Report on preliminary damage localization testing on SiC Solar receiver using acoustic emission

Materials used in solar receivers are exposed to high stresses, i.e. high temperatures (up to 1000° C in current solar towers, 1400°C for next generations, resp. 350 and 700°C for linear concentrators); high spatial thermal gradients (mainly due to the non-uniform concentrated solar irradiation) and high dynamic thermal gradient (e.g. fast during cloud passing or slow due to the daily cycling from dawn till dusk).

Due to these very severe conditions, the materials degrade over time, their properties change, leading to reduced performance and ultimately to the failure and the ruin of the associated structure, increasing the cost of operation. Accurate in-situ measurements are required in order to select the materials (development and qualification stages with SFERA-III Research Infrastructures) or improve their lifetime and the optimal operation of a solar plant (commercial stage). However, the health evaluation of solar receivers is typically observed subjectively during downtime at night, or by sampling parts sent for laboratory analysis (MEB, XRD, chemistry...).

Thanks to recent unique advances, it can be envisaged to be determined objectively in-situ using acoustic techniques, as commonly used in infrastructure buildings such as bridges, sky-scrapers, dams or nuclear power plants. A subset of these techniques has been successfully tested and derived for concentrated solar conditions within SFERA-II as worldwide pioneers using a research solar furnace, carrying on much further the SFERA-I developments about accelerated ageing setups and protocols to assess receivers resistance. Yet enhancements of this work are required in order to further interpret the observed data into broad degradation mechanisms (delaminations, cracks...) which will allow determining the actual remaining margin of the receiver of demonstration or commercial solar plants.

This report presents the assessment and verification of the feasibility of the location of damaging events on a real solar receiver while deploying convenient and simple sensor location. These first steps verification were operated at room temperature and successfully demonstrated the potential of both the location and the identification of impending solar receivers damage thanks to a single acoustic ultrasonic sensor and data processing.