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Seeking rail system for a roof mount system that allows angle adjustment

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  • Seeking rail system for a roof mount system that allows angle adjustment

    I have a standard 4/12 pitch roof which is about 18 degrees. Using the calculators I have determined my fixed angle would be about 30 degrees with a summer angle being around 12 degrees and a winter angle around 50 degrees. If I was to go with a fixed angle of 30, the rail would need a way of changing the angle 12 degrees. I have looked at a couple of popular rail systems and they don't seem to have addressed this need.

    I will be installing 8 panels in portrait which means having the horizontal rails mid panel making hinging the panels more difficult. i.e. if I tip the panels up, the bottom edge would likely be touching the roof, which would mean raising both rails. It would take more rail and cable length to go landscape, but I wouldn't have the issue with tipping the panels. I have the roof space to go landscape or portrait.

    Another thought on the issue makes me wonder if the angle should be optimized for the highest usage months,i.e. June, July and August. If I took that approach, the roof pitch of 18 degrees is closer to the summer angle and might be better than trying to go with the suggested fixed angle of 30?

    Thanks!
    Lew

  • #2
    Run an orientation that's fixed at the same orientation as that of the roof.

    Compare that annual output to the annual output of all the other orientations you're considering in whatever monthly combinations you choose.

    Next, compare the difference in the residual electric bills of each orientation.

    Next, compare the cost difference in making an array parallel to the roof vs. an array at some other orientation. Don't forget any extra engineering to get the design by the AHJ.

    You may find that for the perhaps relatively small loss of output for a roof parallel array, it ain't worth the extra cost/hassle of a tilted array.

    That you don't know that already makes me wonder if you need an education before going further.l

    Comment


    • #3
      Originally posted by J.P.M. View Post
      Run an orientation that's fixed at the same orientation as that of the roof.

      Compare that annual output to the annual output of all the other orientations you're considering in whatever monthly combinations you choose.

      Next, compare the difference in the residual electric bills of each orientation.

      Next, compare the cost difference in making an array parallel to the roof vs. an array at some other orientation. Don't forget any extra engineering to get the design by the AHJ.

      You may find that for the perhaps relatively small loss of output for a roof parallel array, it ain't worth the extra cost/hassle of a tilted array.

      That you don't know that already makes me wonder if you need an education before going further.l
      The basic question was if there is a rack system that is made to allow for various angles? I appreciate the suggestion to just leave it at the roof angle which is simplest. If there is an existing ready made rail system with angle adjustments, it would give me the opportunity to wring out a few more watts at a small initial cost.
      thanks

      Comment


      • #4
        Originally posted by Testshoot View Post

        The basic question was if there is a rack system that is made to allow for various angles? I appreciate the suggestion to just leave it at the roof angle which is simplest. If there is an existing ready made rail system with angle adjustments, it would give me the opportunity to wring out a few more watts at a small initial cost.
        thanks
        The short answer to your question is yes. Google is your friend. Arrays mounted non parallel to their support structure can probably allow for some wringing, but not much and probably not worth what it would cost in terms of toil and treasure. The possible/likely extra engineering alone will probably chew up any long term differential savings. Suit yourself, but until you run some reasonably reliable modeling and then compare the costs of the racking and engineering, you'll never know.

        Comment


        • #5
          Originally posted by J.P.M. View Post

          The short answer to your question is yes. Google is your friend. Arrays mounted non parallel to their support structure can probably allow for some wringing, but not much and probably not worth what it would cost in terms of toil and treasure. The possible/likely extra engineering alone will probably chew up any long term differential savings. Suit yourself, but until you run some reasonably reliable modeling and then compare the costs of the racking and engineering, you'll never know.
          I have been googling for days and haven't found any search terms that revealed an "adjustable angle solar system rail system" or any variant of those words. I am not suggesting a non-parallel installation... I only came here as I was unable to find anything elsewhere. Given people are going to want to install at optimum angle or angles, it seems there is a niche for such a product. What extra engineering would there be? I am not saying it was a great install, but I saw a video on a setup where he used treated 2X4s for his racking to save money and he had the top edge higher, probably for the same reason. He was showing his whole, newly installed, setup and mentioned that the install was just signed off, i.e. accepted. I think it was somewhere in the US.

          If you are aware of such a rack system, couldn't you just tell me the name?

          Comment


          • #6
            1.) I'm not your mother.
            2.) I'm a lousy teacher.
            3.) I'm not an enabler.

            I just took 30 sec. to Google "Adjustable solar mounting system". Several million hits, some of which are well known.

            Try it.

            Some things you will need to learn to do on your own.

