Follow the sun, or any light source, with a low cost stepper motor and two light sensitive resistors (LDR).
Fix a solar panel to the angled flange. It should be 5 volts and at least 100 mA so it can be the power source. Larger panels can be used as battery charger.
If the stepper motor rotates the wrong way, just reverse the 3-wire plug coming from the light sensitive resistors.
In the middle is a small dead zone to prevent oscillation.
Other ministepper projects: