[RE-wrenches] Ideas and racking systems for "stowing" ground mount PV array during snowy winter?

Sun Mar 27 15:02:30 EDT 2022

Hi all, thanks for the thoughts.

I should have been more explicit about my concerns regarding heavy snow
loading on a low-tilt ground mount:

1. The overall rack loading.  This concern can be mitigated by adding more
posts, more beams, more rails, and/or larger versions of each.   Relatively
easy (but does add cost).
2. Module loading versus rating.  Depending on which module, which
orientation, and which testing method, most modules are rated for something
like 60 - 120 psf. For example, the modules I'm looking at have a maximum
downward load of 5400 Pa, or ~112 psf.  Ground snow loads in the area of
this project are well over 200 psf, and over 300 psf in certain pockets.
Adding a third rail helps some, but perhaps not enough.  Steeper tilt
angles definitely help, especially if there is room for the snow to shed.
3. The bottom aluminum frame section of the lowest modules.  I think we've
all seen that bottom module frame bent outward/downward, eventually to
failure, by snow loads (photo attached, from a roof-mounted system in the
same location as my current project).  I haven't tried it, and I'm curious
if anyone else on here has: perhaps this type of failure could be mitigated
or at least reduced by putting the modules in landscape (with rails running
up and down slope) AND adding a third (or fourth??) rail, so that the
bottom module frame has three (or four) module clamps supporting it?
Otherwise, again, steeper angles and snow shedding seem like the only way...

Thanks for sharing your ideas and experiences!
Blake

On Sun, Mar 27, 2022 at 11:03 AM George McClellan via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Good afternoon;
>
> Mounting modules on 3 rails will typically increase the load carrying
> capacity of the array by 30% (or more).  Most module manufacturers list
> this method in their installation manuals, or if not in the manual, they
> have a waiver written for that method.
>
> Be aware that when mounting modules in a heavy snow load region that
> highest static snow load will be concentrated on the lowest module rail in
> the array.  If you mount modules in landscape configuration the load will
> be concentrated on a long side rail and this can sometimes lead to loads
> above what that rail can carry.  The bottom rail may require extra support,
> or consider shifting to portrait mount.
>
> George McClellan | Technical Sales Manager | REC Solar US
> +1 805 704 3226 | www.recgroup.com
>
> On Mar 27, 2022, at 9:52 AM, Jeff Clearwater via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>  Hi Blake,
>
> I'm curious why the assumption that the snow will destroy the array - how
> about 3 rails instead of 2 under the modules?
>
> Blake Gleason via RE-wrenches <re-wrenches at lists.re-wrenches.org>
> March 26, 2022 at 8:39 AM
> Hi all,
>
> I think there's a lot of experience on this list with PV in snowy regions.
>
> I'm wondering if anyone has ideas and/or specific hardware/racking systems
> to allow for easy "stowing" (in vertical or near-vertical position) or
> "seasonal removal" of the ground mount PV modules for the winter (snow)
> season?  Or ideas for a completely different approach to solving the
> challenge I'm facing?
>
> I'm planning a new off-grid system in the Sierra (around 6000') for a
> small commercial community center facility.  The facility is accessible and
> in use only during the summer months.  So, I want to optimize production
> for the summer, and also avoid having the array destroyed by the heavy
> Sierra snow during the winter.
>
> To further paint the picture, here are some more details and constraints:
>
> - System size: 23kW (likely 48 Silfab 490 mods)
> - Must be ground mount (beautiful very tall trees completely surrounding
> all roof options)
> - Must be relatively low profile, visually.  Pole mount not an option
> - Ideally one clean rectangular array 4x12 mods (13' x 90') or two 4x6
> arrays (13' x 45')
> - Array tilt: 10-15 deg (summer use only, must be low-profile)
>
> There is a caretaker who has a seasonal crew, and could be trained to
> "stow" the array each season as long as that process is relatively
> straightforward.
>
> At one end of the spectrum, it could be as simple as disconnecting and
> un-installing all of the modules to store them in a stack underneath the
> nearby deck for the winter.  I'd like to think there might be a more
> "elegant" solution (and less labor intensive, and less wear and tear on the
> modules over the years).  I wondered if there's a clever way to "drop" the
> modules to a near-vertical orientation so they could remain in place during
> the winter (some kind of hinge at the top and release at the bottom).  I
> guess this might require individual rows of modules instead of one large
> array.
>
> (As a bonus, I'd like to keep about four mods (out of the 48) operational
> through the winter for battery maintenance and a few incidental loads.
> These could be vertically mounted on the south side of one of the
> buildings, above the typical snow drift level, for example.)
>
> Thanks in advance for any suggestions, ideas, things you've tried that
> haven't worked, etc!!
>
> Best,
> Blake
>
> --
>
> Blake Gleason, PE | Employee Owner
> Director of Innovation and Technical Excellence
> O: 510-845-2997 x128
> C: 510-867-5878
>
> 1035 Folger Ave.
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-- 

Blake Gleason, PE | Employee Owner
Director of Innovation and Technical Excellence
O: 510-845-2997 x128
C: 510-867-5878

1035 Folger Ave.
Berkeley, CA 94710
www.sunlightandpower.com
License #326203

<https://bcorporation.net/>     <https://www.amicussolar.com/>
<https://calssa.org/>
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