Favorite tool [RE-wrenches] - pathfinder

Bill Brooks bill at brooksolar.com
Wed May 10 12:19:58 PDT 2006


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Randy,

What do you mean by derating the results? Are you saying if the extreme of
the array has a shade factor of 90% (10% loss), you restate it to be only
96% (only 4% loss)? Although there may be some validity to decreasing the
severity of the loss, in reality shading almost always gets worse over
time--particularly related to vegetation that continues to encroach over
time. My recommendation is to test at the extreme and use that as the worst
case. To truly understand shading losses, you would need to do a separate
pathfinder analysis for every series string. If you have two strings in
parallel and one string loses 20% of the series string due to shading, their
will be no power from that string since the open circuit voltage of that
string will be equal or lower than the operating voltage of the illuminated
string.

Bill.


-----Original Message-----
From: Randy Sadewic [mailto:randy at positiveenergysolar.com] 
Sent: Wednesday, May 10, 2006 6:39 AM
To: RE-wrenches at topica.com
Subject: RE: Favorite tool [RE-wrenches] - pathfinder

Hi Wrenches,
We did the same as William and developed a spreadsheet that we use but then,
I use my judgement to derate the shaded portion. Typically, I do a
pathfinder on the boundary area of the array which will have the greatest
shading.  I derate it 60 to 80% depending on the type of shading ie trees
vs. solid objects and type of module.  

Randy



Randy Sadewic
randy at positiveenergysolar.com
NABCEP Certified PV Installer
Positive Energy, Inc.
3225A Richards Lane
Santa Fe, NM  87507
Phone 505 424-1112
Fax     505 424-1113
 
Enjoy the Sun!
 


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