to paint is to gently scuff up the paint surface with a mild abrasive pad like scotch-brite, to create circular micro-scratches that help with mechanical interlocking of the adhesive to the point. Good adhesion results from both chemical bonding and mechanical interlocking.

I don't doubt that the VHB tape is up to the job - the data sheet for the 4950 VHB tape that AMSolar sells says that its dynamic tensile strength bonded to aluminum is 140 psi (with good surface prep). That's pretty impressive! However, the data sheet also says that painted surfaces (like the acrylic enamel on the FWC roofs) have lower surface energy than aluminum, and can benefit from the use of a primer or adhesion promoter in order to achieve good adhesion. So, when I get around to mounting a solar panel on my roof, I'll probably use 3M Adhesion Promoter 111 before applying the VHB tape.
 
NRVHawk, please look at the AM Solar video on installation. It specifically states to not rough up the surface and also that the smoother the surface the better the adhesion. I don't pretend to understand why. they said to clean it, then apply rubbing alcohol, and then heat the surface a little.
 
I've used VHB tape to hold solar panels on two different rigs...no issues, it works great. I don't think you have anything to worry about if you clean well using rubbing alcohol...
 
BillTheHiker said:
NRVHawk, please look at the AM Solar video on installation. It specifically states to not rough up the surface and also that the smoother the surface the better the adhesion. I don't pretend to understand why. they said to clean it, then apply rubbing alcohol, and then heat the surface a little.
Click to expand...
Noted. Thanks for pointing that out. Interesting, as the 3M technical bulletin on surface prep for VHB tape discusses abrading paint for better adhesion. It does say that VHB 4952 is an exception and does better on a smooth surface, but the tape AM Solar sells is 4950 according to their web page.
 
Finally got this solar project completed. Adhesive mounts seem to be very strong. One thing I do not like is the tilt bars I got from AM solar because they require removal of two bolts that secure the panel to the feet. The aluminum roof has so much flex that it is difficult to get the holes lined up to insert the bolt. And that is using a step ladder which I will not have while camping. I can reach the two near the roof edge with my camper step stool, but will have to improvise a way to reach the bolts that are farthest from the roof edge as those need to be loosened for the panel to tilt. I saw a post sometime back where someone inserted a board on top of the rear tire that slipped under the frame on a Tacoma so that should work.

The only significant use of electricity is my 19 quart Truckfridge and today the solar stayed ahead of it as the voltage rose slightly during good sun hours. I will find out tonight how far down the battery goes and then tomorrow see if it recovers lost amps during the day.
 
Just got back from our SC trip and the VHB tape and Dicor seems to be a great mounting option. Not a sign of it coming lose with is exactly what we all want. I just read the truck camper magazine article on FWC's new red color concept and they are using VHB tape it install the siding.
 
Thanks for the report badtoytrd.Do you have the tilt bars from AM Solar? I bought them but so far find it is much simpler to just stick a one gallon water jug under it.

On Saturday morning the voltage on my battery was 12.78. I parked in the sun and without tilting the solar panel. At 4 pm food in fridge still frozen at 25F and battery up to 13.9 so very pleased.
 
BillTheHiker said:
Thanks for the report badtoytrd.Do you have the tilt bars from AM Solar? I bought them but so far find it is much simpler to just stick a one gallon water jug under it.

On Saturday morning the voltage on my battery was 12.78. I parked in the sun and without tilting the solar panel. At 4 pm food in fridge still frozen at 25F and battery up to 13.9 so very pleased.
Click to expand...
I did not get the tilt bars. Flat I pull in anywhere between 120-150W if my Victron says the batteries need that much. I usually don't need much to "top off".
 
Just finished 3 month cross country trip over 7th miles and no problems with the AM Solar panel. The stick-on feet are very strong.

My only complaint is the Truckfridge 18 liter model has a low voltage cutoff that cuts off at about 12.2 volts, and that is using the lowest of three settings for that feature. I will call them to ask if there is a way to bypass the low cutoff entirely.

Correction: when I get up in the morning and the fridge is not running my multimeter shows 12.2 volts on the battery. But I don't know how long it has been off or at what voltage it cut out. Batteries recover some when at rest, but I doubt it recovers from the 10.2 volts in the specs for low cutoff.

Also, this happens only following a day with little or no battery charging, no driving and so sun.

I do not use anything that uses the battery other than the fridge.
 
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