<div>The MPPT controllers have revolutionized how we can do off grid systems. Wider panel choices and greatly reduced wire cost. Have you ever run or remember running 600 watts (or more) of 12 volt panels 150' or so? It was going to take 4 huge wires to counter the voltage drop or move the building closer to the clearing!</div>
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<div>Having to ability to drop a higher panel voltage to battery voltage is a godsend.</div>
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<div>Thanks for the MPPT controllers,</div>
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<div>Bob Ellison</div>
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<div class="gmail_quote">On Thu, Dec 11, 2008 at 7:55 AM, Wind-sun.com <span dir="ltr"><<a href="mailto:windsun@wind-sun.com">windsun@wind-sun.com</a>></span> wrote:<br>
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<div><font face="Calibri" size="2">For larger off grid systems - pretty much anything over 600 watts - we have been recommending only MPPT type controllers, such as the Outback & Xantrex. Since they can match almost any panel size to any battery size, it has reduced our dependence on the often hard to get 12 volt panels.</font></div>
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<div>..................................................................................................<br>Northern Arizona Wind & Sun - Electricity From The Sun<br>Solar Discussion Forum: <a href="http://www.wind-sun.com/ForumVB/" target="_blank">http://www.wind-sun.com/ForumVB/</a><br>
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<div style="FONT: 10pt arial">----- Original Message ----- </div>
<div style="BACKGROUND: #e4e4e4; FONT: 10pt arial"><b>From:</b> <a title="allan@positiveenergysolar.com" href="mailto:allan@positiveenergysolar.com" target="_blank">Allan Sindelar</a> </div></div>
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<div style="FONT: 10pt arial"><b>To:</b> <a title="re-wrenches@lists.re-wrenches.org" href="mailto:re-wrenches@lists.re-wrenches.org" target="_blank">'RE-wrenches'</a> </div>
<div style="FONT: 10pt arial"><b>Sent:</b> Wednesday, December 10, 2008 1:16 PM</div>
<div style="FONT: 10pt arial"><b>Subject:</b> [RE-wrenches] Module Voltage Question for Off-Grid Designers</div>
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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" target="_blank"><u></u><u><font face="g" color="#0000ff" size="2">allan_(at)_positiveenergysolar.com</font></u></a> <br>
<font face="g" size="2">NABCEP certified solar PV installer</font> <br><font face="g" size="2">Positive Energy, Inc.</font> <br><font face="g" size="2">3225A Richards Lane</font> <br><font face="g" size="2">Santa Fe NM 87507</font> <br>
<font face="g" size="2">505 424-1112</font> </p></div></div>
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