There are many ways to mount solar panels on the roof of your RV. You can fasten them to the roof with screws, you can glue them, you can use tilt and swivel mounts (which can be especially useful in winter months to position them toward the sun) or you can come up with some kind of custom mount. However you decide to mount your solar panels, MAKE SURE YOU MOUNT THEM SECURELY. When you are traveling at 65-75 MPH down the road, there is a lot of wind pressure on top of your RV. You could not only lose your solar panels if mounted incorrectly, but you could also kill someone if they fly off your roof and slam into the cars traveling behind you (a little dramatic, but possible).
Since I would personally never trust glue to mount my solar panels, I highly suggest that you secure them properly with screws. I have heard stories of people successfully attaching their panels with adhesives such as Liquid Nails and other heavy duty construction epoxies. The advantage of using an adhesive is that you do not have to puncture any holes in your roof that could potentially leak later. If you mount your panels correctly however, you need not worry about leaks anyway. Therefore, for the purposes of this article, I am going to stick to explaining how to secure them with screws.
How you mount and secure your solar panels on your RV roof will partially depend on the type of roof you have. Let’s discuss a couple of the more common types of RV roofs:
Rubber Roofs (roofs with a thin layer of elastic rubber sheeting) almost always have plywood underneath the entire roof. If you are lucky enough to have this type of roof, you can install your solar panels almost anywhere on the roof since you have a solid base to screw the solar panel mounts into. The only thing you really need to be careful of is making sure that you are not trying to screw into the plywood where a seam between two plywood panels exists.
Fiberglass Roofs also usually have a plywood base underneath. The biggest difference here is that you are going to have to drill pilot holes through the fiberglass prior to screwing them down. If you just screw the screws into the fiberglass, you will cause the fiberglass to crack. Once the fiberglass starts cracking, the crack will keep going – much like when you get a crack in your car windshield and it slowly grows as you hit bumps in the road. Be careful when drilling pilot holes. Drilling can cause cracks also; however, if done carefully it is much less likely. Be sure to drill holes that are large enough to accommodate the screws diameter. If you drill a skinny hole and use a fatter screw it will expand the fiberglass and cause it to crack. Make sure not to drill too far into the plywood, otherwise you will have a screw sized hole in the plywood already and the screw will not be fastened properly.
Metal Roofs do not usually have plywood underneath which means that you are going to have to locate the rafters and secure the solar panel mounts to the rafters (support beams) under the roof. It is not recommended that you secure the panels to the thin metal only since it is not thick enough to hold a screw under pressure and will rip out easily. Finding the rafters in your RV can be tricky. Some metal roofs are flexible enough that as you walk on the roof you can feel the location of the rafters under your feet. If not, you are going to have to find another way to locate them. Sometime you can do this by opening a compartment such as a vent, AC panel, or some other access point on the inside of the RV that allows you to locate some rafters and determine how far apart they are on center. From there, you can go to the roof, identify the location of the rafter you found on the inside and measure to find out where the other rafters should be. Be careful and do your homework. Many RVs are built inconsistently and whimsically and the rafters may not be consistently spaced. Talk to your RV dealer if you are having trouble finding the rafters. It is absolutely imperative that you mount the panels to rafters if you do not have a plywood base.
One other challenge with metal roofs and rafters is that they do not allow you to mount the solar panels wherever you want. Therefore you may not be able to mount them in an ideal location on your RV roof. If that is the case, you may want to consider building a custom mount using aluminum angle iron that spans from rafter to rafter. As long as the angle iron is properly secured to the rafters, you can place the panels anywhere along the angle iron.
One last note, make sure that you are using some kind of foot or mounting bracket to mount your solar panels. The solar panels should not be placed directly on the roof. They need some space underneath for heat dissipation. Similarly, you are going to need to get underneath to check the wiring occasionally so you should be able to remove the panels from the mounting brackets if needed.
Time to Mount the Panels:
Once you have determined where you are going to mount your panels so that you are sure they will be sufficiently secure and not obscured (so as to get maximum sunlight), it is time to screw them down. Since you are going to be putting a hole into your RV roof, it is vitally important to make sure the seal around the screw is watertight. I have heard several suggestions on how to accomplish this along with many different product recommendations. My personal favorite is Dicor, which can be found at many RV suppliers. It is made to seal roof penetrations, remains flexible, adheres well to many different materials and is UV resistant. Make sure to use stainless steel screws. Likewise, if you are mounting your panel to metal rafters make sure to use a “tap” to thread the hole for the screw properly first.
On my RV I have a rubber roof with plywood underneath. I attached the feet to the solar panels and placed them on the roof where I wanted them located and used a pencil to mark the location of the screw holes as well as the outline of the foot itself. I removed the panel and placed a nice dab of Dicor where the mark for the screw holes was located. I put the panels back in place which caused the Dicor to squeeze up through the screw hole and used the outline of the feet to make sure the panels were in the exact location that I wanted them. Using #14 x 1 inch stainless steel screws, I screwed the feet down to the roof. The Dicor gets all over the screw (since it is bubbling up through the screw hole) but that is exactly what I wanted. As the screw goes in, the Dicor gets wrapped around the threads and pulls the Dicor into the hole, creating a nice watertight seal. After I had all the screws in place, I also covered the top of each screw with Dicor to create a watertight seal around the entire screw. Voila, my panels were mounted and secure!