Re: [RE-wrenches] Mixing miss matched modules

[Allan Sindelar]

Dana, Three issues that I see: 1. Unless the MSX66s (I have never heard of MSX-66s, but Solarex made MSX64s - could that be what they are?) have degraded substantially (which is quite possible given their age and the intensity of SW Colorado sun) I'd be careful about low-temp VOC exceeding 150V, the charge control limit. Down here, we're pretty safe, but strict interpretation of the correction factors in the NEC won't allow some modules, and the MSX-64s were premium VOC modules. 2. I would verify MPP output on the Solarexes. In the early 90s they made a bad batch, which had proper Voc and Isc but a straight line for an I/V curve. Dismal real-world performance but hard to test. I had twelve of these that I bought used; later learned about this from Ezra Auerbach, now ExecDir of NABCEP. Solarex never acknowledged the problem publicly, but they replaced my modules at the end of their 10-year warranty. You might want to verify output before reusing them. 3. It isn't likely to work anyway. The MSX-64s will be wired 72 V nom, and will put out (12 X 64 =) 760W. Most modern 230W modules are 60 cell, or 20 V nom, not 24 V nom as you state. So you're trying to match 460W at 40V with 760W at 72 V. The Solarexes will define the MPPT voltage of the controller, pulling the other two modules way above Vmp on the I/V curve, past Voc where current is zero. My guess is that the two would produce close to nothing. If she wins the "can we try it", please promise you'll share the results here. I'd like to learn from your experiment. I went through a similar experiment recently with wanting to combine 10 Astropowers and 12 MSX-77s on a single set of input conductors. Finally determined that 10 of each match Vmp very closely and ditched two MSX-77s to make it work; all rewired to 60V nom. Never tried the mismatched voltage strings; just figured not worth trying on the customer's nickel. Sounds to me like the ex-husband and the ex-wife may have been pretty well suited to each other... Allan Allan Sindelar Allan@positiveenergysolar.com NABCEP Certified Photovoltaic Installer EE98J Journeyman Electrician Positive Energy, Inc. 3201 Calle Marie Santa Fe, New Mexico 87507 505 424-1112 www.positiveenergysolar.com On 7/14/2010 4:34 PM, Dana wrote: Hey all,   I have an off grid client that we are moving the existing sway-backed fixed mount PV array to a new location (the sun gets blocked Nov, Dec And Jan after 1:30PM; the ex-husbands bright idea).   We will be  mounting the existing [12] MSX66 PV on a Wattsun tracker at [2] strings 6 modules @ 126VOC. I still have room for [2] 230watt PV modules that could be mounted in the middle in portrait. There is room on the MX60 charge controller for the additional wattage.  This wattage total would meet her energy analysis currently.   Obviously the additional [2] 230 watt PV modules in series will be at a different voltage, IV curve, & overall characteristic from the  [12] MSX 66 modules [2 strings of 6 in series.]   The client is not thrilled about having to run an additional wire feed [150’] and have an additional and separate charge controller for the additional 460 watts and 24 DC – 19 amps x 1.56 = 30 amps.   I told her that it would affect the whole output and that she might only get 325watts to maybe an additional 400 watt if she was lucky and it might be worse than the 325watts.   I am open to any experiences or points to make to help change the course of this not good idea & experiment that you might like to share to help me change her mind from “can we try it to, OK let’s not do it”, without the usual “trust me I am a wrench and this is a bad idea, and I know best.” Even if I do……..       Thanks,  Dana Orzel   Great Solar Works, Inc E - d...@solarwork.com V - 970.626.5253 F - 970.626.4140 C - 970.209.4076 web - www.solarwork.com Responsible Technologies for Responsible People since 1988"   _______________________________________________ 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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