Reappraisal of solid selective emitters

A simple model was used to calculate the efficiency of rare earth oxide emitters. Results indicate that the emission band of the selective emitter must be at relatively low energy (⩽0.52 eV) to obtain maximum efficiency at moderate emitter temperatures (⩽1500 K). Thus, low-bandgap-energy PV (photovoltaic) materials are required to obtain an efficient thermophotovoltaic (TPV) system. Of the four specific rare earths (Nd, Ho, Er, Yb) studied, Ho has the largest efficiency at moderate temperatures (72% at 1500 K). A comparison was made between a selective emitter TPV system and a TPV system that uses a thermal emitter plus a bandpass filter to make the thermal emitter behave like a selective emitter. Results of the comparison indicate that only for very optimistic filter and thermal emitter properties will the filter TPV system have a greater efficiency than the selective emitter system