Current Status of Thermionic Conversion of Solar Energy

Recent advances in science and technology of materials fabrication, engineering of work functions, and micrometer gap machining between emitter and collector are making thermionic conversion/converter (TEC) of solar energy an emerging technology. As the converter is the lightest of all devices with highest direct power conversion density (per unit area of the converting surface), it has, potential for substituting photovoltaic technology to a large extent and for deployment in space as a power source. This article summarizes the current efforts/technologies in the field, and discusses their inherent merits and demerits towards realizing the goal of achieving high conversion efficiency and simulation of performance evaluation of a solar TEC. We also discuss the use of both metals and nanomaterials, critical roles of work functions of both emitter and collector, collector temperature, absorptivity and emissivity of the surfaces, radiation losses, and use of both metals and nanomaterials in the efficiency of conversion of solar energy. We further deal with the role of correcting thermionic emission current density equation in the simulation of solar TEC performance. We discuss briefly the possible methods of space-charge control in future in a solar TEC.