            Your response belies your ignorance. I suggest you learn more before you buy or attempt to design anything.

            Comment


            • #7
              Originally posted by Testshoot
              The basic question was if there is a rack system that is made to allow for various angles? I appreciate the suggestion to just leave it at the roof angle which is simplest. If there is an existing ready made rail system with angle adjustments, it would give me the opportunity to wring out a few more watts at a small initial cost.
              My experience is that little is available to consumers, to allow convenient tilt change. This is especially true for
              roof mounts, which make it difficult to even access the mechanism. Some think a bolt through 2 members is a
              bearing that will give easy service for decades, I do not.

              One advantage here of variable tilt, is setting more optimum angles for summer and winter production. But
              here the panels will be straight up for snow months, for the absolute minimum effort to keep snow cleared.
              A tilting array has 2 structures, the fixed support and the variable tilt, so that cost might be double that of a
              fixed array. What are your priorities? Bruce (tilting ground mount) Roe
              Last edited by bcroe; 10-24-2018, 08:47 PM.

              Comment


              • #8
                Out in Tucson, Arizona, we have determined (after thousands of installations) that the best angle for our panel systems is right around 21 degrees. We also have very intense summers, so this may be a contributing factor. The difference a couple degrees would have is very minimal though. If you are more Northern, I would set the panels pitched a few more degrees, up to a maximum of 30. Southern orientation has a much bigger effect on production though.

                However, we use a Unirac (unirac.com) railing system that can be set up to be adjustable, with the simple loosening of a bolt. The Unirac system is also made by an American company out of New Mexico. It is a very simple, robust solar racking system. I would highly recommend it.
                Last edited by sdold; 10-26-2018, 04:18 PM.

                Comment


                • #9
                  The key thing that is glossed over is that an array with a different pitch then the roof changes the loading on the roof trusses. If the panels are parallel with the roof, the load is distributed over the entire roof. If the panels are angled to the roof pitch, it turns into a big point load on the truss and I expect at a minimum it needs a PE to review and stamp and most likely will need reinforcing of the truss. It also increases wind uplift substantially. Many older roofs are poorly attached for wind uplift, the typical detail on many joists and trusses are toe nailing them to the top of the wall. If clips were installed that makes big difference and in some areas there may have to be additional details all the way down to the footing. Its a case by case basis and I expect unlike standard rack systems few companies will supply a free PE certification.

                  Comment


                  • #10
                    Originally posted by peakbagger View Post
                    The key thing that is glossed over is that an array with a different pitch then the roof changes the loading on the roof trusses. If the panels are parallel with the roof, the load is distributed over the entire roof. If the panels are angled to the roof pitch, it turns into a big point load on the truss and I expect at a minimum it needs a PE to review and stamp and most likely will need reinforcing of the truss. It also increases wind uplift substantially. Many older roofs are poorly attached for wind uplift, the typical detail on many joists and trusses are toe nailing them to the top of the wall. If clips were installed that makes big difference and in some areas there may have to be additional details all the way down to the footing. Its a case by case basis and I expect unlike standard rack systems few companies will supply a free PE certification.
                    Depending on the layout and the design, most all loads transferred to a roof from commonly seen arrays that have any clearance between the underside of the array and the roof deck are point loads. Those point loads are often (it's hoped) transferred to several rafters or joists, usually with one such roof member supporting several of those attachments.

                    In a parallel to the roof orientation, an array with, say a more/less constant 15 cm. clearance, the point loads are more or less equal to one another, and will more often than not be mostly compressive (downward) in nature from dead load and wind loading.

                    A loading consideration that's usually ignored (and probably justifiably so for most commonly seen parallel arrays) is that in such (common) array design cases, that loading will present itself differently to the roof than the same wind loading without the array. The overall resultant force will probably be similar in either case, but the force will be distributed as a group of point loads for the array case and as more of a distributed variable compressive load in the no array case. Maybe a small point but may need checking or consideration before going further in a design.

                    To be clear, most of any increased loading on a roof from an array and it's consequent resultant loading(s) (with most of that loading upward or downward, but probably some shear as well) comes from the wind loading induced by greater projected array cross sectional area that's caused by the increased elevation of the panels.

                    In general, the greater the difference in array vs. roof orientation and the greater the roof to array clearance, the more the difference in roof loading from array to non array, and probably the greater the magnitude of the array, racking and roof loading, and also the greater the variation in those loads.

                    The change in loading per support will vary with the wind vector and array tilt. The resultant forces (which can be both tensile or compressive) and the moments on each support are what gets transferred to trusses, rafters or other supports.

