interrow shading [RE-wrenches]

[Peter Parrish]

Kurt,

I haven't found a site that solves our problem, and what's more the problem
has no exact statement, but here is what I have come up with:

Start with a flat roof...
Given the height difference between the lower edge and the upper edge of a
tilted module (H), and given that the module row is oriented E-W, and given
the no-shade requirement is between 9am and 3pm (local time) for any day of
the year (yes including Dec. 21st), and given that you are located ~34 deg
latitude...the horizontal distance between the upper module edge (of one
row) and the lower module edge of the next row (to the north) is 2.1H. If
you want to further reduce the shading, you could go to 2.5X. Beyond that,
IMHO, you are not gaining much and losing  a lot of real estate.

Of course, if the roof isn't flat, or the row orientation is not E-W, or you
are willing to live with more shading either during the day or in the
Winter, or you don't live at 34 deg latitude...the numbers will be
different.

And this calculation is a strict "no shade" calculation, and some shading
will reduce but not completely eliminate the power production. I haven't
bothered with this.

What did I do to come up with these numbers? I used a program that gives you
the sun's position any day in the year and then calculated the shadow that a
stick 1 meter high casts on a flat roof and then from that shadow derived
the 2.1X factor. This took me many hours, and I verified it on a 36 kW
project that we did in the city of LA last year.

It would be great if someone would come up with a table that gives the
X-factor, based on latitude and no-shade hours, but I haven't been able to
find one and if any one has found such a table, I for one would be greatly
indebted if they would share it.

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com 

-----Original Message-----
From: Kurt Nelson [mailto:sunwise at cheqnet.net] 
Sent: Friday, January 26, 2007 9:29 AM
To: RE-wrenches at topica.com
Subject: interrow shading [RE-wrenches]


Can anyone recommend a web page or other resource for calculating
interrow shading?  Something that factors in the latitude at the site
(not just CA).

Much thanks in advance -- Kurt

----------------------------------------------------------------

Kurt Nelson
PO Box 309
Cornucopia, WI 54827
715-742-3406
sunwise at cheqnet.net


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