Exergy analysis and optimisation of a two-stage solar thermoelectric generator with tapered legs

Abstract

Numerous previous studies indicate that the performances of thermoelectric generators are enhanced by incorporating legs with variable area geometries. However, there is a dearth of comprehensive optimisation studies on these new thermoelectric generator designs. More so, the few optimisation studies that exist have rather employed unrealistic isothermal boundary conditions in their numerical models. Furthermore, these new leg geometries have not been applied to multi-stage systems. Accordingly, to address these gaps, a numerical optimisation, using ANSYS 2020 R2 software, is performed on a two-stage thermoelectric generator with variable area leg geometries; with optimisation parameters that include: leg geometry (height and area), intensified insolation with external load resistance, i.e., geometrical, thermal and electrical operation of the device. An exergy/irreversibility analysis is also carried out and techniques of minimising thermodynamic losses while allowing for the useful exergy output after solar energy conversion are proposed. Results indicate that, for an optimum leg height, area, concentrated solar radiation intensity and load resistance of 10 mm, 0.7 mm2, 20 suns and 1.3 Ω, respectively. Maximum energy and exergy efficiencies of 7.03% and 7.55% respectively, were obtained for the proposed system. This improves the energy and exergy efficiencies of the standard device by 23.44%.