I’m an engineer. Not environmentalist,” says Michael Polsky, as if to explain why even after spending 17 years developing renewable-energy systems, he’s still enthralled by the sight of 125-foot-long wind turbine blades sweeping elegantly through the sky. It’s the machines that this serial entrepreneur loves. And building. And making profitable deals. After becoming a centimillionaire by developing gas-fired turbines, the 71-year-old has ridden wind power to billionaire status.