Estimation of daily solar radiation from sunshine duration in Thailand

The empirical relationship between solar radiation and sunshine duration in Thailand is studied in this paper. Although regional long-term regional solar radiation has not yet been measured in Thailand, the data of sunshine duration measurements are available. Hence, measurement of global solar radiation is conducted to find the relationship between daily solar radiation and sunshine duration, which is mostly linear. The distribution of regression coe‰cients is examined and the formula that can be applied in Thailand is estimated. The e‰ciency of the proposed formula is validated through its prediction. The result shows that the accuracy of the country-wide regression equations can be comparable to that constructed at each station. Moreover, it is found that the proposed equations are more e{currency sign}ective from May to November than from December to April. The proposed equations are applied to estimate solar radiation in Thailand and the di{currency sign}erences in their prediction are found in the characteristics of statistical distributions between May-November and December-April.