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This paper presents a multi-objective optimization model for the integration of polygeneration systems into energy communities (ECs), by analyzing a case study. The concept of ECs is increasingly seen as beneficial for reducing global energy consumption and greenhouse gas emissions. Polygeneration systems have the potential to play a crucial role in this context, since they are known for producing multiple energy services from a single energy resource, besides the possibility of being fed also by renewable energy sources. However, optimizing the configuration and operation of these systems within ECs presents complex challenges due to the variety of technologies involved, their interactions, and the dynamic behavior of buildings. Therefore, the aim of this work is developing a mathematical model using a mixed integer linear programming (MILP) algorithm to optimally design and operate polygeneration systems integrated into ECs. The model is applied to a case study of an EC comprising nine buildings in a small city in the northeast of Italy. The work rests on the single- and multi-objective optimization of the polygeneration systems taking into account the sharing of electricity among the buildings (both self-produced and/or the purchased from the grid), as well as the sharing of heating and cooling between the buildings through a district heating and cooling network (DHCN). The main results from the EC case study show the possibility of reducing the total annual CO2 emissions by around 24.3% (about 1.72 kt CO2/year) while increasing the total annual costs by 1.9% (about 0.09 M€/year) or reducing the total annual costs by 31.9% (about 1.47 M€/year) while increasing the total annual CO2 emissions by 2.2% (about 0.16 kt CO2/year). The work developed within this research can be adapted to different case studies, such as in the residential–commercial buildings and industrial sectors. Therefore, the model resulting from this work constitutes an effective tool to optimally design and operate polygeneration systems integrated into ECs. [ABSTRACT FROM AUTHOR]

• Cost-effective and sustainable energy systems retrofit for buildings. • 2nd life Li-Ion batteries in polygeneration systems for buildings. • To cut off the natural gas consumption at affordable cost. The building sector represents around one-third of the energy related to the EU CO 2 eq emissions, which makes it a crucial sector for achieving the EU's energy and environmental goals. Thus, the EU has established a legislative framework to foster, among others, the modernisation of the existing building stock through a better energy system integration. In this sense, bearing in mind the needs of energy system retrofit of the public buildings in Spain, this paper carried out a thorough analysis of different trade-off solutions obtained from the multiobjective optimization of a polygeneration system for the TR5 building of the Polytechnic University of Catalunya. The results highlight the selection of PV panels, cogeneration modules and 2 nd life Li-Ion batteries, among others, to achieve cost-effective and sustainable energy systems. By covering the available area, 2000 m 2 , the PV panels attend about 23% of the electricity required for the building. On the other hand, considering the current geopolitical tensions, it presents a potential configuration that allows to cut off the natural gas consumption reducing about 6% the current cost. The study was carried out by using a Mixed Integer Linear Programming model maximizing the Net Present Value of the project considering the environmental impact. [ABSTRACT FROM AUTHOR]

The residential sector plays an important role to combat climate change. It requires alternatives to reduce its energy consumption and greenhouse gases emissions. Thus, polygeneration systems are a suitable alternative enabling efficient use of natural resources with low environmental impact. On the other hand, microgrids are considered a key component for improving power reliability and quality, besides they offer resilient and viable solution for integrating renewable energy sources at a large scale. Accordingly, this paper proposes an approach for the design of polygeneration systems for residential buildings considering them not only as a microgrid but as a smart energy system. A Mixed Integer Linear Programming (MILP) model was developed for the optimization of polygeneration systems considering different constraints which allow the energy system to work as a microgrid. Different thermal and electrical technologies where evaluated under different conditions, finding affordable and sustainable configurations and interesting synergies between technologies. Results show the importance to consider both thermal and electrical demands and technologies simultaneously for the design of energy systems. It is highlighted the displacement of batteries by thermal energy storage to achieve more cost-effective solutions in contrast to the current tendency to uphold battery systems as the key for future energy systems. • Approach for the design of polygeneration systems for residential buildings. • Integration of thermal and electrical energy storage in polygeneration systems. • Energy communities as microgrids. [ABSTRACT FROM AUTHOR]