Importance of the spectral emissivity measurements at working temperature to determine the efficiency of a solar selective coating

• Published in: Solar energy materials and solar cells Vol. 140; pp. 249 - 252
• Main Authors: Echániz, T., Setién-Fernández, I., Pérez-Sáez, R.B., Prieto, C., Galindo, R. Escobar, Tello, M.J.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2015
• Subjects: Absorption; Computing time; Efficiency; Emissivity; Infrared radiation; Mathematical analysis; Solar collectors; Solar heating; Solar selective coatings; Spectral emissivity; Temperature dependence; Thermal solar energy; Spectral emissivity; Infrared radiation; Thermal solar energy; Efficiency; Solar selective coatings
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2015.04.009

The total emissivity of the absorbing surfaces is a critical parameter in the calculation of the radiative thermal losses in solar thermal collectors. This is because the radiative heat losses have a significant economic impact on the final cost of the electricity produced in a solar thermal plant. This paper demonstrates the need to calculate the total emissivity from spectral emissivity measurements at the working temperature of the solar thermal collector, instead of using extrapolated values from spectral emissivities measured at room temperature. Usual uncertainties produced by the estimation of the total emissivity, in which its temperature dependence is only introduced by the Planck function, are analyzed. •Solar thermal collectors efficiency depend on correct total emissivity values.•Room temperature data extrapolation to work temperature is not an accurate method.•Even spectral emissivity with weak temperature dependence leads to critical errors.•Spectral or total emissivity must be measured at work temperature.•The high-temperature radiometry is a good method to determine the total emissivity.