Estimating daily global radiation using two types of revised models in China

Using the daily global radiation data and sunshine hours from 1994 to 1998 at 86 stations in China, the Angström model and the Bahel model are both validated and revised. The parameter a of Angström model is affected by the geological position, especially the latitude and altitude of the used stations, while the parameter b is little affected. The four parameters of the Bahel model are evidently affected by the longitude, latitude and altitude of the used stations. Using the total daily data in 1994–1998 at 86 stations together in China, 15 equations are calibrated, and all these equations can simulate the daily global radiation with relatively high accuracy. The revised equations that using geological positions and altitude to adjust the parameters of both the Angström model and the Bahel model, can give better results than the original models. The terms cos(ϕ) and latitude ϕ in the revised Angström equations have nearly the same effect, while in the revised Bahel equations, the former term can give better results. Using or not using the longitude λ in the revised equations of the Angström model does not change the simulation results largely, while in the revised equations of the Bahel model, the longitude λ has a relatively important effect. Because the parameter b of the Angström model is hardly affected by the positions and altitude of the used stations, the revised equations that just use the basic station information data to adjust parameter a can give nearly the same simulation results as the equations that adjust both the parameters a and b. For the revised Bahel equations, the equations in which all the parameters are adjusted by the geological position and altitude of the used stations can give better results.