<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Hello Allan,<div><br></div><div>We run into the same problem when adding PV's to older off grid systems. I am pretty excited about the 200 watt Evergreen ES-A. WIth a Voc of 22.5 and Vmp of 18.1, it seems like the closest to an "off grid" 12 volt module out there.</div><div><br></div><div>Best</div><div>Jason Lerner</div><div>Waldron Power and LIght Co.</div><div><br></div><div><div><div>On Dec 10, 2008, at 12:16 PM, Allan Sindelar wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"> <div> <!-- Converted from text/rtf format --><p><font face="Times New Roman">Wrenches,</font> <br><font face="Times New Roman">Here's an issue I haven't seen directly addressed, and I would like to know what the rest of you are doing.</font> <br><font face="Times New Roman">It's getting harder to get 24V nominal modules. Because the bulk of industry growth is high-voltage grid-tied applications, modules no longer have to be a standard voltage. Just pick the number of modules to best fit the chosen inverter's string voltage range.</font></p><p><font face="Times New Roman">But for off-grid, the odd cell counts and resulting "nontraditional" DC input voltages challenge the traditional rules of off-grid design. I may be fighting a losing battle here, as the industry changes so rapidly and fundamentally. I have been trying to stay with 72-cell modules for offgrid, as this most readily combines with existing systems with 36-cell modules (12V) and 72-cell modules (24V). </font></p><p><font face="Times New Roman">For example, I will use the new Canadian Solar 170-200W modules. They are 60-cell modules, with a Vmppt of around 28 volts - too low to charge 24V batteries with a standard charge controller. We can use them in any new systems with an MX60 or similar voltage-converting MPPT controller. Two or three in series would charge a 24V battery; 3 in series would charge 48V. Four in series would violate Code, as low-temp voltage would easily exceed 150V. </font></p><p><font face="Times New Roman">Unless 60-cell modules remain a standard in the future, any future array additions would have to be on their own charge controller, in order to match a different I-V curve and MPP voltages into the same battery bank. Is this prohibitive? No, it just runs counter to the longstanding standards of off-grid design that allow modules to be added in the future: these modules will not add well to existing systems, and will not easily allow additional dissimilar modules to be added later. </font></p><p><font face="Times New Roman">I had this same objection to using Day4 modules, although they were better at 16Vnom. Three made up a standard 48V array, so strings could be combined with two-module strings of similar 24Vnom modules.</font></p><p><font face="Times New Roman">Who else is trying to stay with 24V modules? Anyone still using 12V modules in off-grid (residential-scale, not little apps) designs? Who has a crystal ball and knows what modules will be like in 20 years, or even two years? Wat are the rest of you doing?</font></p><p><font face="Times New Roman">Thanks, as usual.</font> <br><font face="Times New Roman">Allan</font> <br><font face="g">Allan Sindelar</font> <br><a href="mailto:allan@positiveenergysolar.com"><u></u><u><font color="#0000FF" size="2" face="g">allan_(at)_positiveenergysolar.com</font></u></a> <br><font size="2" face="g">NABCEP certified solar PV installer</font> <br><font size="2" face="g">Positive Energy, Inc.</font> <br><font size="2" face="g">3225A Richards Lane</font> <br><font size="2" face="g">Santa Fe NM 87507</font> <br><font size="2" face="g">505 424-1112</font> </p> </div> _______________________________________________<br>List sponsored by Home Power magazine<br><br>List Address: <a href="mailto:RE-wrenches@lists.re-wrenches.org">RE-wrenches@lists.re-wrenches.org</a><br><br>Options & settings:<br><a href="http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org">http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org</a><br><br>List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org<br><br>List rules & etiquette:<br>www.re-wrenches.org/etiquette.htm<br><br>Check out participant bios:<br>www.members.re-wrenches.org<br><br></blockquote></div><br></div></body></html>