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Old 11-15-2014, 06:47 AM   #1
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Solar panel mounting options, onto smooth fiberglass roof.

My 1st Solar install continues, now to the mounting of the panels, I got a pile of these aluminum brackets for $20.00 but I am concerned if I have enough service area of 2x3 to get a good bond to the roof? This is on a Winnebago 38J 2005 Fiberglass roof / smooth.
Each panel is 43 lbs. 68 x 37" I will be using 6 brackets per panel. I dont plan on tilting the panels.....
One of the panels will have to be mounted high enough to clear a roof vent.
1st Bonding options? 3m VHB tape or 3m 5200 fast cure?
2nd If screws are needed then what type of screw? just Stainless wood screw? of some type of screw that will expand on the back side of the fiberglass?
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Old 11-15-2014, 09:01 AM   #2
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It looks like you have a lot of contact area with the roof with those brackets. The adhesives should work well. I use stainless sheet metal screws. Plastic expansion anchors as used in dry wall work well. There is just a thin ply of luan. The anchor allows the screw to grip in the foam.

2003 Winnebago Adventurer 38G F53/ V10 605 watts of Solar
1999 Winnebago Brave 35C F53V10 Handicap Equipped
1999 Jeep Cherokee, 1991 Jeep Wrangler Renegade and 2018 Chevrolet Equinox Diesel
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Old 11-15-2014, 02:43 PM   #3
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Our son installed our six panels (235 W) with lag screws into roof. Our previous rig was in a wreck in Mexico a year ago that totaled both pickup and 34' 5th wheel. I checked the panel mountain in the wrecking yard at Acatzingo de Hidalgo (between Vera Cruz and Puebla) and there was no evidence of damage. The solar and glass mat battery system was working perfectly.

However, adhesive seems to work well for almost everyone
Reed and Elaine
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Old 11-16-2014, 07:32 AM   #4
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I used 1/8th inch "Molly" bolts and a lot of Dicor self leveling sealant. The Molly bolts bend and catch the underside of the luan. I ended up drilling 54 holes in my roof, 2 years ago (3 per foot, 6 feet, = 18 screws per panel times 3 panels). No leaks yet. A lot screwing because you have screw each one twice, once to bend the bracket, and then again to mount it.

My combiner box is held on only with dicor. I temporarily taped my cables to the roof and used dicor to "glue" them to the roof between panels and combiner box. Once the dicor set, I removed the tape.

I made similar "L" brackets. In half of them I drilled a hole (on the vertical). The other half, I made slot. There were bolted together in the middle as a "Z", centered in the slot. I mounted them to the panels on the ground using only 1 - 1/4-20 bolt each. The feet already had 3- 1/8th inch holes drilled in them, once on the roof, in position, The feet were adjusted to fit the contour of the roof and then leaned forward. Then marked and drilled the holes for the molly bolts.

Tip: If you decide to drill in your roof, wrap your drill bit with tape, or slip rubber tubing on it, except for the tip end 1/2" or so, to make a stop, so you don't drill too deep.

My panels have been road tested for over 20,000 miles and 80 mph on a few occasions and they are still there. I did slightly angle them to the front to allow the air pass over the top and not under while in motion.

I would think twice about mounting it high enough to clear the roof vent. One or 2 inches is all you need.
06 Hurricane 34FT WH W20 Chassis 8.1L 132K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, WG T4 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee
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Old 11-16-2014, 07:48 AM   #5
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Dicor is such a great product that I was not concerned about drilling holes to put in screws/anchors for mounting my panels. After each hole, I filled the hole with Dicor, then squirted a spot about the size of a silver dollar (remember those?) around each hole. Then, after installation, on top of each screw head, a "Susan B. Anthony dollar-sized squirt." If you complete the install in indirect sunshine or within about 15 minutes, the two patches of Dicor (one under the bracket and one on top of the bracket) will adhere to one another and make a great seal.

I tend to be risk averse ... maybe even too concerned about such things: The image of a panel or six (are your panels going to be bolted to one another?) coming loose and flying off the roof of the MH was too much for me to trust to just double-sided tape (though I hear the new tapes are REALLY good). I also recall a story (maybe it was on iRV2?) a couple years back of a panel that came loose and flew off the back of the MH, but the wires did not let go. The result was a lot of holes in the roof, rear cap, and side of the MH as the panel banged it's way in the breeze down the highway. Nobody injured, but a lot of damage nonetheless.

Better safe than sorry, I always say.

In any event, it's a great project. Have fun with it!

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Ken, Deb, & Gadget (WIT Club, FMCA, SKP, and grateful volunteers with Habitat for Humanity and SOWERs), traveling in a well-behaved 2005 Winnebago Vectra 40FD w/1100w solar, some gee-golly-whizbang, and a TRAILERED 2015 Cherokee TrailHawk toad.
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Old 11-16-2014, 09:52 AM   #6
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A big thank you to every one that has taken the time to post. Now if I can just catch a warm day.....it may break 50 degrees in week or so.
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Old 11-17-2014, 05:44 AM   #7
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I just used VHB 4950 tape on 1x1.5" feet, and was very impressed with the holding power only a few hours after installation. You are supposed to wait 72 hours before testing, but I couldn't resist. I have a pebble grain roof, not smooth, so even though they passed my test, I did use one screw for insurance. Since you have a smooth roof, the VHB will hold em down for sure. I asked about failures on another forum, and no one had seen one first hand. Many people had success stories. One person had a second hand account of one failure from a big solar RV installer and reseller, who said he thought it was end-user error.

OTOH, will your 2x3 feet sit flat on the roof? If the roof is curved enough that they don't quite sit flat, you might need a thicker tape. Bottom line, in your shoes, I would use the tape and relax.
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Old 12-03-2014, 06:06 PM   #8
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I used VHB from 3m to attach my solar panels to my Winnebago's fiberglass roof.My equipment came from BHA Solar. The tilt brackets are machined aluminum angles 24" long. I put VHB on the entire 24" bottom mounting rails for each of 4 panels. There is plenty of hold. I covered each mount at the roof with 4" Eterna Bond tape and sealed around each install with Dicor self leveling sealant to protect from UV deterioration. I check on the roof monthly at least and have seen no signs of mounting failure to date

Sent from my iPad using iRV2 - RV Forum Allen Flanagan
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Old 01-24-2015, 04:45 PM   #9
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Starter hole, Dicor puddle, place the panel, stainless screw, more Dicor on top. That's how mine are attached.
Vince and Susan
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Old 01-30-2015, 05:34 PM   #10
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Just getting ready to install 3 panels on a brand new fiberglass roof of my FR Legacy. Read allllll these posts, but still nervous to NOT use any screws at all. Just had too many adhesive failures on various things over the years. Think I will use at least one screw per foot just to save on sleeping pills.
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Old 02-06-2015, 01:26 PM   #11
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I installed a 30 watt panel to a smooth fiberglass roof using 3M VHB™, aluminum angle, Rivnuts®, stainless steel screws and LocTite®

My thinking was that the bonding surface area of each bracket was far greater than that of the circumference of a stainless steel screw into fiberglass/wood.

2 years later, looks and feels as solid as the day it was installed. I realize that this is coming from the manufacturer, but it seems far more secure than screws:


Just my two cents
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Old 02-06-2015, 03:17 PM   #12
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3M VHB 4 years and two tv's later, never an issue.
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Old 02-06-2015, 03:19 PM   #13
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Old 05-31-2015, 08:34 PM   #14
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One thing that makes me nervous about just gluing is that any upward pressure could cause a separation of the fiberglass roof from the wood underneath as they are both very thin. I'm going to lag mine down.

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panel, roof, solar

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