Q about installing solar panels on a fibreglass top

[Gest]

I'm trying to understand what issues are involved in the mechanical installation of solar panels on a van with a fiberglass top. I am a complete noob.  Do I just drill directly into the top when installing? Any special advice or things to watch out for like bolstering, etc.  I'm thinking I need to do that but I am sure the best way of doing it have been figured out, and once a hole is put in, it's in so that's why I am asking before the holes go in. Thanks.

 

[jonsun]

You can use an expanding grommet or just UV resistant glue, or both. I seen some mention 3M VHB tape. But I dont know about tape, I order that stuff from ebay and it was total garbage. Maybe it was fake IDK.

https://www.amazon.com/3M-Hybrid-Adhesive-Sealant-Multiple/dp/B00VFIQNUC

 

[mudbunny]

I used some pvc blocks glued to the roof with 3m 5200. Then screwed the panel brackets to them. Fiberglass was less than 1/4" thick so not much for screw threads to bite into and more chances for leaks. I heard a lot of good about VHB tape but the blocks were a bigger surface area sticking to the roof.

 

[John61CT]

Personally I'd want a mount that allowed easy future removal.

Rivet nuts (rivnuts) work if you have the thickness, can even put in a backing washer or a bit of thin plate.

Or 3M gel style epoxy with a low cure temp with threaded studs?

 

[SternWake]

Punching a wood or sheet metal screw into predrilled fiberglass and getting good hold requires some skills and poor results require a larger screw, perhaps some more resin too to address the ripped fibers.

However, One can drill and Tap fiberglass for machine threads.

It can hold very well if done right, but the trick of course is doing it right, and haveing at least 1/4 inch thickeness. Obviously my 3rd brake light does not require much inthe way of pull strength But drilling and tapping is just much more desirable than drilling then cutting threads with a sheet metal or wood screw.



Here is how my (750$) 130 watt panel was mounted in 2007

I sanded through gel coat, applied plywood 'feet' to fiberglass with polyester laminating resin thickened with cab o sil. When dry i laminated the feet with fiberglass up the sides of the plywood.

If one uses VHB tape, Use a good amount on aluminum L brackets. Remember surface prep is everything and the VHB is bonding to the paint or gel coat, whose bond strength to fiberglass below might not be so impressive so more surface area is wise to spread the load

 

[blars]

VHB tape requires warm temperatures and pressure to install, and does not reach full strength for a day or two.

 

[jonsun]

expanding grommets will also seal the hole without worrying about any of that

 

[Spaceman Spiff]

The problem with adhesives is that surface prep and curing temperature/humidity is critical.  One can't take any shortcuts.

When mounting my solar panels to thin aluminum I sandwiched the roof between the panel brackets (I made my own with a large footprint) and a wood block on the inside.  You can get nice 1" thick wood plaques in the hobby section of most big box stores with nice routed edges in square, rectangle, round, or oval if it will be seen on the inside and you care.  Gives wood screws something to bite into and spreads the load over more surface area.

I wouldn't trust machine screws into fiberglass as it has a low pull out strength and I would not trust any machine screw with less than three threads engaged.

 -- Spiff

 

[SternWake]

I think the video I linked shows fiberglass when tapped for machine threads has a good pull strength.

I've done some tests of my own and found the strength surprising, as long as the force is straight. A long screw could be leveraged sideways break the fiberglass and then tore out.

But I would not choose this method for solar panels.

My roof in the area where my panel resides has about 5/32" fiberglass then 1/4 inch foam then 5/32 more fiberglass. Some areads have some OSB runners that take a screw nicely, but not necessarily where required for mounting panels.

 

[John61CT]

You'd be amazed at the pull-out and shear strength test results using rivnuts, even in fiberglass and plywood.

Adding correctly sized washer or two, or a bit of thin aluminum plate allows for even heavily loaded ladder racks, more than strong enough for solar panels.