Simulation and Implementation of Single Axis Solar TrackerA Single Axis Solar Tracker is a device that has a freedom of rotation along one axis while the other axis is at a fixed angle

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056

Volume: 07 Issue: 05 | May 2020 www.irjet.net p-ISSN: 2395-0072

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Simulation and Implementation of Single Axis Solar Tracker

Ayush Das1, Sankarshan Durgaprasad2

1Student, Dept. Electrical and Electronics, PES University, Bangalore, India 2Student, Dept. Electrical and Electronics, PES University, Bangalore, India

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Abstract – With the increase in global demand for clean energy, solar energy has become an increasingly popular mode of electricity generation due to its onsite generation capabilities and economic advantages as compared to its counterparts. However, as the name suggests, solar energy is dependent on the availability of sunlight and irradiance on the panel. The level of irradiance varies as the day progresses, this is due to the change in relative position of the panel with respect to the angle of incidence of the incoming light. Due to which stationary solar panels cannot completely harness the total available energy. One such method to increase the solar ray density onto the panel, in turn increasing the energy production, is through solar tracking. In this method, the PV panel follows the movement of the Sun throughout the day. Single axis solar tracker and Dual axis solar tracker are the two types of solar trackers. This paper presents a procedural approach in designing a Single Axis Solar Tracker and discusses in detail the Mathematical modelling, simulation, control and implementation of the same. Key Words: Solar Tracker, Azimuth Angle, PV Panel, Mathematical Modelling, Servo Motor, Transfer Function, Simulation.

1. INTRODUCTION According to the “Executive Summary Report on Power Sector” by the Ministry of Power, Government of India, the solar electricity generation stood at 3.93 TWh (The Kilo Watt Hours) [1] out of 98.76 TWh generated [2] or 3.98% as of December 2019. In addition to the present energy infrastructure and in accordance with the Paris Climate Agreement, Ministry of New & Renewable Energy (MNRE) the target for the year 2020 is at 227 GW [3]. With the foreseeable future projecting that the Government is investing in Solar and Renewable Energy its of utmost importance to develop and use systems that enhance the efficiency of the PV System. For maximum power to be harnessed by the PV panel, the angle incidence of solar rays should be perpendicular to the panel. This is however not possible to obtain in the case of stationary panels due to the change in the relative position between the Sun and the PV panel. Hence the angle of incidence of solar rays on the panel keeps varying. In order to maintain perpendicular irradiance a solar sracking mechanism is used. A solar tracker is used to align the position of the panel at an angle such that the irradiance is perpendicular to the PV

panel. Based on the axis of rotation a solar tracker can be defined as Single Axis Solar Tracker (SAST) or Dual Axis Solar Tracker (DAST).

1.1 Comparison between Single Axis Vs Dual Axis Solar Tracker A Single Axis Solar Tracker is a device that has a freedom of rotation along one axis while the other axis is at a fixed angle or flat. There are different types of Single Axis Solar Trackers these are,

Horizontal Single Axis Tracker Vertical Single Axis Tracker Tilted Single Axis Tracker Polar Aligned Single Axis Tracker

Fig -1: Single Axis Solar Tracker In Figure 1, α - is the fixed angle of the solar panel with the

horizontal. The angle is fixed at latitude of the location. The

Single Axis Solar Tracker moves from East to West during

the day. The average external power from a Single Axis Solar

Tracker is improved by (18-25%) as compared to the fixed

panel [4]. The solar tracker moves from East to West during

the day tracking the Solar Azimuth Angle. The Solar Azimuth

Angle is the Azimuth angle of the Sun’s position [5].

A Dual Axis Solar Tracker is a device that has freedom of

rotation along two axes. It consists of two axes, primary and

secondary. The primary axis can be considered as the

stationary axis in the SAST. The secondary axis is the axis

that tracks the Solar Azimuth Angle. Figure 2 shows solar

panel with two axes of freedom. The types of Dual Axis Solar

Trackers are,

Tip-Tilt Azimuth- Altitude

α




Fig -2: Single Axis Solar Tracker Dual Axis Solar Trackers have higher efficiencies than Single Axis Solar Trackers and work well even during overcast conditions as compared to Single Axis Solar Tracker [6].However, Dual Axis Solar Trackers have greater mechanical complexities and higher initial cost of investment. On account of the limitations of the Dual an Axis Solar Tracker, Single Axis Solar Tracker has been chosen. 1.2 Proposed Approach

Fig -3: Single Axis Solar Tracker

Figure 3 shows the proposed structure for the Single Axis Solar Tracker. The microcontroller will serve as the brain for the system, it will be responsible in adjusting the relative angle of the panel with respect to the Sun rays and the necessary feedback network data to compute further operations.

