## 3 Results and Discussion
### Evaluation of Incident Light Intensity on the Roof and Hood  
To quantitatively assess the results in Section 3.1, we calculated the amount of incident light as if a car equipped with each surface was driving in Miyazaki, Japan. We did not consider partial shadows. While [PERSON] et al. determined ray intensity using METPV-11 [22], our study also incorporated weighting based on the area of each face element. This approach allowed the quantitative comparison of the total incident light intensity for any given date or year.  
In direct sunlight, we applied 100 relative azimuth angles of the Sun to create a box-and-whisker diagram. This analysis clearly demonstrates that direct sunlight has a more significant impact on self-shadowing than scattered sunlight.  
Figure 11: Example of the average incident light of (**a**) direct and (**b**) scattered on the roof and hood during a sunny day.  
Figure 10: Incident light intensity rate on the hood. Red dashed lines represent the solar trajectories corresponding to each date. The yellow dashed line represents the Sun’s direction corresponding to the maximum light intensity.  
Figure 9: Incident light intensity rate on the roof. Red dashed lines represent the solar trajectories corresponding to each date. The yellow dashed line represents the Sun’s direction corresponding to the maximum light intensity.  
We also conducted a yearly comparison of the total amount of incident light (direct + scattered) by integrating the values collected at each date and time point, as detailed in Table 1 below. Let \(I_{\text{total,roof}}\) and \(I_{\text{total,hood}}\) represent the total annual light quantities falling on the roof and hood, respectively. Table 1 also shows the yearly global horizontal irradiance (GHI) at Miyazaki, Japan, calculated using the METPV-20 database. Since the curved shape effect was minimal, the light intensity on the roof was approximately equal to the GHI value. The results showed that over the course of a year, 8% more light was incident on the roof than on the hood. A reason for the reduced light intensity on the hood was self-shadowing, which affects the in-plane distribution of the light intensity. Our proposed framework is effective for optimizing module configuration, including electrical interconnections, to maximize the power generation of VIPVs under the non-uniform light intensity conditions caused by self-shadowing.  
To estimate the energy yield of VIPVs during driving, the orientation of the vehicle along the route should be considered. In Figures 9 and 10, the vehicle faced northward (i.e., the driving direction was north). By arranging the vehicle's driving direction and solar azimuth in a local coordinate system [3], the incident light intensity rate can be estimated under dynamically changing conditions. The dynamic and partial shading from the surrounding environment also influences the output of VIPVs. We have previously evaluated the effect of shading as a contributing factor, as well as the influence of surrounding objects using a fisheye image [3]. The module temperature of VIPVs differs from that of the conventional PV module due to the driving speed and heat release from the internal combustion engine (in the case of plug-in hybrid electric vehicles). Therefore, we plan to estimate the energy yield of VIPVs under actual operating temperatures for a future publication.