Photos: On the fringes of green technology

It's easy--see diagram. Get deuterium and tritium, two heavy forms of hydrogen, and cause a reaction to turn them into helium and a neutron. That reaction releases lots of energy. And you don't get all that nuclear waste like you do with fission either.

Getting past the illustration is the tough part. Tritium virtually doesn't exist naturally. Instead, it can be harvested from lithium heated to millions of degrees. Harvesting more energy out of the process than it consumes is a challenge. Nonetheless, a few companies, such as Canada's General Fusion and Tri Alpha Energy (which raised $40 million in venture funds this year) are trying.