Análisis óptico-térmico de recubrimientos absorbentes solares térmicos bajo condiciones de radiacion solar concentrada basado en medidas espectrales

Abstract

Climate change is one of the major challenge faced by mankind in the 21st century. Solar energy must be harnessed for decarbonising the global energy system. Concentrated Solar Thermal (CST) technology is expected to play a decisive role in supplying heat for medium to high temperature industrial processes. Thermal receivers and solar thermal absorber coatings are key components in CST systems. The monitoring of coating opto-thermal characteristics, such as solar absorptance, thermal emittance and surface temperature, is critical for the efficient and durable operation of such systems. The main objective of this doctoral thesis is to develop a framework for the opto-thermal analysis of solar thermal absorber coatings for CST. The opto-thermal analysis is mostly based on infrared measurement techniques, such as spectrophotometry and multispectral radiometry. The analysis is developed for relevant materials, first under laboratory conditions, both at ambient and operating temperature, up to 800 °C. A new measurement technique is introduced for the in-situ opto-thermal characterisation of solar thermal absorber coatings in Central Receiver Systems (CRS). The opto-thermal performance of a solar thermal absorber coating for CSP applications is sensitive to the concentration factor Cx and the surface temperature T. While solar selective coatings are definitely relevant for parabolic trough collectors, high solar absorptance black coatings are more relevant for central receiver systems, due to the higher concentration factor. Intercomparison measurement campaigns have shown that solar absorptance values derived from room temperature spectral measurements are reproducible with a low standard deviation of 1%, for solar selective coatings, black coatings, oxidized Haynes 230 (H230) and silicon carbide (SiC). For the same materials, a higher standard deviation of ~ 3% was observed for thermal emittance values derived from room temperature spectral measurements. The comparison of thermal emittance values derived from room and operating temperature up to 800 °C show a rather consistent agreement for oxidised H 230, black coatings and SiC. The remote opto-thermal characterization of grey materials such as oxidised H230 and black coatings is feasible in a Central Receiver System using shortwave infrared thermography. Two configurations were respectively analysed for on-sun and off-sun operating conditions