A compact tunable photovoltaic/thermal solar collector for high land-use efficiency and energy dispatchability

Hybrid photovoltaic/thermal (PV/T) systems offer a highly efficient pathway for solar energy utilization. However, traditional PV/T technologies possess a rigid electrical-to-thermal output ratio, which limits their operational dispatchability against fluctuating user demands. Furthermore, maximizing their deployment in built environments is severely hindered by spatial constraints. To bridge the gap between operational flexibility and compact land use, this work introduces a novel photovoltaic photothermal tunable system (PV/PT) that integrates a stationary parabolic reflector with a two-dimensionally trackable and rotatable receiver. Governed by near-axis optics, this compact architecture eliminates the inter-collector mutual shading inherent in conventional parabolic trough designs. Concurrently, the rotatable receiver enables on-demand mechanical switching between electricity generation and thermal collection modes. To precisely elucidate the underlying optical and thermodynamic mechanisms, a multi-dimensional coupled model, which integrates three-dimensional Monte Carlo ray tracing (MCRT) and transient thermal-electrical analysis, was established and experimentally validated. Optical analyses reveal that the receiver maintains a high intercept factor (>90%) across a wide range of incident angles by following an optimized elliptical trajectory. Thermodynamically, the system achieves a thermal efficiency of 76.8% (at a concentration ratio of 16 and 200°C) and a concentrated PV efficiency of 25.0%, while significantly reducing the land footprint by 41.4% compared to conventional technologies. Crucially, transient thermal analysis demonstrates the system's rapid dispatchability, achieving stable mode transitions within 160 s. Economic analysis further indicates a 14.5% reduction in capital cost (265.6 vs. 310.7 USD/kW) compared to conventional PV and Li-battery hybrids, achieved primarily through the elimination of electrochemical storage. This integrated system presents a scientifically robust and economically viable solution for renewable energy integration in land-constrained environments.