Page 112 - Materials Chemistry, Second Edition

8 Scope Definition 97

electricity prices caused by changes in electricity demand (often, natural gas is only
used during peak demand when a relatively high electricity price makes this
technology economically viable). However, the relevant marginal processes to
include in an LCI model are not always the ones that are affected as an immediate
consequence of a decision, i.e. short-term marginal processes. Long-term marginal
processes may be more relevant if a decision leads to large changes in supply or
demand. Long-term marginal processes represent changes in the installed produc-
tion capacity in response to the projected development of electricity demand. Often
it is difficult to identify a single long-term marginal process, which is why a mix of
potential long-term marginal processes is often used. Figure 8.9 shows such a mix
for the long-term marginal electricity technology in the Danish market. See Chap. 9
on the identification of short- and long-term marginal processes.
It can be seen that fewer electricity production processes are part of the mix in
Fig. 8.9 for consequential modelling than the mix in Fig. 8.8 for attributional
modelling. For example, waste as an electricity source is not part of the conse-
quential mix and this is because the long-term planning of waste incineration is
thought to consider projections in future waste volumes (the primary function of
waste incineration is to “get rid of” solid waste) rather than projections in future
electricity demand. On the other hand, the construction of new wind turbines and
coal-fired power plants (and to a very small extent, hydropower plants and rooftop
photovoltaic panels) are thought to consider projections in future Danish electricity
demand. When to consider short- versus long-term marginal processes in conse-
quential LCA and how to identify these are still being debated in the LCA
community.
Note that while the background system is modelled differently in attributional
and consequential LCA, the foreground system is overall modelled in the same
way, the only exception being the handling of multifunctional processes.

Fig. 8.9 Danish market mix
of long-term marginal
electricity processes (low
voltage, e.g. for domestic
consumption) (Treyer and
Bauer 2013)