I think I understand all the dictums about single-strings of PV modules: all the same modules, all the same azimuth and tilt, but I have a "special situation".
We are starting to accumulate a number of "second hand" PV modules. Some have frames slightly damaged by the shipper; some have come from warranty replacements; and some are odd lots that we haven't been able to sell. What I want to do is to set up a demo system composed of two different types of modules. This is my initial design: Total of fourteen modules. Two strings of seven modules each. Each string consisting of four modules of one type (type A) and three modules of a second type (type B). Both module types have 50 cells and the type A module has 155mm-sq cells and the type B module has 150mm-sq cells. So you would think that the performance specs would match pretty well. However, since the type B modules are an earlier vintage, they probably don't have the latest and greatest surface treatment, etc., so the current specs are lower than one might expect. Specs on type A: Voc = 30.8V, Vmp = 24.5V, Isc = 8.70A, Imp = 8.16A. Specs on type B: Voc = 30.6V, Vmp = 24.6V, Isc = 7.38A, Imp = 6.93A. So here's my question: would putting together the strings of four type A and three type B cause any problems? I know the string current would be limited by the type B modules, but above and beyond that, what would be the operating point of the type A modules and what would be the stress if any on the type B modules? I'd like this demo system to last a while and I certainly don't want to see scorch marks on the type B modules after a few months of use. Any thoughts? - Peter Peter T. Parrish, President California Solar Engineering, Inc. 820 Cynthia Ave., Los Angeles, CA 90065 Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 CA Lic. 854779, NABCEP Cert. 031806-26 peter.parr...@calsolareng.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
