Harvesting Solar Thermal Energy With a Micro-gap Thermionic-Thermoelectric Hybrid Energy Converter: Model Development, Energy Exchange Analysis, and Performance Optimization

TL;DR

This paper develops a detailed theoretical model of a micro-gap thermionic-thermoelectric hybrid energy converter, analyzing energy exchange, optimizing performance, and providing insights for solar thermal energy harvesting applications.

Contribution

The work introduces a comprehensive model considering space-charge, near-field, and temperature effects, enabling performance simulation and optimization of the hybrid system.

Findings

Efficiency increases with solar radiation intensity.

Thermoelectric performance depends on waste heat from thermionic stage.

Model can serve as a design tool for practical hybrid systems.

Abstract

We present a comprehensive analysis of a dual, micro-gap thermionic-thermoelectric hybrid energy converter by developing a detailed theoretical model of the system. The Space-charge and near-field effects in thermionic conversion and the temperature-dependent effects in thermoelectric conversion are considered while studying the energy flow through the cascade system. The temperatures and energy exchange channels in the different parts of the system are quantified with a self-consistent iterative algorithm considering the energy balance condition. The model is deployed to simulate the hybrid system performance when energized by a constant heat flux source which could, for example, be concentrated solar irradiance. The effect of solar radiation intensity on the combined system efficiency, and the dependence of the thermoelectric generator performance on the waste heat released from the thermionic top stage, are illustrated with several examples. Based on these analyses, the performance optimization of the hybrid system is carried out. The findings presented in this work offer useful insights into the hybrid generator operation. Moreover, the model developed can be used as a design tool for the practical implementation of such a hybrid system, or for extracting material- and device-related parameters from experimental data by solving the reverse problem.