Performances of thermoelectric module under solar Fresnel concentration
Authors: Xu Qiang-Qiang  , Ji Xu  , Li Ming  , Liu Jia-Xing  , Li Hai-Li  ,   Key Laboratory of Advanced Technique and Preparation for Renewable Energy Materials, Ministry of Education, School of Energy and Environmental Science, Yunnan Normal University, Kunming 650500, China
Published: December 2020

Using Fresnel concentration to collect solar irradiation, the hot-end temperature of the semiconductor thermoelectric generator is enhanced, and the cold end is cooled through a radiator in air. For studying the performance of thermoelectric module under solar Fresnel concentration, a theoretical model of thermoelectric generator under steady condition is built from the perspective of energy flux. The model neglects the convection and radiation heat transfer between the cold and hot end and between the arms, and simplifies the heat conduction only along the arm. Utilizing this model, the temperature gradient on thermoelectric generator (dT/dx), the output current (I), the output voltage (V), and the output power (P) of thermoelectric generator are derived, and the influences of the resistance ratio a(=R/RH2) and the temperature difference ratio b(=T/TH2) on generator output performance under a certain structure parameters of thermoelectric generator are discussed. The results show that with the increase of resistance ratio (a), the output current (I) decreases, however the output power (P) and the conversion efficiency (he) first increase, then decreases. When the resistance ratio a=1, the output power (P) and the conversion efficiency (he) reach their maximum values. When the resistance ratio (a) is smaller, the output power (P) increases rapidly with the increase of the resistance ratio (a). When the resistance ratio (a) is larger, the output power (P) decreases slowly with the increase of the resistance ratio (a). With the increase of temperature difference ratio (b), the output power (P) and the conversion efficiency (he) increase, no matter what the value of the resistance ratio (a) is. It verifies the sensitivity of the output power (P) to the temperature difference. Therefore, with a certain figure of merit, the appropriate adjustment of temperature difference ratio (b) may improve the output power (P) and the conversion efficiency (he). Besides, the load residence should be larger than the internal residence for keeping the high output performance. A Fresnel concentration thermoelectric module, including 6 thermoelectric generators, is employed to experimentally explore its output performances. In experiment, the energy flux density on the surface of the thermoelectric generator is not uniform as desired. The uneven hot-end temperature will degrade the conversion efficiency, and even excessive local temperature may damage the semiconductor thermoelectric generator. A deviation of the thermoelectric generator from the focal plane of Fresnel lens will help to improve the energy flux uniformity and achieve an optimized output characteristics. The required output voltage and output power can be obtained through series/parallel connection of these thermoelectric generators. With the series connection of the thermoelectric generators, the output current is increased. With the parallel connection of the thermoelectric generators, the output voltage is increased.