Favorite tool [RE-wrenches] - pathfinder

[William Miller]

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Bill:

I can guess at what Randy may be thinking.  Using PV watts, each month's 
production is different.  Therefore, shading in one month may mean less 
degradation in output over another month.  I figure the shading for each 
month and apply it to that month's predicted output for a "shading 
de-rated" output.

If the shading is in the winter and is caused by a deciduous tree, I give 
that hour half credit on the Pathfinder scale.  This is just my best 
estimation.  Can you quantify the loss a bare branch makes on an array?

William Miller





At 12:19 PM 5/10/2006, you wrote:
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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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