Output Characteristics of Solar-Power-Driven Thermionic Energy Converter

Abstract

A solar-power-driven thermionic energy converter abbreviated as Solar TEC is operated by illumination of solar light condensed by a large-scale Fresnel lens 105 cm in length and 70 cm in width. It was found that an output current takes large peaks at the lower emitter temperature because the emitter work function closely related to the thermionic electron emission decreases at a constant cesium pressure with decreasing emitter temperature. The maximum short circuit current was 0.73 A at 62 s after the onset of the illumination throughout the experiment for 500 s, where the solar power density on the ground was approximately 800 W/m2. The barrier index also took a minimum value of 2.3 eV at the same time. To increase the output characteristics of the Solar TEC, the emitter and cesium temperatures should be increased along the curve of β=1, where β denotes the space charge neutrality. It was found that the emitter with a light trap is effective in improving the energy conversion efficiency of the Solar TEC, since it realizes high absorptivity and low emissivity at once, which causes the emitter to have high thermal efficiency for solar power illumination.