Optimizing thermophotovoltaic (TPV) systems through photon fate analysis: An experimental case study based on ellipsoidal optical cavities

Abstract

This study presents a comprehensive photon fate framework for thermophotovoltaic (TPV) systems, integrating both numerical and experimental approaches to optimize performance through photon recycling, for different photovoltaic (PV) cells (Si, GaSb, and InGaAsSb). A quantitative analysis of optimal recycling factors reveals their strong dependence on power levels, view factor losses, and PV cell type. Results show lower emitter input power necessitates higher recycling factors for optimal performance. In an InGaAsSb-based TPV system with an emitter input power of 10 W/cm², the maximum electrical output power is P_elc = 2.4 W/cm² (for view factor loss F_VF-loss = 1 %), 1.63 W/cm² (F_VF-loss = 5 %), and 0.87 W/cm² (F_VF-loss = 20 %), corresponding to optimal photon recycling factors of F_rec = 92 %, 79 %, and 44 %, respectively. Experimental validation is achieved using a TPV system with a novel ellipsoidal optical cavity configuration featuring silver-coated annular rings with tunable width-to-diameter ratios (ω/a = 0, 0.2, 0.4, 0.6, 0.8) to precisely control photon recycling factors from F_rec = 0 to F_rec = 0.735. The impact of temperature-dependent recycling effectiveness is analyzed, demonstrating enhancement factors up to ∼210 times at low-temperature operation and ∼80 times at higher temperatures. These results provide insights into operating temperature strategies and establish a practical design framework for optimizing TPV systems. Furthermore, the findings serve as a valuable tool for system-level trade-offs, offering guidance for maximizing efficiency based on system constraints. This work lays the foundation for next-generation TPV system designs, advancing the integration of photon management strategies for high-performance energy conversion.