Preprint Article Version 2 Preserved in Portico This version is not peer-reviewed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

Version 1 : Received: 5 August 2020 / Approved: 6 August 2020 / Online: 6 August 2020 (11:28:27 CEST)
Version 2 : Received: 19 October 2020 / Approved: 20 October 2020 / Online: 20 October 2020 (12:18:01 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. Preprints 2020, 2020080162 (doi: 10.20944/preprints202008.0162.v2). 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. Preprints 2020, 2020080162 (doi: 10.20944/preprints202008.0162.v2).

Abstract

This study refers to the optimization of a Selective Solar Absorber to improve the Sun-to-thermal conversion efficiency at mid temperatures in high vacuum flat thermal collectors. Efficiency has been evaluated by using analytical formula and a numerical thermal model. Both results have been experimentally validated using a commercial absorber in a custom experimental set-up. The optimization procedure aimed at obtaining Selective Solar Absorber is presented and discussed in the case of a metal dielectric multilayer based on Cr2O3 and Ti. The importance of adopting a real spectral emissivity curve to estimate high thermal efficiency at high temperatures in selective solar absorber is outlined. Optimized absorber multilayers can be 8% more efficient than the commercial alternative at 250 °C operating temperatures and up to 27% more efficient at 300 °C. Once the multilayer has been optimized the choice of a very low emissivity substrate such as copper allows to further improve efficiency and to reach stagnation temperature higher than 400 °C without Sun concentration.

Subject Areas

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

Comments (1)

Comment 1
Received: 20 October 2020
Commenter: Davide De Maio
Commenter's Conflict of Interests: Author
Comment: We strengthened our material and methods section, moved at the end of the paper. We added important details about the production process of the samples and materials characterization that were missing. We also added a comparison between simulations and the experimental results to better withstand our hypothesis and findings.
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