Optimum thickness determination to maximise the spectral selectivity of black pigmented coatings for solar collectors

Developments in the synthesis of flat plate solar selective absorber materials via sol–gel methods: A review

“…The terrestrial solar spectral irradiance distribution curve commences at wavelength λ≥0.3 μm, while for λ≥2 μm it is almost insignificant. For temperatures lower than 773 K, most thermal radiation (98%) occurs at λ≥2 μm due to black body radiation [52]. This leads to the following formal definitions.…”

“…One of the most common strategies in preparing a spectrally selective surface is to apply a highly solar absorptive thin film onto a non-selective highly reflective metal substrate (absorber-reflector tandem). The absorptive layers need to be transparent in the infrared region to maintain the low thermal emittance of the substrate [45,52,54]. To further supplement the understanding of these concepts, the absorption, transmission and emission in the solar selective absorber-reflector tandem system are illustrated in Fig.…”

“…The absorption, transmission and reflection phenomena in the absorber material can also be determined by physical effects such as intrinsic properties of the material, interference in a double layer (absorber-substrate), interference effects due to interchanging dielectrics and metals, geometrical trapping by surface roughness, and the size effect of metal particles in insulating matrix [6,52]. One of the most common strategies in preparing a spectrally selective surface is to apply a highly solar absorptive thin film onto a non-selective highly reflective metal substrate (absorber-reflector tandem).…”

“…The increase of solar absorptance rendered by a denser coating unfortunately produces a strong increase of thermal emittance, and so the maximum selectivity of a solar selective material is achieved by optimized layer thickness due to thin film interference. The most usual way to determine this thickness experimentally involves judicious assessment of solar absorptance and thermal emittance for varying thicknesses of samples [52].…”

The Impact of a Silane Pigment Treatment on the Properties of Thickness-sensitive Spectrally Selective Paints

“…The increase in the absorptivity with thickness points to well-established light-absorption and scattering phenomena as the reason for the selectivity. 25 The PC data in Fig. 4, on the other hand, show a more distinct nonlinearity compared to the reference coating and point to another mechanism behind the relation between the selectivity and the thickness of the coating.…”