3.2 Double Counting
Double counting problem is hardly discussed in the literature of TIMES-LCA
linking [5]. Part of the energy and emissions considered in TIMES models is used
to deliver intermediate products that are already accounted in LCI, resulting in
double counting [5, 6]. For example, the output of the cement sector is typically
considered independent of other demands in TIMES models but will be used to
build the infrastructure that is already included in LCIs. As pointed by Ref. [6], this
can be mitigated by presenting relative results between scenarios, where double
counting effects cancel out, to some extent. This limitation is not exclusive of
TIMES models. A recent review of integrated assessment models stated that most
of them miss linkages related to infrastructure and ignore material cycles, which are
the fundamental characteristics of the life cycle perspective [22]. Constructing more
“circular” RES in TIMES models is challenging, as the models need to be calibrated
using national statistics, and these do not necessarily have a high level of detail of
material flows leaving each sector. Studies linking TIMES with EEIO data have
more thoughtfully addressed double counting, erasing manually repeated areas of
the inventory [8–10]. Reference [10] used fixed input-output coefficients to adjust
the exogenously defined demands (e.g. the steel demand from energy technologies
is used to adjust the energy demand of steel production). Ideally, these demand
corrections would be calculated endogenously by the TIMES model, but that would
require substantial additional linking of processes.
3.3 Integrating Life Cycle Emissions in the Optimisation
Problem
Several of the reviewed publications integrated LCA data into the optimisation
algorithm, but only for some parts of the energy system [3, 7–11], with the risk of
introducing a bias. A consistent integration of life-cycle emissions into the optimisation problem is challenging, as it will bias the assessment towards sectors
where accounting of emissions is less complete. Reference [3] noted that imposing
limits on LCA scores for electricity generation greatly affected trade balances
against local production, as trade processes did not have emissions associated.
Consistently including emissions for all processes in a TIMES model (e.g.
end-of-life burdens) would require a one-to-one mapping, which is extremely
time-consuming in large TIMES models. Alternatively, large TIMES models can
include emissions if it is for a limited number of processes. For example, a model
dealing with operating GHG emissions could include emissions from gas distribution or refrigerant leaks or electricity imports (e.g. [25]) without losing consistency. Ultimately, TIMES results should be interpreted taking into account potential
inconsistencies and lack of completeness of the inventories. References [8, 10] are
Integrating Energy System Models in Life Cycle Management
255
Double counting problem is hardly discussed in the literature of TIMES-LCA
linking [5]. Part of the energy and emissions considered in TIMES models is used
to deliver intermediate products that are already accounted in LCI, resulting in
double counting [5, 6]. For example, the output of the cement sector is typically
considered independent of other demands in TIMES models but will be used to
build the infrastructure that is already included in LCIs. As pointed by Ref. [6], this
can be mitigated by presenting relative results between scenarios, where double
counting effects cancel out, to some extent. This limitation is not exclusive of
TIMES models. A recent review of integrated assessment models stated that most
of them miss linkages related to infrastructure and ignore material cycles, which are
the fundamental characteristics of the life cycle perspective [22]. Constructing more
“circular” RES in TIMES models is challenging, as the models need to be calibrated
using national statistics, and these do not necessarily have a high level of detail of
material flows leaving each sector. Studies linking TIMES with EEIO data have
more thoughtfully addressed double counting, erasing manually repeated areas of
the inventory [8–10]. Reference [10] used fixed input-output coefficients to adjust
the exogenously defined demands (e.g. the steel demand from energy technologies
is used to adjust the energy demand of steel production). Ideally, these demand
corrections would be calculated endogenously by the TIMES model, but that would
require substantial additional linking of processes.
3.3 Integrating Life Cycle Emissions in the Optimisation
Problem
Several of the reviewed publications integrated LCA data into the optimisation
algorithm, but only for some parts of the energy system [3, 7–11], with the risk of
introducing a bias. A consistent integration of life-cycle emissions into the optimisation problem is challenging, as it will bias the assessment towards sectors
where accounting of emissions is less complete. Reference [3] noted that imposing
limits on LCA scores for electricity generation greatly affected trade balances
against local production, as trade processes did not have emissions associated.
Consistently including emissions for all processes in a TIMES model (e.g.
end-of-life burdens) would require a one-to-one mapping, which is extremely
time-consuming in large TIMES models. Alternatively, large TIMES models can
include emissions if it is for a limited number of processes. For example, a model
dealing with operating GHG emissions could include emissions from gas distribution or refrigerant leaks or electricity imports (e.g. [25]) without losing consistency. Ultimately, TIMES results should be interpreted taking into account potential
inconsistencies and lack of completeness of the inventories. References [8, 10] are
Integrating Energy System Models in Life Cycle Management
255