Measurements of spectral-band solar irradiance in Bangi, Malaysia

In the present study, a series of global spectral-band solar irradiance measurements over a wide range of optical air masses and atmospheric conditions in the interval of 400-1100nm is presented. The measurements were obtained continuously using 12 Li-200SA pyranometers equipped with different Schott glass, flat, circular, and long-pass filters on a horizontal surface at Universiti Kebangsaan Malaysia (2°55'N,101°46'E) between September 1 and November 30, 2011. By combining the measurements obtained using different filters, obtaining global solar irradiance in various wavebands is possible. To support the experimental data, the results were compared with the simulated results of the Simple Model for the Atmospheric Radiative Transfer of Sunshine (SMARTS2) model. Forecasting performance parameters such as the normalized root mean square error (NRMSE), the normalized mean bias error (NMBE), and R² have been used to test the accuracy of observed data. NRMSE for the whole spectrum varies from 0.7% to 5.3%, whereas NMBE varies from -2.1% to 2.3%. The determination coefficient R² results for all air masses are near 1.0. Simulated and measured data show good agreement over the whole measured spectrum. The measurement of solar radiation using pyranometers equipped with filters is much less complicated, more compact, and is less costly than using spectroradiometers.