Attaching PV Panels to Bigfoot Trailer Roof. - Fiberglass RV


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Old 10-29-2017, 12:12 PM   #1
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Red face Attaching PV Panels to Bigfoot Trailer Roof.

I'd almost spring for flexible PV panels in order to not drill into my roof. But assuming I do use some rack system and standard aluminum framed panels, what's the best way to secure the rack? In other words, what size and length screw and waterproof washer and/or sealant? How deep a screw?

Also, what about bringing the wires into the cabin? I was thinking about going down a vent pipe.

Thanks for the help.
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Old 10-29-2017, 02:37 PM   #2
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stress....

drilling holes in the FG is stressful...especially the ROOF ! I don't envy you one bit....

one thing you have to remember when you get into this solar thing is that the system you start with will NOT be the one you end up with....IME you have to sort of "live" with a system for a while and tinker to get your "optimum"...if that makes sense...

I'm betting you will be adding panels in the future....or realize fairly quickly that you have WAY more horsepower up there on the roof than you need (charge controller going on "maintenance" after only an hour or two)...that's money you didn't have to spend...maybe money that would have been better spent on battery capacity....get my drift?

there are some real nice tiltable set-ups that I have seen on this forum...and they are slick...especially if one is going to stay in one place for a week or a month....(not the case with me BTW)

long story short (yeah, right )....My trailer came with 2 six volt batteries....I started to dabble with solar with a 40W deployable stored inside the trailer...realized I need something on the roof....because I did not want to commit to drilling holes in the roof, I got a second 40W and "temporarily" taped it flat on the roof (with little rubber spacers for underside ventilation) and ran the wires down the fridge vent....no holes anywhere...

after a summer of that, I realized that what I could use now to reach my "optimum" was more horsepower on the roof...so the following spring I added a smaller 30W on the roof the same way...

it's been three years...the panels are still up there taped to the roof....in the spring I check the tape, when it gets to look dodgy I'll replace/renew it....yeah, the glue will probably stick to the roof and be messy....but I am not concerned about the look of my roof, nobody can see up there...(to have my "belt&suspenders" on I rigged a couple of "safety straps" as part of the install to guard against the worst case scenario)

I don't think I will ever be drilling holes in the roof....for the panels anyway.

I'm sure you will be hearing about the crowd that used VHB tape...that is another "no holes" solution....have fun
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Old 10-29-2017, 02:46 PM   #3
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Thanks Franswa,

Taping a framed panel is something I never though of. That's a great solution! I can't quite see if you have them totally flat on the roof and have the wires coming out the side of the frame through a hole. I imagine that's what you did.

Are you using the Eternabond tape? This stuff: https://www.amazon.com/gp/product/B0...A1QKBB5ITCQL76

And please tell me, how did you route your wires into the cabin? That's the next little problem.
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Old 10-29-2017, 02:51 PM   #4
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one key to success with using VHB (very high bond) tape is that you clean the surface well and read the directions carefully. Sometimes you do need to apply a special primer onto the surface before you apply the VHB tape. There are different makers and versions of VHB tape around.

You can go to the 3M website and get specific information about which tape works best for fiberglass and what primer if any should be used for the application. This is a very reliable method of installation but it needs to be done just right for the best adhesion possible.

3M does have a youtube page of videos instructions including applying VHB tape but here is the link to their basic website page of instructions regarding using VHB tape. How to Use
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Old 10-29-2017, 02:56 PM   #5
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I don't have much fear about drilling thru my fiberglass trailer. I used 4 screws to hold my PV panel in place, in addition to sealant. Thankfully there are many high quality sealants available today. My favorites include OSI Quad brand that I buy at the local lumber company, pictured below. These last for decades if protected from the sun and probably for 8-10 years in sun. Sometimes I lay a bit of foil over the wet sealant. The foil blocks the sun and adds decades to the sealant's life. Just be careful, this stuff is very sticky and tenacious, meaning its really hard to get off, as opposed to silicone rubber which sometimes seems to peel off by itself. I also used Quad to seal the PV cable entrance. I check that every year or two just to be obsessive.

Most leaks in RV's come where panels join vents, windows, or most often other panels. The flexing of these joints stress sealants and eventually leaks can result. Our fiberglass trailers have few joints and even the fiberglass around vents and windows is continuous making sealing easier. Leaks from tiny holes in fiberglass seldom leak if good sealant is used.

The oft recommended butyl rubber tape used on vents and windows in RV's has a good reputation, but it eventually leaks. I wonder if Quad would remain leak free. Quad is messier to apply, but longer lasting. I suppose windshield repair folks use a variation of Quad.

OTOH Stick-built RV's have a hard time insuring all those moving/flexing/vibrating corner joints stay weather tight, especially when sealant purchasing contracts go to the low bidder.

Click here for a Good article on choosing a sealant.

YMMV, john
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Old 10-29-2017, 04:55 PM   #6
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what model Nic ???

cable routing....mine is a 17CB.....nothing simpler, fridge vent on the roof...down to outside access to fridge....drill a hole in forward bulkhead...now you're in bathroom area outside access...drill another hole forward and you are under the left dinette seat area....where "all the action is" (power center, water heater, yada yada)

and as said before the panels are sitting up on little rubber "feet" at the corners...providing a little cooling (hopefully) and enough space to slip the wires under frames...it's four screws to remove the vent...there's a three way splice (panel, panel, wire to controller) just inside....tape? I used Gorilla tape cause I had it...
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Old 10-29-2017, 05:02 PM   #7
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panels get hot....

yeah, you can't/ aren't supposed to tape framed panels directly unto a surface ...efficiency drops as heat goes up.......that's why I put mine on rubber "feet"/spacers......cooling might not be the greatest but I also live in a pretty cold place compared to a lot of people...so far so good
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Old 10-29-2017, 05:12 PM   #8
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Franswa, Wow, Gorilla tape. Imagine that. That stuff is really great, I can see it working well. I like the safety cable idea, too. I see, the frames have feet / spacers. I missed that.
Thanks, I get your routing idea, too.

John, may I ask you how long your screws are? And did you attempt to hit anything 'solid' under the fiberglass? Is there a layer of plywood up there your screws are catching? I'm just wondering if one has to try to hit a 'stud' or if any area will do. And thanks for the sealant. I'm always glad for leads to the best products.

I'm going to get up on the roof today and see how big the flat spots are where a panel can fit. I need room for a huge skylight I'm planning as well. So while I hesitate to drill a 3/16" hole I'm looking forward to cutting a giant rectangle.

Thanks to all.
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Old 10-29-2017, 06:17 PM   #9
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I used brackets made by Renogy Solar, that are made for attaching solar panels onto fiberglass roofs. I screwed the metal solar frame to the brackets using self taping aluminum screws, and then used VHB 3M tape with the primer bond enhancer to the roof after scuffing up the area where the tape will be in contact with the roof 1st, with a Scotch bright pad.
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Old 10-29-2017, 07:35 PM   #10
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nice set up David.....

the curved roof lends itself well to your choices.....worth putting 200W up there given location etc.....easy to just glue them to the FG....nice rig

as for Nik....still no year, no model, no registry, no pictures....I'm done with this thread
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Old 10-29-2017, 08:59 PM   #11
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Originally Posted by Nik View Post
John, may I ask you how long your screws are? And did you attempt to hit anything 'solid' under the fiberglass? Is there a layer of plywood up there your screws are catching? I'm just wondering if one has to try to hit a 'stud' or if any area will do. And thanks for the sealant. I'm always glad for leads to the best products.
I made some aluminum brackets for my panel. They each have about a 12 square inch foot print on the fiberglass. See Pic attached.

I used vhb tape, sealant around the edges and one screw per corner. The screws penetrate the fiberglass and were well bedded in sealant. I expect they extend about 3/16 inch below the fiberglass into the Scamp's bubblewrap. You cannot feel them from inside. If you are careful with your pilot hole size in the glass you can get a very good bond with your screw.

I even used some eterna bond tape on the leading edge of the air deflector I added later (not pictured). I don't think that stuff ever comes loose.

If the solar panel were steel a magnetic crane could pick up the whole trailer.


Cheers, john
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Old 10-29-2017, 09:09 PM   #12
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Thanks John,

I like the idea of the overbuilt system of screws and tape, actually. Especially tape on the leading edge.
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Old 10-30-2017, 05:56 AM   #13
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This was my solution for adding semi-flexible solar panels to the roof. This was a photo of my trailer beforehand.



This was my trailer roof later the same day.



Four 60W semi-flexible panels were installed. I wired them in two parallel sets of two panels wired in series, so the system voltage to the solar controller will be 36V. I held them down with Eternabond tape around the entire perimeter. I taped cable tie holders down with the tape too. They entered into the trailer via a Go Power Cable Entry Plate supplied by Escape.

This is one of the panels in my garage. I pre-cut all the pieces of tape ahead of time.

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Old 10-30-2017, 06:03 AM   #14
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BTW, my trailer is not near as long and skinny as those photos in the previous post make it seem.

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