Case Study: Does Ethanol Have a Positive Energy Balance?

Republished From: Environmental Science 2016

Ethanol is touted as a renewable replacement for conventional gasoline that will reduce both U.S. dependence on imported oil and the impact of transportation fuels on the environment. The potential for ethanol to live up to these expectations must be assessed with a systems perspective. Every energy system has many direct and indirect costs and benefits that must be accounted for in a consistent way before comparisons can be made.

David Pimentel, an agricultural and environmental scientist at Cornell University, is a long-time critic of ethanol. Pimentel argues that ethanol is not a viable alternative to conventional fuels because it has many negative economic and environmental costs. In particular, Pimentel finds that ethanol has an energy return on investment less than 1—that is, the quantity of energy in a gallon of ethanol is less than the energy required to produce it. The reason is the large indirect energy costs of ethanol production. The production of corn uses fertilizer, pesticides and other chemicals, machinery, labor, irrigation water, and other inputs.

All of these inputs require substantial amounts of fossil fuels to be manufactured and transported to the farm. More fossil fuels are used to transport the corn and to build, operate, and maintain the ethanol production facility (Figure 1).  According to Pimentel, these direct and indirect energy costs amount to about 130,000 Btu per gallon of ethanol. A gallon of ethanol contains 76,000 Btu. Thus the energy return on investment for ethanol is 0.58 (76,0000 Btu / 130,000 Btu).

FIGURE 1  Ethanol Production  A typical ethanol plant in West Burlington, Iowa (Big River Resources, LLC). Credit: Steven Vaughn/USDA

Scientists at Argonne National Laboratory and the University of California at Berkeley disagree with Pimentel’s results. Their research suggests that ethanol from corn has an energy return on investment of about 1.4, implying that ethanol yields 40 percent more energy than is required for its manufacture. These studies assume a higher yield of corn than Pimentel does, and they account for improvements in the efficiency of energy use on farms and in the manufacture of farm inputs such as fertilizers. Pimentel also includes some costs that the other studies exclude, such as the energy required to make the farm machinery that is used in corn production.

This debate raises an important question: How important is the energy return on investment for a fuel? Ethanol proponents argue that what really matters is that production of ethanol can achieve a net gain: a more desirable form of fuel. Abundant domestic supplies of natural gas and coal can effectively be used to convert corn into a premium liquid fuel that replaces imported petroleum, reduces emissions, and provides an important market for farmers. Others argue that it is ridiculous to tout a fuel as a viable long-term substitute when at best it barely breaks even in net energy terms. An economy cannot sustain itself, much less grow and develop, with energy systems that only break even in energy terms.


• Students will be able to describe why ethanol is close to the energy break-even point.



Hill, E. (2016). Case Study: Does Ethanol Have a Positive Energy Balance?. Retrieved from