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Mounting Panels on Standing Seam Roof - Do I need rails?

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  • Mounting Panels on Standing Seam Roof - Do I need rails?

    It seems that some companies sell mounting systems for standing seam roofs that don't require rails. The only way I could see this work is if the panels were mounted in landscape orientation and you didn't necessarily follow the panel instructions wrt where you can attach the mounts.

    So, do I need rails or not?

    I'm looking at a ~10k system on my new 8/12 pitch standing seam roof.

    Thanks!

    billboe

  • #2
    It will probably depend on the engineering details required by your local building code. Where are you located?

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    • #3
      Originally posted by Ampster View Post
      It will probably depend on the engineering details required by your local building code. Where are you located?
      thanks ampster... i'm in small town central vermont. no building inspector at all.

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      • #4
        No building inspector? What planet are you on? Standing seam clamps work well. Be aware that the manufacturer recommendation is to put one on each seam in order to spread the load. As a result they are really not any less expensive than a rail system. You are relying on the nails (or screws) used to hold the roofing down to now hold your array as well. Building dept here requires us to prove that the roofing was put on with double the usual fasteners. Also be aware that with clamps, the panels are pretty close to the roof with not much ventilation space under them. Maybe not a problem in Vermont, but here in Arizona it is.
        BSEE, R11, NABCEP, Chevy BoltEV, >2000kW installed

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        • #5
          Originally posted by solarix View Post
          No building inspector? What planet are you on? Standing seam clamps work well. Be aware that the manufacturer recommendation is to put one on each seam in order to spread the load. As a result they are really not any less expensive than a rail system. You are relying on the nails (or screws) used to hold the roofing down to now hold your array as well. Building dept here requires us to prove that the roofing was put on with double the usual fasteners. Also be aware that with clamps, the panels are pretty close to the roof with not much ventilation space under them. Maybe not a problem in Vermont, but here in Arizona it is.
          yes, what planet indeed! i'm building a house and did all plumbing and electrical and no one looked at it once. that said, i was pretty meticulous at following code (probably beyond code)...

          thanks for the info on the clamps. we did tell our roofer to double the fasteners so, hopefully that happened.

          so, it does seem that landscape would be the only way to go and the clamps would just fall where they fall (seams are 21" apart)... i do like the idea of a lower profile install (i wouldn't think heat dissipation is too much of a problem for me).

          thanks again!​​​​​​

          Comment


          • #6
            I am over in NH and notice quite a bit of performance loss in summer on hot days with my roof array compared to my other arrays. Note that just because there is no inspector, there is a building code and if you have to make an insurance claim, if the failure is attributable to a non code installation the insurance company does not need to pay. I actually met two different folks from the NE Kingdom area that claimed that when they had a fire due to their off gird system that they didn't get a dime in insurance. I had no need to check the veracity of the claims and in both cases I was talking to an ex spouse so there was probably more to the story .

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            • #7
              Originally posted by billboe View Post
              i do like the idea of a lower profile install (i wouldn't think heat dissipation is too much of a problem for me).
              Not sure why you think you would be special with heat dissipation.... PV modules get hot from the sun light and need air circulation to cool them.
              OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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              • #8
                Originally posted by peakbagger View Post
                I am over in NH and notice quite a bit of performance loss in summer on hot days with my roof array compared to my other arrays. Note that just because there is no inspector, there is a building code and if you have to make an insurance claim, if the failure is attributable to a non code installation the insurance company does not need to pay. I actually met two different folks from the NE Kingdom area that claimed that when they had a fire due to their off gird system that they didn't get a dime in insurance. I had no need to check the veracity of the claims and in both cases I was talking to an ex spouse so there was probably more to the story .
                thanks! good to know about performance loss even in nh...

                and yeah, like i said about my plumbing and other electrical, i'm a stickler for following code (or going beyond code)... still not sure if that would help me in an insurance claim?!?! probably the best would be to pay a licensed electrician to sign-off on the install?!?! not sure that would happen?!?!

                i don't have direct personal experience with an "ex-spouse", but, yeah, there is always more to the story in those situations!

                Comment


                • #9
                  Originally posted by ButchDeal View Post
                  Not sure why you think you would be special with heat dissipation.... PV modules get hot from the sun light and need air circulation to cool them.
                  i didn't mean to say "i was special", just that in northern vt the average highs in july & august are less than 80 degrees, so, i was speculating that overheating would be less of an issue for my install. it sounds like (from peakbagger's nh experience) that i should still pay attention to this...

                  thanks!

