Thermodynamic Characteristics of Near-Field Thermo-Photovoltaics Based on Solar Energy Concentrating System

Due to the mismatch between solar spectrum and photovoltaic cells, solar thermophotovoltaic (TPV) technology attracts much interest. Near-field thermophotovoltaics (NFTPV) can further enhance radiation intensity and obtain optimized performance. This paper investigates the thermodynamic principles of solar NFTPV systems from the perspective of concentrating solar engineering. An NFTPV energy model under concentrated solar systems was established, which incorporated the non-radiative recombination losses in thermophotovoltaic cells to more accurately predict system efficiency. The parametric characteristics of solar NFTPV were analyzed from the perspective of energy balance, such as the effects of absorptance, concentration, and vacuum gap on the system performance. In addition, the shortcomings of NFTPV and the core of performance improvement were discussed; the limit efficiency of solar NFTPV was also investigated. It indicates that increasing the concentration ratio, reducing the vacuum gap, and reducing the absorber emittance can promote the system efficiency. The key to improving the system performance is to reduce the proportion of radiation loss. For micro/nano-film structure, where the vacuum gap is below 100 nm, the optimal concentration ratio was above 500, which is more suitable for dish-type concentrated application. The optimized solar NFTPV system achieved a maximum efficiency of 25.0%. Using micro/nano structure can reduce the need for small vacuum gap and the difficulty of NFTPV design in engineering. Different from previous research targeting a single NFTPV device with constant emitter temperature, this study focused on non-isothermal application scenarios of solar power generation, providing reference for NFTPV applications in solar engineering.