That's never going to happen for the same reason there aren't any photosynthesizing animals : you just don't get the required power output. A human walking use

That's never going to happen for the same reason there aren't any photosynthesizing animals : you just don't get the required power output. A human walking uses about 80 Watts [1]. Assuming no losses that requires a 1/3 m2 solar panel (a perfect one, constantly in full sunlight) to just move during the day. So count on needing 2/3 m2 at the very least. And while robotics have advanced, there is no robot I know of that uses less than 300 or so watts. I think you're right though that there is a market for very large, very heavy vehicles with legs, for where slopes are either too steep, or the region just doesn't have roads. Such vehicles exist, but humans just can't control 4 legged vehicles. It quickly ends in disaster. [1] https://en.wikipedia.org/wiki/Human_power https://en.wikipedia.org/wiki/Human_power [2] https://www.google.com/search?q=solar+power+output+per+square+meter https://www.google.com/search?q=solar+power+output+per+squar...