How To Install Solar Panels on a Fiberglass Roof

The best way to install solar panels on a van is to bolt rigid panels to roof racks. For those of us with high-top fiberglass roofs, this unfortunately isn’t an option. Roof racks tall enough to go over our extra tall roof are nearly impossible to find, and incredibly expensive when you do find or fabricate them. Fiberglass alone isn’t strong enough for bolting panels directly to the roof, and the complex curves that these roofs often have further complicate matters. One of the biggest trade-offs for having the extra headroom is losing the ability to easily mount rigid panels to your roof.

Fortunately, flexible panels are rather good these days. They’re still more expensive, and likely won’t last as long as rigid panels. You also won’t be able to remove them easily once installed. But they work and work well. Here’s how I installed a pair of Renogy 175-watt solar panels on the roof of our van.

Measure Twice

As with anything, make sure the panels you want will actually fit on your roof. Fortunately, this is pretty easy. Just measure the dimensions of your roof, and compare them to the dimensions of the panels, which are easy to find before you buy them. I had to do this a few times because the 200-watt panels I originally wanted sold out before I got them, and I had to figure out a different way to install the differently sized 175-watt panels I could get when we had to panic finish the build after the fire. Fortunately, the two panels side-by-side were the exact same width as our roof, so we lucked out there. We even have space to add a third panel later, should we need more solar charging capability in the future.

Ventilation

Solar panels can generate a great deal of heat as they convert the sun’s rays into electricity. That heat has to go somewhere, or else hot panels won’t be able to work as well as they should. This is why it’s not a good idea to mount panels directly to the roof of your van. The roof already gets hot in the sun, and the panels will only add to that, giving you inefficient charging.

The solution is to provide some ventilation underneath the panels so the heat can get carried off into the air. There are many different ways to do this. Will Prowse, whose website and book on mobile solar systems I highly recommend, suggests putting wood dowels between the panel and the roof to create an air gap. RV with Tito uses the grommets along the edge of the panels to bolt them to the roof with a sheet of corrugated plastic between them. Panel manufacturers say to never use these grommets in a mobile installation, but this method has worked well for him. My Renogy 175-watt panels don’t have these grommets, and I still didn’t feel right about using them if they did. So I mashed a bunch of internet advice together, then installed them my own way.

Installation

I decided to use the same corrugated plastic idea as Tito. I cut it to fit each solar panel, then used a liberal amount of silicone to glue the plastic to the back of the panels. I made sure the corrugation went side-to-side across the van, not front-to-back. Why will become clear later.

Then we test fit the panels on top of the van to make sure they fit and to confirm their final resting place. With both of us on ladders on either side of the van, I applied a liberal amount of silicone to the roof of the van while Trisha held the panel up with a snow brush. (Hey, it’s what we had, and it worked!) Then she lowered the panel back into my reach, and I pressed it firmly down against the roof. Lather, rinse, and repeat for the other side.

I’m not one to trust a single method of adhesion, though. I had part of a roll of Eternabond leftover from the solar install on my previous van. I hadn’t learned about heat considerations at that point, so I taped the solar panel straight to the roof along all four edges. I had enough left to cover the leading and trailing edges of the panels on this van, plus a few small strips along the edges for good measure. I left the sides mostly exposed for airflow, which is why I made the corrugation run side-to-side. If it was front-to-back, it would’ve been completely covered by the Eternabond.

Either of these methods alone is probably enough to hold the panels to the roof of the van. Both of them together are even better. At the time I’m writing this I’ve covered more than 2,000 miles since installing the panels, and have had absolutely no problems whatsoever.

The only other consideration was how to run the wiring to my Renogy DCC-50S charger. I used a BougeRV roof gland to bring the wires inside without letting the weather in, too. This was the only part of the solar installation that required any drilling because the wires have to get inside somehow. The holes are safely contained inside the weatherproof chamber inside the gland. Then I simply cut the wires to size, connected them to the charger, and boom, free electricity. According to the Renogy DC Home app, I’ve generated more than 25 kilowatts of power during the month and a half or so since installing them. On a clear day with no trees blocking the sun, I can top off my house batteries so much that the charger sends some power back to top off the starter battery, just to use some of its excess energy.

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