There's a book called PIC Microcontroller Project Book by John Iovine that is all about
Pic BASIC projects. The last project in the book is a solar tracker that works with two
cds cells with a plate mounted vertically between them which casts a shadow over one
if a solar tracker isn't pointing the whole assembly directly at the Sun.
Then a picBASIC program makes adjustments to the traker to equalize the readings of
each cds cell so the solar panels on the tracker end up pointing at the Sun.

Anyway, I think you could use two of these circuits with a bigger pic to achieve the same
thing with two identical soalr panels or arrays.