Vinod khosla has become the most widely recognized investor in clean technologies—those that generate or save energy with the least environmental impact. He founded Khosla Ventures in 2004 to fund new companies, after being a long-time partner at the giant investment firm Kleiner Perkins Caufield & Byers. His entrepreneurial roots stretch back to 1982, when he co-founded Sun Microsystems, which became a $7-billion workstation and software company. In a one-on-one dialogue, conducted before an audience of energy entrepreneurs and financiers at the recent GoingGreen conference in San Francisco, Scientific American’s Mark Fischetti asked Khosla (an adviser to the magazine) to assess, with his venture capitalist’s eye, which new energy innovations are most likely to succeed and why. Edited excerpts of the conversation follow.