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Energy Dependence, Part 2

A recent op-ed by two professors at the Polytechnic University of New York in the Washington Post makes the case that biofuels offer no long-term alternative to fossil fuels. They write:

But as we've looked at biofuels more closely, we've concluded that they're not a practical long-term solution to our need for transport fuels. Even if all of the 300 million acres (500,000 square miles) of currently harvested U.S. cropland produced ethanol, it wouldn't supply all of the gasoline and diesel fuel we now burn for transport, and it would supply only about half of the needs for the year 2025. And the effects on land and agriculture would be devastating.

It's difficult to understand how advocates of biofuels can believe they are a real solution to kicking our oil addiction. Agriculture Department studies of ethanol production from corn -- the present U.S. process for ethanol fuel -- find that an acre of corn yields about 139 bushels. At an average of about 2.5 gallons per bushel, the acre then will yield about 350 gallons of ethanol. But the fuel value of ethanol is only about two-thirds that of gasoline -- 1.5 gallons of ethanol in the tank equals 1 gallon of gasoline in terms of energy output.

Moreover, it takes a lot of input energy to produce ethanol: for fertilizer, harvesting, transport, corn processing, etc. After subtracting this input, the net positive energy available is less than half of the figure cited above. Some researchers even claim that the net energy of ethanol is actually negative when all inputs are included -- it takes more energy to make ethanol than one gets out of it.

But allowing a net positive energy output of 30,000 British thermal units (Btu) per gallon, it would still take four gallons of ethanol from corn to equal one gallon of gasoline. The United States has 73 million acres of corn cropland. At 350 gallons per acre, the entire U.S. corn crop would make 25.5 billion gallons, equivalent to about 6.3 billion gallons of gasoline. The United States consumes 170 billion gallons of gasoline and diesel fuel annually. Thus the entire U.S. corn crop would supply only 3.7 percent of our auto and truck transport demands. Using the entire 300 million acres of U.S. cropland for corn-based ethanol production would meet about 15 percent of the demand.

It is argued that rather than using corn to make ethanol, we can use agricultural wastes. But the amounts are still a drop in the bucket. Using the crop residues (called corn stover) from corn production could provide about 10 billion gallons per year of ethanol, according to a recent study by the U.S. Energy Information Administration. The net energy available would be greater than with ethanol from corn -- about 60,000 Btu per gallon, equivalent to a half-gallon of gasoline. Still, all of the U.S. corn wastes would produce only the equivalent of 5 billion gallons of gasoline. Another factor to be considered: Not plowing wastes back into the land hurts soil fertility.

Similar limitations and problems apply to growing any crop for biofuels, whether switchgrass, hybrid willow, hybrid poplar or whatever. Optimistically, assuming that switchgrass or some other crop could produce 1,000 gallons of ethanol per acre, over twice as much as we can get from corn plus stover, and that its net energy was 60,000 Btu per gallon, ethanol from 300 million acres of switchgrass still could not supply our present gasoline and diesel consumption, which is projected to double by 2025. The ethanol would meet less than half of our needs by that date.

And they end with the always-inconvenient issue of trade offs:

Finally, considering projected population growth in the United States and the world, the humanitarian policy would be to maintain cropland for growing food -- not fuel. Every day more than 16,000 children die from hunger-related causes -- one child every five seconds. The situation will only get worse. It would be morally wrong to divert cropland needed for human food supply to powering automobiles. It would also deplete soil fertility and the long-term capability to maintain food production. We would destroy the farmland that our grandchildren and their grandchildren will need to live.