A distribution function to predict the hourly global solar irradiance is suggested fitting with published experimental meteorological data in Jeddah, Saudi Arabia, and Hong Kong in China. The predicted formula is used as a source function together with heat diffusion equation and heat balance equation to find the temperature of the glass window and the profile within the salon of the car and its variation with the local exposure interval daytime. The Integral Laplace transform technique is used to solve the problem.