Scientific Publication: A comparative analysis of opto-thermal figures of merit for high temperature solar thermal absorber coatings

DLR, CIEMAT-PSA, and University of Almería published a scientific publication about SFERA-III in the February 2022 edition of the Renewable and Sustainable Energy Reviews. The paper is available in open access.

Abstract

Solar thermal absorber coatings play a key role in the thermal efficiency of receivers for applications in the field
of Concentrated Solar Power (CSP). The development of stable spectral selective coatings with a high solar
absorptance αsol and a low thermal emittance εth is often desired to reduce thermal losses. However, quantitative
indicators describing selectivity and the trade-off between solar absorptance and thermal emittance is seldom
discussed in the literature.

In this review, relevant opto-thermal figures of merit are analyzed for the comparison of reference solar
thermal absorber coatings, including real and ideal coatings, both black and spectral selective. The comparison is
made for a temperature ranging from 25 to 1000 ◦C and for a concentration factor ranging from 20 to 1000,
based on spectral data measured at room temperature from 0.25 to 20 μm.

New figures of merit are introduced, i.e. a normalized selectivity ratio Si, a trade-off factor Ztrade-off, a normalized solar reflectance index SRI and a peak efficiency temperature Tpeak,opt. These metrics are derived
from existing figures of merit and adapted for CSP.

The set of figures of merit analyzed in this review offer a complementary perspective for the detailed characterization
of any coating opto-thermal performance. For solar thermal absorber coatings, thermal efficiency
ηthermal and peak efficiency temperature Tpeak,opt are respectively deemed more insightful than opto-thermal efficiency
ηopt-th and maximum steady-state temperature TSST,max, when comparing the relative opto-thermal performance
of two coating formulations.

References

Title A comparative analysis of opto-thermal figures of merit for high temperature solar thermal absorber coatings

Authors SimonCaron, JorgeGarrido, JesusBallestrín, FlorianSutter, MarcRöger, FranciscoManzano-Agugliaro

Cite as Simon Caron, Jorge Garrido, Jesus Ballestrín, Florian Sutter, Marc Röger, Francisco Manzano-Agugliaro,
A comparative analysis of opto-thermal figures of merit for high temperature solar thermal absorber coatings,
Renewable and Sustainable Energy Reviews, Volume 154, 2022, 111818, ISSN 1364-0321, https://doi.org/10.1016/j.rser.2021.111818.

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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 823802