The Functionality Of The Solar Tracker Engineering Essay

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A movement of the solar tracker where only one axis of movement is covered when moving to ensures the perpendicularity to the sun. The axis covered is whether horizontal or vertical axis. In this method, the location for the solar tracker must first be identified when to setup or construct it. This is because the solar tracker's movement could only covers one axis. If the location and placement of the solar tracker is incorrect, it will be difficult for the solar tracker to keeps its solar panel position perpendicular to the sun.

However, single axis movement is easy to design and developed because it only needed a system for one axis movement. So, to ensure the most optimized from a single axis movement, the tracker's axis must be parallel to earth's axis [1].

Figure 2 - Single axis movement; horizontal (left) & vertical (right) [2]

The single movement method had been used by Tiberiu Tudorache and Liviu Kreindler in their project for Design of a Solar Tracker System where the horizontal axis of the tracker is controlled and the vertical axis is fixed.

Figure 2 - Single axis horizontal movement [3]

2.1.2 2-axis Movement

2-axis movement is tracking system that maintains the solar panel's positions perpendicular to the sun by moving vertically and horizontally. Usually, the control system used for sun tracking is programmable controller, sensors, microprocessors and GPS to ensure accurate movement. To move the solar panel, motors are used. 2-axis movement is quite complex to build because it requires algorithms to linked between the solar movement and rotational adjustment of the solar panels [1].

Figure 2 - Vertical and horizontal 2-axis movement [2]

In 2010, a project of Simplified Solar Tracking Prototype by Nader Barsoun and Pandian Vasant had applied the method of 2-axis movement. To move the solar panel vertically and horizontally to track the sun, photocell was used.

Figure 2 - 2-axis movement method [4]

2.2 Solar Panel Movement Mechanism

Movement mechanism is how the solar tracker will be moved mechanically whether the solar tracker is using single axis or 2-axis movement. The movement mechanism will consist of a motor to drive the movement.

2.2.1 Motor

There are many motors that could be used to drive the movement for solar tracker, the motors that had been used in past projects is stepper motor, stepper motor and 12V DC motor. There are advantages and disadvantages of every type of these motors.

In a project of PIC Based Automatic Solar Radiation Tracker by Romy Kansal in 2008, unipolar stepper motor was used. Stepper motor was used because it not a complex motor since there are no brushes and contacts, low cost, high reliability, high torque at low speeds and high accuracy of motion. However, there are some drawbacks of stepper motor that is if it not controlled properly resonances could occurred and it is also not easy to operate at extremely high speeds. [7]

Figure 2 - Schematic of 2-phase (winding) unipolar Stepper motor [7]

In addition, servomotor also had been used by M. Fazman in his project of Design and Development of a Solar Tracking System in May 2010. Servomotor is a device that could position its shaft to a specific angular position by using a coded signal. The servo will maintain its position of the shaft if the coded signal is continuously given to the servo. The shaft's position wills only changes when the coded signal given is changed. Other advantages are the motor is small, have built in control circuitry and have quite powerful force for its small size [8].

However, stall torque of the servo could be a problem in designing the hardware. This is where the servomotor could not handle and support a load with a large weight [8].

Figure 2 - Example of servomotor [8]

2.3 Sun Position Detecting Method

Another important part for a solar tracker is a sensor to detect the sun position. It is very vital because this is the part that tells the microcontroller the position of the sun. Based on several research that had been done by other researchers, the most commonly used component for a photosensor is a Cadmium Sulfide (CdS) and Gallium arsenide (GaAs) photocell [4] and a shade [9].

The photocell was used because it is a passive component that its resistance react inversely proportional to intensity of light given to it. Based on its dark resistance and light saturation resistance, the photocell is used as a tracker to detect sun movement [4]. The use of photocell alone is not enough; it also needs shader to blocks sunlight from reaching the undesired photocell due to sun position. The used of shader could help the sensor to detect the sun movement more accurately.

