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.parr...@calsolareng.com Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 _____ From: re-wrenches-boun...@lists.re-wrenches.org [mailto:re-wrenches-boun...@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:nickv...@ymail.com> To: wrenches <mailto:re-wrenches@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. _____ _______________________________________________ List sponsored by Home Power magazine List Address: RE-wrenches@lists.re-wrenches.org Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
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