@box said:
It's not quite what you want but Jim made a plugin to attach the camera to the sun so you can track the sun on your structure. Might help.
http://sketchucation.com/plugin/853-attach_camera_to_sun
Not quite the same I think...there's another plugin called Shadowtex (by Renderiza) that does something quite close by tracing a line from the center of every face to the sun's current position, but it uses this information to detect faces that are in shadow.
Maybe this technique can be modified to detect angles between faces and the sun angle? I know nothing about rubyscript, so unfortunately I wouldn't even know how to begin trying to build something like this...maybe one of the gurus here can have a think about it.
J