[RE-wrenches] Hurricanes Forces

Jason Szumlanski jason at floridasolardesigngroup.com
Sat Sep 16 07:15:27 PDT 2017


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> 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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