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  • Roof panel installation

    Greetings everyone Newbie here.

    I'm going to be mounting 9) 77x39 Canidian solar panels in an area that is 24' 3'' wide by 12' high. Regarding the width, my local building code requires an 18" buffer zone on both sides and the bottom. Unless my math is wrong the best I can do is 9 panels of this size mounted in landscape orientation.
    The grid will be three panels across and three panels high.

    The question: Canidian solar (according to their installation sheet) has the mounting anchoring the panels to the rails on the longest edges 4" in from the sides.
    Instead of that configuration, I'm anticipating installing the rails vertical (perpendicular to the 77 in side and anchoring the panels across the narrow side. I've seen a number of installation done that way but was un-sure if the building inspector in North Smithfield RI will go for that?

    Also, I'm in a heavy snow area so I was also thinking of adding a 3rd rail in between the two 'main' rails so the panels would have mount points each instead of 4.

    Comments would be most welcome - thanks in advance.

    Jan

  • #2
    Snow is a lot easier to deal with on a ground mount. Leave a gap between upper and lower panels for
    snow to drop through, which will cut cleaning time and labor. These are mounted portrait with a 6" gap,
    but the next round will be landscape with an 8" gap. Bruce Roe


    PV16D2.JPG

    Comment


    • #3
      NOMB, but I'd stop and reevaluate. After required clearances you have 223.1 ft.^2 to mount panels that have 20.85 ft.^2 of surface. That may be enough, maybe not.

      BUT - and that's a big but for a purpose - you will need more than you may think - maybe a lot more.

      The biggest consideration will probably involve access for snow clearance, either for allowing a free area for the snow to slide off on its own, or for access to get at the snow by hand. Do as you wish, but don't kid yourself - you will need to consider what/how snow will accumulate and how it will be removed, either by itself, with the usual considerations of sudden snow slides, or accumulation with ice dam /blockage considerations. Bruce is the resident expert on how arrays/snowfall interact.

      There is also some possible added space requirements for panel clips/connections that may add an inch or two to net panel dimensions.

      Existing roof penetrations/vents, etc., also usually need code clearance around them. Although tempting, it's never a good outcome covering a vent with a solar panel, both from the standpoint of the vent operation and what it will leave behind on the underside of the covering panel. Doing so will also likely void any warranty.

      Sometimes, ensuring you hit all the rafters with the racking supports requires an array to be shifted in ways that are less favorable to maximizing the array size.

      Lots to consider.

      Welcome to the neighborhood.

      Comment


      • #4
        Originally posted by J.P.M. View Post
        NOMB, but I'd stop and reevaluate. After required clearances you have 223.1 ft.^2 to mount panels that have 20.85 ft.^2 of surface. That may be enough, maybe not.

        BUT - and that's a big but for a purpose - you will need more than you may think - maybe a lot more.

        The biggest consideration will probably involve access for snow clearance, either for allowing a free area for the snow to slide off on its own, or for access to get at the snow by hand. Do as you wish, but don't kid yourself - you will need to consider what/how snow will accumulate and how it will be removed, either by itself, with the usual considerations of sudden snow slides, or accumulation with ice dam /blockage considerations. Bruce is the resident expert on how arrays/snowfall interact.

        There is also some possible added space requirements for panel clips/connections that may add an inch or two to net panel dimensions.

        Existing roof penetrations/vents, etc., also usually need code clearance around them. Although tempting, it's never a good outcome covering a vent with a solar panel, both from the standpoint of the vent operation and what it will leave behind on the underside of the covering panel. Doing so will also likely void any warranty.

        Sometimes, ensuring you hit all the rafters with the racking supports requires an array to be shifted in ways that are less favorable to maximizing the array size.

        Lots to consider.

        Welcome to the neighborhood.
        No way I'd go up the roof on my house back in Canada to clean the snow off the panels in the winter- I had more than enough of that cleaning it on the ground around the house. It would be real PITA: first clean a spot to put ladder on then ... forget-about-it . I'd definitely end up flying off the roof as I had to climb 2 story house roof in the cold + walk on the slippery roof. I'm not afraid of heights or some risk but that would far exceed what I consider safe level.

        Comment


        • #5
          Originally posted by max2k View Post

          No way I'd go up the roof on my house back in Canada to clean the snow off the panels in the winter- I had more than enough of that cleaning it on the ground around the house. It would be real PITA: first clean a spot to put ladder on then ... forget-about-it . I'd definitely end up flying off the roof as I had to climb 2 story house roof in the cold + walk on the slippery roof. I'm not afraid of heights or some risk but that would far exceed what I consider safe level.
          Then, your output would suffer and your roof would be at risk of new/unknown loadings/meltings.

          Hell, in Buffalo roof snow clearance was a regular occurrence - seriously - after shoveling the roof, we could usually then simply jump or walk off the roof into a drift.

          The winters, of course, were worse than the summers..

          Comment


          • #6
            Originally posted by J.P.M. View Post

            Then, your output would suffer and your roof would be at risk of new/unknown loadings/meltings.