                    Comment


                    • #11
                      Originally posted by Testshoot View Post
                      I have been googling for days and haven't found any search terms that revealed an "adjustable angle solar system rail system" or any variant of those words.
                      I did. (Hard to post links here so I won't.) Google Mounting Systems Lambda Light EW+, SolarCity ZS Peak and tenKsolar DUO.
                      it would give me the opportunity to wring out a few more watts at a small initial cost.
                      THAT you are not going to find. It's going to be roughly double the amount of aluminum, and will be expensive. If you want to "wring out a few more watts for small additional cost" add a panel. They are dirt cheap nowadays.
                      . What extra engineering would there be?
                      A parallel installation does not generate a lot of lift in wind. (Well, some. but a small enough amount that most roof mounting systems can rely on lag bolts and the roof structure itself to resist it.) When you start tilting away from parallel that changes. It would not be unusual, for example, to require the homeowner to double up on roof rafters, or replace 2x6 rafters with 2x8.
                      I am not saying it was a great install, but I saw a video on a setup where he used treated 2X4s for his racking to save money and he had the top edge higher, probably for the same reason. He was showing his whole, newly installed, setup and mentioned that the install was just signed off, i.e. accepted. I think it was somewhere in the US.
                      Yep. People get away with all sorts of stuff.


                      Comment


                      • #12
                        Originally posted by J.P.M. View Post
                        1.) I'm not your mother.
                        2.) I'm a lousy teacher.
                        3.) I'm not an enabler.

                        I just took 30 sec. to Google "Adjustable solar mounting system". Several million hits, some of which are well known.

                        Try it.

                        Some things you will need to learn to do on your own.

                        Your response belies your ignorance. I suggest you learn more before you buy or attempt to design anything.
                        None of the tilt solutions I Googled were appropriate for my panels. All of those solutions are for small panels, even ones from companies like Renogy. You found some better keywords than me, but that still didn't lead to a solution. You seem to have missed the step where I said I Googled, but some keywords are more successful than others. I am a master Googler.

                        Comment


                        • #13
                          Originally posted by matsonaustin View Post
                          Out in Tucson, Arizona, we have determined (after thousands of installations) that the best angle for our panel systems is right around 21 degrees. We also have very intense summers, so this may be a contributing factor. The difference a couple degrees would have is very minimal though. If you are more Northern, I would set the panels pitched a few more degrees, up to a maximum of 30. Southern orientation has a much bigger effect on production though.

                          However, we use a Unirac (unirac.com) railing system that can be set up to be adjustable, with the simple loosening of a bolt. The Unirac system is also made by an American company out of New Mexico. It is a very simple, robust solar racking system. I would highly recommend it.
                          Hello sir, Thanks for the info. Your sun and weather is similar to what we have here. It happens I live about 12 miles from Unirac. Heard of them, didn't know where they were based. I checked through their three non-flat roof systems and none of them seemed adjustable. I see their flat roof system has a 10 degree option, but not adjustable.

                          If my roof is 18.4 degrees, that is close to your 21 degrees for your preferred fixed angle. If I go fixed angle and since highest usage is June-August, like it would be there, then the angle should be skewed towards a summer angle. The Optimum Solar Tilt site shows the best fixed angle to be 29.7 degrees. Your 21 would give higher output in the summer which makes sense to me.
                          Thanks!

                          Comment


                          • #14
                            Originally posted by Testshoot View Post

                            None of the tilt solutions I Googled were appropriate for my panels. All of those solutions are for small panels, even ones from companies like Renogy. You found some better keywords than me, but that still didn't lead to a solution. You seem to have missed the step where I said I Googled, but some keywords are more successful than others. I am a master Googler.
                            Why are you wanting to tilt them? You cant adjust the spacing so you will have to go with max spacing. Also most modern pv modules have a much wider angle of incidence so tilting is of less difference for productioon but great difference for loading
                            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                            Comment


                            • #15
                              Originally posted by Testshoot View Post

                              None of the tilt solutions I Googled were appropriate for my panels. All of those solutions are for small panels, even ones from companies like Renogy. You found some better keywords than me, but that still didn't lead to a solution. You seem to have missed the step where I said I Googled, but some keywords are more successful than others. I am a master Googler.
                              Looks to me from my ignorant perspective that a good part of your problem seems to be a general lack of knowledge about what you're trying to do including information about the limitations and possibilities of output or bill offset as f(array orientation), and what's available to accomplish what you think you want. The information and products are in the open literature and commonly available all over the net for the taking.

                              In particular, I was just on the Unirac site and saw a lot of hardware for tilting panels, and I'm pretty much of a Google ignoramus.

                              I think you need to learn more before you design or buy anything, but NOMB/money/life.

                              Comment

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