Bob Mann leans against his wife’s 2006 Volkswagen Jetta in his tool-packed garage. The mechanic and inventor has just converted the car, which is the color of a ripe crab apple, to run on natural gas. He shakes his head.

“It’s a no-brainer. We could jump-start the economy overnight, put 100,000 people to work – easy – and help the environment,” says Mr. Mann, a former Volkswagen technician who’s as comfortable talking about global energy solutions as he is around a socket wrench.