Diffuse-global correlation models at four locations in Thailand

Abstract

Diffuse-global correlation models at four solar monitoring stations in the tropical environment of Thailand have been investigated. These stations are located at Chiang Mai (18.78 °N, 98.98 °E) in the North of the country, Ubon Ratchathani (15.25 °N, 104.87 °E) in the Northeast, Nakhon Pathom (13.82 °N, 100.04 °E) in the Central region and Songkhla (7.20 °N, 100.60 °E) in the South. The models are based on a 12-year period of global and diffuse solar radiation data obtained from these stations. The models relate statistically the diffuse fraction of global radiation as a dependent variable to a clearness index, defined as the ratio of global radiation to extraterrestrial radiation for hourly, daily and monthly average time scales. The model performance was validated against independent data from these stations and satisfactory results were obtained. The models compared favorably with other available models when tested against these independent data.