Erneuerbare Energien und Energieeffizienz Renewable Energies and Energy Efficiency Development and Modelling of a Thermophotovoltaic System
Zugl, Kassel, Univ, Diss
2007
unpublished
Thermophotovoltaic (TPV) generation of electricity is a technology based on the direct conversion of a radiation coming from a heat source into electric power by means of photovoltaic cells. TPV is a highly multidisciplinary technology, which involves and relates different research fields. Heat transfer via conduction, convection and radiation, chemical reaction and diffusion, generation, selection, transmission and absorption of radiation and photovoltaic effect are the different processes
more »
... lved in the device to realize the energy conversion. Due to such a complexity, this technology has not yet reached a mature state: few TPV devices have been so far developed and brought successfully into operation and the highest system efficiency ever measured does not exceed 6.5%. However TPV generators could be soon competitive to other established electric generator technologies in the power range from some W to some kW. TPV, indeed, is a compact, reliable, quiet and safe technology with the potential for low cost and versatile fuel usage. The present PhD thesis describes the development and modelling of a small TPV gas-fuelled prototype based on GaSb cells. Purpose of the work is to realize the first ever TPV system which can be used as tester, working under different operating conditions with different combinations of cells and emitter materials. This would allow to get a better knowledge of the TPV technology and to develop optimization criteria for TPV systems. Besides the development of the prototype, another target of the work is to implement a theoretical simulation model of the TPV device and validate it, in order to realize a simulation tool which can be used for further analysis and optimization of the system. Several studies are already available in the literature, which deal with modelling of fuelled-TPV converters; however they are more focused on the spectral control and cell simulation and none of them takes into account the detailed modelling of the recuperative burner unit, which is indeed a key component where the heat is generated, converted into radiation by the emitter and partially recovered by the recuperative heat exchanger. The present work aims at developing a theoretical model of the whole TPV device: all the components and processes are considered, including also the combustion process and the heat transfer in the recuperator, as well as the reciprocal interactions between them. The thesis can be divided basically in two parts: the first one gives an overview of the TPV technology, while the second one describes the experimental and theoretical work carried out to realize the TPV prototype and the simulation model. v vi The first chapter describes briefly the TPV generation principles and compares this energy conversion technology to the traditional PV technology. A short historical background of TPV is also given. The second chapter treats more in detail of the different components involved in a TPV device: definition of the efficiency, theoretical background, main characteristics and state of the art are given for each process and for a complete TPV system. In the third chapter an overview of the possible applications where TPV could be soon an attractive technology is presented and a comparison is made with the other energy conversion technologies currently available, pointing out efficiency and cost thresholds to overcome in order that TPV becomes competitive. An example case is also given in which the effect of a small TPV system integrated on a standalone PV system is evaluated via simulation. The approach followed to realize the device and develop the simulation model is explained and justified in the fourth chapter, while the fifth chapter deals with the design and the mathematical model of the system. The recuperative burner unit, the optical system, where the radiation is generated, selected and transmitted and the photovoltaic cells are described in detail; peculiarity of the device is its modular design, which allows to modify easily the operating conditions and the configuration of the system: five different emitter materials are used during experimental tests, with both gray and selective spectral properties, and are coupled to a quartz glass absorptive filter. Parallely the mathematical models of the different processes are formulated for each component. Partial differential equation systems are used to define the heat transfer, chemical reaction and flowing of fluids processes inside the device, and are solved for each component with a commercial Finite Element Method based software. A two-band model is used to describe and simulate the spectral control of the optical system. The sixth chapter shows the experimental and theoretical results obtained from tests and simulations, varying the operating conditions and the different emitter materials. The performance of the whole system and of the single components is analyzed and the validity of the different simulation models is evaluated. Some remarks are also made for further improvements of the system.
fatcat:oqa7if4ojrc47lr62ohf344cae