Page 149 - Biofuels for a More Sustainable Future

Life cycle sustainability assessment in the energy sector 135

If system expansion cannot be performed—for instance, if the coproduct
has no equivalent—then physical or economic allocation can be used. In such
cases the impacts of the system are allocated to each coproduct based on
mass, energy content, or economic value.
System expansion and economic allocation have disadvantages, primarily
in their lack of consequentiality: in other words, the presence of a new pro-
cess or industry with large volumes of a particular coproduct will have
knock-on effects on the market, and these effects in turn may render the
chosen substitution or economic allocation obsolete. In contrast, the phys-
ical allocation approaches, such as mass or energy content allocation, do not
face this problem. They may, however, fail to value the utility of the differ-
ent coproducts.
The selection of an allocation approach has been shown to dramatically
influence theoverall results of LCAs in thebioenergysector (e.g.,Stephenson
et al., 2010). As a result, it is advisable to explore the importance of allocation
choices by applying different types of allocation in a sensitivity analysis.

2.5 Benefits, limitations, and weaknesses of LCSA
LCSA yields a large quantity of data due to the need to perform a holistic
assessmentacrossthethreepillarsofsustainability.Itisnotuncommonforsus-
tainability frameworks to include 40 or more indicators (see, e.g., Roth et al.,
2009; Stamford and Azapagic, 2011). Consequently, in cases where an LCSA
isbeingusedtochoosebetweenalternatives,interpretingtheresultsisfarfrom
trivial. Often the best option is not clear: perhaps trade-offs need to be made
between indicators, or value judgment is required, or uncertainty is high.
UncertaintywithinLCSAcanbeexploredusingscenariosorsensitivityanal-
ysis. In the former, the analysis is rerun using different underlying assump-
tions: an approach explored further in Section 3. The challenge in that case
is ensuring that the selected scenarios are truly reflective of the uncertainty
space. In other words, scenario analysis should contain a sufficient breadth
of scenarios to cover the entire likely range of possibilities. In the case of sen-
sitivity analysis, one key parameter is varied at a time to explore the effect on
the overall results of the LCSA. The chosen parameters should either:
1. Parameters that play a leading role in determining the impacts of the
system (e.g., the yield, capacity factor, choice of allocation approach,
use case of the product, etc.); or
2. Parameters that are highly uncertain due to poor input data or reliance
on assumption (e.g., lifespan of the system, costs or environmental bur-
dens of a major input material, etc.).