Page 287 - Materials Chemistry, Second Edition

278 D. Rathore et al.

4.1 Scope and Functional Unit

First step of a LCA system requires a well-defined scope of the study, which
should be compatible to the goal. Functional unit sets the scale for comparison of
two or more products, provides a reference to which the input and output data are
normalized, and harmonizes the establishment of the inventory (Jensen et al.
1997). The main goal for LCA of biofuels is to evaluate the environmental impacts
of the system under examination and to quantify the ecological benefits from the
replacement of the reference system basically conventional fossil fuels. It may also
provide a tool for policy makers and consumers to determine the optimum eco-
friendly fuel (Singh et al. 2010).
Functional unit is the ‘‘quantified performance of a product system for use as a
reference unit’’ (ISO 14044 2006). The functional unit, depending on the goal of
the study, must be expressed in terms of per unit output. LCA practitioners con-
sider four types of functional units for bioenergy studies, i.e., input unit related (per
tone biomass), output unit related (per MJ), unit agricultural land (per ha), and unit
time (per year) (Cherubini and Strømman 2011). Output-related unit most fre-
quently used in bioenergy studies. For energy production, functional unit can be
expressed as ‘‘per kWh energy produced’’ and for transport, it can be ‘‘per km
distance travelled’’ basis. For transport services, the functional unit should not be
expressed in ‘‘unit energy at fuel tank’’; as mechanical efficiency varies from one
fuel to another and from one engine type to another (Power and Murphy 2009).
Scale, if not properly chosen, could be a problem in modeling LCA studies
(Addiscott 2005). Thus, adequate selection of functional unit is of prime emphasis
because different functional units could lead to different results for the same
product systems (Hischier and Reichart 2003; Kim and Dale 2006) and products
cannot be compared accurately.

4.2 Reference System

System analysis is possible by comparing the biofuel system with a targeted
(conventional) reference system. The goal of the study determines the choice of
the reference system (e.g., whether biofuel is intended to replace conventional
transport fuel or coal for electricity or wood pellets for heat). The choice of
reference system influences the results of LCA study; therefore, it is important to
choose an identical reference system to the conventional system (Singh and Olsen
2011). In most biofuel studies, reference system is limited to a fossil fuel system. It
should be noticed that when production of feedstocks for bioenergy uses land
previously dedicated to other purposes or when the same feedstock is used for
another task, the reference system should include an alternative land-use or an
alternative biomass use, respectively (Cherubini and Strømman 2011). In fact,
fossil-derived electricity can be assumed to be produced from oil, natural gas, coal,