1.3 Mathematical Modelling

Fig -4: a) Schematic of DC Motor, b) Block diagram [7] A motor is an electromechanical device that yields displacement as the output for a given input voltage. A field is developed due to the presence of the stationary electromagnet as shown in Figure 4a. Where,

Ra is the Armature Resistance La is the Armature Inductance Ia is the Armature Circuit Current Ea is the Armature Voltage, Vb is the Back EMF Tb is the Torque due to the motor θm is the motor displacement

Since the voltage is proportional to speed in a current carrying armature rotating in a magnetic field we get,

-1

Where Kb is the proportionality constant. Applying Laplace

transform we get,

-2

By applying loop equation for the Laplace transformed

armature circuit we obtain,

-3

The torque urbanized by the motor (Tm) is proportional to

the current in the armature circuit,

-4

Where Kt is the torque constant. Substituting Equation 2

and Equation 4 in Equation 3 we obtain,

-5

Using equivalent mechanical loading on a motor we obtain

the relation,




-6

Where Jm and Bm are equivalent inertia at the armature

and viscous damping at the armature respectively.Using

Equation 6 in Equation 5 and obtaining the ratio between

the ratio of θm to Ea we attain the transfer function

(Equation 7) T(s)

-7

T(s) is represented as G(s) in Figure 4(b).Before proceeding

to the hardware development of the Single Axis Solar

Tracker, a mathematic simulation of the tracker is performed

using the motor transfer function as shown in Equation 7.

This approach is taken to understand and predict the

hardware prior to its implementation. This helps identify

any deviation from the rated characteristics of the Servo

Motor as provided by manufacturer.

2. Single Axis Solar Tracker Simulation

This section will show the simulation of the solar tracker. Prerequisites of simulation involve the constant calculation of the Servo Motor. All Simulations related to the Mathematical Model is conducted on MATLAB Simulink 2020a.

2.1 Servo Motor Constants The weight of the Panel is 3.4Kg. Based on this Servo Motor – “Tower PRO MG996 R” has been chosen. The rated torque of the servo motor is 11kg-cm (6 v). Table 1 depicts the various constants of the Servo Motor calculated from the tests performed on the motor.

Table -1: Servo Motor Constants

MG996 R Servo Motor Constants

SL No. Constant Value Dimension

1 Resistance (Ra) 2 Ohm

2 Inductance

(La)

1.134 x 10-3 Henry

3 Inertia (Jm) 5.5 x 10-3

Kg-m2

4 Viscous Damping (Bm)

0.154 N-

m/rad/sec

5 Back Emf Constant (Kb)

0.537 Volt-sec/rad

6 Torque Constant (Kt)

0.7707 N-

m/Ampere

2.2 Simulation of Servo Motor

Fig -5: Transfer Function Modelling of DC Servo Motor

Figure 5 represents the transfer function model of a DC Servo Motor. 6 Volts DC input has been provided to the transfer function model. The output of the model is 6.41 rad/sec and has an initial overshoot that reaches 6.75 rad/sec. The rated speed of the Servo Motor provided by the manufacturer is 6.34 rad/sec.

Fig -6: Servo Motor transfer function output (Rad/s)

Figure 6 shows the output of the transfer function model without passing through the integrator. The output is in radians per sec. Figure 7. Shows the output of the transfer function model as it is passed through the integrator giving position of the motor in radians.

Fig -7: Servo motor transfer function output (Rad)




2.3 Simulation of Modelled SAST

The single axis solar tracker is responsible to ensure that the PV panel follows the solar azimuth angle. Therefore, a collection of the solar azimuth angle has been made for the location 12.9716° N, 77.59° E.

Fig -8: Servo motor transfer function output (Rad)

Figure 8 shows the solar azimuth angle between sunrise and sunset. With time t = 0 being time of sunrise (6:20 am) and t = 720 being (6:20 pm) being time of sunset for 17th April 2020. The Y axis represents the Azimuth angle where 0 degrees represents the Sun’s position at noon i.e., right above the surface. The Azimuth Angle starts at -100.17° which represents East and finishes at +99.97° W. Each second of the simulation is considered as a minute.

Fig -9: Simulation Model of SAST on Simulink

Figure 9 shows the simulation model of the single axis solar tracker. The tolerance for change in voltage is set to ± 0.3 V (difference in voltage between the two LDR pairs) this reflected for approximately 10-degree change in the position off the Sun. The state chart (Figure 10) consists of the “Stationary State” where the panel is stationary i.e. the error voltage is within the limits of ± 0.3V. “Panel_Moves_1” is the state where the error voltage is +0.3 V this is the movement of the panel from East to West. “Panel_Moves_2” is the state where the error voltage is -0.3V. This movement is from West to East, the controller comes to this state under certain events such as cloudy weather, from night to day where the panel moves back to its original position.

Fig -10: State chart for Microcontroller logic

2.4 Simulation Result of Single Axis Solar Tracker

Figure 11 shows the panel position and the suns position in terms of Azimuth angle.

Fig -11: Panel and Sun Position in Degrees

Fig -12: Error voltage vs Time

Figure 12 shows the error voltage (Difference in LDR pair voltages) vs Time.




