FWC Project M Solar Roof Install Advice

[thesuzukimethod]

Our project M is wired for solar and I added some BlueSea breakers to go along with battery/inverter and 10A solar controller (i.e. everything is wired up, tested, working, etc with the 100W panel on the roof using the SAE port). But for reasons of indecision and lack of time, I've held off installing the panel on the roof of our Project M.

Based on advice/input from 'the internet', I had settled on using VHB tape to adhere two 28" 90 deg. angle brackets flush to the roof, and then eternabond over the elbows to make sure to hold it down, with the option to add a few bolts and sealant on the corners as a just in case (but my hope was to avoid roof penetrations for warranty reasons). The 100W panel attaches to another pair of 28" angles - technically a flip up kit, but I'll likely keep them flush 99% of the time, and also gives a more convnenient way to take the panel on/off if we're not using it during offseason, etc.).

My primary question is how to prep the aluminum roof for the VHB. When i was testing out the solar panel, the sharp edge of a bracket scraped a bit of the white off the aluminum, and I had visions of the VHB tape removing a perfect rectangle of white material that was previously bonded to the aluminum roof. Should I sand down this white to the aluminum where the VHB tape will go? Just rough it up a bit to make sure the tape also hits metal? The VHB is 1" wide, and covers most of the surface area of the 28" rails, and the 4" eternabond strips will overlap off the 1" rail for more protection. This should make this a moot point, but I'd rather over-engineer.

My secondary question is if I should just bite the bolt(ullet) also put a few bolts in the 2 front corners from the start (i.e. the side that will bear wind loads/uplift while driving) from the get-go (see above about over-engineering). The panel is 20" by 48" and would be oriented with the short edge facing forward.

There are lots of successful reports of VHB tape plus eternabond holding solar panels on RVs for years w/o incidenct, but they sand down the gel/coat roof a bit, and they dealing with thicker roof material.

TLR - Any insight on surface prep? last minute advice re: bolts or just VHB/e-bond?

 

[thesuzukimethod]

fyi i got antsy and went with the aggregate advice. clean with alcohol, sand lightly, clean with alcohol again, and installed when it was 105 F out so the bond would happen faster (that last part was not by choice, but the 5952 tech docs said you can even heat to 150 F to enhance speed of bonding.

I will still add eternabond overlap and/or dicor self leveling, plus I decided i would likely put a few bolts through the roof (down the line but before any highway speeds travel) just to lock it down.

 

[97heavyweight]

With the ability for wind to get under the panels I would definitely add some bolts. Does the M campers not come with roof rails? That is how I installed my solar panels on my build (not an M Camper, but homemade). I have also had great luck with Sikaflex 221. Both of my fans are installed with only Sikaflex. They've been rock solid for a year, but they also don't have the ability to allow wind under them that could provide lift.

 

[clydeps]

0. Avoid drilling holes in your roof or walls if at all possible. Every hole is a potential leak, and every through-hole metal fastener is a thermal bridge.

1. Sikaflex 252 used with Sika primer will hold anything onto a roof with just a modest surface area. It's essentially impossible to remove other than by cutting with a wire. This is also strong enough to mount on vertical surfaces for shovel and recovery track brackets etc.

2. Consider using lightweight semi-flexible solar panels. These have no aluminium frame and are a fraction of the weight of glass panels with frames, which helps keep the centre of gravity low.

To mount these panels I bonded (Sikaflex with primer) 50mm square aluminium plates at each panel corner with a countersunk screw sticking up throught the plate to go through the hole at each corner of the panel. One nut with Loctite keeps the screw in place, another nut and lock washer secures the panel.

Some acrylic twinwall sheets under the panels space them off the roof and provide airflow for cooling. I used a couple of lines of Sikaflex (without primer) on the acrylic sheets to secure to the roof and the panels - this is removable if necessary but stops the panels flapping in the slipstream. Protect the front end of the panel with an aluminium angle or channel.