CAMBRIDGE, Mass.--What does it take to pick a winner in the slowly unfolding field of renewable energy ? For starters, alternatives to oil must be able to stand up on their own at some point, without a need for permanent government subsidies, said Bill Joy, once a heavy hitter in the information technology industry and now a partner in investor Kleiner Perkins Caufield & Byers’s greentech practice.

During a Q&A with Technology Review Editor in chief Jason Pontin at the magazine’s Emtech conference Wednesday, Joy pointed out that another key to determining the future of a startup greentech company is whether its approach makes sense intuitively. Investors find new technologies that can displace older technologies because these new technologies are better and make their own case, said Joy. In 1982, he co-founded Sun Microsystems. He went on to serve as its chief technologist for the next 20 years. (Software maker Oracle bought Sun for $7.4 billion in January 2010.)