Impact of size optimisation on the multi-criteria assessment of local cross-sectoral energy supply concepts

Key elements of the energy system transformation are decentralisation, decarbonisation and sector-coupling. Local energy systems are often customarily designed using heuristics for the technology layout. However, optimisation of the design and operation of energy systems is considered a powerful tool. Therefore, we in vestigate the influence of an optimised layout and the coupling of the electricity and heat sector on economic, ecological and technological criteria. Three variations from a reference energy concept are regarded for a case study of unrenovated, residential buildings in the city of Dusseldorf, Germany. The concepts supply the heat and electricity demands at different levels of sector-coupling. In a first step, the concepts are mathemat ically optimised by mixed-integer linear programming with the objective of minimising costs. Afterwards, the results of the criteria metrics are combined in an overall performance score obtained by the Analytic Hierarchy Process. We find that the concepts with an optimised layout do not only have lower costs, but also lead to a significant decarbonisation by several hundreds of kg of CO2 annually. In the case of optimised layout, heat pump and storage units have smaller capacities. Especially, storages are oversized under the used heuristic. Nevertheless, the photovoltaic units are expanded by up to 300% in comparison to the heuristic layout. We thus find an advantage of the optimised layout on the multi-criteria assessment, even though the optimisation has only an economic objective. The coupling of the heat and electricity sector leads to CO2 emission savings and a higher self-consumption of the PV energy produced within the system. The coupled system achieves the highest score under the three criteria, irrespective of the building type. The overall best performance under a sensitivity analysis of the criteria weights is found for the sector-coupled concept in the optimised layout.