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Life cycle sustainability assessment in the energy sector 141

In the case of wood pellets, direct emissions were estimated using the
€
GEMIS v4.71 database (Oko-Institut, 2012). These were integrated with
the other background processes from the Ecoinvent v2.2 database
(Ecoinvent Centre, 2010) using GaBi 4.4 life cycle assessment software
(PE International, 2008). Emissions of heavy metals were calculated using
data on the metal content of virgin wood and the proportions of each metal
emitted to air, as reported by Krook et al. (2004).
In the case of miscanthus pellets, background data are also from Ecoin-
vent v2.2 (Ecoinvent Centre, 2010), while miscanthus composition (includ-
ing heavy metals) was taken from Obernberger et al. (2006) allowing direct
combustion emissions to be calculated in GEMIS. Aerial emissions of heavy
metals were calculated based on Krook et al. (2004) data on the proportion
of metals emitted to air. All data were combined in GaBi 4.4
(PE International, 2008). It should be noted that the elemental composition
of miscanthus is greatly influenced by soil composition, time of harvest, and
the amount of leaf matter harvested. Direct emissions are therefore likely to
be less accurate than those from wood pellets.

Waste disposal
As in Ecoinvent, 50% of the wood ash from combustion is assumed to be
disposed of in sanitary landfill, 25% in municipal incineration, and 25%
via spreading on agricultural land.

3.1.4 Indicators and impact assessment
The sustainability indicators considered in this assessment are presented in
Table 5.5. The quantification of these metrics follows the approaches dis-
cussed in Section 2, with extra detail available in Stamford and Azapagic
(2014).

3.1.5 Interpretation
The results of the case study are shown in… including data on comparator
technologies which are taken from Stamford and Azapagic (2012). Due to
the volume of results, each pillar of sustainability is assessed in turn.
The techno-economic indicators (Fig. 5.6) show biomass to compete
well against the other technologies, benefitting from a potentially infinite
fuel reserve (assuming appropriate management of the biomass resource),
the best dispatchability of all options due to its relatively low capital cost,
and levelized costs that are slightly higher than gas power but lower than
all other options. However, readers should note that this assessment relies