Solar Panels on a Fiberglass Roof


At the Rubber Tramp Rendezvous in Quartzsite, Arizona we installed a solar panel on the high-top van above. Installing one on a fiberglass roof creates new problems so let’s take a look at how we did it.

The first thing we did was install the solar controller inside the van. Using a square we marked where the controller would go, drilled holes in all four corners, then used a jigsaw to cut out the hole.



We need two sets of red and black wires, one long enough to reach the solar panel (these need to be UV resistant), the other long enough to reach the battery. We stripped the end of the wires and connected them to the controller. This Go-Power controller was very well marked, so knowing how to connect it was very easy.



Make sure you put the wires through the hole before you connect them! Then push the controller into place in the hole and use screws to hold it in place. One set of wires goes to the solar panel and the second set goes from the controller to the battery bank. First we run the wires to the battery and strip the wires and crimp on ring ends and then connect them to the battery.



Next you run the wires from the controller, through a hole on the roof and up to the solar panel on the roof. The first picture below shows the wire going through the roof and in the second we see the crimped wires ready to be hooked up to the junction box on the bottom of the panel. The junction box of this panel had no markings, so we used a volt meter to find the positive screw that had power to it, and the negative screw to ground to. There was only one combination that gave us the 17 volts we needed, so we used those screws.



Normally, with the junction box wired you are ready to screw the panel down to the roof. But with a fiberglass roof it isn’t that simple. We were concerned that the wind could rip the screws right out of the fiberglass, so we wanted to reinforce the roof so the screws went into something more than a thin layer of fiberglass. We decided to take off the fancy roof-liner this conversion van came with and use six inch square pieces of plywood underneath the roof. We used screws long enough to go through the roof and into the plywood without going through the plywood. The headliner is held in place with screws, so it is just a matter of finding all the screws and removing them. Pay careful attention to how you take the head-liner down, so you can put it back up the same way.

We wanted to take full advantage of having the headliner off, so we added a layer of Reflectix to the roof. Reflectix does a great job of keeping summer heat out and holding winter warmth in, so the van should be more comfortable year-round. In the pictures below you see the head-liner installed, removed, and the Reflectix laying on the head-liner ready to be re-installed.





We ran into another problem with this solar panel. Because it had an unusually thick junction box, the feet we had bought weren’t tall enough. I looked around my supplies, and found feet from another project and we combined them to get the necessary height. You use feet to mount the solar panel because panels work best when they are cool. The feet lift the panel off the roof so air can circulate under it, keeping it cooler. You can see the feet in the pictures below.




With the feet installed and the junction box wired, we are ready to turn the panel over and screw it into the roof. In the picture below you can see us do that. Working with a solar panel up on the roof of a van is awkward—more hands make the job easier.


Before we screw the feet into the roof, we want to add caulking to the bottom of the feet and the hole in the roof the wire is going through to make it waterproof. We used the Dicor brand caulk because of its outstanding reputation in the RV community. After we screw the feet into the roof, we covered the screws with caulk and put a bead of caulk around the feet.



To screw the feet through the fiberglass roof and into the plywood, I went inside and laid on my back on the bed with my feet up against the roof. I put the plywood under my shoes and pressed up hard with my legs while they screwed down into the plywood. It worked well, and we were able to get a good bite into the plywood. With it screwed in tight to the roof, there was no way the solar panel could ever come off. After that we put the headliner back up and the job was done. The meter on the controller showed we were putting in a full charge!

A word about tools. The only power tools we needed were a cordless drill and a jig saw. Everything else you should have on hand: screwdrivers, wrenches, pliers and stripper/crimper. I do quite a few projects so I have accumulated many assorted odds-and-ends from them. I keep a box of old wires and connectors, and a coffee can full of nuts, bolts and screws.