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<DIV><FONT size=2 face=Arial>Hi Alan,</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>If you want to actually get into the details, you
need an IV curve of all modules involved. You can graphically add them to
see what the IV curve of the array will look like. If there are
mis-matched modules then you will get a curve with a 'double bump' on it.
Then it depends on the control scheme of the controller on which bump it will
find and track on if you are using a peak power tracking controller. If
the mis-match is only a few percent then it doesn't mater which bump is
found. While you can get an IV curve of the new modules, I guess you would
have to measure the IV curve of the old modules to see what kind of degradation
has taken place. Or you just take a few readings (Voc, Isc, Pp) and
adjust the original curve to fit. You can just estimate the curves to see
the magnitude of the problem. I think the case you are talking about will
have a small mis-match. Good Luck with it.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Cary</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Cary Lane<BR>Energy Concepts Corporation<BR>HC 68
Box 11AA<BR>Sapello, NM 87745</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2 face=Arial>Ph: 505-454-0614 ext 4<BR>Toll Free:
877-765-2713<BR>Fax: 505-213-0985</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=2 face=Arial>Email: <A
href="mailto:Cary.Lane@EnergyConceptsCorp.com">Cary.Lane@EnergyConceptsCorp.com</A><BR>Web
page: <A
href="http://www.EnergyConceptsCorp.com">www.EnergyConceptsCorp.com</A></FONT></DIV>
<BLOCKQUOTE
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="FONT: 10pt arial; BACKGROUND: #e4e4e4; font-color: black"><B>From:</B>
<A title=reellison@gmail.com href="mailto:reellison@gmail.com">bob</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A
title=Allan@positiveenergysolar.com
href="mailto:Allan@positiveenergysolar.com">Allan@positiveenergysolar.com</A>
; <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> Thursday, April 29, 2010 4:00
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [RE-wrenches] Solarex module
match question</DIV>
<DIV><BR></DIV>
<DIV class=Section1>
<P class=MsoNormal><FONT color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt">Alan,<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt">Here’s
another thing to look into. Hope my memory is
good.<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt">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 color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt">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 color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt">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 color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt">Bob<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT color=black size=4 face=Calibri><SPAN
style="FONT-FAMILY: 'Calibri','sans-serif'; COLOR: black; FONT-SIZE: 14pt"><o:p> </o:p></SPAN></FONT></P>
<DIV>
<DIV
style="BORDER-BOTTOM: medium none; BORDER-LEFT: medium none; PADDING-BOTTOM: 0in; PADDING-LEFT: 0in; PADDING-RIGHT: 0in; BORDER-TOP: #b5c4df 1pt solid; BORDER-RIGHT: medium none; PADDING-TOP: 3pt">
<P class=MsoNormal><B><FONT color=black size=2 face=Tahoma><SPAN
style="FONT-FAMILY: 'Tahoma','sans-serif'; COLOR: windowtext; FONT-SIZE: 10pt; FONT-WEIGHT: bold">From:</SPAN></FONT></B><FONT
color=black size=2 face=Tahoma><SPAN
style="FONT-FAMILY: 'Tahoma','sans-serif'; COLOR: windowtext; FONT-SIZE: 10pt">
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></DIV></DIV>
<P class=MsoNormal><FONT color=black size=3 face="Times New Roman"><SPAN
style="FONT-SIZE: 12pt"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT color=black size=3 face="Times New Roman"><SPAN
style="FONT-SIZE: 12pt">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>
<DIV>
<P class=MsoNormal><FONT color=black size=3 face="Times New Roman"><SPAN
style="FONT-SIZE: 12pt">-- <BR><BR><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><SPAN class=il><B><FONT color=black size=3
face="Times New Roman"><SPAN
style="FONT-SIZE: 12pt; FONT-WEIGHT: bold">Allan</SPAN></FONT></B></SPAN><B><SPAN
style="FONT-WEIGHT: bold"> Sindelar</SPAN></B><FONT size=2><SPAN
style="FONT-SIZE: 10pt"><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></DIV></DIV></BLOCKQUOTE></BODY></HTML>