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<DIV dir=ltr align=left><SPAN class=393045803-13112008><FONT
face="Comic Sans MS" color=#800000>Hello Kirpal:</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=393045803-13112008><FONT
face="Comic Sans MS" color=#800000></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=393045803-13112008><FONT
face="Comic Sans MS" color=#800000>What is the relative age of these
modules? For starters.... Just curious.</FONT></SPAN></DIV>
<DIV> </DIV>
<DIV align=left>
<DIV align=left><FONT face="Comic Sans MS" color=#000080 size=2>Chris
Daum</FONT></DIV>
<DIV align=left><FONT face="Comic Sans MS" color=#000080 size=2>Oasis Montana
Inc.</FONT></DIV>
<DIV align=left><FONT face="Comic Sans MS" color=#000080 size=2>406-777-4309
local line</FONT></DIV>
<DIV align=left><FONT face="Comic Sans MS" color=#000080 size=2>406-777-0830
fax</FONT><FONT face="Comic Sans MS" color=#000080 size=3><SPAN
class=046344020-29052008></SPAN></FONT></DIV></DIV>
<DIV> </DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
<HR tabIndex=-1>
<FONT face=Tahoma size=2><B>From:</B> re-wrenches-bounces@lists.re-wrenches.org
[mailto:re-wrenches-bounces@lists.re-wrenches.org] <B>On Behalf Of </B>Kirpal
Khalsa<BR><B>Sent:</B> Wednesday, November 12, 2008 8:33 PM<BR><B>To:</B>
RE-wrenches<BR><B>Subject:</B> Re: [RE-wrenches] Trouble Shooting Bad
Diode<BR></FONT><BR></DIV>
<DIV></DIV>Bill and all.......So we were at the site today and these were our
findings:<BR>We covered each solar panel with cardboard 1 at a time.....we
continued to see the same lower voltage on string #2. String #1 had an
expected Voc. <BR>String 1 had a Voc of 368, String 2 had Voc of
312. <BR>We decided to disconnect the entire string. Luckily the
interconnects were accessible without physically removing the modules.......I
love array's that are only 2 rows deep with service aisles all
around.....<BR>The system was 2 strings of 9 BP SX170's connected to a
PVP2800XV. <BR>Module nameplate Voc was 44V. Cell temp of the
modules at time of measurement was roughly 85-90 degrees F. <BR>all
modules were in the 40.1-8 range....except module # 3 from the positive homerun
side was 38.8V, module 6 was 36.6V and module 8 was 10V. <BR>We had
no trouble determining that module # 8 was defective......In these modules I
believe that the entire 72 cells are in a series.string...(am i right?roughly
.5+V per cell.).<BR>Covering 1 module at a time did not give us any indication
as to which panel was defective. The Voc with 1 module covered ranged from
a low of 299VV to a high of 304V. This did not make sense to me as to reducing
the string Voc from 312 to 304 by covering 1
module.........<BR><BR>Anyhow........the 2 modules that had reduced
voltages......1 with ~38V and 1 with ~36V......would you consider those
defective? Worthy of trying to get BP to warranty those?<BR>We will be
filing a warranty claim on the single panel that is obviously
defective.......<BR>Thanks for your advice and
input.....<BR>Cheers,<BR><BR>Kirpal Khalsa<BR>Renewable Energy
Systems<BR><BR><BR>
<DIV class=gmail_quote>On Fri, Oct 31, 2008 at 10:33 AM, Bill Brooks <SPAN
dir=ltr><<A
href="mailto:billbrooks7@yahoo.com">billbrooks7@yahoo.com</A>></SPAN>
wrote:<BR>
<BLOCKQUOTE class=gmail_quote
style="PADDING-LEFT: 1ex; MARGIN: 0pt 0pt 0pt 0.8ex; BORDER-LEFT: rgb(204,204,204) 1px solid">
<DIV lang=EN-US vlink="purple" link="blue">
<DIV>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">Kirpal,</SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">When you parallel,
your voltages have to be the same, so you are correct in that
assumption.</SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">Your assumption about
the diodes is not correct. Diodes don't work like that. You could have a
shorted module (all three diodes shorted) which would lower the Voc by one
module. It looks like you have nearly two modules worth of problems. It could
be a total of 5 bad diodes, but that would be weird. It could be you have a
ground fault, and haven't tripped the GFP yet because of lower sunlight
levels—(it has to be very low sun to stay under 1 amp). You also could have a
wiring mistake, either because the factory reversed wired a module (rare, but
it happens)—that would be 2 modules low; or, you could have skipped two
modules somehow.</SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">It does seem like a
quarter of the bad string is out. Your assumption about bad diodes could be
correct, but it only affects the groups of cells its connected to. Each diode
protects 24 cells—it looks like you have 5 diodes worth of loss. It could be
in 2 modules, or up to 5 modules. </SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">The shading test is
the best way to find bad diodes. Disconnect the bad string from the good one
and take a piece of cardboard the dimension of the module. With your meter
testing Voc on the back string, completely cover each module, one at a time.
