Daniel Epperson's MowBot began with an old push mower and an electric wheelchair. Now it's a hodgepodge of several different technologies for the ultimate tool in lawn maintenance:
This is the Prius of lawnmowers, bringing together hybrid technology to cut the grass with the gasoline powered motor, and to propel the rig with electricity. [Danny's] worked hard to shoe-horn just about every feature imaginable (other than autonomy) into the thing, and that’s why the batteries can be charged from mains, an alternator powered by the gas motor, and now from the PV panel mounted on top of it.
You can see videos of the robot in action at the link. Hopefully Mr. Epperson tackles autonomy next.