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<TITLE>Module Voltage Question for Off-Grid Designers</TITLE>
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<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>
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