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  • Mount failures?

    I'm interested in writeups of how solar mounts fail in the field. Does anybody have favorites (either personal stories, or professional writeups)?

    Here's one:
    http://cinnamonsolar.com/wp-content/...-2014-copy.pdf

  • #2
    That's very interesting, are there any similar studies for standing seam metal roof mounted PV arrays?

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    • #3
      Originally posted by DanKegel View Post
      I'm interested in writeups of how solar mounts fail in the field. Does anybody have favorites (either personal stories, or professional writeups)?

      Here's one:
      http://cinnamonsolar.com/wp-content/...-2014-copy.pdf
      Interesting though it is funded by a flash food manufacturer and much of it is poorly installed systems ( missed rafter lag bolts, no flashing, improvised fastener, mixing metals, poor grounding, poor wire attachments , etc.).
      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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      • #4
        I've never had one of our mounts fail.
        I've never seen any solar mount fail structurally - although have seen leaks due to mounts.
        This includes solar mounts we've removed where they were just screwed into the roof decking without finding the framing.
        I've noticed a lot of "dish TV" mounts that are the same way - not screwed to the framing.

        We are not really in a hurricane or tornado area though.

        Personally, I'm more concerned about the manufactured mounts that require two 5/6" lag screws about 3" apart splitting the top cord of a truss and causing structural failure.
        BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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        • #5
          Originally posted by solarix View Post
          Personally, I'm more concerned about the manufactured mounts that require two 5/6" lag screws about 3" apart splitting the top cord of a truss and causing structural failure.
          Which is why it is important to pre-drill the holes to the right thread root diameter first.
          With bolts you are not tempted to leave out the drilling step.
          I would certainly be worried about any mount system instructions or procedures that advocated just screwing the lag in without pre-drilling.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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          • #6
            I never said we were not predrilling. My issue is with the 2 lag screws which tend to be on the same grain of the wood. One well installed screw has plenty of safety margin for strength. We've done testing showing on how the cheap grade of stuff they call wood now often splits with two lag screws close together.
            BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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            • #7
              I never said we were not predrilling. My issue is with the 2 lag screws which tend to be on the same grain of the wood. One well installed screw has plenty of safety margin for strength. We've done testing showing on how the cheap grade of stuff they call wood now often splits with two lag screws close together.
              BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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              • #8
                Originally posted by solarix View Post
                I never said we were not predrilling. My issue is with the 2 lag screws which tend to be on the same grain of the wood. One well installed screw has plenty of safety margin for strength. We've done testing showing on how the cheap grade of stuff they call wood now often splits with two lag screws close together.
                Now that is just disappointing!
                Maybe a metal saddle over the rafter before putting the lag screw into it? But if you have interior access, the machine bolt and nut are so much better.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                • #9
                  Originally posted by inetdog View Post
                  Now that is just disappointing!
                  Maybe a metal saddle over the rafter before putting the lag screw into it? But if you have interior access, the machine bolt and nut are so much better.
                  And that had just doubled the labor cost.
                  NABCEP certified Technical Sales Professional

                  [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                  [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                  [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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                  • #10
                    Originally posted by Naptown View Post
                    And that had just doubled the labor cost.
                    Compared to bringing in a carpenter to sister the split rafters?

                    I agree that a single lag screw design would be better!
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                    • #11
                      SPAX screws

                      Here is the screw we like to use.
                      Engineered with spec'd pullout strengths. None of this lag screw mystery metal, who made this stuff?
                      Even the high-corrosion versions are way less expensive than S.S.
                      Designed to cut the wood instead of split it, so pilot drill is not needed and saves much time.
                      Now available at your favorite home store.

                      SPAX_Powerlag.pdf
                      BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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                      • #12
                        Originally posted by solarix View Post
                        Here is the screw we like to use.
                        Engineered with spec'd pullout strengths. None of this lag screw mystery metal, who made this stuff?
                        Even the high-corrosion versions are way less expensive than S.S.
                        Designed to cut the wood instead of split it, so pilot drill is not needed and saves much time.
                        Now available at your favorite home store.

                        [ATTACH]7810[/ATTACH]
                        I really do not see how they are "designed to cut instead of split" except for the fact that the root diameter of the thread is much smaller in proportion to the outside diameter than a conventional wood or lag screw thread. Probably greater pullout strength than a conventional screw of the same OD for the same reason.

                        I see that you mentioned "pilot hole". To many people a pilot hole is something that allows the screw to get started and aimed in more or less the right direction.
                        For hard or split-prone wood the hole needs to be a much larger specific diameter which is not much smaller (if at all) than the thread root diameter. With that in place the threads themselves will exert minimal outward pressure on the wood, but may not hold as well as with a small pilot hole. The rated pull-out strength of the screw is, however, specified with the right size hole drilled.

                        It is good to see that there is an alternative. I do not recall seeing them at Big Orange, but I will take a look next time I am there.
                        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                        • #13
                          http://solpowerpeople.com/solar-pv-racking-with-unirac/ has a video with a discussion of failure modes about half an hour in, fwiw.

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                          • #14
                            "I really do not see how they are "designed to cut instead of split" except for the fact that the root diameter of the thread is much smaller in proportion to the outside diameter than a conventional wood or lag screw thread. Probably greater pullout strength than a conventional screw of the same OD for the same reason."

                            The SPAX screws have threads that are specially formed with a cutter-like rough edge on the O.D. that really does saw through the wood instead of split through it. No predrilling needed.
                            BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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                            • #15
                              See the Technical Bulletin on the Unirac site for installation of anti-seize onto bolts. It addresses failures from using too much anti-seize. See http://unirac.com/technical-support/
                              Jeff, BSEE, 22.3KW, 45-240W w/M190, 46-260W w/M250

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