Much hope for an affordable clean-energy solution has been placed on the potential of biofuels like ethanol. Stanford University's Chris Somerville, director of the Carnegie Institution's Department of Plant Biology, shares that optimism—but also says that technologies are improving the prospects of a whole range of alternative energies. He spoke with NEWSWEEK'S Fareed Zakaria last week in Washington, D.C. Excerpts:

Zakaria: Are biofuels going to get us out of the energy trap?
Somerville: It's not a silver bullet. We need a broad basket of solutions. But it certainly can be important—if we could obtain 1 percent solar efficiency on 1 percent of the land in the world, that would be enough to provide all transportation fuels, or about 20 percent of our total energy use.

What would that mean exactly?
It turns out that many plants, such as sugar cane, actually capture more than 1 percent of the solar energy that strikes them. In fact, the theoretical efficiency for plants is above 6 percent, and some plants will do around 3 percent. To give you a sense of how much 1 percent of the world is—it's about 13 billion hectares. So 130 million hectares would be enough at 1 percent efficiency. The Brazilians say they can devote 40 million hectares to sugar cane.

One of the big problems with almost every alternative energy source is that to get to a large-enough scale, it will require huge investments to meet our needs. The secretary of Energy's goal, as I understand it, is to obtain about 30 percent of our transportation fuels from bio by 2030. That's on the order of 60 billion gallons, and would require a very large number of facilities distributed around the U.S. [But] it certainly can be done.