Ethanol versus Gasoline

A United States Department of Agriculture (USDA), Economic Research Service Report number 814 titled "Estimating The Net Energy Balance Of Corn Ethanol: An Update" (PDF) EXT was published in July of 2002. The Conclusion states in part: "Corn ethanol is energy efficient, as indicated by an energy ratio of 1.34; that is, for every Btu dedicated to producing ethanol, there is a 34-percent energy gain." A similar study done in 1995 indicated only a 1.24 energy ratio. The increase is accounted for by an increase in corn yields and greater efficiencies in the ethanol production process. As a result, energy efficiency in the production of ethanol is increasing.

The concept of "input efficiencies for fossil energy sources" was introduced as a component of the study. This was meant to account for the fossil energy used to extract, transport and manufacture the raw material (crude oil) into the final energy product (gasoline). According to the study, gasoline has an energy ratio of 0.805. In other words, for every unit of energy dedicated to the production of gasoline there is a 19.5 percent energy loss.

In summary, the finished liquid fuel energy yield for fossil fuel dedicated to the production of ethanol is 1.34 but only 0.74 for gasoline. In other words the energy yield of ethanol is (1.34/0.74) or 81 percent greater than the comparable yield for gasoline.

Biodiesel versus Petroleum Diesel

A similar study was co-sponsored by the United States Department of Energy and the USDA, entitled, "Life Cycle Inventory of Biodiesel and Petroleum Diesel for Use in an Urban Bus."

The study, published in May 1998, states; "Biodiesel yields 3.2 units of fuel product energy for every unit of fossil energy consumed in its life cycle." The report continues, "By contrast, Petroleum diesel's life cycle yields only 0.83 units of fuel energy per unit of fossil energy consumed." According to this analysis, the energy yield of biodiesel is (3.2/0.83) 280 percent greater than petroleum diesel fuel.

* Life cycle yield in liquid fuel Btus for each Btu of fossil fuel energy consumed.

The positive energy ratio displayed by ethanol and biodiesel is accounted for by the contribution of solar energy collected by the crop from which the fuel is made. This energy is considered "renewable" because a new crop is raised each year. Fossil fuels, on the other hand, originate from fossilized plants and animals stored beneath the earth's surface in a process that took millions of years.

Another consideration discussed in the 2002 net energy report relates to the specific demand for liquid fuels and the relative abundance of energy sources used to make these renewable fuels. The report explains, "Only about 17 percent of the energy used to produce ethanol comes from liquid fuels such as gasoline and diesel fuel. For every 1 Btu of liquid fuel used to produce ethanol, there is a 6.34 Btu gain.