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 <[email protected]
<mailto:[email protected]>> 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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