How does energy produced by the sun (solar) compete with ethanol in terms of land use, life-cycle emissions and cost? These questions are being asked by University of California Santa Barbara (UCSB) Bren School of Environmental Science & Management Professor Roland Geyer. He wants to know what makes more sense, growing fuel crops to supply alternative-fuel vehicles with ethanol or other biofuels or using photovoltaics (PV) to directly power battery electric vehicles (EVs).
“The energy source for biofuels is the sun, through photosynthesis,” explains Geyer. “The energy source for solar power is also the sun. Which is better?”
To find out, Geyer joined former BrenSchool researcher David Stoms and James Kallaos, of the Norwegian University of Science and Technology, to model the relative efficiencies of the technologies at converting a given amount of sunlight to miles driven. The results have been published in the paper, “Spatially Explicit Life Cycle Assessment of Sun-to-Wheels Transportation Pathways in the U.S.,” in the Dec. 26 issue of the journal Environmental Science & Technology. Results showed photovoltaics (PV) to be much more efficient than biomass at turning sunlight into energy to fuel a car.
“PV is orders of magnitude more efficient than biofuels pathways in terms of land use — 30, 50, even 200 times more efficient — depending on the specific crop and local conditions,” said Geyer. “You get the same amount of energy using much less land, and PV doesn’t require farm land.”
The researchers examined three ways of using sunlight to power cars: 1) the traditional method of converting corn or other plants to ethanol; 2) converting energy crops into electricity for BEVs rather than producing ethanol; and 3) using PVs to convert sunlight directly into electricity for EVs. Because land-use decisions are local, Geyer explained, he and his colleagues examined five prominent “sun-to-wheels” energy conversion pathways — ethanol from corn or switchgrass for internal combustion vehicles, electricity from corn or switchgrass for EVs, and PV electricity for EVs — for every county in the contiguous United States.Read More










