Greentech Media

For public transportation, the real cost really is nearly nothing, he said.

"What’s the cost of an [extra] passenger on a train with an empty seat?" he asked.

Assigning a cost to carbon might be the boost many energy-efficiency technologies are waiting for.

While venture capitalists and greentech advocates have often called such technologies "the low-hanging fruit" -- including David Sandalow, a senior fellow at the Brookings Institution and author of the book "Freedom From Oil" who spoke at the symposium -- the technologies received only 5.6 percent of the global cleantech venture-capital investment in 2007, according to the Cleantech Group.

In North America, energy-efficiency investments made up about 7 percent of the cleantech VC total, down from about 10 percent in North America in 2005, when Cleantech Group Chairman Nicholas Parker already said energy management had been considered an "arcane niche" (see Negawatts for Positive Returns).

Discussions at the UC Berkeley Symposium seemed to highlight the concept that energy efficiency, while important, still isn’t sexy.

During one keynote session, John Doerr, a partner with Kleiner Perkins Caufield & Byers, ran out of time to answer several questions relating to energy efficiency, including one about how venture capitalists can make money from energy-efficient technologies and applications.

Sandalow also didn’t address the topic in his keynote speech, but brought up the omission of energy efficiency in a question-and-answer session afterward.

"I have yet to mention in this keynote session efficiency and conservation," he said, calling it "the most important single step."