DESIGN AND IMPLEMENTATION OF AN INTELLIGENT DUAL AXIS AUTOMATIC SOLAR TRACKING SYSTEM

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1 Rev. Roum. Sci. Techn. Électrotechn. et Énerg. Vol. 61, 4, pp , Bucarest, DESIGN AND IMPLEMENTATION OF AN INTELLIGENT DUAL AXIS AUTOMATIC SOLAR TRACKING SYSTEM SOUMYA DAS 1, PRADIP KUMAR SADHU 2, SUPRAVA CHAKRABORTY 2, SANCHARI BANERJEE 1, TUNIR SAHA 3 Key words: Automatic solar tracking system, Dual-axis, Photovoltaic (PV), Light dependent resistor, Microcontroller, Servo motors. A theoretical and experimental study of a microcontroller based dual-axis automatic solar tracking system (ASTS) is presented in this paper. The PV panel rotates automatically based on the intensity of sun light. ASTS helps keeping the solar panels aligned with the Sun in order to obtain maximum solar power at any instance. When in any particular alignment the intensity of light is decreasing, this system has the ability to automatically redirect to get maximum intensity of light. The light energy is detected by four llight-dependent resistor (LDR) sensors that are located on the surface of the photovoltaic panel. Two servo motors have been employed to move the solar panel to a direction with maximum luminous intensity. Design and construction of a small prototype of ASTS is presented here to measured the efficiency over the fixed solar panel. 1. INTRODUCTION The solar PV energy is considered to be one of the most used and famous renewable green energies, which is apparently cleaner and free from production of harmful materials which degrades the environment [1]. Maximizing power output of a solar system is desirable to increase the efficiency.the solar panel are to be aligned properly with the sun in order to squeeze the maximum output from it [2]. Solar trackers are the most accurate and proven technology to increase the efficiency of solar panels. Solar trackers have become a popular means of harnessing solar energy around the world in recent times [3, 4]. Solar energy is widely available and completely free of cost except the cost of technology. Recently, PV systems are popular for utilization of solar energy in electric power applications. Being a semiconductor device, the PV systems are suitable for most operation at a lower maintenance costs which can convert sunlight directly into electricity without any intermitted stage. A typical equivalent circuit of a solar cell consists of a current source in parallel with a diode can be found in [5, 6]. From literature it is clear that development of smart solar tracker maximizes the energy generation. For traditional fixed solar panels the tilt angle is based on the location. The tilt angle depending on whether a slight winter or summer bias is preferred in the system. The PV systems would face true north in the northern hemisphere and true south in the southern hemisphere. Maximum solar tracking is possible when the tilt angle of the tracking PV systems is synchronized with the seasonal changes of the sun s altitude. The azimuth and the elevation angles of the sun were determined by solar movement models whereas control algorithms were executed in a microcontroller in accordance to a given date, time and geographical information of the site of installation [7, 8]. The main objective of this paper is to design the sun tracking solar PV system model which is a device that follows the movement of the sun independent of motor speed. Solar cell produces electricity direct from sun, so it is cheap source of electricity in remote areas. The output of photovoltaic cells is dependent on the intensity of sunlight and the angle of incidence. This paper represents a dual-axis ASTS with high efficiency. The dual-axis ASTS is entirely automatic and keeps the panel in front of sun until sun light is adequate to generate electricity. The unique feature of this system is that instead of taking the earth as its reference, it takes the sun as a guiding source. LDRs constantly monitor the sunlight to rotate the panel towards the direction where the intensity of sunlight is maximum and controlled by the microcontroller based control panel [9 16]. The proposed dual axis ASTS is shown in Fig 1. Fig. 1 Schematic diagram of dual-axis ASTS. 2. SYSTEM ANALYSIS OF DUAL-AXIS ASTS Perpendicular to the solar cell s exposed face is the normal to the cell. The striking angle of sunlight is shown in Fig 1. The angle between the incident sunlight to the normal is the angle of incidence θ. Assuming the sunlight is incident at a constant intensity of λ, the available sunlight to the solar cell for power generation W can be calculated as: W = Aλ sin θ. (1) Fig. 2 Angle of sunlight to PV cell. 1 University Institute of Technology, Department of Electrical Engineering, Burdwan, India, soumya.sd1984@gmail.com 2 Indian School of Mines (under MHRD, Govt. of India), Dhanbad, , India 3 WBUT, West Bengal, , India

