Nestling high among Colorado's snow-capped peaks is Rocky Mountain Institute, a natural-resources think-tank. Visitors in search of insights into the future of energy are shown the passive-solar atrium, the super-efficient toilet and the high-altitude banana farm. But the people who run this place do not have their head in the clouds. Amory Lovins, co-founder of RMI, is one of the world's most energetic visionaries, and like all visionaries he occasionally gets things wrong; but he has also got some big things spectacularly right.