Overall performance optimisation of tapered leg geometry based solar thermoelectric generators under isoflux conditions

Abstract

The performance of thermoelectric devices improves either by changing the thermoelectric material properties or the geometry of the thermoelectric leg. Many research papers show that the tapered leg geometry improves the performance of thermoelectric generators (TEGs). However, they assume isothermal conditions across the hot and cold junctions of both variable area and rectangular area leg-based TEGs. This is rather inaccurate and unrealistic, because when exposed to same heat flux, temperatures vary across the hot and cold junctions of these devices. Scarcely has anything been said pertaining the performance evaluation and optimisation of variable area leg TEGs using realistic isoflux conditions. Therefore, this study presents a thermo-mechanical analysis of variable area and rectangular area leg TEGs, using ANSYS 2020 R2 software, with realistic isoflux boundary conditions instead of previous unrealistic isothermal ones. The leg height, area, external load resistance and optical concentration ratio are optimised. Results indicate that short legs are crucial for maximum power while long legs improve the device efficiencies. Also, although tapered thermoelectric leg TEGs improve the electrical performance of conventional rectangular leg TEGs, they decrease the device mechanical performance and thermodynamic stability. Finally, the optimum ranges in which tapered leg TEG outperforms the conventional device are obtained.