Zombie Power!

While zombies that are merely infected humans can be considered science fiction (if rather far-fetched), the undead variety are pure fantasy. In order to function without air, water, or food for an indefinite period, they would have to be converting their own mass directly into energy. What's more, such a process would have to operate at an extremely high efficiency or else they'd generate massive quantities of waste heat. This is completely ridiculous, but offers the amusing prospect of harnessing the zombies for power generation. Obviously the best mechanism would be to reproduce the biology involved at the cellular level, but a much more direct approach using zombies to push a rotor attached to a generator could be employed. Their aggression, tirelessness, and low intelligence can be exploited by using a moving speaker to constantly lead them, much like the proverbial horse attracted by the carrot on a stick. As a security measure they could be sealed in as they require neither air nor light. You know your science fiction is terrible when it leads to perpetual motion machines.