“Lonnie’s using temperature differences to create pressure gradients,” says Paul Werbos, an energy expert and program director of the National Science Foundation. “Only instead of using those pressure gradients to move an axle or a wheel, he’s forcing ions through a membrane.” Werbos, who spent months vetting the JTEC and eventually awarded Johnson’s team a $75,000 research grant in 2006, describes the JTEC as “a fundamentally new way, a fundamentally well-grounded way, to convert heat to electricity.” Regarding its potential to revolutionize energy production on a global scale, he says, “It has a darn good chance of being the best thing on Earth.”

Johnson is a member of what seems to be a vanishing breed: the self-invented inventor. Born the third of six children in Mobile, Alabama, in 1949, he came into the world a black male in the Deep South during the days of lawful segregation. His father, David, who died in 1984, was a World War II veteran and a civilian driver for nearby Air Force bases. According to his mother, Arline, who is 86 and still lives in Mobile (in a house remodeled with Super Soaker profits), the family was poor but happy. All eight lived in a three-bedroom, one-bathroom house near Mobile Bay, in a neighborhood then being bisected by the construction of Interstate 10.

As a boy, Johnson was quiet and curious, and early on, he developed a fascination with how things worked. “Lonnie tore up his sister’s baby doll to see what made the eyes close,” his mother recalls. As he grew older, he began making things, including rockets powered by fuel cooked up in his mother’s saucepans. At 13, he bolted a discarded lawn-mower engine onto a homemade go-cart and took it atop the I-10 construction site—only to have a bemused policeman escort him back down. It was around then that Johnson learned that “engineers were the people who did the kind of things that I wanted to do.”

It was hardly an obvious career path: then, as now, the profession was dominated by whites. (As recently as 2004, only 1.6 percent of the engineering doctorates awarded in the United States went to blacks.) In high school, a standardized test from the Junior Engineering Technical Society informed Johnson that he had little aptitude for engineering; but he persevered and, as a senior, became the first student from his all-black high school ever to enter the society’s regional engineering fair. The fair was held at the University of Alabama at Tuscaloosa, just five years after then-Governor George Wallace had tried, in 1963, to physically block two black students from enrolling there. Johnson’s entry in the competition was a creation he called Linex: a compressed-air-powered robot assembled from electromagnetic switches he’d salvaged from an old jukebox, and solenoid valves he’d fashioned out of copper tubing and rubber stoppers. The finished product wowed the judges, who awarded him first prize: $250 and a plaque. Unsurprisingly, university officials didn’t trumpet the news that a black boy had won top honors. “The only thing anybody from the university said to us during the entire competition,” Johnson remembers, “was ‘Goodbye, and y’all drive safe, now.’”

Johnson went on to win math and Air Force ROTC scholarships to Tuskegee University, where he received a bachelor’s degree in mechanical engineering and a master’s in nuclear engineering. He joined the Air Force in 1975 and subsequently held jobs at the Air Force Weapons Laboratory, NASA’s Jet Propulsion Laboratory, and the Strategic Air Command—solid, respectable positions that made him a part of the scientific establishment. But at each stop, he felt that his creativity was stifled, and in 1987, at the age of 38, he could take it no longer. He would go into business for himself, he decided, focusing on his own projects, which included a thermodynamic heat pump, a centrifugal-force engine, and a pressure-action water gun. “All I needed was one to hit,” he says, “and I’d be fine.”