Quantifying the impact of solar variability on dynamic start-up of particle receivers under varying geometric parameters

The start-up process of particle-based solar cavity receivers can require several hours due to their high operating temperature targets and significant thermal mass. This duration is not fixed but varies with location, time of day, and solar resource availability. Assuming a constant start-up time based only on steady-state operation overlooks the inherent variability of solar input, leading to significant uncertainty in system performance. This article investigates the influence of key geometric parameters on the dynamic start-up response of a cylindrical cavity particle receiver, considering both steady-state and transient operating conditions. A transient thermal model was developed to predict the time required to reach a target start-up temperature of 1000°C and associated heating rates. Geometric variations included aperture diameter (6–9 m), cavity diameter (8–14 m), cavity length (14–20 m), lining thickness (50–200 mm), and surface absorptivity (0.6–0.9). Two solar input cases were analyzed: (i) constant Direct Normal Irradiance (DNI) values between 600 and 1000 W/m², and (ii) real-time hourly DNI data. Results show that neglecting solar variability can cause both over- and under-prediction of start-up times by up to 80%, depending on geometry and irradiance. This highlights the critical need to incorporate transient solar resource data into start-up modeling for reliable design and operation of particle receivers.