Page 288 - Materials Chemistry, Second Edition

A Comparison of Life Cycle Assessment Studies 279

or other sources, all of which having different GHG emission factors (Cherubini
and Strømman 2011). The impact of different reference system can be observed in
the study conducted by Pettersson and Harvey 2010), where GHG emission sav-
ings of bioelectricity production from black liquor are estimated using electricity
coming from different fossil sources as reference. The Renewable Energy Direc-
tive (EC 2008) requires a 60 % savings in GHG emissions as compared to the
fossil fuel it replaces to allow the biofuel to be used for national renewable energy
targets after 2017. Thus, a detailed description and impact analysis of the reference
system is crucial as well as mandatory for comparing the results of biofuel LCA
(Singh et al. 2010).

4.3 System Boundary

On the basis of goal and scope, initial boundaries of the system are determined.
Davis et al. (2009) concluded that different system boundaries among various
studies of biofuel production from biomass have caused considerable variation in
LCA estimates since they vary not only according to start and end points (e.g., well
to tank and well to wheel) but also over space and time in a way that can dra-
matically affect energy and GHG balances.
Many researchers use the ‘‘well-to-tank’’ system boundary to compare envi-
ronmental impact of biofuels with fossil fuels (Luo et al. 2009; Monti et al. 2009),
while others use ‘‘well-to-wheel’’ or ‘‘cradle-to-grave’’ system (Sheehan et al.
2004; Spatari et al. 2005; Power and Murphy 2009; Stichnothe and Azapagic 2009;
Korres et al. 2010).
The risk of improper boundaries selection include that LCA results may either
not reflect reality well enough and lead to incorrect interpretations and compari-
sons (Graedel 1998; Lee et al. 1995) or provide the perception to the decision
maker that it does not excogitate actual results and thus lower the confidence level
of policy maker in making decisions based on the results (Reap et al. 2008a).
Inconsistency of system boundaries in LCA analysis of biofuel through omission
of the production of various inputs (e.g., enzymes which is used to degrade cel-
lulosic feedstock, fertilizer, pesticides, lime), and utilization of bioethanol (Luo
et al. 2009; Gnansounou et al. 2009) could cause a significant variation on the
outcome of the analysis. A recent example of such problem can be observed in the
debate surrounding the energy balance of ethanol where criteria for the selection of
boundaries (like the inclusion of corn-based ethanol coproducts or energy from
combustion of lignin in cellulosic ethanol) are strong enough to change the results
significantly (Farrell et al. 2006; Hammerschlag 2006). A uniform and clear
determination of system boundaries is necessary to accurately estimate the pos-
sible environmental impacts including GHG emissions in LCA comparisons
between biofuels and conventional fuels (Farrell et al. 2006).