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 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.
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 supposed
to be available within a close time. However, the
future use of this kind of solar PV arrays in low cost installations
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 conventional
photovoltaic arrays, and therefore, a relatively
low pointing error must be achieved for this class of installations.
Since, in large plants, the design and installation is
optimized, they can usually achieve this low error requirement.
Nevertheless, the cost of such optimization is prohibitive
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 depending
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.


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