Dynamic operation of a hybrid air-driven concentrating solar thermal system based on rotary receiver and radial thermocline

Air-driven concentrating solar thermal (CST) systems can supply heat up to 800 °C for supercritical CO 2 (sCO 2 ) Brayton cycles and process heat, but their integrated transient behaviour under variable solar input and hybrid electric heating remains uncharacterised. This study develops a dynamic simulation framework for a 50 kW th air-driven CST prototype, coupling a compact heliostat field, cavity rotary receiver, layered radial-flow packed-bed thermocline storage, medium-voltage electric heater, and shell-and-mini-tube air–sCO 2 heat exchanger. Physics-based component models are validated against experimental data within 5% deviation. Six operation strategies are evaluated across standalone and hybrid layouts with three receiver control modes and two discharge strategies over three consecutive summer days at varying direct normal irradiance (DNI). In single-tank thermocline configurations, the rising storage charge outlet temperature constrains the receiver inlet and couples storage sizing to receiver operation limits. For daytime charging and night-time heat delivery, the minimum storage capacity to avoid receiver-storage decoupling ranges from 29 to 40 h depending on control mode and layout, exceeding two-tank estimates with fixed cold return temperature. Constant-power discharge combined with hybrid electric heating extended stable heat-exchanger operation from 10 to 27 h over three days, confining sCO 2 outlet-temperature variation below 50 °C. Hybridisation increased the three-day input-to-useful-heat efficiency by 5 to 7 percentage points over standalone operation. An adaptive strategy switching from maximum-efficiency to target-outlet-temperature receiver control at certain DNI threshold (700 W/m 2 for current study) with series electric heating for 800 °C charging achieved the highest efficiency of 54.7% and is the recommended configuration.