Gasification of carbonaceous materials using concentrated solar thermal radiation has been considered as one of the promising renewable pathways to produce syngas. In this study, thermal performance of a recently developed solar thermochemical reactor is presented. To analyze the gas-solid flow and heat transfer characteristics of the reactor, a transient three dimensional numerical model has been developed using discrete element method and computational fluid dynamics. Particle collision dynamics has been solved by the spring-dashpot model based on the soft-sphere method. To perform model verification, experiments have been performed using 30kWth fluidized bed reactor prototype under high flux solar simulator. The particulate and thermal characteristics of spout, annulus and fountain of the fluidized bed are analyzed for different irradiation power, loaded powder and gas flow rates. The results indicate that large and small size particles govern the bottom and fountain part of the bed respectively due to gravitational force, and the peak temperature is moved from fountain core to the fountain periphery of the bed when increasing the gas flow rate.