Amory Lovins last year harvested from his small garden more than 30 pounds of bananas, along with guava, mango, papaya, loquat, passion and other exotic fruit. Nothing remarkable in that, except that the energy analyst and chief scientist of the Rocky Mountain Institute (RMI) does not live in the tropics but in an unheated house 6,500 feet up a mountain near Aspen, Colorado, where the temperature falls to -44C and where last week more than two feet of snow fell in less than 24 hours. The fruit is grown in a greenhouse that is part of the sprawling, experimental, super-insulated house at Old Snowmass, built 30 years ago for $500,000 (300,000) and an inspiration for a generation of energy thinkers, designers and sustainable builders. Visited by 100,000 people, it was the archetype for the European Passivhaus movement. "Heating systems are so 20th century," he says. "We have found you actually save money by not putting in a heating system. It's cheaper. The monitoring system uses more energy than the lights." Lovins has always maintained that energy conservation not only pays for itself, but that energy-saving technology can lead to higher quality of life at lower cost. He has advised many of the world's largest companies and dozens of countries how to reduce bills with renewables but has also challenged the giant car, aviation and construction industries to rethink the way they operate. Renewables have scaled up incredibly fast, he says. "Worldwide it is faster than mobile phones. More Kenyans now get first electricity now from solar than the grid. China got more generation from wind in 2012 than from nuclear and it added more generation from non-hydro renewable energy than fossil and nuclear combined. It is now the world leader in seven of the 10 renewable energies and wants to be top in all 10.