When the Voc is not affected by complete shading of a module, that module is
completely bad. If the shaded module only loses a portion of one module's Voc,
then you have one or two, of the three diodes, bad.</SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">This is a great
opportunity to learn how to troubleshoot a PV array. Take the time, and the
effort, to run through it carefully, learn the problems, and report back with
your findings. It's a beautiful thing to learn something new.</SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)">Bill.</SPAN></P>
<P><SPAN style="FONT-SIZE: 11pt; COLOR: rgb(31,73,125)"></SPAN> </P>
<DIV
style="BORDER-RIGHT: medium none; PADDING-RIGHT: 0in; BORDER-TOP: rgb(181,196,223) 1pt solid; PADDING-LEFT: 0in; PADDING-BOTTOM: 0in; BORDER-LEFT: medium none; PADDING-TOP: 3pt; BORDER-BOTTOM: medium none">
<P><B><SPAN style="FONT-SIZE: 10pt">From:</SPAN></B><SPAN
style="FONT-SIZE: 10pt"> <A
href="mailto:re-wrenches-bounces@lists.re-wrenches.org"
target=_blank>re-wrenches-bounces@lists.re-wrenches.org</A> [mailto:<A
href="mailto:re-wrenches-bounces@lists.re-wrenches.org"
target=_blank>re-wrenches-bounces@lists.re-wrenches.org</A>] <B>On Behalf Of
</B>Kirpal Khalsa<BR><B>Sent:</B> Friday, October 31, 2008 10:43
AM<BR><B>To:</B> RE-wrenches<BR><B>Subject:</B> [RE-wrenches] Trouble Shooting
Bad Diode</SPAN></P></DIV>
<DIV>
<DIV></DIV>
<DIV class=Wj3C7c>
<P> </P>
<P>Greetings all......I was hoping i could have someone help me confirm a
troubled series string on a system we have installed.....<BR>System consists
of 16 BP 170 W 24V nominal modules......2 strings of 8 modules.....Vmp of each
module is roughly 34V and Voc of each module is roughly 41V. One string
is under-producing......String 1 Voc is 346V and String 2 Voc is 272V.
String 1 Vmp under load is 270V and String 2 Vmp underload is 270V. I am
hypothesizing that String 2 has a bad diode on the 3rd panel in and is
reducing the Voc of that string by th 2 panels ahead of it in the
string. I am hoping to figure this out without removing the entire
string and checking each panel if possible.....<BR>I think the Vmp is equal
due to the fact that both strings are paralleled in the inverter and the 1st
string is being pulled to the same level V as the 2nd string under
load......Is my logic good?<BR>Thanks for the help and
advice.....<BR>Cheers,<BR><BR></P></DIV></DIV></DIV></DIV><BR>_______________________________________________<BR>List
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clear=all><BR>-- <BR>Sunny Regards,<BR>Kirpal Khalsa<BR>NABCEP Certified Solar
PV Installer<BR>Renewable Energy Systems<BR></BODY></HTML>