Re: [RE-wrenches] Module Load Rating

[Jamie Johnson]

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" <r...@solartechvt.com>
Date: Thu, October 06, 2011 1:41 pm
To: <g...@icarussolarservices.com>, "'RE-wrenches'"
<re-wrenches@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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