Inner-cascaded photovoltaic-thermionic-thermoradiative conversion for concentrated solar power

Abstract

Photon enhanced thermionic emission (PETE) is a promising full-spectrum solar power technology capable of converting super-bandgap photons via photovoltaic and sub-bandgap photons through thermionic emission. However, PETE cathode with an infrared absorber, is usually accompanied with a high thermal radiation loss to the environment. This paper proposes an isothermal thermoradiative enhanced-PETE (iTR-PETE) configuration, where p-type cathode absorbs high-energy photons and n-p junction anode converts low-energy photons for thermoradiative purposes. A thermodynamic model is developed to assess the respective impacts of photovoltaic, thermionic and thermoradiative on solar iTR-PETE conversion. The positive and negative chemical potentials of the cathode and anode work together to increase thermionic power. The iTR-PETE converter achieves an excellent exergy efficiency of 55.43 % at a concentration ratio of 40 and an anode bandgap of 0.1 eV. Photovoltaic determines thermoradiative power, while thermoradiative increases waste heat to the secondary thermal cycle to improve the overall solar conversion efficiency. Along with an additional 4.24 % of power generated at anode, the thermoradiative effect reduces thermal radiation from the PETE converter by 28.54 %. The iTR-PETE combined system achieves a 92.3 % higher conversion efficiency than that of conventional PETE combined system.