In order to achieve high efficiency in a TPV generator, it is important that a high fraction of emitted photons with energies below the TPV cell bandgap are reflected back to the emitter. This can be accomplished in several ways. We present the idea of an internally reflecting egg-shaped double cone with the emitter at one end, an edge filter at the wide center, and the TPV array at the other end. This geometry has so far been studied by means of both ray tracing analysis and by means of measurements with a simulated emitter. A sharp switchover from transmission to reflection in a multiple layer dielectric filter can be achieved only if the angles of incident rays are confined to a fairly narrow angular interval. The two methods both show that the studied optics can lower the angular spread of rays incident, onto the filter and that some 96% of the emitted rays (in the ideal case) reach their goal without passing the filter or being reflected by the filter more than once. The concept of the whole of the wood powder fuelled TPV system is also given. (C) 2002 Elsevier Science Ltd. All rights reserved.