Abstract
This study presents a two-axis solar tracking system equipped with a small concentrator module for electricity generation through a multijunction solar cell. The system can accurately track the sun without the need of calibration for an extended period and operate as a stand-alone system. High-precision solar tracking was achieved by a combination of open-loop and closed-loop controls. A camera tracking sensor was introduced as a feedback device in closed-loop control. Two different types of solar concentrator modules were designed and fabricated. Their concentration ratios were analyzed against solar tracking errors by means of ray tracing software. One is made up of a paraboloidal primary concentrator and a paraboloidal secondary reflector, whereas the other has a paraboloidal primary concentrator and a hyperboloidal secondary reflector. Both modules showed an almost identical concentration ratio of 610 provided that the solar tracker is pointing perfectly at the sun. However, their performance differs considerably when tracking error is present. The maximum power output was obtained near solar noon with multijunction cells, whose average solar conversion efficiency was 21%, much higher than that of conventional photovoltaic systems. Copyright (c) 2015 John Wiley & Sons, Ltd.