[RE-wrenches] REC Solar melt-down

[Peter Parrish]

Let's make sure we are making a distinction between "differential
coefficient of expansion" and "(heat induced) warping". All material (Al
alloy and low-Fe glass among them) undergo a change of dimension as a
function of temperature. Pure aluminum and many of its alloys have a
differential coefficient of expansion of 2.30e-5 per degree centigrade
difference from 0 degrees centigrade. Low iron tempered glass has a lower
coefficient of 0.84e-5. As a result, both aluminum and glass expand when
heated but glass does so more slowly. Over a 45 degree centigrade
temperature increase (from 25 deg C) there will be a 0.65e-3 change, or less
than 1/10th of 1 per cent. Usually this does not create a problem unless the
aluminum and glass are pinned together in some fashion and the length of the
bond is long enough to produce unmanageable changes in dimension. For
example a 150 cm length (long dimension of a PV module) would produce a
relative dimension change of 0.1 cm (40 mils). This is manageable I
understand given the elastomeric sealant that PV module manufacturers' use
when applying the frame to the glass/Si/Tedlar sandwich.  

 

What I suspect is the problem is warping, caused by heating of the aluminum
frame. Work hardened metals (including extruded metal) often have built in
stresses due to the forming process. This stress can be relieved by long
term high temperatures, resulting in the metal piece deforming. I have seen
warping as much as 5% in long extruded parts. If in fact what is happening
is warping, then I suspect that warping cannot be overcome with something
like an elastomeric sealant. 

 

I honestly don't know if manufacturers of extruded metal parts put their
parts through an annealing cycle to remove stresses or not.

 

- Peter

 

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885


 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Joel
Davidson
Sent: Tuesday, June 30, 2009 9:06 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] REC Solar melt-down

 

What frame material has that high a coefficient of expansion?

----- Original Message ----- 

From: Nick Vida <mailto:nickvida at ymail.com>  

To: wrenches <mailto:re-wrenches at lists.re-wrenches.org>  

Sent: Tuesday, June 30, 2009 8:45 PM

Subject: [RE-wrenches] REC Solar melt-down

 

wrenches,


the defect in REC panels is the frame expands past the panel and can
contract and break the glass. Unfortunate, but no big deal in a lot of ways.
I dont know if there is another defect, but that one would warrant a recall
instead of replacing a lot of panels. There was also an article about their
Oregon plant breaking a couple hours after it went online. Im glad to see
they have done a recal. I think it is proper and good business. I think
thier silicon and wafers are fine and well made, and we would hopefully find
out if they werent because they are a major supplier of wafers to several
manufactures. 

 


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