Spectral selectivity of high-temperature solar absorbers

Journal Article · Sat Mar 01 04:00:00 EST 1980 · Appl. Opt.; (United States)

DOI:https://doi.org/10.1364/AO.19.000711· OSTI ID:5567759

Trotter, Jr, D M; Sievers, A J

Numerical calculations of the thermal emissivity epsilon/sub T/H and normal incidence solar absorptivity ..cap alpha../sub s/ of model spectrally selective solar absorbers at high temperatures are reported. The model absorbers consist of Drude metal substrates coated with layers that are successively made better and better approximations to a selective solar absorber. We initially calculate the emissivity of the bare metal substrates epsilon/sup M//sub T/H as a function of temperature. We then coat the metal substrate with a homogeneous dielectric layer of index n/sub L/ and find that epsilon/sub T/H of the coated metal increases monotonically with n/sub L/ from epsilon/sup M//sub T/H at that temperature. The dielectric layer is then replaced by a selectively absorbing layer with the optimum physically realizable spectral absoprtivity, and maximum values of ..cap alpha../sub s/ and minimum values of epsilon/sub T/H are calculated as functions of operating temperature and layer thickness. Finally, we replace the homogeneous selective layer with one having a complex refractive index graded linearly through the thickness of the film. It is found that, compared with homogeneous films of the same thickness, the graded films typically have a higher ..cap alpha../sub s/ and a lower epsilon/sub T/H. For films thick enough to be useful absorber surfaces, however, the imporvements in ..cap alpha../sub s/ and epsilon/sub T/H are small.

• Research Organization: Cornell University, Ithaca, New York 14853
• OSTI ID: 5567759
• Journal Information: Appl. Opt.; (United States), Journal Name: Appl. Opt.; (United States) Vol. 19:5; ISSN APOPA
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
141000* -- Solar Collectors & Concentrators
ABSORPTIVITY
DEPOSITION
ELEMENTS
EMISSIVITY
EQUIPMENT
FILMS
METALS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SOLAR ABSORBERS
SOLAR EQUIPMENT
SPECTRALLY SELECTIVE SURFACES
SUBSTRATES
SURFACE COATING
SURFACE PROPERTIES
SURFACES
TEMPERATURE DEPENDENCE