Originally Posted by Doktari
Hi. I love aluminum. Got any extra. I’ll be over in 5 minutes lol. You will get a different opinion from just about everyone lol? Personally I would use larger than 1/4” SS (stainless steel) bolts to the roof. I’ve been told several times not to overtighten SS as it can twist right off. So biggerbolts makes sense to me. It depends how many there are. Fewer but bigger bolts is less drilling and sealing.
It’s a consideration to have air flow under the panels as the output voltage drops as they get hotter. So I put my panels up on the expedition rack on my van. But now they occupy half my expedition rack and can get caught on branches, etc.
We use ordinary stainless bolts for mounting the panels to aluminum or galvalume unistrut but I’m not sure what grade of stainless they are. Perhaps someone more knowledgeable about metallurgy can answer that.
Stainless can be brittle and break under heavy load. Use a grade "8" bolt. 1/4" x 20, grade "8' has a clamp load of over 3k lbs and 5500lbs of shear strength. I doubt you'll ever see loads on the panels near those numbers. I'm using a rivnut/threaded insert in the roof into the center of a rib. Sikiflex on the threads will seal them.
One problem with bolting the frame together is bolt head or nut causes clearance issues with the panel sitting correctly in the channel. A couple of thin head rivets in each corner should work, ultimately you would want to weld those corners for strength.