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An overview on the development of thermophotovoltaic (TPV) systems heated with concentrated sunlight (STPV) and with a combustion flame (CTPV) is given. Only a few experimental works on STPV are reported. Lifetime investigations of TPV emitters in solar dish concentrators were carried out. A complete STPV system reported in the literature achieved a system efficiency below 0.1 %. In contrast to these experiments we present simulations, which show that an optimised STPV system with Yb2O3 emitter and high efficient Si solar cells is able to achieve a system efficiency in the order of 30 %. Quite more experimental results are reported for CTPV systems, but a series production and commercialisation of CTPV was not achieved, so far. An application for a CTPV system is a portable electrical power supply. The highest system efficiency reported so far is 6 %. Whether this efficiency is sufficient to successfully compete with generators driven by a gas engine or a diesel motor, remains unclear. Another application for CTPV that was reported is a gas fired stove, which produces electricity in addition to heat. The application of a CTPV system for electrically autonomous domestic central heating systems could probably result in a first commercialisation of TPV. For this application, a system efficiency in the order of 1 % is sufficient. A gas fired TPV system is presented, which uses a novel foam ceramic emitter made from Yb2O3 and commercially available Si solar cells. The proof‐of‐concept of this prototype CTPV system could successfully be furnished. Possible applications for this CTPV system are: electrically autonomous domestic heating systems, parking heating systems for vehicles, heaters for caravans and boats or large industrial burner systems.

This paper describes the practical implementation of TPV systems. As a key part of these systems, we developed a new flexible photocell module for TPV applications. The module consists of commercially available monocrystalline silicon solar cells, which were cut into small stripes that are series connected to achieve a high voltage and a reduced current for operation at an illumination density of 5 – 10 suns. For an easy mounting into a heating boiler, the module is highly flexible and can be bent into a cylindrical shape. The rear side of the module is electrically isolated, but achieves a good heat coupling through a covering aluminium foil to the boiler wall. Thus, it can directly be mounted into a water‐cooled boiler housing without the need of an additional water‐cooling circuit. A first test module with an active cell area of 481 cm2 achieved an electricity output of 50 W by irradiation with an Yb2O3 mantle emitter heated with a 20 kW methane burner.

In this paper we report on the development and characterisation of a small TPV prototype system, which uses silicon photocells and a rare earth selective emitter. A simulation model of this system was developed, which allows studying the system theoretically. The fabrication of the selective incandescent mantle emitter from Yb2O3 and detailed measurements of its radiation power and emissivity are presented. The maximum emissivity was 0.85 at 1.27 eV. An emitter temperature of 1735 K was obtained for an approximately 75 cm2 large emitter heated by a butane burner. A SnO2 filter tube was developed. The photocell generator is composed of monocrystalline silicon solar cells and a water‐cooling circuit. The prototype system reached, without a selective filter and without preheating of the combustion air, a record electricity‐to‐gas power efficiency of 2.4 %. We compare the experimentally achieved system efficiency with simulations using our model. The possibilities to further increase the system efficiency are discussed.

A thermophotovoltaic (TPV) system was built using a 12 to 20 kWth methane burner which should be integrated into a conventional residential heating system. The TPV system is cylindrical in shape and consists of a selective Yb2O3 emitter, a quartz glass tube to prevent the exhaust gases from heating the cells and a 0.2 m2 monocrystalline silicon solar cell module which is water cooled. The maximum system efficiency of 1.0 % was obtained at a thermal input power of 12 kWth. The electrical power suffices to run a residential heating system in the full power range (12 to 20 kWth) independently of the grid. The end user costs of the TPV components ‐ emitter, glass tube, photocells and cell cooling circuit ‐ were estimated considering 4 different TPV scenarios. The existing technique was compared with an improved system currently under development, which consists of a flexible photocell module that can be glued into the boiler housing and with systems with improved system efficiency (1.5 to 5 %) and geometry. P...