Wow, that google images is really eerie. So if you look at this tool:
http://www1.solmetric.com/cgi/insolatio ... lookup.cgi
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You'll see that for Danbury Muncipal, CT a perfect setup at 37 degrees tilt and a 179 degree azimuth is 1648kWh/m2. If you adjust that to what your roof is say for example 18 degrees that comes down to 1581 or 95.9% of perfect. Then if you adjust your azimuth to 225 degrees that brings it down to 1514 or 91.9%. So roughly the southwest face of your roof causes only a 4% decrease relative to perfect.
Does your southwest roof get any significant amount of shade?