<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><DIV>Hello Nik,</DIV>
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<DIV>We installed two 4 kW DC PV systems on a Sacramento PV Pioneer home. Both arrays were tilted 18 degrees with one array facing south and the other facing west. The power from both systems fed into the Sacramento Municipal Utility District grid (not the home). After 2 years, SMUD reported (but did not provide data) that the west-facing system produced 20% less energy than the south-facing system. However, PVWATTS estimates the difference to be 11.8% less. My experience with hundreds of systems is that PVWATTS is a reliable estimator for crystalline silicon PV systems if you factor derating properly. It will be interesting to hear what other wrenches have to say.</DIV>
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<DIV>Joel Davidson</DIV>
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<B><SPAN style="FONT-WEIGHT: bold">From:</SPAN></B> "Nicholas Ponzio, Building Energy" <nponzio@buildingenergyus.com><BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B> RE-wrenches <re-wrenches@lists.re-wrenches.org><BR><B><SPAN style="FONT-WEIGHT: bold">Sent:</SPAN></B> Tuesday, October 6, 2009 10:37:32 AM<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B> [RE-wrenches] orientation data<BR></FONT><BR>Hey Folks,
<DIV><BR>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. </DIV>
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<DIV>Thanks,</DIV>
<DIV>Nik</DIV>
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