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    The Usability of PV-TEG Hybrid Systems on Space Platforms
    (IEEE, 2019) Keser, Omer Faruk; Idare, Bugrahan; Bulat, Bayram; Okan, Altug
    Most space platforms use solar cells to harvest energy. However, solar cells cannot utilize the full electromagnetic spectrum. They can only convert the UV (ultraviolet) and visible parts of the solar spectrum (200-800 nm). The rest of the spectrum is absorbed as waste heat and degrades the efficiency of the solar cell. On the other hand, hybrid PV-TEG modules can convert much more of the solar energy spectrum. According to recent research, hybrid PV-TEG modules can increase the efficiency of solar cells up to 30%. There are many studies which show that PV-TEG hybrid systems have better performance than single PV and TEG systems [1-6]. However, data on the usage of hybrid modules in space is very limited or unavailable. In this study, it is aimed to analyse the usage of hybrid PV-TEG systems as a primary power source on satellites. A PV-TEG stackup has been designed through numerically analysis and optimization. It has been observed that if an insulator material with a very low thermal conductivity is integrated into a thermoelectric module instead of a ceramic (Al2O3) substrate, the resulting hybrid PV-TEG module becomes more efficient. Through this approach it is possible to improve the efficiency of the solar cells by 21,9% and the efficiency of the overall system by 2,95% through the use of a substrate material having a thermal conductivity of k=0,01 W/mK.
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    Uzay Platformlarına Yönelik Bir Termofotovoltaik Güç Sistemi Tasarımı
    (Fen Bilimleri Enstitüsü, 2021) Bulat, Bayram; Keser, Ömer Faruk
    Solar cells are used as the primary power generator system for most of the space platforms designed to operate on earth orbits. However, the disadvantages of the solar cells such as having large volume, back up requirement, to be adversely affected by the space environment, having limited operating temperature range etc. constitute a problem forthe space studies. On the other hand, the Radioisotope Power Systems (RTG) which are used in many deep-space missions successfully aren’t preferred for earth-orbit missions due to its disadvantages such as low efficiency, weightiness and having radioactive substance. Taking into account all of these, the need for a new space power system which will be efficient and able to cover all the disadvantages of solar cells and RTGs has emerged. Although, many concept space power systems have been presented in accordance with this purpose, thanks to many advantages and high efficiency potential that it has, it is anticipated by the researchers that the Thermophotovoltaic Generators (TPVG) will be one of the most important research topic in the field of space power systems. In this study, the structure of the TPVG power systems is investigated and a STPVG power system model is developed and presented. As a part of this study, the disadvantages of current STPVG models regarding the efficiency were determined and a STPVG model was designed which has an cylindrical and vertical structured emitter and a TPV cell array that surrounds the emitter 360 degrees. The developed model can be evaluated as the most important finding of this study in terms of resolving all the disadvantages of current STPVG models and being the first STPVG model developed for space platforms. As part of the study, a time-dependent two-dimentional thermal analysis and calculations for power generation and efficiency were conducted in COMSOL Multiphysics simulatıon program. According to results, it has been calculated that the efficiency for power generation in TPV cells is 26,5%. After then, several studies regarding the dimensions of emitter, structure of optical lenses and TPV cell arrays to increase the efficiency of STPVG was conducted and two new STPVG models were presented. Wıth the new STPVG models proposed, ıt has been achieved 35,4% efficiency for the TPV power generation. Besides the calculations for power generation and efficiency, it has been analysed that, it is possible to keep cool the STPVG power system only with using heat-sink and without the need of any active cooling system. As a result of the studies conducted in this research, it is concluded that the STPVG power system which was designed in this research is feasible in terms of future’s power sub-systems for space platforms.