| Abstract |
An important parameter in the analysis provided by the second law of thermodynamics for the evaluation of solar energy conversion systems is the radiation temperature.^The solar radiation is diluted due to atmospheric scattering and absorption, and reflection at the absorber surface.^This dilution reduces the temperature of the sun (as a blackbody source) to an effective radiation temperature.^In the presented study, spectral dilution functions were derived for three components of the absorbed global terrestrial solar radiation (direct beam component + forward Mie component + diffuse component).^The energy and entropy fluxes and effective temperature for each component were expressed in terms of these dilution functions.^They were calculated for different atmospheric conditions using numerical integration over the wavelength.^The effects of the air mass and the atmospheric parameters on these thermodynamic quantities and the maximum conversion efficiency of solar energy were investigated.^An apparent temperature assigned for the sun as a high temperature reservoir for Carnot engine was calculated and found to vary between about 3600 K for clear sky and about 2000 K for highly turbid sky under the given atmospheric conditions. |