Tesis doctoral de Alejandro Datas Medina
This thesis presents a theoretical (part i) and experimental (part ii) analysis of solar thermophotovoltaic systems. In these systems an intermediate material (emitter) is heated to incandescence by solar radiation. The thermal radiation emitted by that material is directed to a photovoltaic cell that converts this radiation into electricity. In this configuration, the photons that are not efficiently used by the cells can be redirected to the emitter using spectral control elements. the first part of the thesis (chapters 2-4) present various analytical models of solar thermophotovoltaic systems. In chapter 2 an ideal system is analyzed and the maximum efficiency limit is determined, which turns out to be 85.4%. Unfortunately, such efficiency is achieved for negligible electric power densities and under severe restrictive conditions. Chapter 3 presents a more complete multivariable model, based on the detailed balance theory, which contemplates (among other things) possible optical losses. The model shows that efficiencies above 30% and electric power densities above 50 w/cm2 are achievable. This requires high solar concentration (above 1000 suns) and a method to enhance the energy transfer from the emitter to the cells (typically, by increasing the emitter area to the solar absorber area ratio). Finally, chapter 4 presents a more realistic model of a system with cylindrical geometry. With this configuration it was demonstrated that efficiencies of 10-15 % and electric power densities of 1-5 w/cm2 can be achieved using currently available components (germanium cells with back-side reflectors and tungsten emitters coated with anti-reflective coatings). chapters 5-8 present the development and characterization of a complete solar thermophotovoltaic system, consisting of a refractive solar concentrator, a cylindrical tungsten emitter coated with hfo2 and an array of germanium cells. In this thesis, special attention is paid to the characterization of the concentrator system and the emitters (chapter 6), to the manufacturing processes of the cell-modules (chapter 7) and to the characterization of the complete system under real operating conditions (chapter 8). This system has provided cell short-circuit current densities of 0.95 a/cm2, electric power densities of 120-140 mw/cm2 and a conversion efficiency of 0.8 %. The estimated temperature of the emitter is in the range of 1300-1500ºc. The low efficiency is mainly due to overheating of the cells (up to 120ºc) and to optical losses in the concentrator, which prevent the achievement of the optimum emitter temperature. It has been estimated that an improvement in both of these aspects would allow the achievement of efficiencies above 5%. The improvement of the photon recycling process between the emitter and the cells could lead to efficiencies close to 10%.
Datos académicos de la tesis doctoral «Development of solar thermophotovoltaic systems«
- Título de la tesis: Development of solar thermophotovoltaic systems
- Autor: Alejandro Datas Medina
- Universidad: Politécnica de Madrid
- Fecha de lectura de la tesis: 01/07/2011
Dirección y tribunal
- Director de la tesis
- Carlos Algora Del Valle
- Tribunal
- Presidente del tribunal: Antonio Luque lópez
- ivan Celanovic (vocal)
- ramón Alcubilla gonzález (vocal)
- donald L. chubb (vocal)