Unlike previous studies, our study improves the energy balance accounting for ethanol
production using opportunity cost principle, rather than the LCA approach which induces infinite
accounting. Following the LCA, the calculation in other studies includes not only the energy of
inputs but also the energy for the production and transportation of these inputs, and even “losses
during electricity generation” [22, p.4]. To prevent infinite accounting, some limitations have been
proposed in the LCA to exclude the energies for building the ethanol facilities and producing the
transportation equipment due to its little amount per liter of ethanol, outdated available data, and
preclusion of a tremendous amount of data [31]. Our study excludes these sources of energy as they
are not associated with direct energy generation for ethanol production. This avoids the problem of
infinite accounting of input energy because at its core the approach is not based on the resources
used to get an ethanol based fuel source but rather what else we could have done with them, for
example, fossil fuel gasoline production. In this sense, the input energy only have value based on the
fact that we can use them to make ethanol-based fuels and this is similar to the value of pure fossil
fuel-based gasoline.
For comparison purpose, our attention is paid to the studies on energy and GHG balance analysis
in the same line of cassava-based ethanol. A comparison of energy balances among different studies
is presented in Table 5. The energy balance is the difference between the reference value and input
energy. The reference value is explained by the energy base of either gasoline or ethanol itself with
the base of 1. Our study uses the energy base of gasoline with the fuel consumption-based
substitution ratio of 1.06 which better suits the opportunity cost approach and is tested recently in
2009.