Brian,

Yes I have done a sun tracker for PV arrays  What do you have in mind.
Will there be a PIC controller?   Basically one can make a quadrature
encoder (a plus sign with some depth for shading) using low sensitivity
phototransisters of CDS cells with shading over them.   There is also
a need to have the home location of the tracker - like overnight have
it return for catching morning sun.    The method I used was to use two
steppers motors and a PC running on a Dig Analog I/O card with
Borland C.    It would be possible to push this into a PIC like a 16C76
type.  Keep in touch...

Eric