[BLDG-SIM] Fwd: Re: Trans.: effect of partial shading on PV performance

[Smita Gupta]

Thanks for the responses.
 
I want to share another response I got for this query,  which seems to go further in accounting for partial shading:

 
>>> Andre Mermoud andre.mermoud at cuepe.unige.ch> 10/4/2004 6:31:24 AM >>

>Dear Mr. Gupta,

A friend of mine transmitted your request to me.

I have a partial answer to your question.
My software PVsyst  performs PV system simulations with partial shadings 
(3D tool).
It takes the partial shadings  on the PV array into account, in the usual 
"linear" way  (i.e. Shading loss factor proportional to the shaded area).
But you may also divide the PV array in "rectangles", each supposed to 
cover about a module string. The program computes the shading factor by 
supposing that when hitten by the shadow, the entire rectangle is 
invalidated. This is of course a rough approximation, but it gives an upper 
limit to the shading losses. The real situation should lie between these 
two values.

In practice, the shading factor applies on the beam component. The diffuse 
attenuation is calculated with the linear one, as it is not specular. 
Therefore the difference between the two values is usually not so important 
(at least under our middle-latitudes climates with 50% diffuse yearly).

You can download PVsyst from www.pvsyst.com, and use it with full 
capabilities during ten days. You will find more details in the contextual 
"help" (which may be invoked from anywhere in the software by typing F1).

Regards,

Abdré Mermoud

NB: You may put this answer on your forum if desired. I don't have access 
to it.

>_____________________________________________________________
>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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>----- Fin du message transféré -----
>
>
>

André Mermoud
CUEPE - University Centre for Study of Energy Problems
University of Geneva
Battelle, bât. A,  7, rte de Drize
1227 Carouge/Geneva
Switzerland

Tél   +41  22   379 06 61
Fax  +41  22   379 06 39
e-mail   andre.mermoud at cuepe.unige.ch

www.unige.ch/cuepe/
www.pvsyst.com





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