Exploring plausible pathways for the decarbonisation of the energy system of countries is becoming increasingly urgent to achieve GHG emission reduction targets. Building and energy sectors have the greatest potential for cutting emissions [1
]. The migration tendency occurred during the last decades from rural areas to cities is expected to continue and some forecasts show that more than the 70% of the world population will be living in cities by 2050 [2
]. Therefore, energy planning of cities is becoming increasingly complex. Although some recent studies identify the necessity of quantitative assessment methods based on the notion of multiple impact pathways, these frameworks are still in their infancy for cities. There are mainly applied nowadays in studies to conduct climate and energy policy analyses on a large scale [3
Currently city energy planners need to combine various complex methodologies and tools with different time steps and scales, for which clear linkages are still unavailable. Studies such as the one carried out by Mirakyan and De Guio [5
] identify the necessity of evaluating city energy planning in an integrated way, combined with territorial planning. Another study carried out by Mattoni et al. [6
], also proposes an approach to cities and territories combining the district scale, the city scale, and the regional scale. It can be said that city energy planning process is still complex due to the lack of consensus on the way to assess and prioritise different alternatives under a common framework.
This paper provides an example of application of a methodology developed for the ex-ante impact assessment of alternative energy transition scenarios for cities, linking energy modelling with holistic impact assessment methodologies. The case study is focused on the analysis of an energy transition scenario for Donostia from 2017 to 2067. The scenario described in this paper is part of a wider study in which the methodology is developed in detail and where 68 alternative energy transition scenarios for Donostia are compared [7
2. Materials and Methods
2.1. Case Study
The area of study comprises five districts covering more than the 40% of the city’s building stock. This study considers the districts of Amara (11,639 dwellings), Cortazar/Centro (8988 dwellings), Antiguo-Ondarreta (3856 dwellings), Gros (9581 dwellings) and Aldezaharra (3332 dwellings). The sum of these districts encompasses the most relevant areas of the city in terms of building stock and population. Each district is evaluated in detail following a bottom-up approach for the data gathering and energy characterisation buildings as it is showed in Table 1
Definition of the Energy Transition Scenario
An energy transition scenario focused on reducing environmental emissions, decreasing the dependence on fossil fuels, and increasing the socioeconomic development of the city and the region is presented in this section. The scenario proposes the simultaneous implementation of several interventions and their staggered deployment across the transition period of 50 years. The interventions included in this study are listed as follows; central heating biomass boilers (CHBB), heat pumps (HP) and passive interventions for buildings (PIFB).
The dimensioning of the scenario has been done according to the existing barriers associated to their implementation such as, the options to replace existing gas oil-fired and natural gas-fired central heating systems with biomass central heating systems and heritage conservation grade of buildings for refurbishment measures. A total of 4.4 millions square meters of heated floor area of residential buildings is refurbished progressively with the following initial distribution: 15% of the existing buildings have an energy certification level of D, 58% level E, 24% level F and 4% level G. It is assumed that all the buildings are refurbished to a level of C according to the energy demands defined for each category. Further detail about the energy demand per building category can be found in the Appendix B
Besides, it is considered that a total of 23,795 existing heating systems are replaced progressively during this period. Table 2
shows the main characteristics for the deployment of these interventions.
Other key parameters considered for defining the scenario such as the annual implementation rate of the interventions, the energy price escalators, the discount rate and the energy technology cost trends are also detailed in the Appendix B
3. Impact Assessment Results
The impact assessment covers the city scale and the regional scale for both the socioeconomic and the environmental dimensions. The life cycle socioeconomic and environmental assessment at the city scale has been carried out through the evaluation of the following impact indicators: Cumulative Net Present Value (CNPV), Cumulative Net Present Cost-Social (CNPC-S), Dynamic Payback Period (DPP), Cumulative Global Warming Potential Reduction (CGWPR), and Cumulative Non Renewable Primary Energy Reduction (CN-RPER). Table 3
shows the economic and environmental impact results of the scenario.
Negative CNPV results shows that although some measures such as the investments in new heating and DHW systems would be cost effective, when they are combined with building refurbishment interventions, the energy transition scenario shows a negative cash flow at the end of the period. On the other hand, the total costs for citizens associated to the energy transition scenario, which considers not only the initial investment but also the costs of energy and the O&M and system replacement costs during the transition period is 338.4 M€.
Results for the environmental dimension show that with the implementation of the transition scenario, CO2 equivalent emission savings of 1.4 × 106 TnCO2eq are achieved. Emission savings of 64% with respect to the values of 2007 would be achieved in the city by 2067. At the beginning of the transition period, there is actually an increase on emissions savings and use of non-renewable primary energy, due to emissions and embodied energy related to the products used on the different measures. Those effects occur throughout the transition period due to the new implementation of interventions, but they are rapidly compensated by the energy savings gained in the use stage.
For the macroeconomic assessment the next two indicators are evaluated: Induced Regional Gross Domestic Product (RGDP), and Regional Production (RP). With regard to the direct, indirect and induced effects created in the economy of the Basque Country, results show that the implementation of the scenario would induce an impact equivalent to an increase in the GDP of the Basque Country of 0.12% and close to 1.26% of the GDP of Donostia.
shows both the disaggregated shock of each intervention and the shock corresponding to the total city energy transition scenario (in cumulative discounted domestic costs in basic prices and in thousands of euros). This reflects the proportion in which the production of commodities would be increased in the Basque Country. This is precisely the exogenous shock used as input for the macroeconomic model.
Moreover, as it is shown in Table 4
a multiplier of 0.82 for GDP and a multiplier of 1.65 for Production are achieved by the energy transition scenario. These values are reasonable considering that there are for a regional economy and not for a national economy. The relevance of considering not only the indirect effects but also the induced effects is also observed in the study. The results show an increase of between 9% and 22% in the impacts created when the induced impacts are also considered.
The impact assessment results achieved for the different indicators evaluated provide a variety of criteria that can be used in order to evaluate the effects of different scenarios. Following this process for comparing different potential scenarios can help designing the optimum energy transition scenario for each city depending on their particular interests.
Results show that the substitution of existing heating and DHW systems by a combination of biomass-fired central heating boilers and heat pumps with building refurbishment is very positive in terms of CO2 emission and non-renewable PE savings. However, current and expected future prices of these interventions do not ensure cost savings for citizens in the defined period. In this regard, policy mechanism designed to accelerate investment on building refurbishment as well as the incorporation of other interventions to the transition scenario, such as natural gas boilers, solar photovoltaic systems, and solar thermal systems can help to balance the global economic cash flow of scenarios across the transition period. These policy mechanisms should aim to make viable refurbishment project taking into consideration additional benefits of building refurbishment, including increased comfort and health of the occupants, on increasing property values, which are not taken into account in this study.
The relatively low macroeconomic impact assessment results on the other hand, show that this type of regional indicators are interesting mainly for a strategic vision and to understand replication potential of interventions in other areas of the city or in other cities of the region.