``The Matrix'' , while a somewhat entertaining film, was based on a premise that made no sense thermodynamically. In the film, the machines use humans confined to pods as an energy source. In an attempt to salvage a modicum of self-consistency, the confined humans were fed using a source derived from deceased humans. Unfortunately, this can never work. A person weighing say 70Kg requires about 2000 Kcal of food energy per day, a little less if they're inactive. A gram of tissue has about 5 Kcal of combustible energy. If a person is converted entirely into a food source, this would yield about 350,000 KCal, enough to sustain a person for only 175 days. Thus, the human generator could never achieve a chain-reacion necessary for a self-sustaining energy source.
However, we as humans do produce plenty of body heat, about 100 watts when we're still and a lot more when we're exercising. This is enough to power many of our devices. It is reported in this week's Nature Materials, that a group from the University of Toronto has devised a polymer based photovoltaic cell that is sensitive to infrared radiation. This paves the wave for making clothing someday that can use sunlight, ambient light, and body heat to power the toys of the modern road warrior.