Optimization of solar receivers for high-temperature solar conversion processes: Direct vs. Indirect illumination designs

High-temperature solar receivers are core components in concentrated solar energy utilization systems. The rational design of solar receivers relies on the fundamental understanding of coupled physics across various scales. We developed a numerical model to assess the solar thermal conversion behaviour under various porous structure designs, material choices, geometrical designs, as well as operational conditions. The 3D model solves a coupled set of equations accounting for mass, momentum, and energy conservations in the cavity and porous media domains. We have optimized the radiative transfer model to resolve the participating behaviour only in the porous domain and non-participating behaviour only for cavity and window surfaces. This cost-effective model enables fast performance evaluation for various design parameters. The windowless receiver, in general, shows higher solar-to-thermal efficiency compared to the window receiver. This superiority in optical efficiency for the windowless case can be surpassed by the window case at high incident solar power with a fixed outlet temperature. For porous media structure, both window and windowless receivers are optimized by the porosity and pore diameter. The solar-to-thermal efficiency was slightly influenced by the cavity inclination. Large porous layer thickness leads to reduced performance for the windowless receivers, while the efficiency reaches a plateau for the window receiver at large thickness. We have provided a comprehensive modeling framework for the design of solar receivers for high-temperature applications using concentrated solar energy which can be easily adapted for receiver under a wide range of designs and operation conditions.