Step 3: Geared clock drive details:
A standard off-the-shelf Intermatic Spring Wound Wall Timer (Model FD12HC), with a 21 tooth spur gear mounted on the 3/16" diameter knob shaft, and a 36 tooth spur gear mounted on the 1/4" threaded axis that holds and rotates the solar panel. The electrical contacts of the Intermatic timer were gutted to reduce drag.
It's important to note that these Intermatic™ clock timers are now in short supply, as the Intermatic™ website no longer seems to be running and hardware stores no longer stock these reliable and well-made devices. There are other brand(s) of household windup clock drive wall timers out there, but they are not well made and are unreliable, and are, simply, false economy.