120 degree azimuth [RE-wrenches]

[Jim Easton]

I understand PVWatts is in the process of revision. I have never trusted its
numbers, and our designer here (James Pinon), who has been playing with it,
tells me that its results appear to be inconsistent with his expectations.

NREL makes HOMER available free, and I have been finding it quite useful. It
will model both on- and off-grid systems & allow one to optimize tilt
angles. Your tax dollars really working for you in this case!

If it is acceptable, I did a little EXCEL program to calculate positioning
of panels not aligned with the mounting surface. Looks different, but makes
more efficient use of modules.

The simplest model assumes output falls off as the cosine of the
misalignment. This is pessimistic, but cosine (60 Deg) is 50%, so I would be
wary of blindly believing the 7.6%.

If you want, contact me off list & I will do a HOMER run for you.

Jim Easton PE
Alternative Energy Technologies
www.altenertec.com
CSL: 852243
9465-B Mission Park Place
Santee, CA 92071
Tel: 619-262-8800
Fax: 619-562-8811
Cell: 858-527-0240

-----Original Message-----
From: Steve Johnson [mailto:stevejohnson at comcast.net] 
Sent: Wednesday, December 20, 2006 7:42 AM
To: RE-wrenches at topica.com
Subject: 120 degree azimuth [RE-wrenches]


Wrenchisimos,

I have a customer that has asked me to design/price a 22kw system for a 
hotel.  The back of the roof is about 26 degrees tilt but facing 120 
degrees, 60 degrees off of due south.  I ran the numbers on PV Watts and 
it showed only a 7.6% loss of power. 

Can anyone comment from experience on an installation 60 degrees to the 
east of south?  I don't want to make a poor recommendation.  Because of 
the site layout there is very little possibility of a canopy/parking 
type installation which is what I would like to do.
the roof is ideal otherwise.

Steve Johnson
LightWave Electric
Nashville, Tennessee


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