Evaluation of elliptical optical cavity for a combustion thermophotovoltaic system

A reflective cavity with elliptical cross-section is proposed to couple a burner to three arrays of thermophotovoltaic (TPV) cells. Burner and photoconverter, with triangular section, are located near the two foci of the ellipse. The elliptical cavity is designed to be inserted into a thermo-electric micro-cogenerator for residential use, which exploits the TPV cells to convert visible and infrared radiation generated by the burner into electricity. Taking into account the key construction constraints, several cavity configurations, which differ for components or optical properties, are analysed by ray tracing simulations. The maximum radiation collection efficiency is 62% for the elliptical cavity and is reduced to 48% by introducing quartz protections around the burner and the receiver. A germanium-based photoconverter is developed and manufactured by metalorganic chemical vapour deposition techniques. Each photoconverter can deliver 180 mW/cm2 (at 230 mV voltage and 55 °C) when illuminated by a blackbody spectrum at 1473 K. The manufacture of the TPV receiver is described and the thermal design aspects are considered. The use of a dichroic filter for a TPV generator configuration based on an elliptical chamber is also evaluated.