This paper describe about the low cost and simple method of solar tracking system for photovoltaic system application. A solar module receives the most sunlight when it is perpendicular to the sun's rays, but the sunlight direction changes regularly with changing seasons and weather. Currently, most solar panels are fixed, i.e., the solar array has a fixed orientation to the sky and does not turn to follow the sun. The angle of the sun is proportional to the energy converted. If the sun is 90° vertical to the solar panel, the energy received is maximum compare to other angles. In this case, a project is developed to track the solar during the movement of the sun from morning till night. The ASTS (Automated Solar Tracking System) is developed by moving the solar panel during anytime of the day that the sun is available and the motor will move the panel to a 90° vertical angle directly to the sun. The system is controlled by OMRON Programmable Logic Controller which will process data from the sensor and convert it to output for the motor movement. As the result, a prototype of Automated Solar Tracking System (ASTS) is operated and able to achieve the objective of this project.
Solar energy systems have emerged as a viable source of renewable energy over the past two or three decades, and are now widely used for a variety of industrial and domestic applications. In current technology condition, the utilization of tracking PV system is an optimum selection for enhancing system efficiency and reducing cost. The amount of power produced by a solar system depends upon the amount of sun light to which it is exposed. The international research shows that tracking system with single-axis can increase more than 20% electricity output while the tracking system with double-axis can increase of more than 40% electricity output [1]. Various schemes have been proposed for optimizing the tilt angle and orientation of solar collectors designed for different geographical latitudes or possible utilization periods [2-3].
Single axis tracking systems are considerably cheaper and easier to construct, but their efficiency is lower than that of two axes sun tracking systems. Nevertheless, as Malaysia is located close to the equator, single axis tracking system is sufficient to produce maximum output power.
As depicted in Figure 1, the Tilt Angle θ of a PV system required at any given time in the year can be expressed as a function of the seasonal Sun's Altitude β as follows:
Tilt Angle θ = 900 - β
Figure 1:
Before the advent of solar tracking, fixed solar panels have been positioned within a reasonable tilt range based on the latitude of the location. A rule of thumb is to select a tilt angle of within ± 150 of the latitude depending on whether a slight winter or summer bias is preferred in the system. The PV array would face "true south" in the northern hemisphere and "true north" in the southern hemisphere. Note that the true south and the true north directions differ from the magnetic south and north direction usually obtained with a compass [4]. Solar tracking is best achieved when the tilt angle of the tracking PV array system is synchronized with the seasonal changes of the sun's altitude and with the geographical insolation level for optimized solar tracking during the day [5].
In this project, a single axis, solar tracking, PLC controlled system was designed and constructed. The system was characterized by a fairly simple electromechanical set up. This is to reduce cost, maintenance and the possibility of failure. Also, this system can be easily installed and assembled. A solarimeter (i.e a device used to measure the amount of solar irradiance and etc) was mounted on a platform which is controlled by the tracking system to investigate the availability of solar radiation on the tracking surfaces.
Approach and Methods
This project aims to develop a solar tracker with optimum tracking from the sun with the positioning of solar panel through dc motor control using PLC. The result of the Automated Solar Tracking System is plot in a graph to analyze the efficiency of the project. The main target of this project is to analyze that the angle of the sun is proportional to the power receive by the solar panel. Hence, this project will then shows that the ASTS will achieve maximum power during daylight.
The sensor detects the sun which will then give an input the PLC and moves the motor to the desired angle. The result is then plotted and an analysis is done in order to prove that the angle of the sun is really effect the power received. Figure 2 shows the flow chart of the ASTS system.
Start
Motor start to move east to west
Detects the sun
Input to PLC
Sensor 2 detects the position
Motor stops
The panel will be vertical to sun
Figure 2: Flow chart of ASTS
In this project, the tracking system takes the sun as a guiding source. Sensors are used to constantly monitor the sunlight and rotate the solar panel to the maximum intensity of sunlight. PLC (Programmable Logic Controller) is used as a device for controlling the output for the motor. If the sun is not visible during a short period due to cloudy weather, the PLC is set with a program which will engage the motor rotation to halt which only will be reactivated due to a sensor which will detect availability of the sun to continue its next cycle.
Figure 3 shows the overall system diagram for the Automated Solar Tracking System (ASTS). The device used is consist of two Light Dependent Resistor (LDR) circuit, one relay circuit, two limit switch , one dc motor and a Programmable Logic Controller (PLC). The LDR 1 circuit detects the availability of sun during 7 am till 7 p.m. Once it detects the sun, the motor will move from east to west (clockwise).
