Panel mounting question

I have a question about mounting solar panels on the roof of my fifth wheel. I would like to install two 60 cell panels in the location indicated on the attached drawing. My concern is both panels will span an area where the roof slop changes. Which will cause the front of the panels to be raised higher then the center. Both panels will be 3" above roof at the front the go down to 1 7/8" for the front panel and 1" for the rear panel. My concern is will the wind at freeway speeds create enough force or lift to cause any damage? Hopefully I am over thinking thing and this is something that is done all the time. Also the mounts will be 4" long so I will 8 sq. in. of area for each mount. I will use Dicor Lap Sealant under and over each mount. What is the recommended screw size and number for each mount? Thank you for your help.
Mike
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Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    I don't have anything specific for your installation other than some general suggestions.

    Do you have an installation manual for your panels. Here is one from Solar World on where the mounts should be and how much force they should withstand...

    www.solar-electric.com/lib/wind-sun/sunmodule-xl-install-guide.pdf

    The design wind force loading runs from 30 psf to 64 to 113 psf for the above panel depending on mounting.

    Your panels are around 17.875 sq foot. A 64 psf rating would be a total load of:

    17.875 sf * 64 psf = 1,144 lbs total force

    So, looking a nominal wind loading for the panels, the mounting (roof/angles/mounts) should withstand >> 1,000 lbs of total force per panel.

    I would be more worried about the roof structure/panel mounts than the panels themselves... Assuming panels are rigidly mounted, no twisting/bending/etc, the glass should be fine. These are about the same thickness as single weight window glass (tempered glass). As long as the mounts/frame are stiff (no flexing), the panels should be OK.

    I doubt you would get 500 lbs of lift on the leading edge of the panels at normal highway speed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mikes240zMikes240z Registered Users Posts: 12
    Thank Bill. I did look at the installation instructions for the panels I'm considering and I agree with you that the weak point is the mechanical connection to the roof. I was hoping that someone could give me some guidance on what to use to attach the mounts to the roof.
    Mike
  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Mike,

    If you put below into Google:

    site:forum.Solar-Electric.com rv roof reinforced

    Or click this link:

    https://www.google.com/search?q=site%3Aforum.Solar-Electric.com+rv+roof+reenforce&ie=utf-8&oe=utf-8#q=site:forum.Solar-Electric.com+rv+roof+reinforced&spell=1

    You will find a few threads on people talking about RV roofs and reinforcement.

    Many RVs are structural lumber construction--Accessing the roof structure from underneath/above and adding plywood/reinforcement at the anchor points should be possible.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mikes240zMikes240z Registered Users Posts: 12
    Thanks again. I will look at google. Also I'll call the fifth wheel manufacture to see what the roof deck is made of.
    Mike
  • Mikes240zMikes240z Registered Users Posts: 12
    I called the manufacture today and found out the roof has 3/8" plywood with 1 1/2" truss every 16". They said there is a truss both sides of the vent so I can just measure 16" from the screws on the vent to find the next truss. So if I move the back 6" I should be able screw into the truss for the front mounts.
    Mike
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