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138 Biofuels for a More Sustainable Future

assumption of wood pellet imports from Canada and the United States to the
United Kingdom. It also considers the use of miscanthus, a popular energy
crop which can also be pelletized, is able to grow quickly, and can thrive on
land that is suboptimal for food production.

3.1.2 Goal and scope definition
The purpose of this case study is to evaluate the sustainability of large-scale
biomass-fired electricity generation in a UK setting. The assessment takes a
cradle-to-gate approach, as outlined by the system boundary in Fig. 5.5. The
functional unit is 1kWh of electricity generated at the power plant.

3.1.3 Inventory analysis
This section outlines the main assumptions and data sources for the
case study.

Cultivation and processing of wood pellets
Life cycle inventory data on wood cultivation and processing into pellets are
taken from Ecoinvent v2.2 (Ecoinvent Centre, 2010), adapted to use the
appropriate national electricity mix. As in Ecoinvent, 28% of the wood is
assumed to be beech, 72% spruce (based on current consumption of each
species). Pellets are produced from the residual wood that is a by-product
of wood planing, with the main product being sawn timber. Therefore allo-
cation is necessary for the impacts of wood cultivation, felling, and planning;
this has been carried using economic allocation because there are no equiv-
alent coproducts, meaning system expansion and substitution is not possible.
However, as global wood pellet demand is increasing greatly (Cocchi
et al., 2011; P€oyry, 2011), a move toward dedicated production of wood
for pellets is anticipated. Thus the study also considers the production of pel-
lets from wood felled specifically for that purpose. In this case, debarking,
chipping, drying, and pelletization take place in the same facility [as is the

Fig. 5.5 System boundary for the LCSA of electricity generation from biomass.