Figure 2 - The use of shader in photosensor [9]

2.4 Control System

A control system is a brain to this project, the main purpose is to receive and processes input data from sensors and processed it. After the all data were processed, it will give output and move the mechanism for the solar panel to be accurately perpendicular to the sun position. One of the most used control system is microcontroller PIC16F877A where it was widely used in automotive, industrial, appliances and consumer applications. PIC16F877A uses Harvard architecture that seperates data bus and address bus that made the flow of data faster and also makes it possible for instructions not have to be 8-bit words. The uses of 14 bits in PIC16F877 for instructions allow all instructions to be one word instructions. The key advantage for this architecture is that while a command is being executed the next can be fetched and this ability could double the execution process [7].

Figure 2 - Harvard architecture used in PIC16F877A [7]

From the capabilities of PIC16F877A, it is very suitable as a control system and development of the project.

2.5 Parabolic Dish Collector

Parabolic dish collector is one of the main types of concentrating solar collector. The structure of this solar collector is quite the same to a large satellite dish. However it uses mirror-like reflectors and a receiver at the focal point. This type of solar collector requires a control system and 2-axis movement tracker to trail the sun movement and concentrate the sunlight onto the receiver. In some applications, a heat engine, such as a Stirling engine, is used as a receiver to generate electricity. Parabolic dish systems can reach temperature of 1000°C at the receiver, and achieve the peak efficiencies for converting solar energy to electricity in the small-power capacity range [10].

Figure 2 - Parabolic dish collector [10]

So, this type of solar device structure is suitable for this project, where it could be implement with the tracking system. Most importantly, it could focus the sunlight at one specific point to increase the sunlight's intensity.

2.6 Law of Reflection

In order to reflect and focus sunlights to a specific point, the properties of sunlight as a light must be known. One of the common properties of lights is its behavior to reflect on a predictable angle that known as law of reflection. The law of reflection is illustrates as figure below:

Figure 2 - Law of reflection [11]

(2.1)

The normal line in the middle separates the angle between the incident ray and the reflected ray into two equal angles. The angle between the incident ray and the normal is known as the angle of incidence (θi). The angle between the reflected ray and the normal is known as the angle of reflection (θr) [11].

2.7 Literature Survey Comparison

Table 2 - Literature survey comparison

NO.

THESIS/ JOURNAL/ REPORT

AXIS OF MOVEMENT

CONTROL SYSTEM

SOLAR PANEL MOVEMENT MECHANISM

SUN POSITION DETECTING METHOD

ADVANTAGES (+) / DISADVANTAGES (-)

1

PIC Based Automatic Solar Radiation Tracker

Not mentioned

PIC16F877A microcontroller

Stepper motor

Solar cell module act as sensor (circuit current measured to determine sun position)

+ Using microcontroller that is easy an commonly used to program and control the system.

- Using solar cell module as sun detecting method is not very effective and hard to control.

2

Design of a Solar Tracker System for PV Power Plant

Single axis (adjustable horizontal axis, fixed vertical axis)

Light detector to determine sunlight intensity

12V DC motor

Main tracker (10mm clear LEDs) and front detector (5mm red LED)

+ Using 12V DC motor gives enough torque to move heavy load ( large solar panel)

- Using just light detector (LED) to control the system is not very reliable because LED is sensitive to light despite its intensity. So, sun positions is not accurately determined

3

Design of a Solar Tracker System for PV Power Plant

Single axis

Intelligent drive unit IBL2403

DC motor

Two luminescent LED with shader

+ DC motor could be used for high load because of its high torque

- Intelligent drive unit IBL2403 as its control system uses high level language TML (Technosoft Motion Language) and it is not commonly used.

4

Simplified Solar Tracking Prototype

2-axis

PIC16F84A microcontroller

12V DC motor

Cadmium sulfide (CdS) and gallium arsenide (GaAs) photocell with shader

+ Using microcontroller that is easy an commonly used to program and control the system.

- cannot detects sun's position accurately because uses only two photo sensor.

5

The Solar Tracking System by Using Digital Solar Position Sensor

2-axis

Digital and logic theory application

12V DC motor

Six phototransistor with parabolic shader

+ Could detect sun position accurately because uses 6 phototransistor with parabolic shader

- Using digital and logic theory application as the control system is not very effective because it is nor programmable and the circuit need to be changed if adjustment is needed

6

Design And Development Of Solar Tracking

2-axis

PIC18F452

Servo motor

Light sensor (CdS) with shader

+ Uses fast and reliable control system

- The used of servo motor for movement mechanism to both axis is not very suitable. The axis with more load requires motor with higher torque.

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