The results, which appear in a paper titled "Spatially Explicit Life Cycle Assessment of Sun-to-Wheels Transportation Pathways in the U.S." and published in the Dec. 26 issue of the journal Environmental Science & Technology, 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," says 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: a) the traditional method of converting corn or other plants to ethanol; b) converting energy crops into electricity for BEVs rather than producing ethanol; and C) using PVs to convert sunlight directly into electricity for BEVs.
Because land-use decisions are local, Geyer explains, 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 BEVs, and PV electricity for BEVs for every county in the contiguous United States.
Focusing the LCA on three key impacts direct land use, life cycle greenhouse gas (GHG) emissions, and fossil fuel requirements the researchers identified PV electricity for battery electric vehicles as the superior sun-to-wheels conversion method.
"Even the most efficient biomass-based pathwayrequires 29 times more land than the PV-based alternative in the same locations," the authors write. "PV BEV systems also have the lowest life-cycle GHG emissions throughout the U.S. and the lowest fossil fuel inputs, except in locatio
|Contact: James Badham|
University of California - Santa Barbara