## 4 Results and Discussion
### Alternative Scenario Outcomes  
In this case, the impact linked to the addition of new RES plants is also considered in the LCA analysis besides that of batteries. The comparison with the results of the previous case (first scenario) in terms of carbon footprint, calculated using the IPCC 100-year characterization factors [44], is listed in Table 5 (Mode 1). The functional unit is still 1 MWh of stored energy. It is clear that, in this case, the results are worse than the previous findings, due to the quota of impact related to the new RES plants. The new values are between 3 (for LFP) and 18 (for NIB) times the previous results. Note that these values are still much lower than those for diesel production. The results completely change if a different functional unit is considered. In particular, the annual average impact of 1 MWh of energy supplied to the users by the entire system is considered (Mode 2). Considering the carbon footprint calculation listed for Mode 2 in Table 5, it is clear that the introduction of batteries to exploit entirely the already existing renewable plants (first scenario) gives only a negligible reduction of the islands' emissions. Contrarily, the increase of the use of renewables and the addition of a greater storage capability provides better results. However, in comparison with the current energy generation systems, there is not a great difference among the different kinds of batteries. Figure 4: Characterization of the assembly phase for LFP (ReCiPe 2016 method-Endpoint (H)). For other impact categories, as shown in Figure 6, different results can be obtained, and, in some cases, the impact of the new system (alternative scenario) is higher than that of the current one. Particularly, water consumption and eutrophication, land use, and mineral resource consumption present higher values due to the addition of PV modules. For the PVs and the wind turbines, the assembly phase and the end-of-life scenario consider the state of the art in Europe. Lastly, to analyze in depth the influence on the results of the location, the damage for Pantelleria and Ventotene is compared for both definitions of the functional unit. For the sake of simplicity, only the results related to the NIB are summarized in Figure 7, but the other batteries present similar outcomes. The values have the same trend among the different calculation modes, but even if the batteries are the same, the impacts are quite different between the two islands. This is important because it demonstrates that the environmental benefit of a battery arrangement depends on the energy system where it is inserted, not only on the battery itself. For example, referring to carbon footprint and excluding the impact caused by the use of diesel, the environmental impacts associated with the battery storage system account for only 13% of total impacts in Pantelleria and 12% in Ventotene. Photovoltaics and wind power plants account for 83% and 3.7%, and 82% and 2%, respectively. Similar results can be found in Reference [13] where a hybrid system combined a large-scale battery energy storage system with renewable electricity generation from wind power and photovoltaics  
Figure 5: Characterization of the end-of-life phase for LFP (ReCiPe 2016 method-Endpoint (H)). on Graciosa island. In Reference [13], the impact of batteries is about 16% while those of wind power and photovoltaics are 47% and 37%, respectively. Note that, in some papers and reports, the unit of storage capacity is used as the functional unit. The values of GWP for this functional unit, which excludes the contribution of the operation phase, are summarized in Table 6. They are comparable with the values listed in References [10; 12], where the authors found that producing 1 Wh of storage causes 110 \(\mathrm{g_{CO2 eq}}\) of GHG emissions. The relatively low values of this work are mainly related to the highest amounts used for the energy density of batteries.