Application of new control strategy for sun tracking F.R. Rubio * , M.G. Ortega, F. Gordillo, M. Lo ´ pez-Martı ´nez Depto. Ingenierı ´a de Sistemas y Automa ´ tica, Escuela Superior de Ingenieros, Universidad de Sevilla, 41092 Sevilla, Spain Received 12 June 2006; accepted 24 December 2006 Available online 26 February 2007 Abstract 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 perfor- mance 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. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Closed loop control; Sun tracking strategy; Low cost two axes solar tracker; Robust performance 1. Introduction Thanks to the technical advances, reasonable priced high concentration solar photovoltaics (PV) arrays are sup- posed to be available within a close time. However, the future use of this kind of solar PV arrays in low cost instal- lations will bring a new type of problem: the necessity of high accuracy solar pointing. High concentration solar PV arrays require greater solar tracking precision than con- ventional photovoltaic arrays, and therefore, a relatively low pointing error must be achieved for this class of instal- lations. Since, in large plants, the design and installation is optimized, they can usually achieve this low error require- ment. Nevertheless, the cost of such optimization is prohib- itive for low cost installations. This paper discusses the design and implementation of a control algorithm for a low cost mechanical structure that can support photovoltaic modules and that acts as a sun tracker. Several classes of structure can be distinguished depend- ing on the classification criteria: • Regarding movement capability, three main types of sun trackers exist [1]: fixed surfaces, one axis trackers (see [2]) and two axes trackers (see [3]). The main difference among them is the ability to reduce the pointing error, increasing the daily irradiation that the solar cells receive and, thus, the electric energy that they produce. A theoretical comparative study between the energy available to a two axes tracker, an east–west tracker and a fixed surface was presented in [4]. As main results, it concluded that the annual energy available to the ideal tracker is higher by 5–10% and 50% than the east–west tracker and the fixed surface, respectively. 0196-8904/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2006.12.020 * Corresponding author. Tel.: +34 9 54487350; fax: +34 9 54487540. E-mail addresses: rubio@esi.us.es (F.R. Rubio), mortega@esi.us.es (M.G. Ortega), gordillo@esi.us.es (F. Gordillo), mlm@esi.us.es (M. Lo ´ pez-Martı ´nez). www.elsevier.com/locate/enconman Energy Conversion and Management 48 (2007) 2174–2184