A solar tracker idea that I have seen is this: two photo sensors with a vertical shield between them. One photo sensor will see sunlight, the other is shaded. A motor turns the sensors toward the lighted one until both see sunlight, then the motor stops.

You may be able to glean some ideas on your implementation from the efforts in designing a solar data logger by these students at Cornell.

http://instruct1.cit.cornell.edu/cou...k28/index.html

Here is a link to a homebrewed solar tracker design. http://pages.prodigy.net/rich_demartile/

hgmjr