The document describes key components of solar tracking systems for concentrating photovoltaics (CPV), including trackers, drives, control units, and accuracy monitoring. It outlines requirements and specifications for CPV trackers. Common tracker designs are described, including a pedestal tracker designed by Inspira. Inspira's SunDog is introduced as a generic sun tracking control unit using a hybrid error model approach. Methods for monitoring sun tracking accuracy with Inspira's system based on an image sensor are also presented. Examples from testing Inspira's control units and trackers on the monitoring system are provided.

1. Luque,A. & Andreev, V. (eds.), Concentrator Photovoltaics Springer-Verlag, 2005
The Inspira sun tracking components
I. Luque-Heredia, J.M. Moreno, P.H. Magalhães, R. Cervantes, G. Quéméré
Inspira, SL
C/Chile, 10, 28290 Las Rozas
Madrid - Spain
Ph/Fax: +34 91630 45 34/ 40 87
e-mail: iluque@inspira.es
INTRODUCTION the least possible cost, both regarding tracker manufacturing
and maintenance, pinpoint different aspects such as the weight
First section in the chapter after introducing the sun tracker as vs. aperture surface relation, the level of physical integration of
an inherent component to most of today’s photovoltaic the drives, which aside from easing assembly may also result in
concentration technologies, and defining its main constituent a significant cost reduction whenever it makes them suitable
elements, will provide an outline of the requirements and for a broader market and increases their production volumes,
specifications regarding accuracy, service conditions, cost, etc. the amount of concrete and rebar required for the foundation,
that start to take shape for these systems within the nascent the allotment of assembly labour between that done in factory
concentrator business, and which are to configure coming and that in field, taking also into account transport costs etc.
industry standards. To follow the present state of the art for the
main tracker elements, essentially the tracker along with its
axes drives on the one hand and the sun tracking control on the
other will be described in some detail in separate sections, and
here taking a sort of phylogenetic approach which will
previously trace the major developments in the past, either
considering their specific originality or the relevant scale of
their deployment. Once their context is displayed, both these
two sections will end with a description of the related
developments made at Inspira. The chapter’s final section will
be devoted to introduce the sun tracking error monitoring
equipment developed at Inspira, which eases in different ways
the performance assessment of CPV tracking systems, both to
tracking developers and CPV system integrators. This last
section will end with some examples of the sun error monitor
operating when used on Inspira’s tracking developments.
THE TRACKER
The tracker, can be divided in three main parts, going from top
to bottom we first have its aperture structure able to support the
photovoltaic concentrator array keeping a specified stiffness
under service conditions, and also displaying the mechanical
means to level and align the array’s elements in order to
maximize concentrator’s electrical power output. This
Azimuth-Elevation drive for CPV pedestal trackers
supporting structure is to be able to turn around two orthogonal
designed by Inspira
axes provided by the tracker, in order to optimally point the
(Tracker Section)
concentrator array to the sun, and only in the case of CPV
based on linear reflective optics, i.e. troughs, can single axis
With this context we will get into a more detailed description
schemes also be considered. In this respect the second basic
of the design issues regarding a pedestal tracker, which appears
element of the tracker comprises the mechanical, hydraulic or
today as the tracking configuration which has been most
pneumatic devices, commonly referred as tracking drives,
commonly chosen and produced within CPV projects, as has
enabling the operation and control of axes turns usually by
also occurred in the solar thermal field where similar accuracy
means of electrical motors. Third main element to take into
specifications have almost always been resolved through the
account, also allowing several possibilities upon design, is that
pedestal heliostat, whose production levels are already
of the foundation given to the tracking structure.
significant enough to enable tracker cost projections for the
expected early industrial stage of a CPV industry. A
Even if the variety of tracker designs presented to date is
description will then be provided of a pedestal tracker designed
considerable, as usually occurs in the infancy stages of any
and produced by Inspira for high concentration modules, with
technology, some of these have already been frequently
special emphasis made on the tracking drive and the overall
revisited and apparently evolve as the most effective in terms
structural design issues involved.
of cost and reliability. In this section they will be described,
referring their constituent parts in accordance with the
classification above, and explaining the design criteria they
intend to optimize. These criteria even if ultimately seeking for

