Multi-criteria optimisation of an energy system and application to the Belgian case

The global warming issue with its resulting climate disturbances is a burning topic. The European Union is seeking, with its Climate Law, to drastically reduce greenhouse gas emissions by 2030 and to achieve climate neutrality by 2050. In this context, energy models are needed to study possible future energy systems that best meet these objectives. Many models exist, but no model encompassing the different facets of the energy sector - electricity, heat and mobility - allows a multi-criteria optimisation of the studied energy system. However, given the challenges associated with the energy transition, it is crucial to be able to assess a system from different, sometimes contradictory, aspects: economic, environmental, technical and social. The present work proposes the implementation of a multi-criteria approach in the EnergyScope TD model, which is currently single objective, but which has the following advantages: integration of all sectors of the energy system, open source, reasonable computation time and possibility of fine temporal resolution, which is necessary to take into account the fluctuating character of renewable energies. In order to achieve a multi-criteria optimisation, key performance indicators were selected that allow for an economic, environmental and societal view and, in order to provide as global a perspective as possible on the energy system under consideration, additional criteria were introduced. For data collection, we followed a "life cycle assessment" approach that takes into account the entire life cycle of the processes involved in the evaluation of the associated impacts. In this task, with the help of SimaPro software, we made extensive use of the ecoinvent database. The application case selected is Belgium in the year 2035. The multi-criteria optimisation allows to obtain a mapping of the technologies to be implemented and the analysis highlights the environmental impacts of the energy system according to the weight associated to each criterion. Finally, a more targeted study of a low-carbon Belgian energy system is carried out. The findings of this case study are likely to be transposable to other countries.