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Table 4. Potential EROI for Advanced Cellulosic Ethanol.
Input (MJ/L ethanol) Value
Agriculture: Fuel 0.19
Agriculture: Electricity 0.00
Feedstock Transport 0.29
Biorefinery: Fuel none required
Biorefinery: Electricity none required
Ethanol Distribution negligible
Fertilizer 0.33
Pesticides/Herbicides 0.10
Less: Coproduct Energy Input none
Allocated to Ethanol: Percent 100
Total Energy Input to Ethanol 0.91
Indirect Energy Inputs 0.13
Total Direct + Indirect Inputs 1.04
Total Energy Output 37.10
Energy Return on Investment 35.70- Conclusions and Summary
An important objective of this paper has been realized. The coauthors agree that the EROI concept
is valuable and can provide important insights about the desirability of particular energy systems. The
reasons for the published differences between coauthors Dale and Pimentel with regard to corn
ethanol’s EROI have been dissected and are shown to be primarily due to allocation issues, not to
inherent problems with the underlying concept of EROI. These results highlight the importance of
performing EROI using transparent methodologies and allocation approaches, clearly defined system
boundaries, and using the best data possible. Lack of crucial data for operating cellulosic ethanol
systems makes these EROI calculations inherently more speculative than those for corn ethanol.
However, farm level EROI’s are relatively high for cellulosic biomass production (ranging from 10:1
to about 50:1 in this analysis). Therefore it is the efficiency of energy conversion in the biorefinery, in
particular the practicality of using residual biomass to power the biorefinery, which will determine
whether cellulosic ethanol systems can reach the very attractive EROIs that seem possible.
Acknowledgments
The first author greatly appreciates the good will of the second and third author to attempt to deal
with their differences in an open and friendly manner through a joint publication. It was not easy
for anyone.
Conflict of Interest
The authors declare no conflict of interest.