Solar control characteristics are described for chemically deposited thin film coatings consisting of an initial layer of
Bi2S3
film of ∼0.05 μm thickness deposited at room temperature (25°C) for 45–75 min from baths containing bismuth nitrate, triethanolamine (TEA) and thioacetamide and a
CuxS
thin film of 0.1–0.25 μm thickness deposited either at room temperature, for 3–6 h, or at 50°C, for 1–2 h using baths consisting of copper(II) chloride, TEA, thioureau (TU),
normalNaOH
and
NH3false(normalaqfalse)
. Air annealing of these films at 150°C for 30 min yield well‐desired solar control characteristics: sheet resistance of 30‐60 Ω/□ which signifies a low thermal emittance; integrated transmittance of 15–32% in the visible region and 11–22% in the near‐infrared region; integrated transmittance of ∼13–25% for solar radiation and a range of shades in reflected daylight. Using a mathematical model, the solar control performance of these coatings in a 6 mm sheet glass is predicted for an architectural window in a tropical location showing that solar radiation rejection of ∼50% is obtainable for a
Tnormalvis*
of 17%.
A mathematical model to predict the shading coefficients (SC) and solar rejection factor (SRF) of various types of chemically deposited solar control coatings is presented. The values of SC and SRF are presented for coatings with soar absorptance in the 50-75% range and solar reflectance in the 10-25% range for typical exterior temperature of 10-50 degrees C. Chemically deposited solar control coatings with a protective polymer coating applied on 6 mm thick sheet glass in architectural windows are seen to provide SC in the 0.3 to 0.75 range depending on the optical characteristics and exterior temperatures. A solar rejection factor of 33-56% is available from the coatings already reported.
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 hb of 0.026 W m-2 K-1 (good vacuum). The analysis shows that the eta of such a collector would be unacceptably low, approximately=25%, for the operating parameter f approximately=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 approximately=75% for f approximately=0.1 degrees C m2 W-1 for epsilon =0.1 with water as the heat transfer fluid and eta approximately=68% with a mineral oil as the heat transfer fluid.
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