2. SUN TRACKING CONTROL is to become a reference component in the coming concentrator
market. In a first section SunDog’s operation procedures will
The sun tracking control, according to the specific nature of its be described, and once this general framework is set its most
technology, embracing the control and eventually the essential elements will be explained in detail, going from the
optimization mathematics toolbox, as well as the tracking error model, to the fitting routines and the tracking
implementation electronics and software, and usually entailing error acquisition strategies involving one or two dimensional
a significant complexity in order to attain the high accuracies space searches as well as power output maximization. Final
demanded, clearly deserves a separate section for its treatment. part to this section will be a description of the embedded
To start, an introduction is to be given relating the state of the electronic system devised for the implementation of these
art evolution of sun tracking control for CPV applications, routines, and its most remarkable hardware features, and also
since its early days till the present trends is to be given. This of its virtual interface Windows software, the SunDog Monitor
review will present the different general approaches to sun which when running on a PC enables a versatile management
tracking control, mainly closed-loop systems based in sun of a connected SunDog unit. Results of some of the tests
tracking sensors, their open-loop counterpart which resorts to underwent by sample SunDog units, both regarding
embedded electronics computing sun ephemeredes, and the so performance and reliability. To end some of the future
called hybrid systems which blend the open and closed loop enhancements envisaged for the SunDog sun tracking control
techniques, incorporating power output feedback in order to units will be advanced.
adjust the core ephemeris to each specific tracker properties.
Within hybrid systems two different approaches can be found,
on the one hand those based on some mathematical model
which attempts to describe tracking error sources to the
greatest possible extent, and by providing the means to
periodically measure tracking errors which enable the fitting of
the model parameters, empowers the model to work from then
on as a secondary correcting stage over the ephemeris and to
switch to pure open-loop tracking. The other attempted hybrid
style places the main difference factor in the fact that no
tracking error model is employed and power feedback
permanently operates fine tuning the ephemeris based
positioning, eventually assisted by error prediction algorithms
in order to reduce adjustment explorations. To end this first
introductory part an account of the requirements and
specifications expected from a sun tracking control system is to
be presented.
SunDog Sun Tracking Control Unit for CPV technologies Off-track angle trace and distribution plots produced by
designed and produced by Inspira Inspira’s Sun Tracking Error Monitor
(Sun Tracking Control Section) (Sun Tracking Accuracy Monitoring Section)
The second main part in this section will be devoted to describe SUN TRACKING ACCURACY MONITORING
Inspira’s SunDogTM sun tracking control units. This is the most
integrated sun tracking control equipment within the error To aid the completion of the development cycles of the coming
model based hybrid approach developed to date, and at the CPV technologies, and implement eventual production
same time having been devised as a general purpose system automation, and quality control processes, specific
compliant with any CPV tracking concept, it is our view that it instrumentation and machinery will have to be developed. In

3. this respect assessment of sun tracking accuracy, should not be
overlooked, and even more by those players raising very high REFERENCES
concentration concepts over the 100X frontier. Some analyses
point out that the acceptance angle of present designs in 1. Luque-Heredia, I. Moreno, J.M., Quéméré, G., Cervantes,
concentration optics may be overestimated even at their R., Magalhães, P.H. “CPV Sun Tracking at Inspira”
theoretical bases, therefore further stressing the requirement of Proceedings of the 3rd International Conference on Solar
sun tracking accuracy. Instrumentation for the monitoring of Electric Concentrators for the production of Electricity or
sun tracking operative performance, providing enough Hidrogen, Scottsdale, 2005
sensitivity to gauge the sub-degree accuracy ranges required by
high concentration systems, is to be required, and has been 2. Luque-Heredia, I. Moreno, J.M., Quéméré, G., Cervantes,
proven feasible at Inspira based on present solid state image R., Magalhães, P.H. “SunDog STCU: A Generic Sun
sensors. Tracking Control Unit for Concentration Technologies”
Proceedings of the 20th European Photovoltaic Solar
In this section we present a complete tracking error monitoring Energy Conference, Barcelona, 2005
system for photovoltaic concentrators, which comprises a
sensing device based in a solid state image sensor housed along 3. Luque-Heredia, I., Gordillo, F., Rodríguez, F. “A PI
with its signal conditioning electronics inside an enclosure Based Hybrid Sun Tracking Algorithm for Photovoltaic
integrating a collimator, and the processing software to run in a Concentration” Proceedings of the 19th European
PC receiving the sensor’s data by means of a serial connection. Photovoltaic Solar Energy Conference, Paris, 2005
A collimated sunbeam impinges on the image sensor which
provides as output the Cartesian coordinates of the sunspot on
its surface, and these can be converted to an off-track angle.
Data acquisition, display, processing and transmission along
with system management, is performed by different add-ons
developed within the SunDog Monitor software. This system
may be taken as a virtual peak power output, in order to work
as feedback for hybrid sun tracking control routines, providing
very precise error measurements and enabling the assessment
of the strategies developed, or it can also be calibrated against
the true peak power of an operating concentrator thus
providing long term statistics of its tracking performance.
To end this section some examples of the sun tracking error
monitor when working on Inspira’s sun tracking control units
and trackers will be provided, which apart from illustrating the
monitoring system operation will serve as a good estimate of
the validity of the approach followed on the design the SunDog
sun tracking control unit.
TENTATIVE CHAPTER INDEX
To summarize the plan described above, the following index
for the chapter can be proposed:
1. Introduction
1.1.System description
1.2. Requirements and specifications
2. The Tracker
2.1. Parts description & design issues
2.2. Common tracking configurations
2.3. A CPV pedestal design by Inspira
2.3.1. The drive
2.3.2. Structural design
3. The Sun Tracking Control Unit
3.1. The different approaches
3.2. Inspira’s SunDog STCU
3.2.1. System description
3.2.2. Error model and parameter fitting
3.2.3. Error acquisition routines
3.2.4. Hardware & software implementation
4. Sun Tracking Accuracy Monitoring
4.1. Description of Inspira’s tracking error monitor
4.2. SunDog STCU monitoring case example