It actually seems like a straightforward problem for solar energy. Just have a little "bot barn" with a solar roof and local storage, and the bots return to the

It actually seems like a straightforward problem for solar energy. Just have a little "bot barn" with a solar roof and local storage, and the bots return to the bot barn for a recharge. That's almost a trivial problem. Keep in mind the bots don't have to be very large; certainly not human-sized. Something the size of a roller skate, maybe, with specialized weed-killing tools. And if it encounters something too big or weird to handle on its own, it can mark it on a map and send an alert for human intervention.