Comprehensive Energy Balance Analysis of Photon-Enhanced Thermionic Power Generation Considering Concentrated Solar Absorption Distribution

TL;DR

This paper provides a detailed energy balance analysis of photon-enhanced thermionic emission (PETE) for concentrated solar power, highlighting realistic efficiency limits and the importance of spectral absorption modeling.

Contribution

It offers a comprehensive, realistic energy analysis of PETE devices considering spectral absorption and photothermal effects, which was lacking in previous idealized models.

Findings

Maximum power output of 1.6 W/cm² at 100× concentration

Energy conversion efficiency around 18% at 100× concentration

Photon-enhancement ratio below 10, decreasing with higher concentration

Abstract

The present article reports a comprehensive energy balance analysis of a photon-enhanced thermionic emission (PETE) device when it is used for concentrated solar power (CSP) generation. To this end, we consider a realistic PETE device composed of a boron-doped silicon emitter on glass and a phosphorus-doped diamond collector on tungsten separated by the inter-electrode vacuum gap. Depth-dependent spectral solar absorption and its photovoltaic and photothermal energy conversion processes are rigorously calculated to predict the PETE power output and energy conversion efficiency. Our calculation predicts that when optimized, the power output of the considered PETE device can reach 1.6 W/cm$^2$ with the energy conversion efficiency of $\sim$18 \% for 100$\times$ solar concentration, which is substantially lower than those predicted in previous works under ideal conditions. In addition, the photon-enhancement ratio is lower than 10 and decreases with the increasing solar concentration due to the photothermal heating of the emitter, suggesting that PETE may be an adequate energy conversion process for low-to-medium CSP below $\sim$100$\times$ concentration. These observations signify the importance of a rigorous energy balance analysis based on spectral and spatial solar absorption distribution for the accurate prediction of PETE power generation.