Thermophotovoltaic array configuration under non-uniform irradiance in a radioisotope thermophotovoltaic system

Based on the radioisotope thermophotovoltaic (RTPV) prototype, the non-uniform irradiance distribution on the surface of the thermophotovoltaic (TPV) array was measured and reconstructed at heat source temperatures ranging from 900 °C to 1200 °C. The reconstructed irradiance distributions are in good agreement with the calculation results with the irradiance uniformity N of about 70%. Twelve topologies were designed and examined with interconnection resistances explicitly modeled. The research shows that irradiance non-uniformity and interconnection resistance compete to determine the optimal topology. For the reconstructed distribution, the hybrid topology 3S25P-RC is optimal when the interconnection resistance is below 1.45 mΩ, with the network efficiency of 99.37% and the system efficiency being about 17.1% higher than that of the all-series configuration. When the interconnection resistance is above 1.75 mΩ, the 15S5P-C becomes preferable. Busbar resistances dominate the losses. Moreover, an optimized RTPV system with the heat power of 250 W was constructed by shortening the emitter-to-array distance, with the uniformity rising to 91% and the average irradiance to 0.63 W/cm 2 . Ohmic losses then surpass mismatch losses, shifting the design focus toward ohmic loss control. Over a 20-year mission with the heat power attenuating from 250 W to 210 W, the network efficiency of the corresponding optimal topology 5S9P-RC remains 99.28% and the system efficiency is stable around 20%. These findings provide practical guidance for RTPV array configuration optimization and are applicable to other TPV architectures with continuous irradiance gradients over planar arrays.