Announcement

Collapse
No announcement yet.

Need help calculating the wind and snow loading of my array

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    Originally posted by RShackleford View Post
    Came across this thread in search, and maybe asking here is better than starting a new thread ...

    I am not doing a tracking system, just a simple ground mount, clamping panels to a pressure-treated frame with SS hardware. My panels (Talesun TP660P) can apparently be clamped on the long sides or the short sides, with allowable loading of 5400Pa and 2400Pa, respectively. Any simple way (without hiring an M.E.) of figuring out if I can get away with assuming 2400Pa loading ?

    I can use the ground-mount design tool that IronRidge provides; even though I'm not using their hardware, I imagine their loading calculations would depend only on the size, height, and tilt of the array. For a design, they quote shear, moment, and uplift in pounds; perhaps I can simply divide the uplift by the array's area, and then convert to Pascals ? However, I come up with something 200Pa, so that's probably not right.
    RS: FWIW, have you used at least an online unit converter to better understand what 2400 Pa represents? It equals 0.348 PSI or about 50 PSF. I grew up with Imperial units, so I like PSI and PSF; they mean something to me that Pascals just don't. Anyway, typical residential first-floor live loads are specified at 40 PSF. Snow loading can range from 20 to 50 PSF or more, depending on where you are. Wind loading can be in a similar range, again depending on your location, terrain, surrounding buildings or hills, etc. You need to find out what values for these loads apply in your neighborhood, which you should be able to get from your local Building Safety department (or AHJ).

    Listen to JPM, who is offering sound advice. Either 1) you need a building permit and that comes with a list of requirements, which may include engineering; or 2) you don't need a permit, but still should want to ensure your system is soundly designed and constructed. In either case your system design needs to be, at minimum, reviewed by a PE with experience in that sort of structure.

    If you just want to get an initial "wet finger in the wind" estimate of how beefy your wooden structure would need to be, you could multiply 50 PSF by the total area of the panels in square feet. A typical panel is around 18 SF, so figure around 900 lbs total load from each panel. If you figure uplift, down force, and horizontal drag force could all be that high, that should be very conservative (unless you're in hurricane alley or Buffalo, NY). Then depending on how many panels are supported per "A-frame" (and assuming your design looks something like a series of triangular frames, each consisting of two posts and a "rafter" across the top), you can design the A-frame to support the total load for that group of panels. Again being VERY general, the structure should end up being somewhat beefier (maybe 2X) than what you'd need to support a backyard deck of the same total area.

    All I'm giving you here are some ideas for how to think about the problem, using back-of-the-envelope calculations. If it seems like your approach holds water, then the next step is to enlist a qualified engineer to draw up a design. Nobody can give you any detailed help based on a textual description of your intended approach.

    Comment


    • #32
      Yeah, I figured that 2400Pa is about 50psf. But I think the panel mfg'r is just sayin the panels can handle that; doesn't necessarily seem like I should assume they ARE going to see that, as far as the rest of the structure.

      Snow loading here is 20psf. Wind is 115mph I think, which is comical, as it's pretty wooded and we had a marginal hurricane in 1996 and there wasn't enough wind at ground level to blow the lawn furniture around.

      I don't follow you on the triangular A-frames. Are you talking about a system that faces east and west, not south ?

      P.S. I need to figure out what that 3" pipe and those 6ft pilings are gonna cost; the IronRidge system is starting to look more and more attractive.

      Comment


      • #33
        In my experience calculating this type stuff, if panels are horizontal there is going to me no wind load on the panel surface (but full snow load), if the panels are vertical you would use the wind speed charts in the building code book and multiply out the forces with the surface area to get the force on the panel surface. If the panels are at a 45 degree angle then the answer you get from the vertical setup and multiple that by .707 This is because sin 90 =1 and sin 0 =0 and sin 45 = .707 (I do this in cad normally but math works also)

        This can also be done inversely for the snow load if you are in a snow area.

        This is how I have shown it on my drawings to the inspector. The first time I had to have a PE double check me and the PE came up with a different answer. In the end the PE was wrong and the inspectors have left me alone after that. We are not always right so it is nice to be able to be double checked in these types forums.

        Snow loads are huge and I see a lot of arrays in snow area that just aren't strong enough to meet code but people naturally keep the snow off the structures so it works and doesn't fail.

        Comment


        • #34
          Take this FWIW: For anyone interested, google " Calculating external loads on solar panels" for more sources of information as to what is involved in designing for external loads on structures such as solar arrays.

          At the end of the day, if a design is done per ASCE 7 - 16, "Minimum Design Loads and Associated Criteria for Buildings and Other Structures", my bet is if the calcs are done correctly they'll be acceptable to most building authorities and AHJ's in the U.S.

          I've done a fair amount of structural design of plant equipment and structures and that's the bible for that portion of the engineering for most types of equipment, commercial industrial or residential, at least in the U.S. and a significant portion of the rest of the developed world.

          Go to what's recognized as the authoritative source if you want to do it right.
          Last edited by J.P.M.; 11-21-2019, 02:05 PM.

          Comment

          Working...
          X