Design guidelines for thermo-photo-voltaic generator: The critical role of the emitter size

In the last decade, the thermo-photo-voltaic (TPV) generator has gained an increasing attention as cogeneration system for the distributed generation sector. Nevertheless, these systems are not fully developed and studied: several aspects need to be further investigated and completely understood. The aim of this study is to highlight and outline the main design guidelines for a thermo-photo-voltaic (TPV) generator with a specific attention to the emitter section. More in details, an investigation of the role of the emitter size will be developed by considering its influence on spectral efficiency (defined as the ratio between the emitted radiation in the useful range for photovoltaic conversion and the introduced power with fuel); by using simplified assumptions, the spectral efficiency as a function of the emitter area in four different TPV configurations will be estimated. The achieved results show specific power values per unit emitter area significantly larger than in prototypes realized up to date. Further, the developed analysis allows to show the role of the optical filter and of the air pre-heating exchanger in order to increases the spectral efficiency of the system, being equal the considered power density.