Experimental demonstration of a two-color shortwave infrared thermometer for the opto-thermal characterization of receivers and hot surfaces

Abstract

Absorbers of state-of-the-art central receiver solar power systems (CRS) consist of high-temperature metallic tubes with coatings that have a very high absorptance in the solar spectrum. The temperature monitoring system of such absorbers, needed to avoid overheating, is commonly based on longwave infrared (LWIR) thermography. These systems rely on knowing the thermal band emittance map of the absorber surface. However, coating degradation can result in changes in LWIR band emittance in the LWIR spectrum. Undetected degradation can lead to under-estimation of temperatures, overheating and damages to coating and absorber tubes. Measuring absorber surfaces’ temperatures independent of their band emittance is, hence, desirable. Ratio thermometry can be used to calculate the temperature distribution on a surface by comparing the sensor response of a camera for two spectral bands. A shortwave infrared (SWIR) ratio thermometer system has been developed by DLR and CSPS for CRS applications. In simulations of the system’s utilization in a commercial CRS plant, it was shown that under favorable conditions the simultaneous determination of the surface band emittance and temperature is possible. However, the desired accuracy could not be reached for on-sun operation (solar blindness). In the current work, the SWIR ratio thermometer system was tested under lab conditions to prepare a testing campaign at a commercial CRS plant. This work is being developed within the framework of the LEIA project.