Andy:
I thought that a small sensor consumes much less energy when i go all over the place searching for the sun. Once sun optimal position was found then I can move the solar cell to same position as the sensor.
However maybe I can sense the output power of the solar cell and when it decreases due to sun movement i can use this drop for a rescan!
If yellow leds are good sensors as steve suggested i can make a dome array with them this way I dont need any motors and much less power for scanning.

Steve:
Great idea, why didn't I think of that grrrrr!
good sat dish actuators cost less than 20 pounds in here and guess what, they already have position sensors in them!.
regards
Mahmood