May 7, 2009 at 5:01 PM ET
|Click for graphic: See |
how biomass is converted
into ethanol or electricity.
Suppose you take an acre's worth of switchgrass and turn it into ethanol for your flex-fuel car, while your neighbors take their acre's worth and burn it in a power plant to generate electricity for their plug-in hybrid. Which car would go farther?
If you guessed that your car would, you'd be way off. About 7,000 miles off, in fact.
In a study published online today by the journal Science, researchers say using biomass to generate electricity is more efficient for transportation than making biofuels - and might actually do more to cut CO2 emissions as well.
So does that mean bioelectricity is better than bioethanol? Wrong again.
"Currently, at a commercial scale, we're only beginning to explore these two different scenarios," said lead study author Elliott Campbell, an engineering professor at the University of California at Merced. "In both cases, it really remains to be seen which technology pathway can develop quicker."
Another co-author of the study, Stanford University's David Lobell, said the analysis was meant to spark a debate, not settle one.
"What we are hoping is that this will open up a broader discussion on renewable energy for transportation, and not just renewable liquid fuels," Lobell told me. "It wouldn't surprise me if there are some strong reactions to this study, on both sides. Our hope is just to bring this general point to the forefront: Maybe we should be thinking about how efficiently we use our land, and not just about what's the best way to do ethanol."
The enthusiasm over ethanol has cooled a bit over the past couple of years, due to concerns about food-vs.-fuel price competition and as well as the environmental and mechanical downsides of ethanol production. In addition, last year's plunge in gasoline prices made ethanol less economically attractive.
Nevertheless, ethanol production has been growing, and that trend appears likely to continue as the technology advances. Just this week the White House highlighted the promise of cellulosic ethanol - which is a better option than the corn-based ethanol currently on the market. This type of ethanol could be produced from non-food cellulose, ranging from wood chips and yard waste to high-yield grasses such as miscanthus and switchgrass.
The tricky part is that the cellulose can also be used to fire electric power plants, usually in co-production with coal. In the study published today, Campbell, Lobell and the Carnegie Institution's Christopher Field ran the numbers to see which energy pathway would provide more get-up-and-go for next-generation automobiles.
They gathered up a wide range of existing statistics for energy costs and benefits - including the cost of raising the crops, the cost of making and disposing of the cars, the efficiency of ethanol-fueled vs. electric-powered cars and the value of at least some of the byproducts. Then they put all those factors together to come up with the "miles per acre" (or kilometers per hectare, if you swing that way) for the two different pathways.
"The final metric that we showed is not the type of metric that you see in many previous bioenergy studies, so that's something new," Campbell said.
The verdict? When it came to converting switchgrass, the average payoff was 81 percent higher for electric vehicles than for ethanol-fueled vehicles, primarily due to the higher efficiency of the all-electric drive. For a small SUV, that translates to 15,000 miles per acre for electric vs. 8,000 miles per acre for ethanol.
The bioelectricity pathway also resulted in more than twice the benefit when it came to reducing greenhouse-gas emissions over the vehicle's life cycle.
So why go to the effort of making ethanol at all? Even though their figures look better for bioelectricity, the researchers acknowledge that liquid biofuels will have to be part of the energy equation for a long time to come. For one thing, not all transportation vehicles can just be plugged into an outlet. "I don't think anybody is talking about electric planes anytime soon," Lobell said.
And even when it comes to highway transportation, there are good reasons for preferring liquid fuel to electrical juice. "We don't use electric cars because, unless you're talking about specialized applications like forklifts or golf carts, they are not terribly efficient," said rocket scientist Robert Zubrin, who gives biofuels a strong boost in a book titled "Energy Victory."
"All this stuff about the efficiency of ethanol compared to burning switchgrass for electricity misses the point," Zubrin told me. He said liquid-fueled vehicles beat out electric vehicles in the earliest days of the automobile and will continue to do so, primarily due to convenience and cost considerations.
He pointed out that it takes just a couple of minutes to put enough ethanol blend in your gas tank to go more than 100 miles. "Imagine trying to put that much energy down a wire in a minute, or 10 minutes," Zubrin said.
Plug-in hybrid electric vehicles rely on battery power as well as liquid fuel to extend their range - but the dual propulsion system makes such cars thousands of dollars more expensive as well as more complicated to produce, Zubrin said. President Obama's recent call to put a million plug-in cars on the road by 2015 may sound impressive, but it would hardly make a dent in the energy situation.
"There are 200 million cars in the United States," Zubrin said. "That means that in 10 years he will have replaced one-half of 1 percent of the nation's cars."
Mandating the production of more flex-fuel cars - which are capable of using alternative-fuel blends or straight gasoline - would produce a much quicker and larger payoff, according to Zubrin and other biofuel boosters. Such a mandate is contained in the Open Fuel Standards Act, currently under consideration in Congress.
"Flex-fuel adds only $100 to the cost of a new car," Zubrin said. "We'd have 30 million to 50 million of these things on the road in the next three to five years."
Promoting alternative fuels could yield a geopolitical payoff as well.
"By making flex-fuel the American standard to sell a car in the U.S.A., this would compel the foreign automakers to switch, too," Zubrin said. "That is how we destroy OPEC - because, you see, it's a question of creating opportunity for alternative-fuel makers to enter the market. ... Liquid fuels are what is needed to replace oil."
Bioethanol vs. bioelectricity? Or both? Experts on all sides of the debate agree that both will be needed - it's just a question of where to put the policy emphasis.
"The current situation is that there are lots of different things you can do with biomass and fossil fuels," the Carnegie Institution's Field told me. "As we build up the infrastructure for biomass one way or the other, it will tend to lock us into using that approach over the life of a factory, which could be 10, 20 or 30 years."
So which blend of energy resources should we go with? Feel free to weigh in with your comments below.
Update for 2:40 p.m. ET: Before you comment, here are three more considerations to throw into the mix:
More about energy alternatives: