Semi-passive solar tracking concentrator
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© 2014 The Authors. Published by Elsevier Ltd.A solar tracking concentrator (STC) has to adapt to the changes in the sun's position throughout the day and even more so, throughout the year. The function of sun tracking is to keep the sun's rays perpendicular to the absorber's cross-sectional area through a constant orientation, which requires an accurate electro-mechanical system that increases the cost of the whole concentrator. Sun tracking enables solar radiation to be concentrated in a limited and well-defined area of a receiver where the thermal energy collected is stored and then transformed into other kinds of energy. This heightens the prospects for the STC to use as little energy and movement as possible for solar tracking so as to achieve such a concentration. For this reason, a semi-passive solar tracking concentrator (SPSTC) whose configuration requires a minimal mechanical effort and reduced movement for sun tracking is proposed. It mainly consists of a micro-heliostat array, a Fresnel lens and a receiver. The array tracks the position of the sun to reflect the sun's rays toward the Fresnel lens, which remains horizontal, reducing wind loads over the whole system. The receiver, located on the lens focus, remains stationary, releasing its weight on the sun tracking system and thus reducing the energy required for movement. The SPSTC's kinematics for both altitude and azimuth tracking on a 25°39'15"N latitude is analyzed. An optimum fixed array's tilt of 49.054° was found to maximize the effective Fresnel lens area by reducing blocking and shading, both caused by the position of the array above the lens.