Researchers at the University of Newcastle are investigating refractory thermionic materials which are able to operate at high temperatures with the purpose of directly converting heat to electrical energy. The ability of these materials to operate at elevated temperatures increases the heat-to-electricity conversion efficiency and makes them ideal for CST applications.

Thermionic emission occurs when the thermal energy of electrons becomes high enough for the electrons to be able to breakaway from the surface of a material – similar to the way water evaporates from a boiling kettle. In a thermionic converter the emitter material is heated to a sufficiently high temperature (1200-1500ºC) in an evacuated enclosure. Electrons which are boiled off from the emitter are then condensed on the collector surface which is maintained at a lower temperature. The movement of electrons from the energy level of the hot-to-cold surfaces generates electrical energy. Some heat is also transferred between the emitter and collector. This lost energy could be partially recovered via steam turbine/ generators since the collector operates at temperatures between 400-600ºC.

This project aims to develop a working prototype device for the direct conversion of the sun's energy to electricity. This conversion process has two main advantages. Firstly, the large operating temperature difference between the emitter and collector give the process a high thermodynamic efficiency. Secondly, the whole solar spectrum can be utilised in the conversion process. 

Fact Sheet: Fabrication of Thermionic Devices (PDF 281KB)