[BLDG-SIM] effect of partial shading on PV performance

[Griffith, Brent]

Smita, 
Your understanding of how EnergyPlus accounts for PV shading seems to be correct.  I would add that for the advanced PV models, cell performance is a function of incident radiation and that it is important to reduce this before applying the model.  With EnergyPlus, you can use single-module arrays and define separate surfaces for each module. This way the shading will be handled separately for each module.  But currently in EnergyPlus, the whole array performance would not be treated any differently than summing up each module's contribution.  You could take the output from each surface/module and reassemble the performance of the array outside of the program.   This is in general a hard thing to model as one would need a large amount of data on exactly how the modules in the array (and cells in the modules) are wired with bypass and blocking diodes.  Nowadays, clever electrical engineering can minimize the degradation effects of shading, so it isn't always the case that entire strings go dead.    

Brent Griffith

 -----Original Message-----
From: postman at gard.com [mailto:postman at gard.com]On Behalf Of Smita Gupta
Sent: Friday, October 01, 2004 4:50 PM
To: BLDG-SIM at gard.com
Subject: [BLDG-SIM] effect of partial shading on PV performance



Hi,
 
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. 
 
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.
 
Any help and advise regarding this issue is appreciated.
 
Thank you,
 
 
 
PS- 
eQuest output for PV performance states that
"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"
 
Smita Gupta
Energy Analyst, LEED AP
 
Buildings & Appliances Office
California Energy Commission
1516 Ninth St. MS-25
Sacramento, CA 95814
Phone: (916) 657-4034
Fax: (916) 654-4304



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