14-08-2012, 12:56 PM
Solar Tracker
[attachment=31453]
Abstract
Solar energy is rapidly gaining notoriety as an important means of expanding renewable
energy resources. As such, it is vital that those in engineering fields understand the
technologies associated with this area. My project will include the design and
construction of a microcontroller-based solar panel tracking system. Solar tracking
allows more energy to be produced because the solar array is able to remain aligned to
the sun. This system builds upon topics learned in this course. A working system will
ultimately be demonstrated to validate the design. Problems and possible improvements
will also be presented.
1. Introduction
Renewable energy solutions are becoming increasingly popular. Photovoltaic (solar)
systems are but one example. Maximizing power output from a solar system is desirable
to increase efficiency. In order to maximize power output from the solar panels, one
needs to keep the panels aligned with the sun. As such, a means of tracking the sun is
required. This is a far more cost effective solution than purchasing additional solar
panels. It has been estimated that the yield from solar panels can be increased by 30 to
60 percent by utilizing a tracking system instead of a stationary array [1]. This project
develops an automatic tracking system which will keep the solar panels aligned with the
sun in order to maximize efficiency.
This paper begins with presenting background theory in light sensors and stepper motors
as they apply to the project. The paper continues with specific design methodologies
pertaining to photocells, stepper motors and drivers, microcontroller selection, voltage
regulation, physical construction, and a software/system operation explanation. The
paper concludes with a discussion of design results and future work.
2. Background Information
This section presents background information on the main subsystems of the project.
Specifically, this section discusses photocell and stepper motor theory in order to provide
a better understanding as to how they relate to the solar tracker.
2.1. Light Sensor Theory
Light sensors are among the most common sensor type. The simplest optical sensor is a
photoresistor which may be a cadmium sulfide (CdS) type or a gallium arsenide (GaAs)
type [2]. The next step up in complexity is the photodiode followed by the
phototransistor [2].
2
The sun tracker uses a cadmium sulfide (CdS) photocell for light sensing. This is the
least expensive and least complex type of light sensor [2]. The CdS photocell is a passive
component whose resistance in inversely proportional to the amount of light intensity
directed toward it. To utilize the photocell, it is placed in series with a resistor. A
voltage divider is thus formed and the output at the junction is determined by the two
resistances. Figure 1 illustrates the photocell circuit. In this project, it was desired for
the output voltage to increase as the light intensity increases, so the photocell was placed
in the top position.
2.2. Stepper Motor and Driver Theory
Stepper motors are commonly used for precision positioning control applications. All
stepper motors possess five common characteristics which make them ideal for this
application. Namely, they are brushless, load independent; have open loop positioning
capability, good holding torque, and excellent response characteristics. [3].
There are three types of stepper motors: permanent magnet, variable reluctance, and
hybrid [3]. The arrangement of windings on the stator is the main distinguishing factor
between the three types [3]. Permanent magnet motors may be wound either with
unipolar or bipolar windings [3].
The sun tracker uses a unipolar step motor. As such, discussion will be limited to this
type of stepper motor. Unipolar motors have two windings with each having a center tap
as shown in Figure 2 from [4].
3
Figure 2 – Unipolar Stepper Motor Coils
The center taps are connected to a positive voltage while the coil ends are alternately
grounded to cause a reversal of the field direction in that winding [3]. Figure 2 shows a
4-phase motor. The number of phases is equal to two times the number of coils. The
motor is rotated by applying power to the windings in a sequence as shown in Figure 3
from [4].
Figure 3 – Standard Drive Sequence Example
The motor may also be half-stepped. Half-stepping is achieved by first energizing one
coil, then two coils, then one coil, etc., in a sequence as shown in Figure 4 from [4]. This
project utilizes half-stepping and is further discussed in Section 3.5.
4
Figure 4 – Half-Step Drive Sequence Example
Lastly, a control circuit is needed to drive the stepper motor. The basic control circuit for
a unipolar stepper motor is shown in Figure 5 from [3]. The motor driving circuit
specific to this project is explained in Section 3.5.
Figure 5 – Unipolar Motor Control Circuit
3. Project Design Methodology
This section will discuss the methodology involved in the design of the solar tracker. The
project was divided into parts to make the design process modular. The project consists
5
of reading a series of light sensor values, comparing them, and then positioning a motor
to align with the greatest value which corresponds to the sun’s position. Follow-on
sections discuss hardware and software design considerations.
3.1. Light Sensor Design
As presented in Section 2.1, the sun tracker uses a CdS photocell for light detection. A
complementary resistor value of 10 KΩ was used to construct the circuit shown in Figure
1 in Section 2.1. In this configuration, the output voltage will increase as light intensity
increases.
The complementary resistor value should be chosen such as to achieve the widest output
range possible. Photocell resistance was measured under dark conditions, average light
conditions, and bright light conditions.
