I remember back in, I think the 60's.. A magazine called Popular Electronics, (now deceased as I recall) did a story on building a "Solar Sundial"
This unit consisted of some solar panels, and some shaded solar cells.. IF the sun was shining more on the clockwise one,, a motor was activated till the two shaded cells were balanced (there was a vane between them) to the bigger panels always faced the sun.
Now this was designed as a Sundial, novelity item.
But if you put bigger panels on it.. Automatic sun tracker.
Add two more solar cells with a horizontal vane instead of a vertical one and it's a 2-axis sun tracker.
Several companies have tried to patent such designs (Solar trackers) however the PE article makes it kind of hard to do that.