The Scale of Biofuels
Math Warning! There is a little math in this article, but it is easy to follow.
The Obama administration is promoting biofuels and other alternative energy as a source of future jobs. The National Renewable Energy Laboratory (NREL) has a section on biofuels if you want a primer on the subject. Biofuels can be derived from corn, soybeans, switch grass, algae, and a host of other plants. Corn is the worst and by many estimates it takes as much or more energy to grow and process the corn into ethanol (a form or alcohol) than the energy that is stored in the liquid.
Soybeans are much more efficient than corn at producing biofuel. A model of the process was built by the U.S. Department of Agriculture (USDA) and the U.S. Department of Energy (DOE) in a report titled: Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus. From that study soybeans are 66% energy efficient. It takes 1/3 of the available energy in the final biofuel to plant the seeds, grow the plant, harvest the seeds, and process them into fuel. That is for every 3 units of biodiesel energy you only have to spend 1 unit of carbon energy.
The 66% efficiency is great, but you have to also factor in other parts of the system – the soybeans do not grow in isolation. They exist in a system that includes land use and economics. The US had 75,208,000 acres planted in soybeans in 2004 according to USDA National Agricultural Statistics Service. The same source lists total US cropland at 434,164,946 acres.
Some environmental blogs give ranges of 100-150 gallons of biodeisel per acre of soybeans and Wikipedia gives a range of 40-50 gallons per acre.
If we just take the highest number anywhere – 150 gallons per acre, then soybeans yield a net energy, in biodiesel, of .66 X 150 or 99 gallons of fuel per acre. If we take every single soybean grown in the US and make biodiesel out of them we would get 7,445,592,000 gallons of biodiesel per year.
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