Mounting Solar Panel questions

Finally The camper is wired, the batteries are installed, charge controller is all set; so it is time to mount the solar panels.

I am mounting two 100W Renogy panels, spaced 1" above the roof, with 2" x 3" x 2"wide 'L' brackets, 4 per panel.
The panels fit across the roof and the roof frame is 1" aluminum square tubing, going front to back.

My questions are:

1- Will four #10 sheet metal screws plus 3M 5200 adhesive be enough to hold a panel to the roof? My roof is corrugated aluminum, so I only have ~1.25" wide flat spot for adhesive. I could easily add a second fastener on the 3" leg, but anything more and I will have to go to a different mounting solution.

2- Is it advisable to slightly tilt the panels to the front? If so, how much? I have read claims that tilting slightly helps rain clean the panels. It also insures that air flow doesn't get under the panel to lift it while driving. Panels are to be rigidly mounted, not adjustable.

Thanks for your help. -- Spiff

How thick is the aluminum?

Aluminum is a bit soft to rely on purely a threaded fastened without a backing plate.

The 3M 5200 is pretty incredible stuff, but it takes forever to dry, especially in a non humid environment. the fast cure versio is still slow, and i believe it loses some of the properties of the regular cure version.

I would add some tilt as it is better to not have puddling on the panel. Hard to really say what wind forces will be doing on any specific vehicle at speed. Air might be actually forcing down on the panel rather than trying to rip it off. I think you'd have to mount a gopro up there and tape a bunch of streamers up there and takeit up to highway speeds to determine that.

I'd use as much surface area as possible and as many large diameter Stainless steel fasteners as possible, and make sure the aluminum itself is well adhered to the substrate too.

Make sure to rough up the aluminum where the 3m 5200 goes and wipe with Denatured/ isopropyl alcohol or a solvent to ensure maximum mechanical tooth. Might want to paint the 5200 with something as well to help protect it from UV damage. I know is is somewhat resistant to it, but it will eventually crack. It was designed for through hull fittings on boat. not exactly a High UV light environment.

I'd use a bolt.
Bob

spaceman, when you say corrugated aluminum I am assuming a rv. that aluminum is not strong enough to mount anything to. you have to at least find the stringers(roof rafters) 2x2 wood on most rv's. mount though those at the very least. highdesertranger

I used sheet metal screws to secure my solar panel, but that was into steel and I used 24 of them. I would not do it with aluminum as it won't hold the screws very well. Can you post pictures of the brackets and explain where the 1" aluminum tubing is? At minimum I'd want to use bolts to attach the bracket with some beefy fender washers or a piece of steel under the roof. Use nylon lock nuts.

As for the adhesive, it can only be as strong as what you are attaching it to. In this case, you'd be gluing it to the paint on top of the aluminum. Personally, I'd rather just use good bolts with some weaker silicone glue to keep it from wiggling around. That way I could remove it later on if I need to.

My vehicle and all mounting hardware is aluminum other than the bolts which are grade 8 but only 1/4 bolts with large fender washers on either side. Anyway, I didn't use any tilt, just didn't make sense for what I was doing, it would have been a fine ideal and helped with some rain pooling however, I'm thankful I didn't. Those solar panels seriously heat up my roof, managed to get up there today and fit one inch of insulation under them, never could have done that if I didn't mount them flat.

My entire point to this is I used rivets and think it was the best choice. Keep in mind however, rivets are good for shear not pull. Anything else would have rattled itself free long ago, I'm sure of it.

Good luck to you!

Thanks guys for your expertise. Sorry it took so long to get back; friend needing help took priority.

Panels should get mounted today, I'll post pictures when done. Sounds like bolting through is the safest route. Now I just have to figure out how to make the nuts and fender washers look nice inside. Pulling the ceiling down would be a major task I don't want to do right now. Panels will have a 2° tilt (front down).

Highdesertranger - the camper is a '77 FWC Grandby with an aluminum frame. Roof frame is 1" square thin wall Al tubing, front to back, with cross supports welded front, middle and back. 30 mil corrugated Al skin, screwed to frame, with 1/4" plywood ceiling inside, stapled to frame (installed by previous owner, still in good shape).

Sternwake - love to do an experiment with camera and streamers, but that will have to wait for another time; too much to do. 5200 will be used to adhere the combiner box onto the roof, so I have it and will have to use it (good for ~24 hours after puncturing seal). It will be sandwiched and never see the light of day. Self leveling caulk around edges and over fasteners (again, have it, might as well use it, won't be any good next time I need it).

Thanks again. Update when finished. -- Spiff

3m 5200 can be kept usable for weeks after puncturing seal, if you keep it in the fridge, in a Zip lock baggie with air purged.

2 x 100 watt solar panels installed, wired, and delivering amps

Picture 1: Panels are tilted 3° to front of camper, mostly for rain runoff; wired in parallel in a combiner box on roof, spliced to AWG 4 welding wire. Four 'L' brackets mount each panel to roof, with six grade 5 bolts through frame holding the panels on (plus 5200). Combiner box is 3/4 inch standard plastic (not sure what kind) outdoor rated junction box used to bring power into a house. It has a 3/4" ID x 1" long extension in the bottom that goes through the roof, protecting the wire through to the interior. Combiner box is attached with 5200 only. The putty that is used to seal lines coming into a house was used to seal the panel wire side of the junction box.

Picture 2: Looking at the right front floor of camper. Battery box is an air tight Sterilite gasket box with a 2" breather to outside in the lower right. AWG 4 welding wire comes down from the roof, through a 60 amp ANL fuse, to a Morningstar TS-45 charge controller. From the TS-45, through another 60 amp fuse to the positive terminal of the battery. Negative side of batteries runs through a 500 Ω shunt. The shunt is connected to a Trimetric 2030 (upper right, out of picture).

The system is charging, although I do not yet know how well. Overcast skies have conspired to limit output. I had a plug in charger on the batteries overnight, with box open and vent caps off, and I was surprised the next morning by the slight sulfer smell in the closed up camper. FLA batteries definitely need to be vented outside!

Thanks to all who gave their expertise on mounting the panels. Those suckers aren't coming off without taking the roof with them

-- Spiff

Nice! I like the junction box on the roof. Do you have anything holding the battery box in place? Those things move easier than you think and can do some damage when they pick up speed.

Reducto said:

Nice! I like the junction box on the roof. Do you have anything holding the battery box in place? Those things move easier than you think and can do some damage when they pick up speed.

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Yes, the battery box will fit inside its own compartment (~6" high walls on the left and back sides) allowing the box to (hopefully) remain air and liquid tight. Haven't decided what to use to keep the batteries in place in the box; they can move about an inch total in both directions.

-- Spiff

Reducto said:

Nice! I like the junction box on the roof. Do you have anything holding the battery box in place? Those things move easier than you think and can do some damage when they pick up speed.

Click to expand...

Not to mention leaking acid all over you and your van in a roll over accident. I like to build a 2x4 frame and then fasten the batteries to the floor with the OEM style battery hold downs. This holds them in place very nicely and is a big improvement in safety.