Figure 3: System's block diagram
The LDR circuit is use as a sensor to detect solar for the whole system. The output from this circuit is a relay which will work as a switch that connects the logic '1' to the PLC. They are two LDR circuits used. One is to detect sun availability and the other for sun positioning. The complete circuit of LDR is shown in Figure 4. Variable resistor (22 kΩ) is varied to 3.16 kΩ for the circuit to detect sun ray only. This must be check so that the circuit won't respond to other light source (etc. torchlight, fire, and lamp). The circuit works with a 9Vdc power supply.
Figure 4: Light Dependant Resistor circuit
The system's prototype is shown in Figure 5. LDR 2 which is placed inside the black cylinder on top of the board is used to detect positioning of the sun during daylight. Once it detects the sun, it will then stop the motor on that angle so that the board is vertical to sun for maximum sun irradiation.
Figure 5: ASTS prototype
Every time the sun moves, the angle will change and the LDR 2 detects it until the motor rod touch the limit switch 1(west) which will turn the motor rod back to initial condition. Relay circuit is used to move the motor clockwise and counter-clockwise where the input of the relay is a 24Vdc form the output of PLC. Limit switch 2 detects the motor rod once it returns to its initial condition (east). The output of limit switch 1 and limit switch 2 is connected to PLC where it will then trigger the relay and move the motor counter-clockwise.
Result and Discussion
The ASTS was tested under real sun condition as shown in Figure 6. Reading of the module power, current and light irradiation is plotted in graph of Figure 7, 8 and 9. The data were captured from 8:00 am until 7 pm. Thus to prove the efficiency of the ASTS, still position of 45°, 90° and 135° is taken due to see the difference of each reading. The data of irradiation, voltage, current and ambient temperature have been measured using solar measuring device manufactured by SolarC and Compass clinometer by SUUNTO in order to measure the tilt angle. Each of the reading were done by actual time and place with the ASTS device were placed and every 15 minutes, the reading of each components were taken by using a special measurement device of MACSOLAR. Due to performing the ASTS without a real solar panel, the device clearly shows that the tracking system positioning at every angle changed rapidly with the movement of the sun
Figure 6: ASTS prototype tested under the sun
From the graph shown in Figure 7, the maximum solar power is charged at 45° at the 10:45 am. The minimum solar power is the most at angle 135° during the morning. In the afternoon, the minimum solar power is the most at angle 45°. At angle 90°, the graph shows quite an expectable and fair result at which the graph at morning and afternoon is fairly going down slowly and at equal steep. As can be seen, the maximum power charges are obtained at the angle which the device is set to. This device implemented tracks the solar source automatically and its angle is unquestionable having the abilities to provide the optimum solar power from the sun.
Figure 7: Average module power in %. (Pn).
From the graph shown in Figure 8, the maximum solar cell voltage can be obtained at almost all the angle as the different between each solar cell voltage gotten from the various angle are of not much different. For instance, at 10:00 to 11:00 am, it can be seen that the graphs are going fairly the same pattern for all the angles except for 135° this is due to the vast different of sun exposure to that particular angle. Note that 135° angle is facing the west. Hence it is expected that at 135°, the minimum solar cell voltage is produced during the morning. In the afternoon, the minimum solar power is the most at angle 45° due to its position facing the east. The graph of angle 90° run smoothly and almost equally to following the pattern of graph of the device angle. However, it is noticeably that the graph of the device angle possesses the higher yet optimum solar cell voltage charge.
Figure 8: Average module voltage in %. (Un)
From the graph shown in Figure 9, the maximum light intensity is averagely at the 1:00 pm of the device angle, which is at 1045.25 W/m2. The vast different of the device angle efficiency in measuring the light intensity is shown at the 11:00 am. The value at this point is so much higher than the other three angles. At angle 45°, the light intensity is having the average small amount at all hours. However, in the morning the angle 135° shows the lowest light intensity due to its position facing to the west. The angle 90° shows almost optimum value of light intensity except for the morning time as in the afternoon the graph pattern is fairly exact to the graph produce by the device angle.
Figure 9: Average value of light intensity (irradiation).
Conclusion
A solar tracker is designed employing the new and simple principle of using small adjustable light sensors, providing a variable indication of their relative angle to the sun. By using this method, the solar tracker was successful in maintaining a solar array at a sufficiently perpendicular angle to the sun. The power increase gained over a fixed horizontal array was in excess of up to 30%. The system developed in this study provides easy installation, low cost, simple mechanism, good performance and easy programming tracking system.
Acknowledgments
The authors would like to thank to Universiti Malaysia Pahang for their financial support under research grant Vot: RDU08/03/12.
