1. SET2009 - 8th International Conference on Sustainable Energy Technologies, .Aachen, Germany.
August 31st to 3rd September 2009
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A Study on the Development of High Accuracy
Solar Tracking Systems
Seung Jin Oh1 , Jun Ho Hyun1, Yoon Joon Lee1,
Kuan Chen2, NG Kim Choon3, Young Soo Lee4, Wongee Chun1
1
Nuclear &Energy Engineering Department, Jeju Nat’l Univ., Jeju, Korea
2
Department of Mechanical Engineering, University of Utah, Utah, USA
3
Department of Mechanical Engineering, Nat’l Univ. of Singapore, Singapore, Singapore
4
Solar Thermal and Geothermal Research Center Korea Institute of energy Research
ABSTRACT: Solar trackers play a central role in concentrating the sun light into an optical
fiber where at one end of fiber, a high-density light beam could emerge for indoor illumination,
high suns PV applications. Many solar trackers have been developed in the market but they are
relatively expensive and high accuracy of trackers may pose long term reliability problems. A
key component of the motion controller of trackers is the software, where flexibility, easy-of-
use and integration with other I/O ports are parameters for consideration. In this paper, we
demonstrate that a cost-effective solution with the off-the-shell software, such as the LabVIEW.
It offers solution with excellent accuracy in tracking as well as the output concentration in the
fiber reaching up to 200 suns. The tracker system takes advantage of global positioning data
(GPS) for the geographical location before applying the simultaneous controls such as the open
and closed loop operations. The closed loop feedback control with CdS sensors proves
effective in making real time corrections for gear backlashes or under an adverse disturbances
arising from strong winds, etc.
Keywords: Solar tracker, LabVIEW, Solar Position, Sunrise and Sunset time, Mini-dish
1. INTRODUCTION Such equipment works best when pointed
directly at the sun, increasing the
Solar energy is reliable and cost-effective effectiveness over the non-tracking systems
as compared to other forms of renewable but it is at a marginally higher cost and
energy. The solar energy emits no pollutant system complexity.
into environment, and it has been widely The accuracy of the solar trackers
accepted. Systems without a solar tracking depends on the types of application:
system, although are lower in the initial Concentrators meant for solar cells and day-
investment, but they have lower output. lighting systems would require higher
Hence, the motivation to study solar energy degree of accuracy, ensuring the
systems with solar trackers is high as concentrated sun rays are directed at the
evident by the voluminous publications. prescribed numerical aperture near the focal
A solar tracking system is a device for point. Typically, concentrator systems are
orienting a day-lighting reflector, solar either a single-axis or two-axes devices.
photovoltaic panel or concentrating solar Large power plants or high temperature
reflector or lens toward the beam radiation facilities may employ multiple ground-
of the sun. The sun's position with respect to mounted mirrors and an absorber target with
earth varies both with the seasons and time or without secondary concentration. One of
of day as the sun moves around the earth. the key components of a motion controller

2. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany
31st August to 3rd September 2009
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in a tracker is software where the C- and declination angles with respect to the
language and Visual Basic are often used, celestial equator or plane.(see Figure 1.)
and manufacturers of trackers have supplied
their systems with libraries for these
algorithms. The problem, however, is that it
is difficult for a user to integrate such codes
into the one main program. In this study, we
have employed a common platform based
on a commercially available code, the
LabVIEW, which is easily adapted by any
user.
2. Solar Position and Sunrise & Sunset
Figure 1: The horizon coordinator and the
Generally, there are two methods celestial equator
available for solar tracking: An optical
method and the astronomical method to give In this figure, the Solar altitude(h) is the
the position of the sun rays at any time angle between a line that points from the site
instance in a day. The optical method is towards the centre of the sun, and the
called the “closed loop system”, it uses horizon. The solar azimuth(A) is the angle
several feedback sensors such as a photo- between the line from the observer to the
sensor and a position sensor and a sun projected on the ground and the line
comparator that differentiate the output from the observer due south.
signals of sensors and thus, continuously The declination(δ) is one of the two
adjusting the system towards a brighter spot. coordinates of the equatorial coordinate
Such a method has a drawback, i.e., it system, the other being either right
cannot track the sun in a cloudy day without ascension or hour angle. The declination is
an extensive algorithm. comparable to latitude, projected onto the
The astronomical method, on the hand, celestial sphere, and is measured in degrees
employs the longitude and latitude data of a north and south of the celestial equator. One
location in-situ and it has the advantage of of the coordinates used in the equatorial
simple programming, high degree accuracy coordinate system for describing the
and less error. However, the inherent position of a point on the celestial sphere.
disadvantage is that it requires the starting The hour angle(H) of a point is the angle
position of tracker to be always same from between the half plane determined by the
day to day and the operating motors are Earth axis and the zenith (half of the
easily subject to the “backlash” effect due to meridian plane) and the half plane
continuous adjustments from the GPS data. determined by the Earth axis and the given
For these reasons, we have combined these point. The solar altitude and azimuth are
methods in this study. given by Eq.(1) and (2).
2.1 Algorithm for solar tracker sin θ e = sin δ sin φ + cos δ cos φ cos H (1)
In this Solar tracking algorithm, the solar
altitude ( θ e ) and azimuth ( θ a ) are computed cos δ sin H (2)
sin θ a = −
in accordance to the location or site. The cosθ e
tracker device must be positioned
horizontally to implement the altitude and
azimuth angles along with the hour angle

3. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany
31st August to 3rd September 2009
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θ e : Solar elevation( altitude) 3. Major component and Development
θ a : Solar azimuth
3.1 Major component
δ : Declination The ultimate goal of this study is to
φ : Latitudeof observer develop a high accuracy solar tracking
H : Hour angle system with an optical and an astronomical
method. At first, the solar tracking system
2.2 Sunrise and Sunset time begins to work by using the calculated
The solar tracking system must be altitude, azimuth, sunrise time and sunset
returned to the initial position after the sun time. The system, then, compensates the
disappears below the horizon, otherwise it malfunction by a feedback device (CdS)
must be started to track the sun after the sun when it encounters urgent problems that the
appears above the horizon. backlash of gears occurs owing to a strong
The sunrise and sunset time are calculated wind and non-precision caused by non-
by Eq.(3). exacted initial position
Four CdS sensors were used as a
T=H+α-(0.06571ⅹt)-6.622 (3) feedback device. CdS sensor is a sort of
variable resister whose internal resistance
where, for sunrise,
varies with optical energy. Cds cell
t = N+((6-lngHour)/24)
generally become close to an insulator and
For sunset,
when a light ray is incident on the surface of
t=N+((18-lngHour)/24)
cell, its internal resistance drops with the
incident energy.
T= Sunrise or Sunset time
When the system becomes perpendicular
H= Hour angle
to the sun, it casts shadow on all sensors,
N= day of year
and then the output voltage drops with the
α=Right ascension
resistance increasing.
lngHour =(longitude)/15
Unless otherwise, each sensor compares
the outputs and make the system to move
A Right ascension(α) is the celestial
forward higher valued sensor.
equivalent of terrestrial longitude and
The principle of working of the solar
measures an east-west angle along the
tracking system developed in this study was
equator.
showed in figure 3.
Figure 2 shows the block diagram of
LabVIEW for calculating the sunrise and
sunset time, which are compared with those
of KASI.
Figure 3: The principle of solar tracking
system
(a) (b)
Figure 2: The algorithm for solar tracking; The application written by LabVIEW
(a) the altitude and azimuth, (b) the sunrise calculate the solar position as well as sunrise
and sunset time. and sunset time and determine the steps of

4. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany
31st August to 3rd September 2009
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step motors to transfer the signal to Motion 3.2 Application Software
Controller. Motion Controller transfers the
signal relevant to the each axis to two step In this study LabVIEW was used for
motors that revolve as many as input steps. developing the algorithm and application
If the error signal occurs at the feedback programme.
sensor, the application will set up the steps LabVIEW (short for Laboratory Virtual
and compensate the position of solar tracker. Instrumentation Engineering Workbench) is
Hardware for developing the system a platform and development environment
includes NI-7352 motion controller, stepper for a visual programming language from
drive, UMI(Universal Motion Interface) and National Instruments. The graphical
2-axis stepper motor. language is named "G". Figure 5 shows the
A Mini-dish was used to verify the control application developed in LabVIEW.
performance of solar tracking system. As soon as the application runs, the solar
The mini-dish is 30cm in diameter and altitude and azimuth angle, sunrise and
has a hole in the middle of dish in which a sunset time are calculated on a real time
optical fibre is connected in order to basis at SubVI in the loop showed in Figure
transmit concentrated rays. The 2nd mirror is 5 (a). In order to compute the number of
installed at the top of mini-dish which step of motors the solar altitude and azimuth
transmits concentrated rays into the optical angle are then input into another loop in
fibre. which the step-angle(0.144) and the gear
Figure 4 shows the main components of ratio are multiplied and the final steps are
solar tracking system. This system has 2- outputted out of loop. The sunrise and
axis; both X-axis and Y-axis are rotated by sunset time are transmitted to (c)loop and
stepper motors. A bevel gear with 2:1 of those then are compared with the present
gear ratio was used at X-axis and sprocket time during calculating steps. If the sunrise
gear and chains were used at Y-axis for time corresponds to the present time, the
power delivery. Stepper drive and UMI system begins to track the sun from the
were installed in a lower part, which power initial position, otherwise, if the sunset time
the stepper motors. There is a frame in a corresponds, the system halts after returning
upper part at which the mini-dish and the to the initial position.
CdS sensors were installed.
The height of the system is 75cm and the
width is 40ⅹ40 cm. The frame was made of
aluminium profile.
Figure 5: The block diagram for system
Figure 4: The main components of solar control.
tracking system.

5. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany
31st August to 3rd September 2009
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The final steps outputted from (a)loop are It was found that the average errors were
transmitted to (b) loop in which the less than 1 second. Figure 8 shows the still
command was transferred to the Motion shots of the solar tracking system where the
controller. In (b) loop the real-time values of concentrated beam emerged from the other
four CdS sensors are read and compared end of the fibre. The concentrated beam
with each other. could be used either for space illumination
If all signals of sensors are equal, the or for irradiation onto the multi-junction
system continues to work in an open loop. If cells for electricity production at high
any signal of sensors differs with others, the efficiency. The emergence of the
direction is decided in the loop and concentrated beams at the end of fibre is a
transmitted into (d) loop. In (d) loop, the testimony of the accuracy achieved by the
direction command is continuously solar tracker.
transferred to the Motion Controller until all
of the outputs of sensors are equal.
4. Discussion
Figure 6 and 7 show the results that the
solar altitude and azimuth calculated in this
study was compared with those of
KASI(Korea Astronomy & Space Science
Institute).
The experimental conditions are as
follows;
Figure 6: Solar altitude.
• Location : Jeju city, Jeju do, Korea
• Longitude : Long. 126˚15΄60˝ E
• Latitude : 33˚ 30΄ 30˝ N. Lat.
• Date : 1st of January, 2009
• Time : 00:01~ 24:00
The maximum error of the solar altitude
angle was 0.0371 degree at 4 pm (local
time). Otherwise, the minimum error was
0.0006degree at 10 am (local time). The
maximum error of the solar azimuth angle
was 0.0823 degree at about 1 pm (local
time), otherwise the minimum error was Figure 7: Solar azimuth.
0.0012 degree at about 5 pm (local time). It
was found that the both maximum errors 5. CONCLUSION
were occurred at dawn but this has not effect
on the result as there is no sun.. In this study, the solar tracking system
The sunrise and sunset time were was fabricated and has achieved high
calculated for the month of January, 2009, accuracy for the tracking of the sun rays.
which were compared with those of KASI.

6. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany
31st August to 3rd September 2009
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Figure 8: The still shot of the solar tracking system operating at three time intervals of
the day.
Our tracker system is cost effective and REFERENCES
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ACKNOWLEDGEMENT
This work is supported by the grant
(No.R33-2008-000-10166-00) of the World
Class University (WCU) programme of the
Korea Science & Engineering Foundation.