## 5 Analyses and Discussion  
### Analyses of the Impacts on the Degree of Efficiency of PV-Powered Vehicles  
If generally better environmental conditions can be obtained at PV-powered charging stations as compared to PV-powered vehicles, as proposed in References [7; 11; 12], the question as to why we should focus on PV installations in electric vehicles arises. First, if a PV-powered charging station is only available at the vehicle owner's home, then the car cannot be charged, for example, when the owner takes the car to work. As such, the PV energy from the PV-powered charging station needs to be either supplied to the power grid or stored in another battery until the vehicle's high-voltage battery can be charged. As seen in Figure 7, when choosing a parking space, the driver has an influence on the cardinal direction of the vehicle (\(\psi\)) relative to the sun. Commonly, the PV panels of a PV-powered charging station face the sun at an ideal angle. In the Northern Hemisphere, for PV panels at a charging station, \(\psi=180^{\circ}\) (alignment towards the south). In this way, as  
Figure 19: \(\lambda\) for trip from sports hall to botanical garden. Figure 20: \(\lambda\) for trip from botanical garden to sports hall. seen in Figure 11, on a sunny day, the highest solar radiation level can be obtained around 1:00 p.m. (daylight saving time). Figure 21 shows a model from Fujimi, a manufacturer of the Toyota Prius, at a scale of 1:24. This model is used to illustrate the impact of the vehicle's cardinal direction on the efficiency of the PV installation. The location of the standard 156 mm \(\times\) 156 mm poly-Si along the roof of the vehicle is indicated in the figure. Figure 22 shows the simulated PV energy from the different rows of PV cells if the vehicle were oriented towards the south (\(\psi=180^{\circ}\)). Comparing the simulated results in Figures 22 and 23, we can see, for example, that at 10:00 a.m., PV cells in row one produce about 0.5 W, or 15% more, with \(\psi=135^{\circ}\) than with \(\psi=180^{\circ}\). However, this increase in output power only occurs in the morning. In the afternoon, because the vehicle is oriented to the southeast and facing away from the sun, the output power will be lower. Figure 24 shows the worst-case scenario that is possible when the vehicle is oriented towards the north. Even though the output power of PV cells in rows 6-9 is improved, the output power of PV cells in rows 1-4 will be reduced. As a result, the total output power of the PV installation is reduced. With \(\alpha=0^{\circ}\), PV cells in row six are unaffected by the vehicle's cardinal orientation. As seen on the model in Figure 21 and based on the simulation results shown in Figures 22-24, PV cells on top of the curved surface are affected by the shape of the roof and the resulting longitudinal angles of PV cells, and the vehicle's orientation relative to the sun. Theoretically speaking, the driver can improve the output power of the PV installation for a certain period of time if the car is oriented at a beneficial angle towards the sun, as shown in Figure 19.  
In driving conditions, the roof can receive an uneven amount of irradiation. Even though the width of the roof is small, some parts will receive more irradiation on average  
Figure 23: Simulated power at MPP (\(P_{mpp}\)) for \(\psi=135^{\circ}\). Figure 24: Simulated power at MPP (\(P_{mpp}\)) for \(\psi=0^{\circ}\). than other parts. Figure 25 illustrates the distribution of the average solar radiation level when driving from the sports hall to the botanical garden, as seen in Figure 19. As in Reference [13], each part of the roof was monitored by one sensor unit, from which the average was calculated. As seen in Figure 25, due to shade from trees on the right-hand side of the street, that side will receive the least solar radiation. The middle area of the roof will receive more irradiation, but still less than the left side of the roof. These circumstances need to be taken into account when connecting PV cells together to form a PV panel.