[RE-wrenches] orientation data

[Peter Parrish]

Hi Nik,

 

I was surprised to read your post as I have worked with many customers in
southern California to optimize their systems through judicious choice of
tilt and azimuth.

 

I ran a quick A-B comparison 34deg/180deg versus 34deg/270deg - and found a
20% reduction. If I changed the tilt so that the orientation was
10deg/270deg - the reduction was 14%.

 

Of course the time-of-day and time of year production changes too and that
is a more complicated matter.

 

So, I must be missing something. What sort of comparison did you perform
exactly?

 

As for PVwatts, it does NOT properly take into account local seasonal
variations. This can easily be demonstrated by punching up a Los Angeles zip
code, setting azimuth to 180 degrees and varying the tilt angle and noticing
that "latitude tilt" gives the greatest annual production. Our Mediterranean
climate here in southern California (we get almost all our rain and most of
our cloud cover between November and March) should make a tilt somewhat less
than our local latitude the optimum choice. And it isn't. So I have stopped
telling people that PVWatts properly takes into account "micro climates"

 

There are other more graphical depictions of annual energy production, and
I'll try to dig out an example for you.

 

- Peter

 

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


 

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Nicholas
Ponzio, Building Energy
Sent: Tuesday, October 06, 2009 10:38 AM
To: RE-wrenches
Subject: [RE-wrenches] orientation data

 

Hey Folks,


Anybody have real data to compare productions for south-facing vs,
west-facing PV array? PVWatts is only showing about a 7% derating for facing
west. 

 

Thanks,

Nik

 

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