Rail expansion

FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
A thought just struck me. Do installations take into account expansion of the rails? A 24 foot aluminum rail will expand about four tenths inch from winter to summer here in Maine. That's a lot of movement on the feet, & the bolts, especially if you don't have flashing. Even with flashing, should this be taken into account? I was planning on having a solid 44 foot rail, (two 22' bolted together), but now I'm thinking at least one expansion joint, but maybe two? No panels shall span a joint. Here's a sketch. The top one is 22 foot rails, the bottom one is 11 foot rails. Red blocks are expansion joints, free to move. I will make an inner slide & secure it to one leg, let it slide in the other. I'd leave enough slack in the wires. Any thoughts?


  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: Rail expansion

    I don't think it will be a problem. Plus, everything else is expanding/contracting also.
  • mr.radonmr.radon Solar Expert Posts: 158 ✭✭✭✭✭
    Re: Rail expansion

    I know for a fact that Unirac's Solarmount limits the length of a rail without an expansion joint. Check out their website and design guides they have on line. I know when I spec'd out a system for my office I ran into this. it could be as simple as breaking the run.

    PS - just checked, Unirac has the following quote: "Thermal breaks are required every 36 feet"
    "Notes on Thermal Expansion:
    SOLARMOUNT-I is designed to minimize the effects of thermal expansion by allowing the beams to expand and contract independently between connections
    and attachments. To minimize the effect of thermal expansion, restrict continuous beam lengths to 36 feet or three standard beam lengths."
  • dreesdrees Solar Expert Posts: 482 ✭✭✭
    Re: Rail expansion

    I know that the ProSolar rail splices are designed to allow for expansion/contraction.

    I can't imagine that you'd want to have a panel span one of the expansion joints, but they don't mention that in their instructions. I would imagine that the panels would expand/contract at the same rate of the rails since the panel frames are also aluminum.
  • FrxddyFrxddy Solar Expert Posts: 113 ✭✭✭✭
    Re: Rail expansion

    Alrighty! You found the exact information I was looking for. It will work perfectly with my layout to have one expansion joint on each rail. No panel will span the joint.

    Thank you so much!

  • SkiDoo55SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    Re: Rail expansion

    My guess would be that the expansion would be more for the rails to roof attachment than the rails to Panel attachment. Correct the panel frames and the rails will expand at very close to the same rate, being of similar materials. Wood or other material will expand at different rates. Possible to have roof attachment failure after several years of the brackets/standoff being stressed.
    No thermal expansion joints in large aircraft wings! Tip to Tip.
    Don't forget the approved bonding jumpers across any joints in your rails.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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