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<DIV>eQUEST calculates the performance of a PV system assuming NO
shading on the array. It also outputs a shading report to give you an idea
of how much shading the array receives over the course of the year, so that you
can make a judgment regarding the impact of shading on PV performance.
eQUEST does not attempt to assess the impact of shading on PV performance
for the reason you describe. </DIV>
<DIV> </DIV>
<DIV>PV degradation due to shading depends not only on how many cells in a
series are shaded, but also whether that row of cells is in parallel with
other rows, and how much sunlight those rows are receiving, and the
characteristics of the inverter. The interaction is complex and I am
not an expert on PV systems; however my understanding is that
several unshaded rows of cells can impress enough voltage across the
partially-shaded rows to wipe out most of their output.</DIV>
<DIV> </DIV>
<DIV>To simulate this degradation in detail would require defining
the spatial geometry of each module in the array relative to the shading
surface, the series/parallel relationships of the modules in the array, diodes
that allow shaded cells in series to be bypassed, a description of
the inverter characteristics, etc. I am not aware of any programs
that model PV systems in this detail, but would be interested in knowing whether
any exist.</DIV>
<DIV> </DIV>
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style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=Sgupta@energy.state.ca.us
href="mailto:Sgupta@energy.state.ca.us">Smita Gupta</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=BLDG-SIM@GARD.COM
href="mailto:BLDG-SIM@GARD.COM">BLDG-SIM@GARD.COM</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, October 01, 2004 3:49
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [BLDG-SIM] effect of partial
shading on PV performance</DIV>
<DIV><BR></DIV>
<DIV>Hi,</DIV>
<DIV> </DIV>
<DIV>A PV related query again. This time I would like to find out if
anyone can suggest an algorithm or tool that accounts for the effect of
partial shading on an array. From what I understand, EnergyPlus and
eQuest algorithms factor the effect of shading through adjusting the
effective irradiation incident on the surface to which the array is attached.
Please correct me if I am wrong in understanding this. </DIV>
<DIV> </DIV>
<DIV>But the effect of partial shading is quite different depending on the
location of the actual cell in series. The shaded cell depending on its
location in the series can degrade the performance a lot more than
proportional to the % of area shaded. Can anyone confirm if any tool or
algorithm takes into account his fact.</DIV>
<DIV> </DIV>
<DIV>Any help and advise regarding this issue is appreciated.</DIV>
<DIV> </DIV>
<DIV>Thank you,</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>PS-
<DIV>eQuest output for PV performance states that</DIV>
<DIV>"NOTE: PARTIAL SHADING OF A PV ARRAY CAN SEVERELY DEGRADE ITS
PERFORMANCE, BUT IS NOT TAKEN INTO ACCOUNT SEE REPORT LS-SH FOR SHADING
INFORMATION"</DIV>
<DIV> </DIV>
<DIV>Smita Gupta<BR>Energy Analyst, LEED AP</DIV>
<DIV> </DIV>
<DIV>Buildings & Appliances Office<BR>California Energy Commission<BR>1516
Ninth St. MS-25<BR>Sacramento, CA 95814<BR>Phone: (916) 657-4034<BR>Fax: (916)
654-4304<BR></DIV></DIV><PRE>
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