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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>A dampening of the knee of the IV curve would be indicative of
higher series resistance. The higher series resistance would also increase
cell temperatures as shown in the thermo image. The cooling off of the cells
under open circuit conditions would also correlate to the higher series
resistance, whereas there would be no current flowing generating heat through
the cell resistance under open circuit conditions. The question then becomes
why would some cells have high resistance. Could be cell fractures, albeit odd
that they would be random within the module, and also random in the group of
modules shown. I\u2019m guessing it was only this one string, perhaps this crate of
modules was banged up in shipping or something.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Here is a link to an article about the relationship between
series resistance and fill factor. http://www.pveducation.org/pvcdrom/solar-cell-operation/series-resistance<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Mike Kocsmiersky<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Principal<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Spirit Solar Inc.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>(413) 734-1456<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Corey Shalanski
[mailto:corey@joule-energy.com] <br>
<b>Sent:</b> Thursday, May 17, 2018 6:19 PM<br>
<b>To:</b> RE-wrenches@lists.re-wrenches.org<br>
<b>Subject:</b> [RE-wrenches] PV Cell Temperature Variation<o:p></o:p></span></p>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<div>
<p class=MsoNormal>On a recent utility-scale PV installation we noticed a
strange phenomenon on a single string on a single inverter. An IV curve
(attached) reveals that the measured performance characteristics for this
string (solid line) are significantly less than the expected values (dotted
line). For reference, the ambient temperature was 31°C and the irradiance was
1010 W/m².<o:p></o:p></p>
<div>
<p class=MsoNormal><o:p> </o:p></p>
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<div>
<p class=MsoNormal>The phenomenon that more so caught our attention is apparent
on a thermal image (also attached) of the modules in this string. For lack of a
better term I would describe the distribution of cell temperatures as
resembling a "checkerboard" or "scattershot" (random)
pattern, ranging between roughly 55°C and 70°C. Interestingly this phenomenon
was only apparent while the inverter was operating, i.e. with the inverter
turned off the modules revert to a much more uniform temperature distribution
nearer to 55°C, instead varying by only a couple degrees across the entire
module/string.<o:p></o:p></p>
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<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>There was no apparent physical damage to the modules.<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
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<div>
<p class=MsoNormal>Can anyone offer any suggestions about what might be causing
this phenomenon?<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
</div>
<div>
<p class=MsoNormal>--<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>Corey Shalanski<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>Joule Energy<o:p></o:p></p>
</div>
<div>
<p class=MsoNormal>New Orleans, LA<o:p></o:p></p>
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