2 384 Soumya Das et al. 2 Here, A represents some limiting conversion factor in the design of the panel because they cannot convert 100% of the sunlight absorbed into electrical energy. Assuming a linear relationship between light intensity and voltage produced, the resolution in angle the microcontroller can produce is: 1 1 V RES θ RES = cos VOC, (2) 2 VOC where V RES is the resolution voltage the microcontroller can produce. The angle between the backs of the panels is δ which means that the angle between the normal to the faces of the panels, denoted as β, is δ. If the angle of the sun to some reference point denoted as alpha α and V OC is the maximum approximate open circuit voltage of the solar panel, the voltage across solar panel can be ideally represented in an equation: ( ) V = 0.5V cos α+ β/ V [V]. (3) If the panel is placed in a direction such that it opposes to face towards the sun, then the voltage across solar panel can be ideally represented in an equation: V = 0.5V cos(α β/2) + 0.5V [V]. (4) To incorporate the angular position of the tracker p according to the same reference point as the sun, the equations were modified to be: V = 0.5V cos((α p) ± β /2) + 0.5V [V]. (5) Given that the earth rotates a full 360 in 24 hours in an east-to-west direction, the following equation can be given for the angle of the sun to the zenith of the point on the earth given in the east-west direction henceforth called the x direction: Zx ( t ) = (6) The variable t is the amount of time from midnight on the first day of the simulation in hours. To find an equation for the sun in the north-south direction, henceforth referred to the Y direction, the tilt of the earth s axis to its orbit around the sun is given at So as the earth orbits around the sun, the equator s Y angle to the sun goes from 0 at the vernal equinox to 23.5 at the summer solstice back to 0 at the autumnal equinox then to 23.5 at the winter solstice and finally back to 0 at the vernal equinox again. Given that this value fluctuates over the 365 day or 8760 hour, the angle to the zenith on the equator is given as: ZYequator ( t) = 23.5 sin 2π / (7) The time variable t is now the measure of hours from the midnight on the vernal equinox. However, because the point chosen might not be at the equator, the latitude also comes into effect. Positive latitude is the angle of the point specified on the earth s surface north of the equator. Negative latitude is consequently south of the equator. So to bring the latitude into the equation, Z Y is now the difference of the latitude angle, defined as φ, to the angle of the sun to the equator: ZY ( t) = φ 23.5 sin π / (8) Now that equations for the X and Y angle of the sun to the zenith of some point on the earth have been derived, the amount of available sunlight radiation to that point can be calculated. NASA defines this amount of radiation under perfectly sunny and clear conditions to be a function of the cosine of the angle of the sun to the zenith. So the radiation percent coming from both individual directions is defined as: ( ( )) ( ( )) R = cos( Z ) = cos 15 t 12 (9) X X R = cos( Z ) = cos φ 23.5 sin π / 4380t.(10) Y Y And then the total radiation of the sun hitting a point on the earth s surface at latitude Φ at time t in hours from midnight on the vernal equinox is: R = R R = cos(15 ( t 12)) T X Y cos( ϕ 23.5 sin( π / 4380t) ). (11) 3. PROPOSED SYSTEM CONFIGURATION This enables the solar panels to interface the tracker to obtain the maximum solar radiation. Since the focus of the experiment is on embedded software control, the microcontroller is the heart of the system. The total system depends upon a program in Arduino flashed in the microcontroller ATMEGA-8L. The microcontroller selected for this project had to be able to convert the analog photocell voltage in the digital values and provide 2 output channels to control the servo motor rotation. The design of ASTS is divided into two parts, hardware development and programming development. Block diagram of microcontroller and associated circuitry is shown in Fig. 3. Fig. 3 Block diagram of microcontroller and associated circuitry ELECTRICAL SYSTEM The electrical system consists of the PV cells, battery, four LDR sensors, the voltage regulator, microcontroller ATMEGA8L. LDR sensors sense the sunlight intensity and provide feedback to a microcontroller ATMEGA8L. This micro controller processes the sensor input and provides two PWM signals for the movement of servo motors. A 8 MHz crystal oscillator was also used to provide the necessary clock input. This speed is sufficient

