THEORETICAL EFFICIENCY OF AN ALL-GLASS TUBULAR SOLAR COLLECTOR USING A CHEMICALLY DEPOSITED SNS-CUXS ABSORBER INSIDE THE INNER TUBE

Theoretical efficiencies of an evacuated-tube solar collector using a chemically deposited SnS-CuxS absorber thin film (alpha = 0.91) in contact with the working fluid are presented. A mathematical model is developed and solved numerically to yield photothermal conversion efficiencies eta of the collector for the heat transfer coefficient h(b) of 0.026 W m-2 K-1 (good vacuum). The analysis shows that the eta of such a collector would be unacceptably low, congruent-to 25%, for the operating parameter f congruent-to 0.1-degrees-C m2 W-1 which represents the typical operating condition of an evacuated-tube solar collector. However, the use of a low emissivity (epsilon) transparent coating applied to the outer surface of the absorber tube (i.e. in the place of the spectrally selective solar absorber coating in the conventional all-glass evacuated-tube collector) can yield eta 75% for f congruent-to 0.1-degrees-C m2 W-1 for epsilon = 0.1 with water as the heat transfer fluid and eta-68% with a mineral oil as the heat transfer fluid.