Chapter 5 - Spectral solar irradiance estimation under clear sky

Abstract

The aim of this work is to estimate spectral solar irradiances at ground surface under clear sky conditions by its modeling, where the three radiation solar components are required: direct, diffuse, and global. The importance of spectral solar data is every day increasing in the field of solar power under the necessities of Photovoltaic and Concentrated Photovoltaic systems. A spectral solar radiation model was developed, named SSolar-GOA, which is easy to replicate and use, with fast computation and sufficient accuracy. The core of the model is the analytical expression for the total scattering transmittance based on the theory of "adding layers" of Ambartsumian, and the absorption by atmospheric gases is based on "band model" parametrized expressions. The SSolar-GOA model gives the solar global spectral irradiance by multiplication of the absorption and scattering transmittances and the extraterrestrial spectrum. Direct normal spectral irradiance is given by the Beer-Lambert-Bouguer law, and hence, the diffuse component is obtained as difference. The spectral resolution of the model is moving in the values of most commercial spectroradiometers (1-10 nm). Model data are compared with experimental solar spectral irradiance measurements for three different cases, from very low to very high turbidity conditions, taking measured model inputs. The comparison shows the features of the SSolar-GOA model and its uncertainties.