3 385 An intelligent dual axis automatic solar tracking system 3 for the required applications. Total system configuration is shown in Fig 4. Fig. 4 Configuration of the proposed dual-axis ASTS LIGHT DEPENDENT RESISTORS MODEL For capturing maximum light energy four light dependent resistors (LDR) have been used. LDR is a resistor which shows negative temperature gradient, its resistance decreases with increasing light intensity or in short exhibits photoconductivity. The resistance of an LDR is extremely high. Once illuminated the light resistances will drop dramatically [17]. The main controller receives an analog input from the LDR. Figure 6 shows LDRs connected to PV panel SOLAR PANEL The PV cells are a device that helps to convert the solar energy into electrical energy. The solar panel selected is capable of generating 0.3 watt power. As the manufacturer specification, it weight about 10 g with a dimension of 60 mm 45 mm 3 mm. Table 1 Specification of PV panel Cell type Cristallyne silicon Cell number 10 Operating temperature 20 C to +60 C Maximum power (P max ) 0.3 watt Voltage at P max 5 V Current at P max 50 ma Short-circuit current (I sc ) 0.57 A Open-circuit voltage (V oc ) V 3.3. BATTERY This is because the amount of power the solar panel collects varies depending on the strength of sunlight. For a stand-alone or a grid fallback system batteries store the energy and provide a constant power source for the electrical equipment. Typically, this energy is stored in deep cycle lead acid batteries. The input voltage 9V DC is injected to the printed circuit board (PCB) after necessary stepping down from the adapter. This 9 V dc supply goes to 7805 voltage regulator from where the output 5 V dc spread to all logic circuitry. Figure 5 shows the circuit of power supply of the ATMEGA8L. Fig. 6 Light dependent resistors model. The internal analog-to-digital converter (ADC) compares the solar panel sensor voltage. The analog input from the light sensor goes to the ADC port of the microcontroller and the digital signal is displayed in the LCD display. 4. MOTORS Two servo motors have been used to move the solar panel at maximum light source location sensing by LDR. In order to accurately hold a position servo motors need a pulse every 20 ms. Micro controller gives two different PWM signal for the movement of solar panel through servo motor. The internal 512 KB EEPROM is used to maintain the compiled memory of microcontroller after the power goes out. The microcontroller Atmega8L is compiled with the help of Arduino. Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. 5. SOFWARE/SYSTEM OPERATION Fig. 5 Configuration of the proposed dual-axis ASTS. Programming language was utilized for the project. It is more than sufficient to assure design objectives while enriching the level of understanding of the programming language. In this paper the software operation is alienated into two parts. The first part is initial positioning prior to powering up the system; the photocell must be manually set to a zero point. The second part deals with the tracking of sun light. This is the heart of the program. When the tracker has set its primary position to sun light, it is ready to align itself more preciously and continue tracking the light. The total software operation is compiled in Arduino. This compiled program control the total hardware operation that is the tracker and the servo motor will rotate according to this program. The flow of the software procedure is shown in Fig. 7.

4 386 Soumya Das et al RESULTS AND DISCUSSION It is necessary to compare the experiment results of the fixed panel with the intelligent solar tracker system to know the acceptability of the proposed model. For preparing the experimental setup of dual-axis ASTS, 0.3 watt solar panel and two servo motors are used here and it is shown in Fig. 8. The required data are collected through performing simple experiment. The open-circuit voltages are recorded using a practical display (LCD) connected to the solar cells. A clear sunny day in the month of April (10 th April, 2015) is selected for performing the experiment. The average temperature recorded was around 36 C. At first, the system starts scanning the angle in which solar intensity is maximum and align it at the maximum solar intensity position. As the motor speed is very low, motor speed parameter can be neglected and the system only focuses on tracking of sun intensity. Fig. 7 The flow of the software procedure. Table 2 Experimental measured data table Fig. 8 Experimental set up of ASTS. The experiment results of the traditional fixed system and the designed dual-axis tracking system are shown in Table 2. In Fig. 9, it is observed from the plots, the solar tracker is able to follow the sun angle. In the plot, the smart solar tracker produces a higher power output as compared to the static PV panel. TIME OF DAY 9 AM 10 AM 11 AM 12 PM 1 PM 2PM 3 PM 4 PM FIXED AXIS SOLAR PANEL Voltage V 1 [V] Current I 1 [A] Power P 1 [W] DUAL AXIS SOLAR PANEL Voltage V 2 [V] Current I 2 [A] Power P 2 [W] % Increase in efficiency

5 387 An intelligent dual axis automatic solar tracking system 5 REFERENCES Fig. 9 Fixed and dual axis panel power comparison. The output power of the smart tracker was compared with the fixed panel design in order to determine the efficiency of the solar tracker system. As expected the overall efficiency generated by the tracking panel is higher than that of static panel. Here the efficiency in power of the dual axis tracker model compared to that of the fixed axis system: ( P1 P2 ) η = 100 %. P1 Therefore, the average increase in efficiency in power of the dual axis tracker model with respect to that of the fixed axis system: ( P1 P2). AVG η = 100 % P From Table 2, the average efficiency of intelligent solar tracker (obtained from experiment results) is increased up to 23 % weigh against to traditional fixed panel. As compared various other solar trackers as seen in [18], the average efficiency is around 15 to 19 % and hence, the proposed design is a little higher and comparable to the existing design. The experimental data show that at present a PV system is capable of supplying small amounts of energy required at a place that is far away from an electric grid or any other source of energy. Though this experimental setup is very small, but if it works for a smaller one, then this principle could be used in bigger panel. 7. CONCLUSION This paper presents the design and testing of a dualaxis smart solar tracker. The ASTS model is developed using microcontroller ATMEGA-8L. Based on the results obtained, it can be concluded that the system will react at its best because a maximum voltage is produced as compared with a traditional fixed system. In order to get maximum output regardless of motor speed, the system is made to track and follow the intensity of the sun. 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