unconsumption:

Several years ago, George Mason University graduate student Jason Force had a modern idea for the technology: Because grass pellets are just as good as wood chips for this kind of system, why not create a lawn mower with it? It could power itself with the grass it harvested. It could also be self-guiding, like a Roomba, so users would not longer have to mow their own lawn.

He got to work on the self-guiding aspect five years ago. The idea grew into a startup called EcoMow Technologies. Its team began working on the chemical engineering last year.

(via Within a few years, a self-powered robot could be mowing your lawn — Tech News and Analysis)