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  • Vertical mounting bi-facial panels

    I saw this article in Solar Builder proposing ground-mounting bi-facial panels vertically. They say it doubles as a fence. The idea fascinates me.

    Vertical Reach.jpg
    I wondered if it was a good idea in terms of sun utilization and did some quick runs of PVWatts to try to answer this question.

    #1: New England location, South facing, 30 degree from horizontal, all else default. 5194 kWh/year.
    #2: New England location, East facing, 90 degree from horizontal, all else default. 2832 kWh/year, to model one side of a vertical panel.
    #3: New England location, West facing, 90 degree from horizontal, all else default. 2826 kWh/year, to model the other side of a vertical panel.

    No model is perfect. This one is far from perfect. For starters, it ignores stray backside radition like ground reflections. But despite the limitations, do you think this is a fair way to compare a standard ground mount (#1) to a horizontal ground mount (the sum of #2 and #3)?

    Do you have a better idea for comparing this approach using bi-facial panels to a traditional ground-mount using bi-facial panels?
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

  • #2
    Yea: SAM. That'll allow user input for the albedo which is fixed in PVWatts at 0.2, and in any case is not only incident on the backside of a bifacial but incident on both sides of a bifacial panel in any and all orientations and from any and all directions, and in any case for more reasons than is possible to talk about here, is nearly impossible to measure much less predict. If by stray backside radiation you are referring to albedo, that component of radiation is always present on a surface of any orientation.

    Aside from SAM you can also use a model that can can do a reasonable job on a bifacial array. I'd also suggest a 45 deg. tilt for New England or closer to array location latitude.

    Doing as you suggest is probably not an unreasonable 1st approx. for the specific case of E-W facing vertical bifacials but less so for other orientations. Another factor: Most models won't work for array or module tilt angles > 90 degrees, and most go completely haywire when combined with tilts > 90 deg. and azimuths >270 but <90degrees (i.e., the backside of a single face panel tilted in the regular fashion at less than 90 deg. and oriented toward the equator.

    I wrote a model about 30 years ago or more that will, for example, model irradiance on a surface of any orientation which used, along with direct irradiance, diffuse fractions of irradiance, and an albedo estimate which used view factor geometry. See a decent heat transfer text that gives radiation heat transfer a reasonable treatment for more info if you're interested. One such tome is by one of my mentors: Kreith, "Principles of Heat Transfer" (ISBN # 0-06-043774), or see Rosenow & Hartnett: "Handbook of Heat Transfer" (ISBN # 0-07-053576-0).The model I did at the time was too complicated for anything less than a mainframe computer back in the day, but the big problem was verification by measurement because the cosine correction factor for most every pyranometer then (and still), as well as the reflection characteristics of most glazing materials at what are usually low incidence angles makes measurement accuracy either too poor or too irrelevant to measure.

    Anyway, PVWatts does a fair job for it's intended purpose and it can be bastardized and made to do things it's writers probably never foresaw, such as what you suggest. For the specialized case of a vertical E-W facing array, doing 2 single face runs is probably not terribly far off in terms of output compared to a double faced array, but much less so for other orientations. One example: Even for the subject orientation(s), the cell temp. of the bifacial will be higher than 2 white backed arrays and will need to be accounted for.

    All that aside, that's one of the ugliest fences I've ever seen. It's so ugly it wouldn't be fit to enclose barfatorium.
    Last edited by J.P.M.; 05-26-2021, 10:02 AM.

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    • #3
      Once bi-facial solar panels cost the same per foot as fencing that will be a great idea!

      Seriously, I'm sure there are cases where a solar fence might make sense when conventional won't do but in my opinion, bi-facials panels are a solution looking for a problem.
      Dave W. Gilbert AZ
      6.63kW grid-tie owner

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      • #4
        Originally posted by azdave View Post
        Once bi-facial solar panels cost the same per foot as fencing that will be a great idea!

        Seriously, I'm sure there are cases where a solar fence might make sense when conventional won't do but in my opinion, bi-facials panels are a solution looking for a problem.
        I don't see how a fence like that could stand up to high winds which would be an issue down here in Florida.

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        • #5
          Originally posted by azdave View Post
          Once bi-facial solar panels cost the same per foot as fencing that will be a great idea!

          Seriously, I'm sure there are cases where a solar fence might make sense when conventional won't do but in my opinion, bi-facials panels are a solution looking for a problem.
          Yea, mostly +1 but given what I think I might know by training, education and experience, I don't think they're as much of a solution as a B.S. marketing gimmick peddled to people who don't know better.

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          • #6
            Originally posted by SunEagle View Post

            I don't see how a fence like that could stand up to high winds which would be an issue down here in Florida.
            That's a design consideration. If the panels have a cert. or calculation saying they're good for the site conditions, the posts and the rest of the support structure are a matter of design.

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            • #7
              Originally posted by azdave View Post
              Once bi-facial solar panels cost the same per foot as fencing that will be a great idea!

              Seriously, I'm sure there are cases where a solar fence might make sense when conventional won't do but in my opinion, bi-facials panels are a solution looking for a problem.
              Bifacial mono panels have a lower degredation rate of about .45%/yr vs .55%/yr. They are probably more reliable as they will not have backsheet failures since they are glazed on both sides. The main drawback is the extra weight. LONGi LR4-72HPH panels weigh 23.3kg, vs. the 72HBD panels at 27.5kg.

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              • #8
                Originally posted by J.P.M. View Post

                That's a design consideration. If the panels have a cert. or calculation saying they're good for the site conditions, the posts and the rest of the support structure are a matter of design.
                I agree the design of the panel would make a difference but I am skeptical of any solar panel of handling 130 mph winds at a 90 D angle.

