A multi-objective approach to design integrated multi-energy systems for efficient and sustainable decarbonization at the regional level

The decarbonization of the energy sector is among the highest priorities in the European Union’s effort to reduce its greenhouse gas (GHGs) emissions, avoid the worst effects of rapid climate change, and transition to a more sustainable economy. Multi-energy systems (MESs) have emerged as powerful and flexible solutions to integrate renewable energy sources (RES) in the energy grid and support the decarbonization of heating and transport. In MESs, multiple energy vectors and sectors that are traditionally planned and operated independently like electricity, heating and cooling, fuel and transport are coupled with each other at various levels, from demand to storage and generation, with the aim of increasing the efficiency, resilience, and sustainability of the whole system.  
The transition to carbon-neutral energy systems may come with significant costs, especially in areas where the social and economic opportunities are tied to carbon-intensive activities or where the land-use change to accommodate RES carries significant environmental and social impacts. In these contexts, where multiple stakeholders with competing objectives are involved, multi-objectives modeling tools can be used to support decision-makers in identifying the most suitable technical configuration of MESs to fulfill the decarbonization and economic goals while considering the needs of the territory involved and the assets and resources already available. 
This work presents a novel approach to identifying optimal solutions when designing MES under multiple competing environmental, economic, technological, and social objectives. We use the multi-scale energy systems modeling framework CALLIOPE to simulate the optimal management of a MES with high temporal resolution under a specific system configuration. These configurations are explored via a Multi-objective Evolutionary Algorithm, to extract Pareto-optimal MES designs and highlight synergies and trade-offs between multiple objectives. 
The new framework is applied to the Sulcis Iglesiente (SI) Province in Sardinia, Italy; a territory that already faces severe socio-economic challenges which are at risk of being exacerbated by the planned phase-out of the local coal power plant. Together with the economic end emission targets, the analysis includes objectives such as land-use allocation for renewables, air quality, and local job opportunities and losses. 
The resulting MES configurations, as expected, highlight a strong conflict between the maintenance of the previously carbon-intensive assets and the reduction of GHGs emissions. From the demand side, substituting fossil fuel boilers with heat pumps to exploit the excess electricity production that follows the expansion of the already existing renewable resources pool (mainly via new on-shore wind turbines) represents a good solution to increase efficiency and reduce the overall carbon footprint. However, from the generation side, fully compensating for removing the fossil fuel-based power plant would require massive investment in on-the-ground photovoltaic, and wind turbines (off-shore and on-shore), which may be too costly in terms of investment, surface allocation and landscape degradation.