Folks,
Voc does not degrade as much as Isc, but neither is key. Both Vmp and Imp degrade. We call this a degradation of Fill Factor. This happens with all PV systems and the degradation rates for current and voltage are very similar. Imp and Isc degrade because less light gets to the cell from etching glass, yellowing encapsulant and IR coating on cells changing. Vmp changes because of increased contact resistance of conductors on the cells and other contact points. Voc is unimpacted by contact resistance since there is no current flow. Bill. From: RE-wrenches [mailto:[email protected]] On Behalf Of Ray Walters Sent: Wednesday, June 04, 2014 11:30 AM To: RE-wrenches Subject: Re: [RE-wrenches] Module Degradation - voltage or current? I agree that Voc doesn't seem to degrade as much. I've had a chance to measure several modules over 20 years old, and the Voc is only dropping about 1/2 the rate suggested by others here. I think a more appropriate number might be 0.25% V drop/ year. R.Ray Walters CTO, Solarray, Inc Nabcep Certified PV Installer, Licensed Master Electrician Solar Design Engineer 303 505-8760 On 6/4/2014 11:36 AM, Nathan Charles wrote: So I read this paper, Smith, R. M., Jordan, D. C., & Kurtz, S. R. (2012). Outdoor PV Module Degradation of Current-Voltage Parameters, which seems to seems to suggest that Voc doesn't degrade like Isc degrades. Based on that and other data I've seen it seems like panels that degrade at 0.5%/year are outliers on the low side. Thoughts from other wrenches? On Tue, Jun 3, 2014 at 11:59 PM, Bill Hoffer <[email protected] <mailto:[email protected]> > wrote: Dana Bill Brooks, passed on past data, ( correct me Bill if I am out of date here) recommends 1% Power loss per year with approximately 0.5% current and 0.5%voltage. That is also what Solar Energy International Best Practices curriculum recommends. Based on some newer data from larger projects requiring testing to actually determine those values for the Bankability requirements ( PVsyst PAN files), I believe we are seeing lower numbers than that now. In general, quality of modules are higher than the older modules. We of course are usually not privy to those results and may not even be getting the same level of binning for small residential projects as the MW projects do. 0.5% V loss per year seems like a like a good conservative number to me, especially if you add a little buffer (1-2%) in there. Bill On Tue, Jun 3, 2014 at 3:41 PM, Dana Brandt <[email protected] <mailto:[email protected]> > wrote: Hi Wrenches, Does anyone know what percentage of module degradation over time is voltage and what is current? I'm wanting to make sure we give ourselves plenty of breathing room on the minimum Vmp of the inverters over the long term so need to try to anticipate how much voltage we'll lose on the array over 30 years. Thanks, Dana Dana Brandt Ecotech Energy Systems, LLC www.ecotechenergy.com <http://www.ecotechenergy.com> [email protected] <mailto:[email protected]> 360.318.7646 <tel:360.318.7646> _______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] <mailto:[email protected]> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org <http://www.members.re-wrenches.org> -- William Hoffer 161 SE Fourth Ave P.O. Box 1823 White Salmon, WA 98672-1823 [email protected] <mailto:[email protected]> _______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] <mailto:[email protected]> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org <http://www.members.re-wrenches.org> -- Nathan Charles Engineer NABCEP Certified PV Installation Professional #042013-20 Paradise Energy Solutions (717) 283-2021 direct _______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] <mailto:[email protected]> Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm <http://www.re-wrenches.org/etiquette.htm> Check out or update participant bios: www.members.re-wrenches.org <http://www.members.re-wrenches.org> --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com
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