Modelling and performance analysis of a novel thermophotovoltaic system with enhanced radiative heat transfer for combined heat and power generation

Solid-state energy conversion technologies such as thermophotovoltaics (TPV) have attracted much interest recently in the development of high-performance combined heat and power generation (CHP) systems because of the merits such as vibration-free operation, long working life, and versatile fuel source. However, current work is limited in power density, system efficiency, and power to heat generation ratio that are constrained by the device structure and working principle of existing techniques. In this work, we propose to apply zero-gap TPV (zTPV) to create a new type of CHP system that can potentially address the limitations in existing systems. zTPV, different from conventional TPV with a vacuum or gas-filled gap between the thermal emitter and photovoltaic cell, possesses an infrared-transparent intermediate solid layer. Our theoretical analysis, combining electromagnetic, thermal, and power generation modelling in zTPV, has confirmed that an one-order-of-magnitude higher thermal radiation dictates the energy conversion in zTPV. The significantly higher thermal radiation is due to the energy transfer of low-loss high-wavevector electromagnetic modes. In conventional TPVs, these modes are not allowed to transport in the gap, and thus not able to contribute to energy conversion. In contrast, the inserted infrared transparent layer allows the transport of these high-density modes, leading to much higher power density (over one order of magnitude enhancement), higher power conversion efficiency (nearly 25% improvement), and high power to heat ratio that is relevant to the system efficiency improvement in CHP applications. The novel device configuration of zTPV allows us to propose a hybrid CHP design that integrates zTPV with thermoelectric (TE) arrays into an ultra-compact CHP device. The effect of different system parameters is modelled and analyzed to demonstrate the high performance of the hybrid CHP.