Models for calculating daily global solar radiation from air temperature in humid regions - A case study

Solar radiation is an important parameter for the proper design of solar energy conversion devices and building energy systems. As air temperature is readily available at most meteorological stations, the models based on air temperature for estimating solar radiation are more attractive and practical. To improve the air temperature-based models' performance in humid regions, the effects of seasonality and relative humidity are introduced to (Hargreaves and Samani [1982]: Journal of the Irrigation and Drainage Division 108, 225-230) and (Bristow and Campbell (BC) [1984]: Agricultural and Forest Meteorology 31, 159-166) correlations, and thus six candidate models are proposed in this article. These models are tested at Guangzhou station in China with humid subtropical climate influenced by the Asian monsoon as a case study. Results show that relative humidity has a greater effect than that of seasonality on the air temperature-based models for daily global solar radiation estimation, and the models of BC family including the effects of seasonality and/or relative humidity give better estimates. Accordingly, a strategy for selecting an optimum model for estimating daily global solar radiation in the humid regions is proposed.