In recent years the US has focussed on adding ethanol to its gasoline as it believes that it will help reduce dependence on foreign oil and reduce greenhouse gas emissions. In 2006 4 billion gallons of renewable fuel were added to gasoline, in 2007 it was 4.7 billion, and then in 2012 that number grew to 7.5 billion gallons.
The problem is that a life cycle assessment has shown that ethanol has only a modest effect on reducing CO2 emissions, and may actually lead to an increase. Corn ethanol production also consumes 40% of the US corn crop, and as the US produces 40% of the world’s corn, prices around the globe have increased, and food shortages have occurred.
An alternative to using biofuel in vehicles, is to power a vehicle by electricity. Using electricity generated in a coal plant would defeat the purpose of using and EV, but electricity from solar power could very well make EV’s the most efficient transport method on the road.
Roland Geyer, a professor at the UCSB Bren School of Environmental Science & Management, asks whether growing crops to make alternative fuels is more efficient and effective than using photovoltaics to directly power an EV.
“The energy source for biofuels is the sun, through photosynthesis. The energy source for solar power is also the sun. Which is better?”
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The results of this study, released in a paper titled, “Spatially Explicit Life Cycle Assessment of Sun-to-Wheels Transportation Pathways in the U.S.”, show that photovoltaics are far more efficient than biofuels at converting the suns energy into miles driven.
Three ways of converting sunlight into energy to power a car were considered; using corn to produce ethanol, using the biomass of corn to directly create electricity of an EV, and using PV cells to convert the solar energy directly into power for the EV. The researchers identified using PV cells to directly power the EV as the most efficient method for powering a vehicle by energy from the sun.
“What it says to me is that by continuing to throw money into biofuels, we’re barking up the wrong tree. That’s because of a fundamental constraint, which is the relative inefficiency of photosynthesis. And we can’t say that right now biofuels aren’t so great but they’ll be better in five years. That fundamental problem for biofuels will not go away, while solar EVs will just continue to get more efficient and cheaper. If they’re already looking better than biofuels, in five years the gap will be even greater. A search for a silver bullet is under way through synthetic photosynthesis, but using genetic engineering to improve the efficiency of photosynthesis is a pipe dream. If there is a silver bullet in energy, I think it’s solar power.”