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A Study on the Development of High Accuracy Solar Tracking Systems


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A Study on the Development of High Accuracy Solar Tracking Systems

  1. 1. SET2009 - 8th International Conference on Sustainable Energy Technologies, .Aachen, Germany. August 31st to 3rd September 2009 Page 1 of 6 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. 2. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany 31st August to 3rd September 2009 Page 2 of 6 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. 3. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany 31st August to 3rd September 2009 Page 3 of 6 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. 4. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany 31st August to 3rd September 2009 Page 4 of 6 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. 5. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany 31st August to 3rd September 2009 Page 5 of 6 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. 6. SET2009 - 8th International Conference on Sustainable Energy Technologies. Aachen, Germany 31st August to 3rd September 2009 Page 6 of 6 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 the algorithm is relatively simple, combining the advantages of both the [1]1. J. Meeus, Astronomical Algorithms, optical and the astronomical methods. Willmann-Bell Inc. 1991 A series of studies with the solar tracker [2]1. J.W. Spencer, Fourier series yield the following results. representation of the position of the sun, Search 2, 172, 1971. (1)The calculated solar altitude and azimuth [3]M. Iqbal, An Introduction to Solar for the 1st of January, 2009 were Radiation, Academic Press, 1983. compared with those of KASI, and the [4]P.I. Cooper, the absorption of solar average errors are less than 0.018 degrees radiation in solar stills, Solar Energy 12, during the day. pp. 333~346, 1969. (2)The calculated sunrise and sunset times [5]R. Walraven, Calculating the position of for the month of January, 2009 were the sun, Solar Energy, Vol. 20, pp. compared with those of KASI, and the 393~397, 1978. average errors are found to be less than 1 [6]B.J Wilkinson, An improved FORTRAN second. program for the rapid calculation of the (3)The solar tracking system is found to be solar position, Solar Energy, Vol. 27, pp. accurate and cost-effective and it can be 67~68, 1981. used in many fields such as data- [7]NREL, "Solar Position Algorithm for processing, concentrated PV, the Solar Radiation Applications," 2008. photocatalyst generation of hydrogen, [8] and contributing to the harnessing of the, Calculating Sunrise/Sunset solar energy. in Suffolk, Virginia. 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.