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<title>Module Voltage Question for Off-Grid Designers</title>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Esteemed colleagues,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Having just hired a licensed electrician for
our renewable energy company we find that he cannot use our liability insurance
to cover him on pulling electrical permits here in <st1:place w:st="on"><st1:State
w:st="on">Massachusetts</st1:State></st1:place>. It seems that he has to
have his own certificate despite being listed as an electrician under our
liability policy.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Any insights?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Conrad<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Cotuit Solar<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Allan Sindelar<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, December 10, 2008
3:16 PM<br>
<b><span style='font-weight:bold'>To:</span></b> 'RE-wrenches'<br>
<b><span style='font-weight:bold'>Subject:</span></b> [RE-wrenches] Module
Voltage Question for Off-Grid Designers</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Wrenches,
<br>
Here's an issue I haven't seen directly addressed, and I would like to know
what the rest of you are doing. <br>
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.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>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). <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>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. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>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. <o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>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.<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>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?<o:p></o:p></span></font></p>
<p><font size=3 face="Times New Roman"><span style='font-size:12.0pt'>Thanks,
as usual. <br>
Allan <br>
</span></font><font face=g><span style='font-family:g'>Allan Sindelar</span></font>
<br>
<a href="mailto:allan@positiveenergysolar.com"><font size=2 face=g><span
style='font-size:10.0pt;font-family:g'>allan_(at)_positiveenergysolar.com</span></font></a>
<br>
<font size=2 face=g><span style='font-size:10.0pt;font-family:g'>NABCEP
certified solar PV installer</span></font> <br>
<font size=2 face=g><span style='font-size:10.0pt;font-family:g'>Positive
Energy, Inc.</span></font> <br>
<font size=2 face=g><span style='font-size:10.0pt;font-family:g'>3225A <st1:address
w:st="on"><st1:Street w:st="on">Richards Lane</st1:Street><font size=3
face="Times New Roman"><span style='font-size:12.0pt;font-family:"Times New Roman"'>
<br>
</span></font><st1:City w:st="on">Santa Fe</st1:City> <st1:State w:st="on">NM</st1:State>
<st1:PostalCode w:st="on">87507</st1:PostalCode></st1:address></span></font> <br>
<font size=2 face=g><span style='font-size:10.0pt;font-family:g'>505 424-1112</span></font>
<o:p></o:p></p>
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