[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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