Energy Balance/Life Cycle Inventory for Ethanol, Biodiesel and Petroleum Fuels
Minnesota Department of Agriculture (MDA)
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Ethanol versus Gasoline
A United States Department of Agriculture (USDA), Economic Research Service Report number 721 titled "Estimating The Net Energy Balance Of Corn Ethanol" was published in July of 1995. The Conclusion states in part: "Corn ethanol is energy efficient, as indicated by an energy ratio of 1.24, that is, for every Btu dedicated to producing ethanol, there is a 24-percent energy gain." In a presentation published in September 1996 "Ethanol Balance of Corn Ethanol Revisited", the authors of the 1995 study reported an increase in the energy ratio of corn ethanol to 1.34. This was done to account for increased corn yields and greater efficiencies in the ethanol production process than had been considered in the first study. As a result, they conclude that there is a 34 percent energy gain in the production of ethanol.
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 0.74. In other words, for every unit of energy dedicated to the production of gasoline there is a 26 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.
Bio-Diesel 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.
Summary - Energy Balance/Energy Life Cycle Inventory
Fuel-------------Energy yield------------Net Energy (loss) or gain
---------------------------------------------------------------
Gasoline-------------0.74----------------------(26 percent)
Diesel---------------0.83----------------------(17 percent)
Ethanol-------------1.34----------------------34 percent
Biodiesel-------------3.20---------------------220 percent
* Yield in liquid fuel Btus per Btu of fossil fuel energy dedicated.
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 1995 net energy study relates to the specific demand for liquid fuels and the relative abundance of energy sources used to make these renewable fuels. The study states, "Ethanol production utilizes abundant domestic energy supplies of coal and natural gas to convert corn into a premium liquid fuel that can replace petroleum imports by a factor of 7 to 1."
MDA Contact
Ralph Groschen, Agricultural Marketing Services Division
Agriculture Marketing Specialist
