Brian,
The best I've been able to do, thus far, is static representations of select direct/reflected rays, using transparent colors:
http://sketchup.google.com/3dwarehouse/details?mid=c63b8d66ebe146e5b2174b2fd0759d18
Collector.jpg
As Gaieus wrote, the sun-tracking feature of SketchUp is perfect for this kind of study. You can demonstrate hour/date changes, as well as the effect of changing the latitude/longitude for different locales.
Regards,
Taff