Rough and Straightforward Estimation of the Mismatching Loss by Partial Shading of the PV Modules Installed on an Urban Area or Car-Roof

Solar panels used for EV charging stations and car-roof PV are often partially shaded and lead to substantial energy loss. It is known that this mismatching loss can be reduced by increasing the number of parallel strings. First, a probability model was developed using a one-year solar irradiance monitoring around the car body in 5 directions. The developed model successfully matched to the measured solar resource in each direction and succeeded to quantify the probability of the partial shading on the car. Another related issue of the inherent mismatching loss of the car-roof PV is non-uniform illumination caused by the curved shape of the panel. This can also be modeled by ray-tracing simulation. Then, we calculated the PV output affected by mismatching due to various sunlight patterns and partial shade patterns by Monte Carlo method. It was found that the average efficiency asymptotically approached 1 - 1 / N (N is the number of strings). We also examined the relationship between partial shade quantity and power generation loss in a 30 kW solar system array and verified the above model.