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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>
<DIV><FONT face=Calibri size=2></FONT> </DIV>
<DIV>..................................................................................................<BR>Northern
Arizona Wind & Sun - Electricity From The Sun<BR>Solar Discussion Forum: <A
href="http://www.wind-sun.com/ForumVB/">http://www.wind-sun.com/ForumVB/</A><BR>..................................................................................................</DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=allan@positiveenergysolar.com
href="mailto:allan@positiveenergysolar.com">Allan Sindelar</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=re-wrenches@lists.re-wrenches.org
href="mailto:re-wrenches@lists.re-wrenches.org">'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>
<DIV><BR></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 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>
<P>
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