Analysis of terrestrial solar radiation exergy

Based on Candau’s definition of radiative exergy, the exergy of the extraterrestrial and the terrestrial solar radiation are computed and compared by using the solar spectral radiation databank developed by Gueymard. The results show that within the spectrum region from 0.28 to 4.0 μm, the total energy quality factor (i.e., the exergy-to-energy ratio) of extraterrestrial solar radiation is about 0.9292, and that of the global terrestrial solar radiation is about 0.9171 under US standard atmosphere condition and zero solar zenith angle. The terrestrial solar spectral radiation exergy flux is large in the near ultraviolet and the visible light region. The reference radiation exergy spectra are obtained under atmospheric conditions consistent with ASTM standard G173-03. The effect of tilt angle on the terrestrial solar radiative exergy for inclined surface, and the effect of air mass on total energy quality factor of the terrestrial solar radiation for horizontal surface are analyzed. With the increase of tilt angle, the terrestrial solar spectral radiation exergy flux initially increases and then decreases, the total energy quality factor of the diffuse part decreases monotonically, while that of the direct part is invariant. The total energy quality factor of the direct, the diffuse and the global terrestrial solar radiation all decrease with the increase of air mass