Dual feedback closed-loop control for one-axis solar trackers of parabolic trough collector systems

Due to the demand of thermal energy in the world, it has become a necessity to increase the efficiency of concentrated solar power systems; the solar tracker systems, is one of the most important elements for such a task. This paper presents a novel control strategy for single-axis solar tracking systems. It incorporates the signals of a solar sensor of photodiodes and a shadow-based visual detection device to reduce the solar tracking error by means of a dual feedback closed-loop control, in a commercial parabolic trough collector. Experimental results of four days outdoor solar tracking are presented as follow. The proposed dual feedback control is compared with a conventional single feedback control, and both loops employ an on-off control algorithm. The mean solar tracking errors were, respectively, ±0.82° and ±0.11°, with the conventional closed-loop control with photodiodes and with the proposed dual control that incorporates the shadow-based visual detection device. Furthermore, this difference in error implies an 80% decrease in tracking error and generates a 15% increase in thermal efficiency.