Solar selective absorber coating for high service temperatures, produced by plasma sputtering

Abstract

Spectrally selective absorber coatings, deposited on engineering material substrates such as stainless steel, have been developed for service as efficient solar photothermal energy converters. The selective solar absorber is based on a multilayer of thin films, produced by sputtering. The main solar absorber is a metal/ceramic (cermet) composite, such as, Mo/Al2th or Mo/Si02, with a graded metal concentration. Such a cermet layer, strongly absorbs radiation over most of the range of the solar spectrum but is transparent to longer wavelength radiation. The cermet layer is deposited on a highly reflecting infrared metal layer. Two more layers were added: An AhO diffusion barrier layer which is deposited first on the substrate and an AI O or a 5i02 antireflection layer which is deposited on the top of the cermet film. In order to better understand the spectral reflectivity of the multilayered selective coating, a procedure for the calculation of the optical properties was developed.After the R&D development phase was successfully completed, a full scale production coating machine was constructed. The production machine is a linear in line coater. The selective coating is deposited on stainless steel tubes, translating in the coating machine while rotating about their axes, along their axial direction. Measurements of reflectance, solar absorptivity, a, thermal emissivity, C, and high temperature durability, are all parts of the quality control routine. The results show values of a in the range 0.96 -0.98. The thermal emissivity at 350CC is in the range 0.16 -0.18. Thermal durability tests, show no degradation of the coating when subjected to up to 65O in vacuum for one month and when passed through a temperature cycling test which includes 1200 cycles between temperatures of 150CC and 450CCfor a period of two months.

AlMoN based spectrally selective coating with improved thermal stability for high temperature solar thermal applications

“…Commercialization of a few of these coatings such as Mo-SiO 2 , W-Al 2 O 3 and Mo-Al 2 O 3 has been successful for use in receiver tubes for solar thermal power generation (Antonaia et al, 2010;Esposito et al, 2009; http://dx.doi.org/10.1016/j.solener.2015.06.047 0038-092X/Ó 2015 Elsevier Ltd. All rights reserved. Lanxner and Elgat (1990)). Recently, researchers have used optical metamaterial absorbers for high temperature solar thermal energy applications .…”

“…In recent years, various cermets and absorber-reflector tandem concept based coatings have been developed for high temperature solar thermal applications (Selvakumar and Barshilia, 2012;Esposito et al, 2009;Antonaia et al, 2010;Lanxner and Elgat (1990); Selvakumar et al, 2015;Rebouta et al, 2015;Jyothi et al, 2015;Liu et al, 2015;Valleti et al, 2014;Gong et al, 2015;Liu et al, 2014). Our group has developed various transition metal nitride/oxide based solar selective coatings for high temperature solar thermal applications (Selvakumar et al, 2015;Jyothi et al, 2015;Selvakumar et al, 2010).…”

Development of W–SiO2 and Nb–TiO2 solar absorber coatings for combined heat and power systems at intermediate operation temperatures

“…1) on molybdenum infrared reflector deposited on stainless steel. Stainless steel has too high infrared reflectance to be used as reflector and the standard solution for mid-temperature absorbers is to deposit a Mo infrared reflector to lower the thermal emittance [2]. The optimization procedure started with sputtering the metal and ceramics in the cermets separately as semitransparent films on glass to determine their optical constants.…”

“…The commercial type of coating used for these applications has since the first STE plants in the 1980th been a cermet (ceramic-metal) composite of Mo-Al 2 O 3 [2]. This type of coating has recently been improved by replacing the infrared reflector coating with silver, stabilized with thin silicon dioxide layers on both sides to prevent degradation [3].…”

Absorber materials for solar thermal receivers in concentrating solar power (CSP) systems

“…The absorber tube is covered by a borosilicate glass tube to keep the vacuum and to reduce the heat losses. A publication by Lanxner and Elgat of the Siemens-Solel predecessor LUZ from 1990 [20] describes the production of the absorber tubes at that time. Polished stainless steel tubes (mean roughness index R a < 0.2 μm) are heated in vacuum for 10 minutes at a temperature of 600°C.…”