# Optimal Sizing of Battery Energy Storage System for Implicit Flexibility in Multi-Energy Microgrids
## 3 Results
### Case Study and Data  
The MEMG analyzed in this study is located on the Leonardo campus of Politecnico di Milano [29]. A simplified schematic representation of the system is provided in Figure 3. The electrical network operates at medium voltage (MV) and includes 11 substations, 10 of which are currently interconnected, while the remaining one is planned for future integration. The entire microgrid is connected to the city's distribution grid through a single POD. Connected to the electrical network are 10 PV systems, with a total installed capacity of approximately 1 MW. The campus also hosts several EV charging stations operating in vehicle-one-grid (VIG) mode, allowing unidirectional charging from the grid to vehicles. On the thermal side, the system includes a district heating network composed of 29 thermal exchange substations, which supplies heating to the campus buildings during the winter season. The core of the combined heat and power generation is an ICE unit with an installed capacity of 2 MW electric and 1.7 MW thermal. In parallel, two industrialgas-fired boilers provide an additional 12 MW of thermal capacity, ensuring adequate heat supply during thermal peak demand periods. For space cooling during the summer season, the campus does not rely on a centralized cooling network. Instead, cooling is provided by distributed units across the campus buildings, predominantly consisting of electric heat pumps. Additionally, an absorption chiller is in place, which utilizes waste heat from the CHP unit to generate cooling energy, thereby improving overall system efficiency through trigeneration. Finally, the system includes two diesel-fueled gensets, which are only activated in emergency islanding scenarios.  
In this study, it was not possible to model all the loads and energy generation units present on the campus due to the lack of reliable and sufficiently long-term historical data. Figure 4 provides a schematic representation of the components that are included in the block-based modeling framework used in following analysis. Specifically, we consider the electricity demand associated with the 10 substations currently connected to the MV microgrid, the power production from seven PV plants, for a total peak power of around 820 kW, the ICE operating in CHP mode, the two active industrial gas boilers, the total thermal demand of the campus, and the cooling demand served by the absorption chiller. Additionally, the simulation includes the connection points to the external electricity grid (POD) and to the natural gas network (PDR). Based on this MEMG configuration, we hypothesize the installation of a BESS to evaluate its techno-economic impact.  
To evaluate the techno-economic performance of the MEMG across different seasons, we consider its operation over a full year, taking 2024 as the reference. The data for electrical demand, thermal demand, and cooling demand (converted into thermal equivalent), plus those referring to PV generation, are obtained from on-site measurement devices installed across the campus. Table 1 reports the annual energy values for the system's loads and PV generation. It can be observed that PV generation accounts for approximately 7.1% of the total annual electrical demand, with the remaining portion supplied by the ICE or the utility grid. The total thermal load is around 10 GWh per year and is met by the ICE and the two available industrial boilers.  
The techno-economic parameters employed for each unit in this study are reported in Appendix A, along with the relevant references used, in Tables A1-A3. The various tariffs applied to electricity and natural gas are reported in Tables A4 and A5. Additional parameters used in the analysis are listed in Table A6.  
Figure 3: Simplified schematic of the MEMG at the Leonardo campus of Politecnico di Milano.