Ethanol's Energy Return on Investment: A Survey of the Literature 1990−Present

Various authors have reported conflicting values for the
energy return on investment (rE) of ethanol manufacture.
Energy policy analysts predisposed to or against ethanol
frequently cite selections from these studies to support their
positions. This literature review takes an objective look
at the disagreement by normalizing and comparing the data
sets from ten such studies. Six of the reviewed studies
treat starch ethanol from corn, and four treat cellulosic
ethanol. Each normalized data set is also submitted to a
uniform calculation of rE defined as the total product energy
divided by nonrenewable energy input to its manufacture.
Defined this way rE > 1 indicates that the ethanol
product has nominally captured at least some renewable
energy, and rE > 0.76 indicates that it consumes less
nonrenewable energy in its manufacture than gasoline.
The reviewed corn ethanol studies imply 0.84 ≤ rE ≤ 1.65;
three of the cellulosic ethanol studies imply 4.40 ≤ rE ≤
6.61. The fourth cellulosic ethanol study reports rE = 0.69 and
may reasonably be considered an outlier.