Performance optimization of a solar-driven alkali metal thermoelectric converter coupled to thermally regenerative electrochemical cycles

In order to improve the solar energy conversion efficiency, a novel coupling system comprised of a solar col-lector, an alkali metal thermoelectric converter (AMTEC), and thermally regenerative electrochemical cycles (TRECs) is constructed, in which the waste heat of AMTEC is used to drive TRECs to generate electricity. Taking into account the main irreversible losses, the analytical expressions for the efficiency and power output of the coupling system model are deduced. The optimum selection criteria of the system's critical parameters are provided by introducing a multi-parameter combined objective function. Meanwhile, the efficiency and power output density are calculated under different given weight factors. Furthermore, the impacts of the surface temperature of the absorber, the current density in AMTEC, the electrolyte thickness, the regeneration efficiency of TRECs, and the incident spectral solar irradiance on the systemic performance at a given solar concentration ratio are evaluated in depth. Numerical calculation examples illustrate that with a solar concentration ratio of approximately 200, the maximum efficiency and maximum power output density of the coupling system are 28.57% and 49.51% higher than the solar-driven AMTEC system, respectively. Finally, the influences of the solar concentration ratio on the parametric optimum selection criteria are investigated. The present study may provide some new insights to enhance the efficiency of solar energy conversion.