Snowmass, Colo.

A quarter-century ago, in the wake of America's first energy crisis, a young scientist named Amory Lovins came to the Rocky Mountains and built himself a radical house based on a radical idea. The country could save both energy and money, he believed, by combining common sense and unconventional technology.

Mr. Lovins did achieve substantial energy savings, and many of his innovations, from better insulation to multiple-pane windows to more-efficient refrigerators, eventually became familiar fixtures in American homes.

But on the second part of Mr. Lovins's ambition -- saving money -- the calculus has been more complicated. The advances that allowed him to create a roomy home with a tiny carbon footprint came with a hefty upfront cost.

Now, Mr. Lovins has completed a renovation that he hopes will demonstrate how much more energy-efficient houses can become. But the project also serves as a reminder of the still-enormous gulf between what is technologically possible and what society is able or willing to pay for.