Optical and Structural Characterization of Nickel Coatings for Solar Collector Receivers

Abstract

The development of spectrally selective materials is gaining an increasing role in solar thermal technology. The ideal spectrally selective solar absorber requires high absorbance at the solar spectrum wavelengths and low emittance at the wavelengths of thermal spectrum. Selective coating represents a promising route to improve the receiver efficiency for parabolic trough collectors (PTCs). In this work, we describe an intermediate step in the fabrication of black-chrome based solar absorbers, namely, the fabrication and characterization of nickel coatings on stainless steel substrates. Microstructural characteristics of nickel surfaces are known to favorably affect further black chrome deposition. Moreover, the high reflectivity of nickel in the thermal infrared wavelength region can be advantageously exploited for reducing thermal emission losses. Thus, this report investigates structural features and optical properties of the nickel surfaces, correlating them to coating thickness and deposition process, in the perspective to assess optimal conditions for solar absorber applications.

Structural and optical properties of copper-coated substrates for solar thermal absorbers

“…9 we cannot correlate ε T and thickness, as ε T values are extremely spread for all the considered thicknesses. Moreover, we can observe that the average emittance is around 0.06, a value which is comparable with that obtained for Wood nickel coating [21] (that, however, has the advantage to be much more reproducible). On the other hand, Cu coatings have the advantage over Ni of allowing a much easier black chrome deposition, with a more homogeneous Cr layer on the final product.…”

“…However this is not a problem in the operating range of mid-temperatures PTC (200 ÷ 300 C). [21]. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)…”

“…Substrates for copper electrodeposition have been chosen to be stainless steel AISI 304 samples with a preliminary nickel coating (Wood bath for Ni [21], 0.9 mm Ni thickness). The composition of Cu sulphate acid bath [25,26] was CuSO 4 $5H 2 O 225 g l À1 and H 2 SO 4 concentrated 33 g l À1 .…”

“…Moreover this creates an "absorber/reflector tandem" having both the high solar absorbance of the black exterior deposit and the low thermal emittance of the metallic inner coating [20]. Recently we investigated morphological and optical properties of nickel substrates [21]. However, copper coatings are known to be possible substrates for black chrome depositions as well [17,22,23].…”

Impact of a Bright Nickel Interlayer on the Performance of Solar Absorber Nano Coatings Deposited by Electroplating on Copper Substrate

“…Bright nickel layer caused slight decreases in thermal absorbance. The copper nanoparticles deposited on copper showed a high absorption in the wavelength range from 300 to1100 nm to reach a maximum value of 93.191%, while this value reduced in the presence of bright nickel to 87.73% [18].…”