Sensor for Detecing Sun's Direction

You might search on "equatorial clock drives", as used to aim telescopes. For certain reflective geometries, the speed can be altered by a 2:1 ratio.

Try these links -

1) Solar tracker http://solartracker.greenwatts.info/solar_tracker_LM339_pcb.htm

2) http://www.redrok.com/led3xassm.htm#led3xc3

• The Mk.1 eyeball works in the absence of cloud cover.
• The position of the sun in the sky is calculable given the date, the local time, the longitude and the latitude.

The simple solution is to use several photocels and feed the input to A/D in controller then to see which photocell is getting most of the light.