>>6454616Not just early sets, but modern Power Functions has its own solar panel.
This solar panel is packaged along with the E-Motor and a sort of dynao doohickey whose name I can't remember that's used as supplemental materials for Lego Education stuff. They can be used alone, or in tandem with NXT for a medley of experiments.
https://www.youtube.com/watch?v=n1vphpzKJt0