## 4 Discussion  
According to the characteristics described in the literature, the V2G mode is the one that presents the most benefits and least negative effects for the grid [24]. However, it is not clear that such apparent benefits actually result in it being a more environmentally sustainable option. The results show that it is the integration mode that presents the highest CO\({}_{2}\) emissions and is therefore the worst option. In this mode, emissions will be from 88.2% (best case) to 125.6% (worst case) of the average emissions value of an ICV (177.15 gCO2e/km): in the best scenario, an EV will have less 11. 8% than an ICV and in the worst case, it will have 25.6% more emissions than an ICV. These results show that V2G mode increases CO\({}_{2}\) emissions and therefore reduces the benefits of using EVs. In G2V mode, emissions will range from 74.1% (best case) to 111.4% (worst case) of the average emissions value of an ICV: in the best scenario, an EV will have 25.9% less than an ICV, and in the worst case, it will have 11.4% more emissions than an ICV. The results for V2G and G2V modes show that the need for communications, control, storage, and data processing infrastructures (that cause emissions due to resource use and energy consumption in manufacturing) and their operation over time (which implies energy consumption) can lead to the option of using an EV instead of an ICV being more unsustainable. For NC and WCNC modes, emissions will range from 67.3% (best case) to 88.0% (worst case) of the average emissions value of an ICV: in the best scenario, an EV will have 32.7% less than an ICV, and in the worst, case it will have 12% fewer emissions than an ICV. These values are consistent with those recognized by the European Environment Agency (EEA), which state that in the best case scenario, an EV will have 17 to 30% fewer emissions compared to an ICV, but it may in some cases have more emissions than an ICV considering the 2018 mix of energy production electricity in the EU [30]. These results are also in line with the results of [25]: \"When comparing equal sizes, the EVs had 20-27% lower life cycle impact than the ICEVs\". The NC and WCNC interconnection modes are those that bring the most benefits to environmental sustainability, as they have the lowest CO\({}_{2}\) emissions. This is due to the fact that they do not need communications, control, storage, and data processing infrastructures. The results obtained are consistent with reservations at EU level about the expectations of the environmental benefits of large-scale EVs: \"For a sustainable mobility system, electric vehicles alone will not be enough. Furthermore, production of electric vehicles will still require substantial resources and generate pollution\" [30]. Previous studies focused on analyzing the life cycle of an EV have already shown that the benefits of EVs for large-scale sustainability are small and may not even exist (depending on the size of the EV, the manufacturing country, or the mix of electricity production). But the results of the present study show that this also depends on the mode of large-scale EV integration in the grid. The results show that the integration mode that is considered in the literature as the most promising (particularly at the economic level) for the EES (V2G) is the worst from the point of view of CO\({}_{2}\) emissions, that is, for environmental sustainability. As the NC and WCNC modes are the ones with the least emissions, but the ones that present the most problems for the EES, it will be necessary to find an EV percentage threshold that allows for the safe operation of the EES without having to resort to a complex system of communications and data processing (which would increase emissions). In this way, CO\({}_{2}\) emissions are minimized. The present study focuses on environmental sustainability, but to have a broader (more macro) perspective, an analysis of economic sustainability should also be carried out.