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  • How to maximize area of the roof for PV?

    Hello, Solar panel comunity!

    If every solar panel would be economically rentable to be placed, how do we maximize the area in order to place the most PVs posible? Is there any way to know besides my trial and error method?

    [LEFT][COLOR=#252C2F][FONT=Helvetica][SIZE=13px]This is purely for academic purposes. I know the scenario may seem a bit unrealistic at first, and even comparable with commercial uses, but in cases where the roof could give place to more PV if they were 200

  • #2
    For some reason, my post keep getting into a bad format. More info, and one example, where I use the area of the roof as a square first, and then all of the available one (1m from roof edges for safety) -
    Attached Files
    Last edited by Miguel Sousa; 07-01-2018, 12:52 PM.

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    • #3
      The number of panels that can be installed on a flat roof requires more information and design then to just trying to fill up the space.

      You have to follow your local building and fire codes along with having a structural design that calculates how much weight your roof can handle. You also need to know the amount of panel tilt to maximize your production to keep shadows from adjacent panels falling on other panels.

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      • #4
        Originally posted by SunEagle View Post
        The number of panels that can be installed on a flat roof requires more information and design then to just trying to fill up the space.

        You have to follow your local building and fire codes along with having a structural design that calculates how much weight your roof can handle. You also need to know the amount of panel tilt to maximize your production to keep shadows from adjacent panels falling on other panels.
        Yes, exactly! I sent it as an attachment in my reply. It's assumed that the roof can handle every weight of the fixed structure panels, the tilt of 10 and 1m from roof edges.

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        • #5
          generally speaking on flat roofs you have other concerns like setbacks, walk ways, obstructions, shadows, etc. For the most part we line up the solar arrays with the roof and get the best layout. Many of the layout software packages have auto layout algorithms that find the best PRODUCING not highest fit (most production is what you want after all).
          I would generally not use the algorithms but some do.

          If you really want the highest fit you do an East / West arrangement with back to back 10 degree tilt. It is very difficult to work on and provides almost no isles etc, but fits a lot and produces a lot. also costs a lot.


          Also neither of your designs are very good as generally the border wall has some height to it so the first row is shadowed on the due south one and the angled one has several shadowed.
          There are no setbacks so it doesn't work for most big cities that require fire code setbacks from the front of the building and an isle to the back on one side.
          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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          • #6
            Originally posted by ButchDeal View Post
            generally speaking on flat roofs you have other concerns like setbacks, walk ways, obstructions, shadows, etc. For the most part we line up the solar arrays with the roof and get the best layout. Many of the layout software packages have auto layout algorithms that find the best PRODUCING not highest fit (most production is what you want after all).
            I would generally not use the algorithms but some do.

            If you really want the highest fit you do an East / West arrangement with back to back 10 degree tilt. It is very difficult to work on and provides almost no isles etc, but fits a lot and produces a lot. also costs a lot.


            Also neither of your designs are very good as generally the border wall has some height to it so the first row is shadowed on the due south one and the angled one has several shadowed.
            There are no setbacks so it doesn't work for most big cities that require fire code setbacks from the front of the building and an isle to the back on one side.
            I did an interrow distance with the shadow of 21st December at 3pm.
            Was my fault of zooming in too much, but the roof as an north area which is clear and, since it's mostly shadow, I didn't take it into account, so it can also serve for other purposes - fireman, HVAC systems, etc.
            I didn't take the isle into account though.

            In your opinion, if the area is too restricted, should the PVs try to be always roof oriented ? Is it also a big disadvantage in terms of instalation to have multiple rows ( for example, 2-5-5-5-2) with 200

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            • #7
              the advantage to lining up with the building is it is easier to do layout, and easier to tie into the rafters / joists for attaching the racking. IF you are planning to do ballasted, then you need engineering stamp that the structure can handle the added weight which is difficult with out reviewing the structure of the building which may not be available.

              You often can not easily set the inter row spacing on ballasted either only on non-ballasted can that be adjusted. Also you sometimes get best production with shorter inter row spacing than winter solstice as there is little production in that time anyway but that is a different issue.

              You often have to leave the full front or major front of the building open (NY for example) for ladder access.

              Do the sides of the building extend above the roof surface? if so you want to set back from them to avoid shadows.
              OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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              • #8
                I tried to look in all the legislation of the fire code in my country (Portugal), but I couldn't find anything related to it, only about the rest of the building, materials, street access to it, etc. but nothing on the roof and ladder access specifically.

                No, the sides don't extend above the roof surface. So, if everything is right in terms of structure (and let's assume, for now, also for the fire code), and without going too extreme with the fitting, like the east-west, since, as you said, is too costly, if the azimuth change provides with + 1 solar panel, it should be worth considering, even though it can be a worst orientation, like 170

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                • #9
                  Originally posted by Miguel Sousa View Post
                  I tried to look in all the legislation of the fire code in my country (Portugal), but I couldn't find anything related to it, only about the rest of the building, materials, street access to it, etc. but nothing on the roof and ladder access specifically.

                  No, the sides don't extend above the roof surface. So, if everything is right in terms of structure (and let's assume, for now, also for the fire code), and without going too extreme with the fitting, like the east-west, since, as you said, is too costly, if the azimuth change provides with + 1 solar panel, it should be worth considering, even though it can be a worst orientation, like 170
                  on something this small an east west would no or small gaps would produce the most and fit the most.
                  OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                  • #10
                    Ok, so I will go for the smaller gap study. Thanks a lot for all the help!

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                    • #11
                      One last question! Is it worth to consider a bit of a bigger structure to stack 2 PV instead of one? At least, in the last row, since it doesn't cast shadow? Or is it too vulnerable to wind loads?

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                      • #12
                        Originally posted by Miguel Sousa View Post
                        One last question! Is it worth to consider a bit of a bigger structure to stack 2 PV instead of one? At least, in the last row, since it doesn't cast shadow? Or is it too vulnerable to wind loads?
                        Such an arrangement will, in all likelihood increase the wind loading. How much of an increase, what to do about it and at what cost is up to the design(ers) to contend with. There's no way to tell from here.

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                        • #13
                          Originally posted by Miguel Sousa View Post
                          One last question! Is it worth to consider a bit of a bigger structure to stack 2 PV instead of one? At least, in the last row, since it doesn't cast shadow? Or is it too vulnerable to wind loads?
                          anything like that would NOT be ballasted due to wind load.
                          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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