Lee
I worked on a job on Washington pass in Washington state about 12 years ago, near the border of Canada in the North Cascades wilderness area. Design snow load was specified 200 #/sq ft as I recall (far greater than the forces on a module at 120 mph wind load) and the Cascades are known for wet heavy snow storms. Mt Baker Ski area (very close as the crow flys to the pass) had the record recorded snow fall of over 1,140 inches total for the 1998-99 snowfall season. The storm that took out the array was over 200" in one storm, they had to shut down to dig the lifts out, riding the lifts afterwards the snow was over the towers and well above the chair lifts! It was a low pitch metal roof (in snow country a big no no). I ran main beams North and south and then connected Solarex rails going East to West. The rails were 4 inches above the roof, leaving the modules approximately 7" above the roof. The melt freeze melt freeze process you mentioned built up under the modules until it frost upheaved and broke every module shattering the glass from behind. The mounting system actually held the frames down! It was a 3Kw system that had to be replaced (some how covered by warranty???). Now every winter they take the array down until the spring (was not being used during the winter anyways). So I have experienced one rare time the situation you are asking about, but it was a severe weather situation and an uncommonly low sloped roof for the environment. I have never heard of it ever happening to anyone else, but if I had to design for this location again I would do it very differently! A rare occurrence, probably outside of the 100 year storm statistic, but it did happen and it was my first job as a solar engineer! That's my story and I am sticking to it! Bill On Aug 5, 2010 12:47 PM, "Lee Bristol" <leebris...@standardsolar.com> wrote: Wrenches, Has anybody come across an analysis of the potential damage to a flat roof from snow on solar modules melting to form an ice layer on the roof and then forming subsequent layers as more snow melts or slides down the modules? If the sheet gets thick enough then the next bit of water could form ice layer under edge of panel and lift it up. Seems very unlikely to me but the prospect has questions....and prospect questions must be answered. Thanks! Lee -- Lee Bristol NABCEP Certified Solar Designer/Installer Chief Technology Officer Standard Solar, Inc. 1355 Piccard Drive Rockville, MD 20850 (301) 944-5105 (240) 479-1510 (c) www.standardsolar.com _______________________________________________ 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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