## 4 Discussion
### Simulation of the \"Lightyear\" Use Case  
Many factors can influence the performance and gains obtained with a VIPV system on a passenger car. The existing vehicles with a high level of consumption per km and a high influence of the thresholds due to extra-consumption to charge PV energy in the battery have low performances. It is interesting here to simulate a use case with a reduction in the consumption per km, with a large surface of PV and with a small consumption of the electrical architecture as compared to PV installed power. For this, the considered consumption is 109 Wh/km, the value given for a Lightyear 0 vehicle [21]. The battery size of this vehicle is 60 kWh, and the solar roof peak power is 1.05 kW.  
First, simulations allow the comparison of the annual energies of the VIPV system normalized for 1 kW at midlife between the vehicle with 0.312 kWp and Lightyear 0. The previous vehicle is a solarized electric vehicle, which has the characteristics of average existing electric vehicles in terms of consumption (157 Wh/km), roof surface (1.44 m\({}^{2}\)) and battery size (50 kWh). Solarizing here means adding a VIPV system to an existing electric vehicle model. The Lightyear 0 is a vehicle integrating solar since its conception. Equation (2) in Section 2.4 yields eight as a maximal frequency of recharge with the grid of this vehicle. Thus, the model considers a charge with the grid only every eight nights. For the case of an average solarized electric vehicle, the considered charge with the grid is every five nights. Table 8 shows the results of the comparison of these configurations between a Lightyear vehicle and a solarized vehicle.  
Table 8 shows that the useful energy's variation is not linear. It is due to the thresholds related to extra consumption of the vehicle to use the PV's energy as explained in Section 3.2. The higher peak power can even double the useful energy per kWp in the case of a high shading level and directly charging the HV battery.  
Figure 15 shows the yearly distance covered by VIPV in Paris for a solar vehicle with the main characteristics of Lightyear 0 in terms of solar roof peak power, energy consumption per km, battery nominal energy and with grid recharge every eight nights.  
Figure 15: Yearly distance covered by VIPV in Paris with Lightyear 0 main characteristics 0.981 kWp (Middle)/1.05 kWp (BOL) solar roof, 109 Wh/km consumption and 60 kWh battery.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Only System Losses** & **Shading 0\%** & **Shading 30\%** & **Shading 49\%** \\ \hline Charge via 12 V battery & 0\% & 10\% & 21\% & 35\% \\ \hline Charge via 48 V battery & 0\% & 9\% & 20\% & 33\% \\ \hline Charge in the main battery & 0\% & 27\% & 55\% & 97\% \\ \hline \hline \end{tabular}
\end{table}
Table 8: Percentage of increase in energy per kWp for a solar vehicle (Lightyear 0 main characteristics) compared to a solarized electric vehicle’s performance.  
This figure shows that the values are much higher than in the case of a solarized electric vehicle. In the worst case, in terms of shading level and in average Europe in terms of irradiance, the solar electric vehicle with the characteristics of Lightyear 0 can cover 2888 km. This is due to the cumulative effect of high peak power, which is discussed above, and to low consumption per km. Unfortunately, the company which manufactured the Lightyear 0 vehicle declared bankruptcy in January 2023 [22]. One of the causes may be the high price (\(\ell\)250,000) and small production volume of this vehicle. Solarizing existing electrical vehicles has the advantage of affordable cost, enabling large selling volumes and the inconvenience of low performances. Therefore, multiplying the carbon footprint by a large number of vehicles gives a positive balance under favorable conditions.