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<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'>Alan,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'>Here’s
another thing to look into. Hope my memory is good.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'>Seems
that I remember that Solarex had some bad modules a few years ago and it was
discussed on the list. You might want to check that they are all working as
they should before you start adding to the collection.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'>I guess
the first question is, is the array still putting out what it did when first
installed?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'>Finding
a bad panel out of a rack is a project, and hopefully you will not have to do
that but it is at least worth the question<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'>Bob<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=4 color=black face=Calibri><span
style='font-size:14.0pt;font-family:"Calibri","sans-serif";color:black'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext;
font-weight:bold'>From:</span></font></b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext'> 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, April 28, 2010
3:20 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] Solarex
module match question<o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Calling the old-timer off-grid 12V graybeard
Wrenches...<br>
I am reposting this to the list in hopes of shakin' up a response, as nobody
tried to answer my request for help.<br>
<br>
In short: in theory, if you force an array to operate at a voltage above its
MPP, current drops off significantly on the string I/V curve. In this case, if
I add a fixed array of substantially larger current and <i><span
style='font-style:italic'>slightly</span></i> higher Vmp (due to both what's
currently available having a slightly higher module Vmp, and 14 years of module
degradation), will the new array force the old array to operate at too high a
Vmp and thus substantially reduce its contribution to overall PV input?<br>
<br>
And a related question: the customer reminded me that he still had two
additional matching Solarex MSX77 modules stored away. <i><span
style='font-style:italic'>If</span></i> I could mount them on the existing
12-module Wattsun tracker, and <i><span style='font-style:italic'>if</span></i>
I wired them as two strings of seven modules (84Vnom), would that solve this
issue, by boosting string voltage enough to maintain current closer to Isc?<br>
<br>
I'd appreciate any good advice.<br>
Allan<br>
<br>
Original post:<br>
<br>
Wrenches,<br>
We have an off-grid customer with a system that has been growing since 1996; we
have cared for it intermittently since 2000.<br>
<br>
The customer has two tracked arrays currently. One has ten Astropower AP120s
for 1200 nominal watts, but that's not the topic today; it'll come up in 5
years or so. The other older array is 12 Solarex MSX77s, polycrystalline with
16.9Vmp, 21Voc (when new). The rest of the system is a SW4024, two Solar Boost
50s (one is currently failing) and two strings of 800 a/hr Rolls cells. <br>
<br>
The client wants to add 1,200 to 2,000 watts of additional PV. The problem is
that we have two sets of existing buried conductors between arrays and BOS and
don't want to dig up for more. Also, he wants to upgrade charge controllers,
and has had past failures of the SW inverter - in fact, he keeps a spare put
away for the next failure.<br>
<br>
I have suggested that by upgrading the inverter to a modern pure-sine 48V unit,
we can accomplish the array upgrade using the existing input conductors. I can
rewire the Solarexes from 6 24Vnom strings to two 72V strings and have plenty
of copper to add more array without voltage drop issues. (The AP120s can be
brought in as 2 60V strings to a separate FM60 or T80 or similar). This also
lets me work with existing 60 or 80A charge controllers, which I can't do at 24V.<br>
<br>
The customer likes this approach, so here's my question: What modules would you
suggest as having good compatibility with the existing Solarexes? I would
assume that any polycrystalline 72-cell module would be fairly close but not
ideal. I would especially expect the lower-rated ones within a particular size
category to be better choices, as they would have lower Vmp to more closely
match the existing. But would similar monocrystalline be close enough? Too high
a voltage in the dominant (new) array drags the voltage above MPP, which
reduces output considerably on the Solarexes. Also, I can't find the
temperature coefficient for the old modules, and I suspect that degradation
over 14 years has lowered the MPP of them anyway. <br>
<br>
I think of using 12 Kyocera KD135s Mitsubishi 125s or 130s; Solarworld's
discontinued SW175 (mono), Sharp 123s, or possibly some Suntech monos. But I'm
certainly open to advice and suggestions here.<br>
<br>
Also, while the existing arrays are on Wattsun DA trackers (customer's choice),
the new array will be pole-top. I'm not too worried about tracking/fixed
mismatch, as voltage quickly matches even with non-optimal orientation. But
I'll take advice here too.<br>
<br>
<br>
Thanks.<br>
Allan <o:p></o:p></span></font></p>
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<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>-- <br>
<br>
<o:p></o:p></span></font></p>
<p class=MsoNormal><span class=il><b><font size=3 color=black
face="Times New Roman"><span style='font-size:12.0pt;font-weight:bold'>Allan</span></font></b></span><b><span
style='font-weight:bold'> Sindelar</span></b><font size=2><span
style='font-size:10.0pt'><br>
<a href="mailto:Allan@positiveenergysolar.com" target="_blank"><span class=il><u>Allan</u></span><u>@positiveenergysolar.com</u></a><br>
NABCEP Certified Photovoltaic Installer<br>
EE98J Journeyman Electrician<br>
<b><span style='font-weight:bold'>Positive Energy, Inc.</span></b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b><span style='font-weight:bold'>505 424-1112</span></b><br>
<a href="http://www.positiveenergysolar.com/" target="_blank"><u>www.positiveenergysolar.com</u></a></span></font><o:p></o:p></p>
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