A car-roof photovoltaic has enormous potential to change our society. With this technology, 70% of a car can run on the solar energy collected by the solar panel on its roof.

Since it is to be accepted the majority of the customers, it should be painted as the normal car-painting. This paper estimated the energy yield loss by the automotive painting and setting the goal of the energy conversion efficiency with coated photovoltaic on the car-roof.

The estimation is not as simple as the spectroscopic transparency calculation but needs to consider angular weighting, the curvature of the panel, mismatching loss by the advanced multi-junction solar cells. To estimate the practical value of the target performance, we first monitored the PV module using three-junction solar cell (30 % efficiency) in outdoor for three years. We also developed the new energy yield model, because the conventional model only considers irradiance and temperature.

The newly-developed model successfully explained the seasonal trend of the energy yield of the spectrum-and-angular sensitive three-junction photovoltaic module. We also combined the ray-tracing simulation for consideration of the curvature of the car-roof. With the new and validated (by 3 years) energy generation model, we could define the target base PV efficiency for several car-painting, like blue, gold, red, green and grey.