Wow... My immediate idea is exactly the oposite from the one proposed in the article:

Have robots that can "live" by eating "food"! Imagine a robot, say a "spider" or a "mouse", that roams around a city, collecting food (and has a form of a "stomach", similar to say the one that cows have, where there are bacteria, dissolving food and producing glucose), and it can use that glucose to generate electricity, indefinitely... An interesting idea!