[attachment=31453]
Abstract
Solar energy is rapidly gaining notoriety as an important means of expanding renewable
energy resources. As such, it is vital that those in engineering fields understand the
technologies associated with this area. My project will include the design and
construction of a microcontroller-based solar panel tracking system. Solar tracking
allows more energy to be produced because the solar array is able to remain aligned to
the sun. This system builds upon topics learned in this course. A working system will
ultimately be demonstrated to validate the design. Problems and possible improvements
will also be presented.
1. Introduction
Renewable energy solutions are becoming increasingly popular. Photovoltaic (solar)
systems are but one example. Maximizing power output from a solar system is desirable
to increase efficiency. In order to maximize power output from the solar panels, one
needs to keep the panels aligned with the sun. As such, a means of tracking the sun is
required. This is a far more cost effective solution than purchasing additional solar
panels. It has been estimated that the yield from solar panels can be increased by 30 to
60 percent by utilizing a tracking system instead of a stationary array [1]. This project
develops an automatic tracking system which will keep the solar panels aligned with the
sun in order to maximize efficiency.
This paper begins with presenting background theory in light sensors and stepper motors
as they apply to the project. The paper continues with specific design methodologies
pertaining to photocells, stepper motors and drivers, microcontroller selection, voltage
regulation, physical construction, and a software/system operation explanation. The
paper concludes with a discussion of design results and future work.
2. Background Information
This section presents background information on the main subsystems of the project.
Specifically, this section discusses photocell and stepper motor theory in order to provide
a better understanding as to how they relate to the solar tracker.
2.1. Light Sensor Theory
Light sensors are among the most common sensor type. The simplest optical sensor is a
photoresistor which may be a cadmium sulfide (CdS) type or a gallium arsenide (GaAs)
type [2]. The next step up in complexity is the photodiode followed by the
phototransistor [2].
2
The sun tracker uses a cadmium sulfide (CdS) photocell for light sensing. This is the
least expensive and least complex type of light sensor [2]. The CdS photocell is a passive
component whose resistance in inversely proportional to the amount of light intensity
directed toward it. To utilize the photocell, it is placed in series with a resistor. A
voltage divider is thus formed and the output at the junction is determined by the two
resistances. Figure 1 illustrates the photocell circuit. In this project, it was desired for
the output voltage to increase as the light intensity increases, so the photocell was placed
in the top position.
2.2. Stepper Motor and Driver Theory
Stepper motors are commonly used for precision positioning control applications. All
stepper motors possess five common characteristics which make them ideal for this
application. Namely, they are brushless, load independent; have open loop positioning
capability, good holding torque, and excellent response characteristics. [3].
There are three types of stepper motors: permanent magnet, variable reluctance, and
hybrid [3]. The arrangement of windings on the stator is the main distinguishing factor
between the three types [3]. Permanent magnet motors may be wound either with
unipolar or bipolar windings [3].
The sun tracker uses a unipolar step motor. As such, discussion will be limited to this
type of stepper motor. Unipolar motors have two windings with each having a center tap
as shown in Figure 2 from [4].
3
Figure 2 – Unipolar Stepper Motor Coils
The center taps are connected to a positive voltage while the coil ends are alternately
grounded to cause a reversal of the field direction in that winding [3]. Figure 2 shows a
4-phase motor. The number of phases is equal to two times the number of coils. The
motor is rotated by applying power to the windings in a sequence as shown in Figure 3
from [4].
Figure 3 – Standard Drive Sequence Example
The motor may also be half-stepped. Half-stepping is achieved by first energizing one
coil, then two coils, then one coil, etc., in a sequence as shown in Figure 4 from [4]. This
project utilizes half-stepping and is further discussed in Section 3.5.
4
Figure 4 – Half-Step Drive Sequence Example
Lastly, a control circuit is needed to drive the stepper motor. The basic control circuit for
a unipolar stepper motor is shown in Figure 5 from [3]. The motor driving circuit
specific to this project is explained in Section 3.5.
Figure 5 – Unipolar Motor Control Circuit
3. Project Design Methodology
This section will discuss the methodology involved in the design of the solar tracker. The
project was divided into parts to make the design process modular. The project consists
5
of reading a series of light sensor values, comparing them, and then positioning a motor
to align with the greatest value which corresponds to the sun’s position. Follow-on
sections discuss hardware and software design considerations.
3.1. Light Sensor Design
As presented in Section 2.1, the sun tracker uses a CdS photocell for light detection. A
complementary resistor value of 10 KΩ was used to construct the circuit shown in Figure
1 in Section 2.1. In this configuration, the output voltage will increase as light intensity
increases.
The complementary resistor value should be chosen such as to achieve the widest output
range possible. Photocell resistance was measured under dark conditions, average light
conditions, and bright light conditions.