When it Comes to Electric Cars' Future, What's Better: PV or Biofuels?
February 13, 2013
As the slow road to the acceptance of electric vehicles in the United States continues, there are bound to be all kinds of studies that pop up about how best to power EV's.
There are, of course, questions about the popularity of EVs, and of the obstacles that currently are in their way: The idea that there just aren't enough charging stations in America, that demand for electric vehicles isn't that high, and the fear by many that the lithium batteries that power them just aren't strong enough.
But looking at electric vehicles from another perspective, a new joint study by a distinguished professor from the University of California at Santa Barbara and a scientist from the Norwegian University of Science and Technology has examined the question of which alternative energy would be best for powering electric vehicles: Photovoltaics (PV), which could help directly convert sunlight into fuel, or biofuels, using traditional methods of turning corn and other plants into ethanol, and energy crops into electricity?
The study examined the effects of biofuels and PVs on direct land use, greenhouse gas emissions, and lifecycle greenhouse gas.
As it turned out, in all three categories, the competition wasn't even a fair fight. Photovoltaic cells were found by Dr. Roland Geyer of the Bren School at UC-Santa Barbara and his team to be more than 29 times more efficient, and found to be beneficial in all other parts of the lifecycle assessment as well.
"We were really surprised that it was that big of a gap," Dr. Geyer told me in a recent phone interview. "And really, in most cases it's more than (29 times) more efficient; that was just the low end."
"If your only choice is biomass or photovoltaics," Geyer continued, "and your metric is best use of the sun, then photovoltaics are much more efficient than biomass at turning sunlight into energy to fuel a car."
The new study, published in the journal Environmental Science and Technology, investigated the relative efficiencies of biofuels and PV cells by focusing on traditional ways of turning corn and similar plants into ethanol, turning some energy crops into electricity, and using PVs to directly convert sunlight into fuel.
Geyer explained that he got the idea to study this topic while teaching a class about energy sources and energy management; he said one thing that always surprises his students is when he makes them calculate the energy convergent efficiency of sunlight; i.e., how much sunlight that hits a corn crop over the course of a year is actually used and accepted by the crop.
"For all field crops and any kind of corn, it’s less than 1 percent of the energy in the sunlight that gets used," Geyer said. "So one student asked me, after hearing that, 'shouldn’t we just rip out the corn and put in PV cells instead?' And that began our research."
Geyer said he also wanted to investigate the topic due to the "crossroads" he sees in environmental transportation.
"On the one hand, we're making all these plug-in hybrids and battery electric vehicles fit for the road, but on the other hand we've never made more corn ethanol in this country; 40 percent of our corn goes into ethanol production," he said. "I think we're at a crossroads with vehicles where we could either go down the biofuels road, or the electric vehicles road."
To start the study, Geyer and research partners David Stoms and James Kallaos examined five major "sun-to-wheels" energy conversion pathways for every county in the U.S.:
- Ethanol from corn for internal combustion vehicles
- Ethanol from switchgrass for internal combustion vehicles
- Electricity from corn for battery-powered vehicles
- Electricity from switchgrass for battery-powered vehicles
- Photovoltaic electricity for battery-powered vehicles
The only slight twist Geyer said he put on the data was the decision not to use average corn yields, using maps instead, saying "we wanted to be spatially explicit."
To explain how the researchers reached their conclusion, Geyer explained that for every megajoule of electricity needed for an electric vehicle, you need four megajoule of corn ethanol for the same amount of energy. With an electric power train having roughly four times the energy conversion efficiency of the power train of an internal-combustion engine, Geyer explained, you can calculate the difference using PVs and biofuels rather simply.
In Delaware, Iowa, if you had 27.7 square meters of cornfield, then harvested the corn and turned into ethanol, then put that into a vehicle, you could travel 100 kilometers before running out of power.
If you put in solar radiation and had that same 27.7 square meters of cornfield, and used PVs to drive an electric vehicle, you could drive 15,400 kilometers before conking out.
"So clearly," Geyer said, "harvesting sunlight for transportation is the way to go."
As the cost of solar technology continues to drop, the researchers believe that electric vehicles will show an advantage over biofuel combustion cars, and that subsidies that keep investing in biofuels are in essence “barking up the wrong tree.”
While biofuels may improve within the next five years, solar electric vehicle technology is accelerating at a fast pace, making the gap between the two all the more pronounced.
I asked Geyer if he thought EV manufacturers "got" this, and would actually change or alter how they proceed.
"I did see on the Nissan Leaf website that they had teamed up with a solar installer called Sun Power, but outside of that I haven't seen much else," Geyer said. "I think our data is a pretty compelling argument for PVs.
It's been a bad few weeks for biofuels in the news, and not just because of the Geyer study. Another report, from researchers at Lancaster University in England, found that crop-based biofuels may also possibly worsen air pollution and create health problems for humans.
In the researchers' case study, around 72 million hectares of land were converted into biofuel crops like willow, poplar or eucalyptus trees in order to produce high amounts of ethanol. (One hectare is a metric unit that's comparable to 2.47 acres).
These crops are characterized by high tree density (1,500 to 3,000 trees per hectare) and have high yields, but the researches at Lancaster found that they have the characteristic of releasing higher levels of the chemical isoprene as they grow than do traditional crops.
What is isoprene? It's a reactive volatile organic compound that when mixed with other pollutants in the air like nitrogen oxide, produces toxic ozone.
According to the authors of the study, this pollution can cause lung problems and affect the brain, kidneys, and eyes, and is blamed for the deaths of about 22,000 people a year in Europe. The increase in isoprene emissions created by these new crops will lead, according to the study, to an extra 1,365 premature deaths per year, costing society $7.1 billion.
The researchers suggest planting biofuel crops far away from population centers or zones of intense agricultural production with the aim of limiting ozone formation. Genetic engineering could be used to reduce isoprene emissions.
Now obviously this is just one study, but given the potential for health hazards resulting from biofuels, the health risks they could potentially pose if genetically engineered certainly deserves further scrutiny.