Aerospace engineer KR Sridhar always dreamed big: He used to work with NASA on technology to convert carbon dioxide into oxygen to support life on other planets or let humans breathe air on Mars. But as the Soviet Union fell and the space race slowed, Sridhar pivoted to providing clean energy technology for the rising global middle class. He cofounded Ion America in 2001-renamed Bloom Energy five years later-with a focus on fuel cells that deliver cleaner, on-site, off-grid power.