                  Comment


                  • #10
                    Originally posted by billboe View Post

                    i didn't mean to say "i was special", just that in northern vt the average highs in july & august are less than 80 degrees, so, i was speculating that overheating would be less of an issue for my install. it sounds like (from peakbagger's nh experience) that i should still pay attention to this...

                    thanks!
                    yes. Ambiant temperature is a contributor to heat in the temperature of the array but most importantly is ventilation.
                    It is not so much "overheating" as just heating. The PV modules can take the heat but performance drops with their temperature. prevent air from cooling them and the temperature will jump, production will thus suffer.
                    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                    Comment


                    • #11
                      Originally posted by peakbagger View Post
                      I am over in NH and notice quite a bit of performance loss in summer on hot days with my roof array compared to my other arrays.
                      peakbagger... i'm curious of what type of roof you have? ours is a light blue standing seam. does roof color & material matter in terms of heat dissipation of pv panels?

                      Comment


                      • #12
                        Originally posted by billboe View Post

                        i didn't mean to say "i was special", just that in northern vt the average highs in july & august are less than 80 degrees, so, i was speculating that overheating would be less of an issue for my install. it sounds like (from peakbagger's nh experience) that i should still pay attention to this...

                        thanks!
                        I think with your 8/12 pitch, the air flow would be better than on a flatter roof. Or, as you say, less of an issue. Other factors such as the height of the standing seams, the height the brackets add to the install and the color of your roof would be what I would pay attention to.

                        Comment


                        • #13
                          Originally posted by Ampster View Post

                          I think with your 8/12 pitch, the air flow would be better than on a flatter roof. Or, as you say, less of an issue. Other factors such as the height of the standing seams, the height the brackets add to the install and the color of your roof would be what I would pay attention to.
                          thanks ampster! the height of the seam is an inch... i do seem to remember there are options in the height of the clamps/brackets... i'll attach a photo of the roof in question. i installed the conduit (1" emt) you can see on the top left of the roof for pv wiring (it goes directly to my basement next to the main panel).


                          rh roof - noexif.JPG

                          Comment


                          • #14
                            Originally posted by Ampster View Post

                            I think with your 8/12 pitch, the air flow would be better than on a flatter roof.
                            Why would you think that ? If you are referring to the bottom line of array operating temperature, and separate from the matter of optimum array orientation for electricity production, that's most likely not true or correct.

                            There will probably be a larger vector component of vertical forces as a result of wind on a non horizontal roof or any structure, but not got any thing to do with "better air flow", whatever that means.

                            For starters, I'd suggest you get your terminology correct. Most roofs are flat, but many/most are not horizontal. You sure you mean "flatter" and not "more horizontal" ? Also, are you assuming the array is parallel to the roof surface. At least some arrays are not with that number/%age tending to go up as the location gets farther away from the equator - like northern VT.

                            I'm not going to give you a lesson in fluid mechanics and heat transfer, but in general, most wind vectors have a significant horizontal component ("The wind is from the south at 5 MPH", that sort of thing).

                            For max. air flow (and assuming a high heat transfer rate on the way to a lower array temp. is one big reason for your use of the word "better") across a 2 sided flat plate, a plate orientation parallel to the largest vector component of a fluid (usually that's the horizontal component for wind) will result in the greatest amount of air velocity and mass flow rate of air over/across a flat plate (in this case a PV array). FWIW, that orientation will usually also produce the smallest orthogonal (non parallel) wind force on the plate component, but that's off topic.

                            Off parallel (to the direction of greatest vector component of the wind) plate/array orientations result on lower wind velocities on the upwind face and much lower wind velocities, approaching zero, on the downwind face as compared to the parallel plate orientation air velocities.

                            Greater air velocities mean greater heat transfer which means lower plate/array temps. The greater the heat transfer, the lower the temp. difference between the plate and the ambient air/surroundings and so the lowest array temp. for any given ambient conditions.

                            So, with the proviso that there's sufficient/good clearance between a roof surface and a solar array, air flow and thus the heat transfer will, again, depending on the particulars of the application, have a greater probability of being larger for a horizontal array orientation than for a non horizontal array orientation.

                            Not that it's strictly related to your statement about air flow, but for those more probable ambient conditions, for a horizontal array orientation and for a given irradiance input, a lower array temp. will be the result.

                            You're again out of your knowledge range. I don't care about your state of ignorance. I do care that your popping off and spreading misleading and incorrect information based on what looks mostly like uninformed and ignorant opinion can cause others to come to incorrect conclusions that can affect a design, both in terms of safety and efficient for and that na. That's rude and inconsiderate.

                            Stick to what you know.

                            Comment


                            • #15
                              Originally posted by billboe View Post

                              peakbagger... i'm curious of what type of roof you have? ours is a light blue standing seam. does roof color & material matter in terms of heat dissipation of pv panels?
                              I have tan asphalt shingle roof. Far better than black shingles but still gets toasty on a warm day. its roughly a 30 degree pitch. If I put my hand at the top edge of the panels it

                              BTW in getting in pissing match with an insurance company the key is that it was installed to the code in effect at the time not necessarily that it was inspected. The insurance company starts out trying to not pay anything and then its up you to prove that the loss is not related to the installation or materials. As usual I am not a lawyer nor do I play one on TV
                              Last edited by peakbagger; 04-04-2019, 01:14 PM.

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