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:[email protected]> [email protected] Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885 _____ From: [email protected] [mailto:[email protected]] 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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