Not so much a power source as it a power storage method, you still need some sort of fuel to run 'em. They'll probably start with something like hydrogen because it's easiest to work with at that level from a technological perspective, but I'm hoping we'll see other fuels soon. An almost solid-state generator that has a fuel hopper with an enzyme-based culture living in it that breaks stuff down into something that can run the microturbines would be pretty sharp.
Shovel a bunch of grass clippings and coffee grounds in, ala Mr. Fusion, and away it goes. Maybe it doesn't produce kilowatts, but the mechanical simplicity plus the promise of being able to build these in mass quantity could have pretty big consequences down the road.
