All sky modeling daylight availability and illuminance/irradiance on horizontal plane for Mahasarakham, Thailand

This paper presents the results of a study on all sky modeling and daylight availability for the tropical climate found in the central region of the northeastern part of Thailand (16°14′N, 103°15′E). The required components of sky quantities, namely global and diffuse horizontal irradiance and global horizontal illuminance for saving energy used in buildings are estimated. The empirical sinusoidal model and a novel sinusoidal model, which consists of polynomial or exponential functions, are validated. A and B values of the empirical sinusoidal model for all sky conditions are determined and developed to become a new function in the polynomial or exponential form of the sky conditions. Observation results from one year’s total data indicate that the luminosity and the energy from the sky on a horizontal plane in the area around Mahasarakham are much greater than those of Bangkok. The accuracy of the validated model is determined in terms of the mean bias deviation (MBD), the root mean square deviation (RMSD) and the coefficient of correlation (R2) values. Comparison of the estimated solar irradiation values and the observed values revealed a small error slide as well.