Thermal modeling of a secondary concentrator integrated with an open direct-absorption molten-salt volumetric receiver in a beam-down tower system

An upward-facing three-dimensional secondary concentrator, herein termed Final Optical Element (FOE), is designed to be used in a beam-down tower in combination with an open volumetric direct-absorption molten-salt receiver tank acting simultaneously as a thermal energy storage system. It allows reducing thermal losses from the open receiver by decreasing its aperture area while keeping minimal spillage losses. The FOE is exposed to high solar fluxes, a part of which is absorbed by its reflector material, leading to material degradation by overheating. Consequently, the FOE may require active cooling. A thermal model of the FOE under passive cooling mechanism is proposed as a first step to evaluate its sensitivity to some design parameters. Then, it will be used to evaluate the requirements for the active cooling system. The model provides insights on the FOE thermal behavior and highlights the effectiveness of a design modification on passive cooling enhancement. First prototype tests under reduced flux and with no active cooling will be used for model adjustment.