Dana, Excellent question.
More than 20 years of PV degradation research conducted by NREL and others has shown the dominant loss to be in the Isc and fill-factor aspects of PV performance due to increasing effective series resistance. Voc stays essentially stable over the life of the PV module. Vmp will decrease over time depending on the severity of the impact on fill factor. With 0.5% average annual degradation in PV wattage, and attributing [say] 80% of the wattage reduction to a decrease in current, the balance of the difference would be a reduction in Vmp. A copy of one such study is here. www.nrel.gov Document: Photovoltaic Degradation Rates - An Analytical Review By: Dirk C. Jordan and Sarah R. Kurtz Journal Article NREL/JA-5200-51664, June 2012 Contract No. DE-AC36-08GO28308 Dan Lepinski -------------------------------------------- On Tue, 6/3/14, Dana Brandt <[email protected]> wrote: Subject: [RE-wrenches] Module Degradation - voltage or current? To: "RE-wrenches" <[email protected]> Date: Tuesday, June 3, 2014, 5:41 PM 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 [email protected] 360.318.7646 _______________________________________________ List sponsored by Redwood Alliance List Address: [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 Check out or update participant bios: www.members.re-wrenches.org
