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The article referenced below discusses detailed PV simulation
w/shadowing, and compares measured and simulated results. The
simulations and measurements did not seem to match very well as I
recall. <br>
<br>
<b>Partial shadowing of <font color="#ff0000"><b>photovoltaic</b></font>
arrays with different system configurations: literature review and
field test results <small> • <font face="Times New Roman, Times, Serif"
color="#737373">ARTICLE</font></small><br>
</b> <i>Solar Energy, Volume 74, Issue 3,<nobr>
March 2003</nobr>, <nobr>
Pages 217-233</nobr> </i><br>
Achim Woyte, Johan Nijs and Ronnie Belmans<br>
<br>
For the level of rigor of DOE2/eQuest, it would be useful if the user
could define a custom curve of array %degradation vs. array %shadowing
to at least explore a system's sensitivity to crude assumptions (no
effects from shading, output proportional to %illuminated, complete
shutdown from any shading) and still be coupled to the hourly analysis
of utility rates inside DOE2. This would probably require an additional
input or two to locate the array on the wall or roof for DOE2, for
those cases where the array is smaller than the surface on which it is
mounted. <br>
<br>
<a class="moz-txt-link-abbreviated" href="mailto:stvgates@pacbell.net">stvgates@pacbell.net</a> wrote:
<blockquote
cite="midMDAEMON-F200410012116.AA1615984pd80000360576@gard.com"
type="cite">
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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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<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">-----
Original Message ----- </div>
<div
style="background: rgb(228, 228, 228) none repeat scroll 0%; -moz-background-clip: initial; -moz-background-origin: initial; -moz-background-inline-policy: initial; font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>From:</b>
<a title="Sgupta@energy.state.ca.us"
href="mailto:Sgupta@energy.state.ca.us">Smita Gupta</a> </div>
<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>To:</b>
<a title="BLDG-SIM@GARD.COM" href="mailto:BLDG-SIM@GARD.COM">BLDG-SIM@GARD.COM</a>
</div>
<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Sent:</b>
Friday, October 01, 2004 3:49 PM</div>
<div
style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><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>
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