# Optimal Sizing of Battery Energy Storage System for Implicit Flexibility in Multi-Energy Microgrids
## 3 Results
### Techno-Economic Impact of BESS Deployment
Notably, the integration of  
Figure 5: NPV over a 10-year horizon for each BESS configuration evaluated. Figure 6: Comparison of annual operational cost components between the reference scenario (without BESS) and the BESS configuration that minimizes annual costs (2 MW/4 MWh). the BESS leads to a non-negligible increase in self-consumption--from 12,638 MWh/year to 12,991 MWh/year, a rise of approximately 2.8%--thereby minimizing interactions with the public grid. As a reference, the total energy exchanged with the external network drops from 1312 MWh/year in the reference scenario to just 243 MWh/year in the BESS-integrated optimal scenario, representing a reduction of approximately 82%. As a result, all consumption-based charges expressed in _EUR/kWh_ also decline proportionally. It is important to emphasize, however, that these reductions are not due to the exploitation of _negative electricity injection._ For the analyzed MEMG conditions, it is not economically advantageous to perform pure arbitrage by withdrawing and injecting electricity through the BESS at the zonal DAM price. Under the considered modeling assumptions and 2024 Italian DAM prices, the amount of electricity negatively injected into the grid remains negligible over the year. Moreover, the BESS proves to be effective in peak shaving operations, resulting in a reduction of capacity-based charges by approximately EUR 24 k annually, representing a decrease of 77.91%. Finally, Figure 7 shows that the presence of the BESS reduces revenues from electricity exports to the grid. This is primarily due to a shift in operational strategy: instead of injecting surplus energy during high-price periods, it is often more economically advantageous to store that energy for later use. This deferred use enables further arbitrage, contributes to peak reduction, and allows the CHP unit to be turned off more frequently--leading to additional O&M savings. Lastly, the figure shows that excise duties--representing a large portion of the POD costs--remain unchanged, as they are applied per unit of energy consumed and are unaffected by the scheduling strategy. Fixed monthly charges (EUR per POD/month) also remain constant. The following analysis investigates how the integration of a BESS affects the operation of the conventional gas-fired generation units and their thermal efficiency. Table 3 reports the capacity factor (CF) of the CHP unit and the two gas boilers, along with the amount of heat dissipated to the environment. For completeness, the CF of the BESS is also included for the configuration with storage. In the BESS-integrated scenario, the CHP unit operates less frequently. This is primarily because the BESS enables more efficient use of on-site electricity generation, both from the CHP and from the PV systems. Instead of injecting excess electricity into the grid, the surplus is stored in the BESS and later used to meet local electrical demand. This shift reduces the need to operate the CHP, particularly during periods when only electricity is required and no thermal demand is present. As a result, the system avoids producing heat that cannot be utilized and would otherwise be dissipated into the atmosphere. Consequently, the configuration with the BESS also shows a notable  
Figure 7: Comparison of annual POD cost components between the reference scenario (without BESS) and the BESS configuration that minimizes annual costs (2 MW/4 MWh). decrease in wasted thermal energy (\(-6.4\%\)), reflecting a more efficient and flexible use of the existing generation assets. Lastly, we analyze how the 15-min power flows within the MEMG change in the presence of the BESS compared to the benchmark configuration without storage. To do this, two representative days are selected: 15 July 2024, corresponding to the annual peak in electrical load (around 3.5 MW); and 12 December 2024, the day with the highest hourly zonal DAM price in the _NORD_ bidding zone for the selected period (around EUR 25/MWh).