More of my EV kick coming through. A solar tracker is used rotate a solar panel to get optimum energy from the sun. This one uses LEDs as the light sensor and mosfets to drive the output to rotate on a single axis. He even reduced the duty cycle on the fets so no heatsink is needed. Mounting in a peanut butter jar keeps the circuit dry and allows the sun to shine through. (The designer sells these, but has circuits up on the site)