19 September 2011 Closed-loop control for power tower heliostats
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In a Power Tower solar thermal power plant, alignment and control of the heliostats constitutes one of the largest costs of both time and money. This is especially the case in systems where individual heliostats are small (~1m2). I describe a closed-loop control system that generates the required feedback by inducing small mechanical vibrations in the heliostat reflector surface using piezoelectric actuators. These vibrations induce time-dependent changes in the reflected wavefront that can be detected by photosensors surrounding the thermal receiver target. Time and frequency encoding of the vibrations allows identification of a misaligned heliostat from among the thousands in the system. Corrections can then be applied to bring the reflected beam onto the receiver target. This technique can, in principle, control thousands of heliostats simultaneously.Outdoor testing of a small-scale model of this system has confirmed that such a system is effective and can achieve milliradian tracking accuracy. If such a system were implemented in a commercial plant, it could relax the accuracy specification required of the heliostats as well as provide an automated alignment and calibration system. This could significantly reduce the installed cost of the heliostat field.
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Mark R. Convery, Mark R. Convery, } "Closed-loop control for power tower heliostats", Proc. SPIE 8108, High and Low Concentrator Systems for Solar Electric Applications VI, 81080M (19 September 2011); doi: 10.1117/12.898564; https://doi.org/10.1117/12.898564


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