                Although there are a lot of ground mounted systems around here that seem to make it through our storms so maybe the vertical fence would survive.

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                • #9
                  Originally posted by SunEagle View Post

                  I agree the design of the panel would make a difference but I am skeptical of any solar panel of handling 130 mph winds at a 90 D angle.

                  Although there are a lot of ground mounted systems around here that seem to make it through our storms so maybe the vertical fence would survive.
                  You can be as skeptical as you wish and I might tend to agree with you in a lot of designs.

                  Because a panel's orientation is not known a priori at the design stage, for any code compliant wind design I ever performed or was ever associated with, if not stated otherwise, worst design conditions (including gust and bluff conditions) were assumed. Since a wind vector that's normal to a panel will probably exert the greatest normal wind loading, and there are more than a few ground mounts with vertical panel orientation, I'd expect (and come to think of it so probably would Bruce) that condition would be covered up to and including the stated allowable wind speed or design wind pressure rating unless otherwise stated on the data sheet.

                  There's also the issue of combination loads such as snow and wind, for both dead, and live.

                  Treating that as a separate subject for this conversation, commonly, for structures including buildings and appurtenances and other structures or attachments to structures, the max. load criteria for wind loadings is commonly stated as max. allowable wind velocity using the worst vector conditions that the design conditions stipulated for that structure. For some reason, panel data sheets seem to commonly state max. wind pressure in units of lbf/ft2 or kN/m^2 (= kiloPascals). That's also done in the rest of engineering but was less common when I was designing structures.

                  As an example, my Sunpower 327 data sheet shows a max. allowable wind loading of 50 lbf/t^2 front and back. That translates to a wind velocity of ~ 141 M.P.H. without modifications/reductions for structure importance, gust or other factors as determined by the design engineer.
                  Last edited by J.P.M.; 05-26-2021, 11:51 PM.

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                  • #10
                    Originally posted by J.P.M. View Post

                    You can be as skeptical as you wish amd I might tend to agree with uou in a lot of designes, but [

                    Because a panel's orientation is not known a priori at the design stage, for any code compliant wind design I ever performed or was ever associated with, if not stated otherwise, worst design conditions (including gust and bluff conditions) were assumed. Since a wind vector that's normal to a panel will probably exert the greatest normal wind loading, and there are more than a few ground mounts with vertical panel orientation, I'd expect (and come to think of it so probably would Bruce) that condition would be covered up to and including the stated allowable wind speed or design wind pressure rating unless otherwise stated on the data sheet.

                    There's also the issue of combination loads such as snow and wind, for both dead, and live.

                    Treating that as a separate subject for this conversation, commonly, for structures including buildings and appurtenances and other structures or attachments to structures, the max. load criteria for wind loadings is commonly stated as max. allowable wind velocity using the worst vector conditions that the design conditions stipulated for that structure. For some reason, panel data sheets seem to commonly state max. wind pressure in units of lbf/ft2 or kN/m^2 (= kiloPascals). That's also done in the rest of engineering but was less common when I was designing structures.

                    As an example, my Sunpower 327 data sheet shows a max. allowable wind loading of 50 lbf/t^2 front and back. That translates to a wind velocity of ~ 141 M.P.H. without modifications/reductions for structure importance, gust or other factors as determined by the design engineer.
                    Cool. Good to know that those puppies can stand up to a steady gale.

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                    • #11
                      I do not see any wiring, are they hooked up? The usual thought with fences is
                      that you can touch them, I would not consider that safe in a high voltage string
                      system. Strength wise they are mounted by the most extreme dimension, usual
                      mounts are closer around the center of mass.

                      The vertical mount would allow minimum snow pickup. In theory if faced E-W,
                      with same sensitivity on both sides, they could produce good power early and
                      late in the day, each REPLACING 2 panels I use to do that. BUT that leaves a
                      big drop out in output around solar noon. I got this curve for about 61 deg elevation.
                      Guess some south facing panels could fill that in.

                      PVm17Jn16.jpg

                      Then, what, about dispersed light under clouds? My multiple panels all work
                      together to boost energy collection, can a 2 sided panel accept dispersed light
                      from both sides under clouds? Bruce Roe

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                      • #12
                        I too considered installing a vertical rail with bifacial panels. The rationale is depicted Bruce's diagram above. With all south facing panels one gets a production profile that is tall and narrow, usually resulting in surplus solar energy that has to be stored or exported to the utility at a price far less than what they charge you to import it! The combination of a South facing roof array and a E-W facing vertical bifacial array will produce a much wider, shorter production profile, which is much more conducive to self consumption.
                        I did the same calculations for my home but ended up with estimated production that was slightly less than the S facing array. However the increase in self consumption and reduced need for battery storage would more than make up for the small reduction in production.
                        My county required an engineering report looking at ability to withstand windows. Only a few bafacial panels have equal production on both sides. I couldn't find a commercially produced solar rail but think I have seen one or two advertised since then. Ideally, the wires would run inside the lower rail. My intended location had low foot traffic potential.

                        Until battery prices fall substantially, maximizing self consumption is crucial.

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                        • #13
                          Not sure if I would want a lawn anywhere near one of those fences. Objects thrown by lawnmowers might be real problem.

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                          • #14
                            I haven't been able to find actual data on how productive the backside of a bifacial panel is. The data sheets say something like "up to" 25% more output - as it depends on reflected sunlight which can vary widely. How much will the backside of a bifacial panel produce if it was placed in full sun? I can't find that data anywhere, but my understanding is the backside is nowhere near as productive as the front side.
                            BSEE, R11, NABCEP, Chevy BoltEV, >3000kW installed

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