            Hell, in Buffalo roof snow clearance was a regular occurrence - seriously - after shoveling the roof, we could usually then simply jump or walk off the roof into a drift.

            The winters, of course, were worse than the summers..
            Buffalo is a snow capital and gets much more snow than most of the places across the lake in Canada- some weird atmospheric/location phenomena. In fact, at least twice as much compare to where I lived north of Toronto. Even single doze was quite enough .

            Comment


            • #7
              Thanks for the input everyone, but frankly I see 100's of solar installations near me with panels mounted on the roof(s), typically with the 1 1/4 clamps between them.
              This particular roof I'm targeting typically melts snow quickly as it gets a lot of sun. It also has an access point above it so I could spray some warm water towards an ice dam to get it going if that ever happened - so far on this roof I've not had to do that.

              The real question is, is it an acceptable practice to mount the rails perpendicular (vertical) to the long side for panels with a landscape orientation? I'll be using the Unirack rail system.
              Also do building inspectors typically review a rail installation before the panels are mounted? And another question is there a limit or best practice on the use of rail splices?

              Thanks
              Jan

              Comment


              • #8
                The trouble with a landscape orientation is that the mounting rails will run parallel to and fasten to the roof framing which is on either 16" or 24" spacing which is not going to coincide with where you need them for the panels. It can be done, but will probably need more rails in places. It is also harder to get the array to be straight as the rails are not horizontal to help with this. We avoid landscape orientations like the plague. If I was doing a 12' wide roof, I'd use the more standard 60 cell panels which are 66" long and two rows would be just 11' in portrait orientation.
                Ask your building dept up front what they do. Some require multiple solar inspections, some won't let their inspectors get on ladders.
                Splice rails all you want, we can handle rails up to 23' long (7 panels) in order to minimize splices. Splices need grounding jumpers across them unless you are using panel clamps that have integrated grounding.
                BSEE, R11, NABCEP, >1200kW installed

                Comment


                • #9
                  I don't recommend leaving a gap on roof mounted panels which may not apply to the OP but could apply to someone reading this thread. Probably a good idea for ground mounts where the snow has a place to go but I would be concerned that a big ice lump will form at each gap on a roof mount. I find that the snow does slide but it does get caught up at the seams between panels, eventually the snow lets loose but it takes longer due to the seams. Fewer seams to traverse when installed vertical compared to horizontal.

                  If its ground mount plan on getting the lower edge of the array quite high off the ground or plan on running a snow blower (with the chute pointed away from the panels) as the snow will build a pile at the lower edge of the panels covering the lower edge of the panel. If you do form a lump of snow you do need to keep at it as daily freeze thaw will tend to convert this lump to ice making it difficult to remove. I drive by big commercial solar farms in Massachusetts and they but the panels up tight with no gap. Its interesting to see the farms during heavy snow years as on occasion the snow piles between the rows of panels will form up and go over the panels. There usually isn't enough room between the panel rows so In most cases they just lave the leave the field alone and let it melt out. Hopefully they set up the strings so that they don't loose all the production.

                  Comment


                  • #10
                    My recommendations are for ground mount; a gap isn't useful if there is a roof directly below it. The
                    gap will considerably reduce the size of the pile of snow at the bottom of a ground mount. Landscape
                    mount is to reduce snow removal labor.

                    I see roof mounts as pretty much hopeless under snow, though some owners attempt to clear them. A survey
                    would probably reveal that over 90% of the snow landing on roof mounted panels is left to melt. For 4 years my
                    panels have been cleared of snow at sunrise after a storm, though I have gotten a lot more efficient in doing
                    so. Bruce Roe

                    Comment


                    • #11
                      Please double check the firefighter pathways requirements for a roof top solar. RI should have something like this: http://osfm.fire.ca.gov/pdf/reports/...cguideline.pdf (which is for CA).
                      Best way to know for sure - have a chat with the building department folks and ask them what are the residential fire pathways requirements for rooftop solar. Better to know this now during design than to have fire department reject the permit...

                      Comment


                      • #12
                        Originally posted by JanS48 View Post
                        Thanks for the input everyone, but frankly I see 100's of solar installations near me with panels mounted on the roof(s), typically with the 1 1/4 clamps between them.
                        This particular roof I'm targeting typically melts snow quickly as it gets a lot of sun. It also has an access point above it so I could spray some warm water towards an ice dam to get it going if that ever happened - so far on this roof I've not had to do that.

                        The real question is, is it an acceptable practice to mount the rails perpendicular (vertical) to the long side for panels with a landscape orientation? I'll be using the Unirack rail system.
                        Also do building inspectors typically review a rail installation before the panels are mounted? And another question is there a limit or best practice on the use of rail splices?

                        Thanks
                        Jan
                        Your specific panels will have an installation guide to indicate allowable support rail configurations, and the impact of each choice on the mechanical rating.

                        Likewise, the Unirac manuals will provide guidelines for splice locations... above a certain length, you have to worry about the effects of thermal expansion, and include some relief. The splices will need to be located within some distance of the nearest attachment point, and will also have an allowable cantilever distance the rail can overhang the last attachment on the end.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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