A small number of vehicles on U.S. roads are already indirectly powered by the sun. Ostensibly, some of America's electric cars use power derived from solar panels. And the fuel cells that bolster a growing fleet of hybrid cars and buses rely on hydrogen converted by photovoltaic cells.
But America is a liquid fuel kind of nation. To help wean American's off their love of gasoline, researchers at Harvard have found a way to turn solar energy into liquid fuel. It's like gas -- only good for the environment.
The liquifying process relies on bacteria. After a sort of a artificial leaf -- similar to a photovoltaic cell -- splits the absorbed sunlight into hydrogen and oxygen, a lab-engineered bacterium (Ralstonia eutropha) is introduced. The bacteria combines the hydrogen with carbon dioxide to create a liquid fuel called isopropanol.
The unique approach combines the powers of an inorganic catalyst with a biological system -- the integration of human engineering with the biological wonders of the natural world.
"We're almost at a 1 percent efficiency rate of converting sunlight into isopropanol," lead author Daniel Nocera explained. "There have been 2.6 billion years of evolution, and Pam and I working together a year and a half have already achieved the efficiency of photosynthesis."
Researchers are hoping to ramp up to 5 percent efficiency soon. The research was published this week in the journal PNAS.
"This is a proof of concept that you can have a way of harvesting solar energy and storing it in the form of a liquid fuel," said co-author Pamela Silver. "Dan's formidable discovery of the catalyst really set this off, and we had a mission of wanting to interface some kinds of organisms with the harvesting of solar energy. It was a perfect match."