This is my little solar tracker i designed a year ago.
The circuit is based on beam robotics (Biology, Electronics, Aesthetics, and Mechanics)
A single solar cell, connected to a step up converter, charges a small super capacitor(1F)
Two little solar cells are used as light sensors,the circuit turns a small motor to the brightest spot.
To make this little solar tracker useful i placed a eneloop solar charger on top of it.