Table -2: Azimuth Angle Comparison

Solar Azimuth Angle and Position Detected By Solar Tracker

Time Solar Panel |Error|

6:20 am -100.17° -100°

0.17°

8:20 am -94.61° -100° 5.39°

10:20 am -88.07° -86.01 2.06°

12:20 pm 4.35° 5.79° 1.44°

2:20 pm 89.98° 87.86° 2.12°

4:20 pm 95.05° 96.01° 0.96°

6:20 pm 102.26° 99.87° 2.39°

Table 2 shows the Azimuth angle comparison between the Sun and the Azimuth angle detected by the solar panel. Based on the results it is observed that the error voltage is within 10 degrees. This model will be used to design the physical model.

3. Single Axis Solar Tracker Hardware Aspects This section will focus on the hardware approach in designing and implementing the Single Axis Solar Tracker. 3.1 Hardware Components used

The following components were used for the functioning of the Single Axis Solar Tracker

Arduino Uno R3 (Micro Controller)

MG996 R Servo Motor

9V Battery or Power Bank

6V DC Power Supply (For the Servomotor)

2 pair of 5(2x5) LDR (Photoresistors)

Solar Panel

Connecting Wires

3.2 Hardware Simulation of the Single Axis Solar Tracker

In the below figures 13,14,15, a simulated model of the mechanical structure designed on Blender is made so that the structure will be able to support a Solar Panel of weight 3.4kg and 43cm X 66.5 cm in dimensions.

Fig -13: General view of simulated Structure

Fig -14: Front view of SAST

Fig -15: Side view of SAST

3.3 Hardware Implementation and Algorithm

Design of Single Axis Solar Tracker

Fig -16: Algorithm Flowchart




Arduino Uno R3 is used as the controller, brain, of the system. It is expected to handle every logical operation needed by the system as shown in Figure 16.

The LDRs form an integral part of the Solar Tracker, as they provide data fed back to the microcontroller for better and more accurate adjustments to the panel.

The LDRs (First set of 5 LDR’s are represented as LDR1 and the second set of 5 LDR’s are represented as LDR2 in Figure 17) are placed on the opposite edges of the Solar panel which are then connected in series as shown in figure 17.

Fig -17: Algorithm Flowchart

The difference in voltage drop (Error) between each LDR is read by the microcontroller, as the feedback data. Logically, the voltage drops between the two pair LDR’s (LDR1 is first set 5 of LDR’s and LDR2 in the second set of 5 LDR’s in Figure 17) must be the same, which means that the panel is in the most ideal position. If the Error Voltage is not within the threshold value then the side of the panel which has a lower LDR voltage drop has more sunlight. Hence the microcontroller is be programmed such that servomotor turns to equalize the voltage drops between the two LDR pairs. Note that all LDRs are not identical so a calibrated threshold should be tested and validated. In this system, as mentioned earlier the threshold was found to be 0.3V.

Fig -18: Physical Structure

Using the above simulated models as a reference the physical structure is fabricated, as shown in figure 18.

4. Conclusion In this paper the need and advantages of a Solar Tracker in a PV System has been presented. Accounting the differences and the limitation of a Dual Axis Solar Tracker, a Single Axis Solar Tracker has been chosen. A holistic approach has been followed and proposed to construct a Single Axis Solar Tracker. Simulation of the mathematical model has been performed on MATLAB Simulink 2020a to verify and predict the behavior of the system. 3D Modelling software Blender has been used to conceptualize the mechanical design based on which the physical model was constructed. This approach yields a stable and an accurate Single Axis Solar Tracking system.

ACKNOWLEDGEMENT We would like to express our gratitude towards Associate Professor Sushmita Deb, Department of Electrical and Electronics Engineering, PES University who has guided us throughout the course of this work.

REFERENCES [1] Ministry of Power, Government of India, “Executive

Summary on Power Sector”, January-2020 pg.6.

[2] Ministry of Power, Government of India, “Executive Summary on Power Sector”, December-2019 pg.5.

[3] Government of Gujarat, Renewable Energy Sector Profile, pg.3.

[4] Akbar, Hussain & Fathallah, Muayyad & Raoof, Ozlim. (2017). Efficient Single Axis Sun Tracker Design for Photovoltaic System Applications. IOSR Journal of Applied Physics. 09. 53-60. 10.9790/4861-0902025360.

[5] Sukhatme, S. P. (2008). Solar Energy: Principles of Thermal Collection and Storage (3rd ed.). Tata McGraw-Hill Education. p. 84. ISBN 978-0070260641

[6] R, Dhanabal & Bharathi, V. & Ranjitha, R. & Ponni, A. & Deepthi, S. & Mageshkannan, P.. (2013). Comparison of efficiencies of solar tracker systems with static panel single-axis tracking system and dual-axis tracking system with fixed mount. Intern. J. Eng. Technol.. 5. 1925-1933.

[7] Norman S.Nise, Control Systems Engineering, 7th Edition Pg.78 Fig.2.35.

https://en.wikipedia.org/wiki/ISBN_(identifier)

https://en.wikipedia.org/wiki/Special:BookSources/978-0070260641

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Simulation and Implementation of Single Axis Solar TrackerA Single Axis Solar Tracker is a device that has a freedom of rotation along one axis while the other axis is at a fixed angle