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Life cycle sustainability assessment in the energy sector 139

case at RWE’s Georgia pelletization plant, one of the largest in the world
(Georgia Biomass, 2011)].
In all cases, the resulting pellets have a moisture content (MC) of 10%, a
3 3
dried mass of 650kg/m , and a net energy density of 12,164MJ/m . These
figures are in good agreement with those given by other sources, such as the
UK Forestry Commission’s Biomass Energy Centre (Biomass Energy
Centre, 2012).

Cultivation and processing of miscanthus
The use of miscanthus as an energy crop is growing in popularity worldwide.
As is the case for wood, pellets have been considered due to their homoge-
neity and high energy density making them favorable from the perspective
of large power plant owners.
As a relatively new energy crop, long-term fertilizer and herbicide
requirements are uncertain (and ultimately depend on site-specific condi-
tions). Some trial sites have not required fertilizer, whereas others have,
therefore this study assumes a 50:50 split between cultivation with and with-
out fertilizers. Specific requirements are taken from Gilbert et al. (2011).In
both cases glyphosate is used as a weed killer. Cultivation occurs over a
period of 23years, 21 of which are harvested with an average yield of
14 oven-dry tonnes/ha, which is thought to be typical based on UK expe-
rience (Gilbert et al., 2011).
Late harvesting is assumed (March/April as opposed to December) in order
to minimize moisture content. Typical MC at late harvest is below 20%
(Hopwood, 2010), and the MC of the pellets is assumed to be10%.Any drying
of miscanthus is not accounted for: it is assumed that air drying will be
sufficient. The miscanthus is baled, chipped, and fed into a pelletizer to form
a final product with a net calorific value of 15.65MJ/kg (gross¼17.2MJ/kg).

Fuel transportation
After production in the United States/Canada, wood pellets are assumed to
be transported 100km by rail to the nearest port, then shipped to the United
Kingdom on a Supramax-class transoceanic freight ship [capacity 51,500t, as
specified in Ecoinvent (Ecoinvent Centre, 2010)]. Distances have been esti-
mated as straight-line shipping routes using a mapping tool (Free Map Tools,
2012) and are therefore likely to be slightly underestimated. The routes are
described in Table 5.4. An average of the biomass trade routes above is
assumed, that is, one-third of the fuel comes from British Columbia,
one-third Nova Scotia, and one-third Georgia. Following arrival in the