## 3 Results
### Calculation of \(CO_{2}\) Emissions
If local communication and monitoring networks that include homes are added, there is an increase of 63%, which means that after 20 years, networks in homes correspond to values between 11.1 PJ and 23.3 PJ of exergy destroyed. Exergy is defined as the maximum amount of useful work that can be obtained from a system [27], meaning it is the part of the energy used that is available to produce useful work. The analysis of the exergy efficiency of a system reflects its sustainability or environmental impact [33; 34]. Thus, a direct relationship can be established between the exergy destroyed in a process and its CO\({}_{2}\) emissions [34; 35]. The study by [26] considered the period from 2020 to 2040 and the city of Vienna, with a number of inhabited dwellings of 977,875.5 on average. In the study, they considered two inhabitants on average per dwelling. This study can be a good reference for calculating the emissions associated with the communications and metering infrastructures required for the G2V mode, since this mode of operation requires this type of infrastructure and approximate level of processing. For V2G mode, the type of infrastructure required will be even higher than that recorded in the study by [26]. In NC and WCNC mode, no relevant communications infrastructure is required. According to the EU, there are less than 300 vehicles per 1000 inhabitants in the city of Vienna [36], but on average, there are 530 vehicles per 1000 inhabitants in the EU [37]. Therefore, it was decided to use the EU average value to calculate emissions per vehicle, considering that, on average, the impacts in an EU city will be approximately proportional to those obtained for Vienna. For this study, the scenario was considered in which 50% of the vehicles in a city are EVs. Per week, in Portugal and on average, cars travel between 50 and 200 km, and 9000 km per year [32], resulting in around 25 to 30 km/day; therefore, these reference values were considered for the present study. According to the study by [26], on average, exergy consumption is from 0.554 PJ (\(1.539\times 10^{8}\) kWh) to 1.165 PJ (\(3.236\times 10^{8}\) kWh) per year, for the entire city. Considering an average of 530 vehicles per 1000 inhabitants (we consider the average value of 1,955,751 inhabitants and that 50% of vehicles are EVs), we obtain 518,274 EVs, which corresponds to between 296.94 kWh/EV and 624.38 kWh/EV and per year. Using the EU mix of 596 gCO2e/kWh (in coherence with the calculations in the previous point), we obtain between 176,980.52 and 372,130.56 gCO2e per EV and per year. Considering an average circulation of each vehicle of 9000 km per year [32], emissions between 19.66 gCO2e/km and 41.35 gCO2e/km are obtained due to communications and metering infrastructures. These values only consider the basic infrastructure of a smart grid/smart metering, considering one interconnection/control point per EV (considering that it will usually be connected with charging control at night and close to the home). It can be considered that these values are a reasonable approximation in the case of G2V mode, but in V2G mode, the network will have to be larger and more complex. This is due to the fact that in this mode, EVs must be connected to the grid whenever they are not in circulation, therefore both during the day and at night, and both near the home and in professional or public places. Therefore, for V2G mode, it was considered that there will be two interconnection and control points for each EV, and therefore more communications infrastructure is needed. In this mode, much more processing is also required, as there is more complexity in data management and algorithms, and a greater quantity of data to store. For all these reasons, in this study, it was considered necessary to approximately double the amount of smart metering infrastructure and its consumption over time. It was considered that there is no relevant change in the infrastructure in the homes. Thus, the total exergy that is consumed becomes 17.9 PJ to 37.6 PJ for 20 years in V2G mode.