THERE is an indisputable elegance to the idea of transforming garbage into fuel, of turning icky, smelly detritus into something valuable. But big drawbacks have prevented the wholesale adoption of trash-to-gas technology in the United States: incineration is polluting, and the capital costs of new plants are enormous. Gasification systems can expend a tremendous amount of energy to produce a tiny amount of electricity. Up to this point, it hasn’t seemed worth the trouble. Mike Hart thinks that he has solved those problems. In a former Air Force hangar outside Sacramento, his company, Sierra Energy, has spent the last several...