Biofuel potential
As the price of crude oil continues to rise, political leaders and public officials have called for increased reliance on biomass-based fuels, such as ethanol made from corn and biodiesel made from soybeans, as substitutes for petroleum-based fuels. What is the potential contribution of biomass-based fuels to relieving America¿s dependence on petroleum (of which 60% is now imported from foreign sources)?
To answer this question I calculated the amount of ethanol and biodiesel that could be produced from the 2004 US corn and soybean crops and compared it to our nation¿s annual consumption of petroleum. Crop totals are from the US Department of Agriculture; the biofuel potentials of corn and soybeans are from industry sources.
The 2004 US corn crop totaled about 11.7 billion bushels, the largest ever. One bushel of corn yields 2.66 gal of ethanol, so hypothetically the 2004 crop could be converted into 31.122 billion gal of ethanol. However, a portion of the energy in the ethanol represents energy invested in growing, harvesting, transporting, fermenting and distilling the corn. According to the corn ethanol industry, the energy yield is 1.67 btu for each btu consumed in production, or a net yield of about 40.1% of total ethanol produced. Multiplying the hypothetical 2004 production of corn ethanol by this factor leaves a net yield of 12.48 billion gal. But ethanol has less energy content than petroleum. One gallon of crude oil contains about 138,100 btu, while a gallon of ethanol contains about 84,100 btu, or about 60.9% of petroleum. So on an energy-equivalent basis, 12.48 billion gal of ethanol would equal about 7.6 billion gal of petroleum.
Using the same methodology, one can calculate the potential contribution of soy-based biodiesel (soybeans constitute about 90% of the total US oilseed crop). The 2004 US soybean crop was 3.15 billion bushels, also an all-time record. One bushel of soybeans yields about 1.4 gal of biodiesel. The energy yield of biodiesel is about 3.2 btu for each btu consumed in production, or a net of 68.75%, a much better rate than ethanol from corn. The energy content of a gallon of biodiesel is much higher, 128,000 btu, about 92.7% of petroleum.
The 2004 US soybean crop converted to biodiesel would equal about 2.81 billion gal of petroleum (3.15 billion bushels times 1.4 gal of biodiesel per bushel is 4.41 billion gal; adjusted for net yield, 4.41 billion gal times 68.75% is 3.032 billion gal; in terms of energy equivalency, 3.032 billion gal of biodiesel would equal 2.81 billion gal of petroleum).
The entire 2004 US corn and soybean crop, converted to biomass fuels, could replace about 10.41 billion gal of petroleum (7.6 billion as ethanol and 2.81 billion as biodiesel). Petroleum is measured in 42-gal barrels; the 10.41 billion gal biofuel total would be equivalent to 248 million bbl of petroleum. The US consumed about 7.49 billion bbl of petroleum last year, or about 20.5 million b/d. This means that the total biofuel potential of the record 2004 US corn and soybean harvests would offset about 12 days of US petroleum consumption, or about 3.3% of our total yearly petroleum consumption. Given that most of the US corn and soybean crop is already committed to other uses, this analysis indicates that biomass-based fuels will have a negligible role in reducing US petroleum consumption, which in turn underscores that replacing petroleum in the US economy will be a monumental challenge.
Ted Lofstrom
Ellis & Associates Inc.
Minneapolis, Minn.