[RE-wrenches] Hurricanes Forces

Jason Szumlanski jason at floridasolardesigngroup.com
Sun Sep 17 12:39:37 PDT 2017


I can't rule out loose hardware, but most of the modules that were plucked
show evidence of significant bulging from wind uplift. We use impacts, but
go back over them after installation is complete because things can shift
around and loosen hardware.

Small tornadoes, high gusts, and even Venturi effects between adjacent
buildings are plausible explanations for some losses I've seen. I went to a
home with a damaged solar pool heater. It wasn't bad - one panel was torn
up, but their pool cage and the pool cage on two adjacent homes were a
total twisted mess. Damage is very localized - much like you see with
tornados that seemingly pick winners and losers. It's not just the speed of
the wind, but the direction.

There is a beer distributor in town that recently had a 1.1MW rooftop array
installed by a competitor from out of town. My understanding is that it's a
total loss. Worse yet, the panels punctured the roof in so many places that
the facility has to shut down completely. This appears to be the biggest
solar disaster from the storm, but I have not looked into the 2MW solar
field at the local university or any utility owned fields. Early reports
still seem to indicate relatively few issues in percentage terms.

Jason




On Sat, Sep 16, 2017 at 9:12 PM, Ray <ray at solarray.com> wrote:

> 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> 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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