Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity and Cut-Off Wavelength

Version 1 : Received: 5 August 2020 / Approved: 6 August 2020 / Online: 6 August 2020 (11:28:27 CEST)

How to cite: De Maio, D.; D'Alessandro, C.; Caldarelli, A.; Musto, M.; De Luca, D.; Di Gennaro, E.; Russo, R. Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity and Cut-Off Wavelength. Preprints 2020, 2020080162 (doi: 10.20944/preprints202008.0162.v1). De Maio, D.; D'Alessandro, C.; Caldarelli, A.; Musto, M.; De Luca, D.; Di Gennaro, E.; Russo, R. Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity and Cut-Off Wavelength. Preprints 2020, 2020080162 (doi: 10.20944/preprints202008.0162.v1).

Abstract

A multilayer structure on a metallic substrate has been optically simulated and the optimization procedure aimed at obtaining Selective Solar Absorber (SSA) is discussed. This study refers to flat high vacuum thermal collectors and the overall Sun-to-thermal conversion efficiency has been evaluated using analytical formula and numerical thermal model. Both methods are in agreement and they have been validated using experimental results on a commercial absorber. The importance of a low emittance value to obtain high thermal efficiency at high temperatures and high stagnation temperature in selective solar absorber is highlighted. Optimized absorbers can be 8% more efficient than the commercial alternative at 250 °C operating temperatures and up to 27% more efficient at 300 °C. A stagnation temperature higher than 400 °C can be reached without Sun concentration if the proper design is adopted.

Subject Areas

thermal emittance; conversion efficiency; selective solar absorber; thermal energy; evacuated flat panel; solar energy

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