[RE-wrenches] Module Load Rating
Dave Click
daveclick at fsec.ucf.edu
Mon Oct 10 05:47:48 PDT 2011
Hi Jamie-
Yes, it would certainly make sense for manufacturers to put forward the
wind pressures in a consistent manner. Maybe the next SolarPro module
roundup could include some of this info if someone has 100 hours to
spend contacting someone knowledgeable at each module manufacturer...
I agree that if Schott specs a UL test for 50 psf (ie a test of 75psf)
they should call it that. Claiming 75psf under UL 1703 should therefore
include testing at 112.5psf.
On 2011/10/7 10:26, Jamie Johnson wrote:
> Dave, thanks for the clarification on the difference between NRTL and
> IEC tests.
> Wouldn't it make sense for the manufacturers to put the negative and
> positive test and certified (warranted) pressures on the data sheets or
> in the installation manual so there is no confusion for the installation
> community?
> In other words, they could state if they used a safety factor in the
> test for determining maximum module loads both uplift and downforce.
> Also please clarify. If Schott specifies a UL test for a 50psf working
> load and with the 1.5x safety factor the module is tested to 75psf, then
> in my mind that module is only rated for 50psf for installation
> purposes, the safety factor is not counted.
> If Schott wants to state a working load of 75psf then their modules
> should be UL tested to 112.5psf? Or am I missing something here?
> **
> *Jamie Johnson
> NABCEP Certified PV Technical Sales Professional
> NABCEP Certified Solar PV Installer
>
> General Manager*
> *SOLAR POWER ELECTRIC*
> **
> **
>
> -------- Original Message --------
> Subject: Re: [RE-wrenches] Module Load Rating
> From: Dave Click <daveclick at fsec.ucf.edu
> <mailto:daveclick at fsec.ucf.edu>>
> Date: Fri, October 07, 2011 9:31 am
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org
> <mailto:re-wrenches at lists.re-wrenches.org>>
>
> UL 1703 is a 30 psf positive (downward) or negative (upward) load, or a
> design load designated by the manufacturer. I've never seen a module
> advertising a 30psf loading requirement--everything I've seen is at
> least 50psf--which I take to mean that this "designated" design load is
> usually spec'd by manufacturers to be 50 psf. 30 psf is pretty weak.
>
> The UL tests themselves then actually go to 1.5 times that design load
> as a safety factor. The load tests last 30 minutes. As I understand it
> (based off a coworker's conversation with a Schott rep), this is why
> Schott advertises that their modules withstand 75psf front and back.
> The
> rep questioned why all manufacturers weren't advertising 75psf.
>
> IEC 61215 also tests both upwards and downwards loading. Since it's
> written by some French people, they specify a 2400 Pascal load,
> which is
> 50.1 psf, for both the front and back of the module. They do this in
> three cycles of tests (50psf front, 50 psf back being one cycle).
> However, "if the module is to be qualified to withstand heavy
> accumulations of snow and ice," then during the third cycle they go to
> 5400 Pa for the FRONT loading. 5400 Pa is 112.8 psf. Each load test
> lasts 1 hour. If a module manufacturer claims 113psf uplift resistance
> then either they misunderstand the IEC standard or they make the
> Hulk of
> PV (without the smash). Note that the IEC standard does not have the
> 1.5
> safety factor.
>
> Some test labs offer a package deal where they test modules to UL and
> IEC requirements at the same time to qualify a module for worldwide
> sale-- so they go through each test and pick the harder requirements
> (between UL and IEC) so that passing each test means the module is
> certified to meet both standards. IEC's 50 psf loading may have caused
> some manufacturers to designate the 50 psf load for UL. Or, module
> manufacturers just do the 50psf IEC load which corresponds to a
> "designated" 33.3 psf load for UL times that 1.5 factor.
>
>
>
> On 2011/10/6 17:03, Jamie Johnson wrote:
> > Rich, It is my understanding that modules are tested to 113psf
> downforce
> > or snow load and 52psf uplift for their NRTL listing (uplift is also a
> > load rating denoted as negative pressure) (don't have a copy of the
> > testing procedures in front of me however I have confirmed this with
> > more than one module manufacturer in the past).
> > It seems to make sense as many framed single glass modules appear to
> > have a wider lip under the glass and a narrow lip above the glass,
> there
> > may also be other reasons.
> > There are a few manufacturers out there that have had additional
> testing
> > done and will certify their modules to 75psf or 113psf uplift, usually
> > they have 2 layers of glass and/or a thicker AL frame and are also
> > heavier like the Schott 300 watt module.
> > Since all of our installs are in a High Velocity Windzone Area,
> when we
> > have a module manufacturer with single glass normal AL frame modules
> > that claim 113psf loads (uplift) we will always challenge them on
> it and
> > see if they will actually stand by that claim, in every single case
> > after researching it, they have backed away from the claim and
> > acknowledged that their modules will only withstand 52 or 53psf
> uplift.
> > It is important to understand that the load rating listed on the
> > marketing material (downforce or snow load) is usually not the same as
> > the uplift or negative pressure rating.
> > In our area of FL for a 130MPH windzone, our uplift or negative
> > pressures on a module can range from -32 to -49PSF although our
> > downforce is usually lower around +16. In a 140MPH windzone you can
> > easily exceed a normal module uplift rating of -52PSF, and although
> > adding a 3rd rail may reduce frame stress, it will do little to
> keep the
> > glass from blowing out in a hurricane.
> > As to the honesty question, IMHO the guilty parties are most
> likely the
> > marketing dept staff who lack technical expertise.
> > Hope this helps.
> >
> > *Jamie Johnson
> > NABCEP Certified PV Technical Sales Professional
> > NABCEP Certified Solar PV Installer
> >
> > General Manager*
> > *SOLAR POWER ELECTRIC*
> > **
> > **
> >
> > -------- Original Message --------
> > Subject: [RE-wrenches] Module Load Rating
> > From: "Rich Nicol" <rich at solartechvt.com
> <mailto:rich at solartechvt.com> ><mailto:rich at solartechvt.com>>
> > Date: Thu, October 06, 2011 1:41 pm
> > To: <gary at icarussolarservices.com
> <mailto:gary at icarussolarservices.com>
> > <mailto:gary at icarussolarservices.com>>, "'RE-wrenches'"
> > <re-wrenches at lists.re-wrenches.org
> <mailto:re-wrenches at lists.re-wrenches.org>
> > <mailto:re-wrenches at lists.re-wrenches.org>>
> >
> > Hi Wrenches –
> > I’ve noticed discrepancies in load rating methods for various
> > modules and wondered if there was any insight from the installer
> > community. REC claims 113 PSF, Sharp claims only 50PSF. Solarworld
> > notes 50PSF load rating, but 113 PSF snow load rating. I’m assuming
> > the difference is that snow load rating is greater because its
> > assumed to be widely distributed, but yet its still per square foot
> > so perhaps not. Is a Sharp module such as the 240NUQ-240F2 as
> > durable as REC, Evergreen, Solarworld etc and they are just more
> > honest in their portrayal of load rating.
> > Thanks for your help,
> > Rich
> > **
> >
> >
> >
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