Concentrator photovoltaics for parabolic trough solar collectors

In order to meet the climate targets, it is crucial to replace the existing energy sys- tems, which are largely based on fossil energy sources, with renewable technologies. Photovoltaic systems are already contributing to a lower-carbon atmosphere and yet their share of the electricity market is still small at 2 0095 5 %. While the efficiency of conventional crystalline silicon solar cells has stagnated at 25 % over the past decades, new efficiency breakthroughs have been achieved steadily in the field of multi-junction solar cells designed for concentrated sunlight, most recently peaking at 47 0095 1 % . To take advantage of such high efficiencies, these more expensive solar cells require concentrating optics - in the form of a mirror or lens that redirects the solar radiation onto the cell - in order to use them economically. Since these concentrating optics can be quite complex and costly, it is important not to negate the solar cell's efficiency gain by incorporating overly expensive optical designs. For this purpose, parabolic trough collector systems could be deployed, which have been successfully used in thermal systems for decades due to their relatively simple construction and their good scalability. The idea of this work is to combine the high electrical efficiency of multi-junction solar cells with the relatively simple concept of a parabolic trough collector to generate electrical and thermal energy simultaneously. Using parabolic mirrors facing the sun, sunlight is concentrated on the solar cells, which generate electrical energy and transfer the exhaust heat to a heat transfer fluid to exploit additional thermal energy. The hybrid absorber required for this purpose was completely developed and tested in the course of this thesis. In a field test, lasting several weeks, it was demonstrated that the hybrid absorber concept worked successfully with high efficiencies. In real operation, a maximum solar cell efficiency of 30 % could be measured based on direct normal irradiance (DNI). At system level, an average electrical efficiency of 26 0095 8 % and a thermal efficiency of 48 0095 8 % were measured, which corresponds to an overall efficiency of 75 0095 5 % (DNI based, optical efficiency). Furthermore, the hybrid absorber was successfully tested and measured at heat transfer fluid temperatures of up to 90 C . This thesis describes the theoretical design, development and characterization of the hybrid collector, addressing the issues of feasibility, challenges, potential applications and efficiencies. (author)