[RE-wrenches] Hurricanes Forces

Sat Sep 16 18:12:15 PDT 2017

Is it possible there may have been loose mounting hardware here and 
there?  I've found quite a few loose clamps over the years on many 
different systems from myself and reputable dealers.  I've found that 
using a impact driver really causes trouble; I now hand tighten 
everything.  Many of the threaded aluminum type blocks can seize up when 
tightened at speed with a driver, and no lube.  They seem tight, could 
pass a torque wrench test, but actually are seized up.

We've recently had a pole mount that ripped modules right off their 
still tight mounting bolts, which I could only explain by a mini 
tornado.  This could be the explanation in your random failures too.  
Another possibility are a vortex  or turbulence created by the nearby 
trees or the structure itself in very high winds.  We like to model wind 
loading as a simple vector force, when we all know the reality is 
extremely dynamic.

Ray Walters

Remote Solar

On 9/16/17 8:15 AM, Jason Szumlanski wrote:
> I generally agree on all points. I'd love to use three rails on all 
> systems, but there is an economic factor, and as Tom mentions, a third 
> rail doesn't necessarily stop glass being sucked out or a tree landing 
> on the array. At what point do we cease over-engineering the mounting 
> structure and the module itself? I can see hardening backup systems 
> and critical infrastructure (utility scale solar included), but 
> residential grid-tie systems should be built with an acceptable loss 
> criteria. I know I might take some heat for that statement, but given 
> the anecdotal evidence of the small percentage of issues relative to 
> the installed base we have, I think it's the right answer.
>
> Also, one thing we are seeing (small sample size) is modules being 
> plucked from random parts of the array, not necessarily on the lower 
> or side edges. Very odd.
>
> Jason
>
>
>
> On Fri, Sep 15, 2017 at 3:52 PM, Tom Lane <tom at ecs-solar.com 
> <mailto:tom at ecs-solar.com>> wrote:
>
>     Hurricanes wind create both suction up lift and direct pressure
>     against the glass frame wall of the module -- if a module is to be
>     held securely it must be attached 1/3 or 1/4 of the way from top
>     to bottom by each of the two rails . If modules are facing due
>     South and the wind force comes from the east or west the force
>     will start pealing off one module at at time . For example if the
>     winds shearing force is from the west the first module on that end
>     should have an extra rail in the middle with two extra clamps
>     BECAUSE when that first one goes it will start peeling off each
>     one one at a time until that wind band passes . It is critical on
>     raise systems on flat roofs that the two end modules use the
>     struts with two ( 11/2 sets of mounting hardware per module) and
>     the first three or at least first two modules be X braced with
>     aluminum L bars bolted with 3/8 bolts across the back struts in
>     front of and back of the struts with the L bars to prevent peeling
>     down the row or bank of modules the same as modules mounted flat
>     on a roof . Enough suction force from high wind speeds can suck
>     the glass right out of the frame wall - using three rails per
>     module , two each 1/4 of the way from the top and bottom and one
>     directly in the middle can help . I also suggest using only 60
>     cell modules in wind zones over 150 MPH with two rails minimum
>     maybe even three on high rises .The frame walls on 72 cell modules
>     is trying to hold too much glass in place for just two rails .  On
>     ground mounts that are adjustable lower the array to 15% or less
>     and on smaller home owner ground arrays attach motorcycle tie down
>     straps on the end corners and middle hooked to extra D rings
>     attached to the array ( especially to the corners of Top of Pole
>     Racks ) to mobile home screw in ground anchors AND if possible
>     strap plywood over the glass front . GatorTom PS : having
>     insurance is a good investment when a monster 100' Live Oak tree
>     topples forward onto your array . Or a car or boat gets blown onto
>     your roof .
>
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