DEVELOPMENT OF A SIMPLIFIED ESTIMATION METHOD FOR SPECTRAL DIRECT BEAM SOLAR IRRADIANCE INCLUDING ULTRAVIOLET, VISIBLE, AND NEAR-INFRARED IRRADIANCE

In this paper, a simplified regression equation that estimates spectral direct beam solar irradiance between 0.3 and 2.5 μm under all-weather conditions from broadband direct beam solar irradiance, is presented. Furthermore, three kinds of correction equations to correct the regression equation are created using solar direct beam transmittance, air-mass, and precipitable water. Using these equations, we calculated the all-weather spectral direct beam solar irradiance and compared it with the measurements. It was found that average of root mean square error for the estimated spectral direct beam solar irradiance decreased by 45.2% due to the effect of using all correction equations.