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Wrenches,<br>
I'm posting this for Carl Bickford, prof emeritus of the renewable
energy training program at San Juan College in Farmington, New
Mexico. I'll forward your responses to him.<br>
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<p class="MsoNormal"><o:p></o:p>I have a very interesting and
talented friend who is rebuilding a blue-water sailboat for
a round-the-world trip. He is well versed in solar and is
trying to use a relatively large array to charge a big
battery bank that will be used for propulsion as well as
general electrical. The propulsion system will be backed up
with a propane generator he is building himself out of a
Toyota truck engine.<o:p></o:p></p>
<p class="MsoNormal">As you can imagine, there is no place on
a sailboat where shading isn’t a problem. He and I were
wondering if there were products out there that could MPPT
either individual modules, or small groups of them for 12 V
battery charging. I have seen such things for the inputs of
grid-tied inverters, but nothing yet for off-grid. The other
choice is to go with many small MPPT charge controllers like
the ones from Solar Converters.<o:p></o:p></p>
<p class="MsoNormal">Any advice you can offer?<o:p></o:p></p>
<p class="MsoNormal">Take care,<br>
Carl<o:p> <br>
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<p class="MsoNormal">Carl Bickford<br>
Professor of Engineering and Renewable Energy<o:p></o:p><br>
San Juan College<o:p></o:p><br>
4601 College Blvd.<o:p></o:p><br>
Farmington, NM 87402<o:p></o:p><br>
505-566-3503<br>
<a class="moz-txt-link-abbreviated" href="mailto:bickfordc@sanjuancollege.edu">bickfordc@sanjuancollege.edu</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> <br>
I offered the suggestion below. Certainly open to other and
better ideas.<br>
Allan<br>
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<p class="MsoNormal">I have not encountered this situation, so
I have no advice from experience. At 12V, it's hardly an
issue as it is with high voltage parallel strings, where a
few shaded cells can cause a whole string to drop out of the
inverter's MPPT. At most, a shaded cell weakens the output
of that module. And since it's charging batteries, there's a
greater amount of head room.<br>
<br>
I would suggest looking into Blue Sky Energy's "i" series -
smaller MPPT controllers that can be networked. We seldom
use them, as our residential applications are different. But
you could put a controller on a group of modules and network
several together. One advantage, I think (you'd want to
check this) is that Blue Sky's MPPT algorithm is analog,
unlike Outback and others: on the old Solar Boost series,
the MPPT boost was set with a trim pot to a particular
voltage above battery voltage; the target is to set it to
where the boost was greatest. You could set this boost
slightly lower than peak, and output just a little below
MPP. That way the overall output would be minimally reduced,
and a modest amount of shading would not cause the shaded
module to drop below collective MPP as readily.<br>
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<br>
<font face="Times New Roman, Times, serif"><b>Allan Sindelar</b></font><br>
<small><a href="mailto:Allan@positiveenergysolar.com"><font
color="#000099" face="Times New Roman, Times, serif"><u>Allan@positiveenergysolar.com</u></font></a></small><font
face="Times New Roman, Times, serif"><br>
<span style="font-size: 10pt;">NABCEP Certified Photovoltaic
Installer<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder and Chief Technology Officer<br>
<b>Positive Energy, Inc.</b><br>
3209 Richards Lane (note new address)<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
<a href="http://www.positiveenergysolar.com/"
target="_blank"><u>www.positiveenergysolar.com</u></a><o:p></o:p></span></font>
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