# Measurement and Modeling of 3D Solar Irradiance for Vehicle-Integrated Photovoltaic
## 5 Conclusions  
As a result of increasing concerns of greenhouse gas emissions in the transportation sectors, the fuel and engine of the car are required to consider the total emission of CO\({}_{2}\) on a well-to-wheel basis. The typical approach is an electric vehicle (EV) [47] charged by the electricity generated by renewable energy like solar power [48]. The primary energy should be renewable energy; otherwise, a significant reduction of the greenhouse gas emission will not be expected [49]. However, this approach relies on the infrastructure of the distribution of clean electricity (PV power station installation, grid construction and connection, distribution of the clean electricity, and installation and operation of the EV charging station). It is much more convenient that the car collects solar energy and runs by it (or at least extending the range of mileage supported by its PV modules to reduce the frequency of charging). Solar-powered vehicles are now seriously discussed, and we have several feasibility reports [2; 3]. In principle, it is feasible by the improvement of both PV and car technologies to run a majority of electric vehicles on solar energy. However, as it is often the case of the early feasibility study, it is not supported by the real solar resources of the car running in the real environment. The motivation for our study is to know the real and active solar energy for the car through both modeling and measurement. For modeling, we developed a simple shading model using uniformly distributed (density and height) shading objects and random driving orientation using a simple combination of the collimated direct sunlight, uniform diffused sunlight, and reflection by road and shading objects. For the validation of the model, we used an array of pyranometers mounted on the car in five axes and monitored the solar resource around the car for one year. The model was validated in x, y, and z-directions local to the car as well as the angular distribution of the main beam of the solar irradiance on the car roof. Additionally, we developed the curved surface of the car roof and car body using the correction method. Commonly the car roof and car body are curved, and car manufacturers want PV panels that are also curved to fit the car body. The measurement (indoor testing) and performance (outdoor operation) in the standard PV panel was established by the fact that the PV panel always has a flat surface. We had to construct both the testing method and operation model from the beginning considering the three-dimensional density of the photon energy absorbance. Our solution is to introduce a curve-correction factor that keeps compatibility with the current testing equipment and standards. The curve-correction factor can be calculated by the ray-tracing calculation, once both the curve profile (possibly by CAD file) and angular distribution of the solar irradiance (also given by those mentioned above by the new solar resource model on the car body). Another crucial factor that affects energy yield from the VIPV is the mismatching loss either by the partial shading or non-uniform distribution by the curved surface. Currently, we developed a Monte Carlo simulation assuming that random numbers give the non-uniformity and ratio of the partial shading. Here is a summary of the conclusion in technical issues:  
1. A simple shading model to VIPV was developed and validated by one-year monitoring on the solar irradiation on the car roof and car body in five axes. 2. The curve-correction model of the curved surface of VIPV was developed. 3. A mismatching model using Monte Carlo simulation was developed to analyze the partial shading of VIPV. Conceptualization, K.A. ; methodology, Y.O. ; software, K.A. ; validation, Y.O. ; investigation, Y.O. ; data curation, Y.O. ; writing--original draft preparation, K.A. ; writing--review and editing, Y.O. ; visualization, K.A., and Y.O. ; supervision, Y.O. ; project administration, M.Y. ; funding acquisition, M.Y.