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<span lang="EN-US">The aim of this paper is to study the effect of dissimilarity of the intrinsic characteristics of the light dependent resistor (LDRs) on optical sun tracking systems, designed for solar power concentration applications such as parabolic trough collectors, Fresnel mirrors concentrators, and concentrated photovoltaic, a comparative study was done between a sun tracker based on LDRs chosen randomly with and without an initial calibration of the offsets, and a sun tracker based on LDRs selected meticulously thanks to a black box test bench, developed especially for this purpose. By choosing two light dependent resistors randomly, the dissimilarity between them can reach 23.2%, which cause a bad sun tracking even with initial offset calibration, in the other hand, and by the use of selected LDRs using the test bench, the dissimilarity drops to 0.06%, which meets requirements of solar power concentration systems.</span>

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The aim of the solar water heater designed for Tahala grid project, is to provide renewable energy to the residents of Tahala village in southern of Morocco, our contribution as LERED* laboratory to this project consists of the creation of a novel solar water heater, with a long lifetime, high efficiency, reliability and quality, that uses solar concentration instead of direct exposition in the hope of reaching high temperatures even during cold weather and the winter season. In order to evaluate the performances of this new solar water heater, it was necessary to build a full-scale solar water heater test bench station, which allows to monitor the thermal station remotely, in order to start new experiments, measure various parameters such as cumulated thermal energy, the maximum reached temperature, efficiency, and so on, in order to compare the performances of each solar water heating technology in various weather conditions. In this study, we choose to test and compare three solar water heater technologies: water-in-glass evacuated tube collectors, selective surface flat-plate collectors, and the novel design that consists of a Fresnel mirrors concentrator with a water-in-glass evacuated tube collector with a dual sun tracking system. The result of experiments shows that under normal weather conditions, the Fresnel mirrors concentrator efficiency reached 48%, followed by the evacuated tube collector that have an efficiency of 42.3 %, and then come at the last position the flat-plate collector with an efficiency 36.3%.