IMPROVING THE EFFICIENCY OF A PHOTOVOLTAIC SYSTEM BY INCORPORATING TRACKING SYSTEM AND MPPT: A REVIEW <s> Fig. 4 <s> An electromechanical system to follow the position of the sun was designed and built at the Solar Evaluation Laboratory of the Technical University Federico Santa Maria (UTFSM) in Valparaiso. It allows the automatic measurement of direct solar radiation with a pyrheliometer. It operates automatically, guided by a closed loop servo system. A four-quadrant photo detector senses the position of the sun and two small DC motors move the instrument platform keeping the sun’s image at the center of the four-quadrant photo detectors. Under cloudy conditions, when the sun is not visible, a computing program calculates the position of the sun and takes control of the movement, until the detector can sense the sun again. The constructed system was tested in the climatic conditions of the city of Valparaiso, Chile. The presented tracker proves the effective work of a simple and cheap mechanism, which can be adapted to also work with larger following installations like solar cell panels, concentrators, etc. <s> BIB001 </s> IMPROVING THE EFFICIENCY OF A PHOTOVOLTAIC SYSTEM BY INCORPORATING TRACKING SYSTEM AND MPPT: A REVIEW <s> Fig. 4 <s> The application of high concentration solar cells technology allows a significant increase in the amount of energy collected by solar arrays per unit area. However, to make it possible, more severe specifications on the sun pointing error are required. In fact, the performance of solar cells with concentrators decreases drastically if this error is greater than a small value. These specifications are not fulfilled by simple tracking systems due to different sources of errors (e.g., small misalignments of the structure with respect to geographical north) that appear in practice in low cost, domestic applications. This paper presents a control application of a sun tracker that is able to follow the sun with high accuracy without the necessity of either a precise procedure of installation or recalibration. A hybrid tracking system that consists of a combination of open loop tracking strategies based on solar movement models and closed loop strategies using a dynamic feedback controller is presented. Energy saving factors are taken into account, which implies that, among other factors, the sun is not constantly tracked with the same accuracy, to prevent energy overconsumption by the motors. Simulation and experimental results with a low cost two axes solar tracker are exposed, including a comparison between a classical open loop tracking strategy and the proposed hybrid one. � 2007 Elsevier Ltd. All rights reserved. <s> BIB002
Operation of the hybrid system BIB002 A dual-axis tracker with four photo detectors was designed by Roth, Georgiev and Boudinov BIB001 . A computer was used to control two DC motors to orient the panel. If the sensors are unable to detect the sun, such as while the sun is covered by clouds, the position of the sun is calculated by a computer program to orient the panel until the detector could sense the sun's position. The computer program makes use of the existing solar tracking formulas to determine the position of the sun.