Post on 05-Apr-2018
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The Sun Seeker
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Table of Contents
Chapter no. Description Page no
0. Synopsis
1. Introduction
2. Theory Of Operation
3. Block Diagram
4. Circuit Diagram
5. List Of Components
6. Testing And Analysis
7. Conclusion
8. Bibliography
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Synopsis
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SOLAR SUN SEEKER
The aim of our project is to overcome the second problem associated with the use of solar energy as
mentioned earlier. For this a Digital based automatic sun tracking system is proposed. This project
helps the solar power generating equipment to get the maximum sunlight automatically thereby
increasing the efficiency of the system. The solar panel tracks the sun from east to west automatically
for maximum intensity of light.
OBJECTIVE
a) To fabricate a DC motor control card interfaced with driver circuit.
b) To construct a model prototype solar cell movement system with a mechanical assemble to move
the panel from 1800 E to W.
c) To design an electronic circuit to sense the intensity of light and to control DC motor driver for thepanel movement.
d) To construct an emergency light inverter circuit i.e. to operate tube light with the help of charged
battery from the solar panel.
INTRODUCTION
Energy plays a vital role in almost all the areas of human life. Energy is required to sustain andimprove the standard of living. In the present machine age we just cannot imagine life without energy.
Today, every country draws its energy needs from a variety of sources.
All energy sources are of consuming nature. For example, thermal power generating station consumes
coal in huge quantities, or it may consume fuel at numerous liters. Hydraulic power station would not
need raw material, but need water flow; it depends completely on water flow. So when there is no
flow of water at required level this station is of no use. The coal or fuel used in thermal power station
creates environment pollution by leaving toxic gas output. Then all of these power stations need lot of
mechanical sections like turbine and etc. to get power. Even windmills also need mechanical section
to produce power.
THE SOLAR OPTION
Solar energy is a very large, inexhaustible source of energy. The power from the sun intercepted by
the earth is approximately 1.8*1011MW, which is many thousands of times larger than the present
consumption rate on the earth of all commercial energy sources. Thus in principle, solar energy could
supply all the present and future energy needs of the world on a continuing basis. This makes it one of
the most promising of the unconventional energy sources. In addition to its size, solar energy has two
other factors in the favour. Firstly, unlike fossil fuels and nuclear power, it is environmentally clean
source of energy. Secondly, it is free and available in adequate quantities in almost all parts of the
world where people live. Also it has no heavy mechanical section and is free from noise.
However, there are many problems associated with its use, the main problem is that it is dilute source
of energy. Even in the hottest regions on the earth, the solar radiations flux available rarely exceeds 1KW/m, which is a low value for technological utilization.
The second problem associated with the use of solar energy is that its availability varies widely with
time. The variation in availability occurs daily because of the day night cycle and also seasonally
because of the earths orbit around the sun.
To rectify these above problems the solar panel should be such that it always receives maximum
intensity of light. For existing solar panels, which are without any control systems typical level of
efficiency varies from 10% to 4% - a level that should improve measurably if the present interest
continues.
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BLOCK DIAGRAM
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COMPONENT LIST
1) IC
2) DC Motor
3) Solar Cell
4) Power Supply
5) Inverter
6) Battery
DETAILED DESCRIPTION
SOLAR PANEL: -
A solar cell uses the photovoltaic effect to convert radiation from the sun into electrical energy. The
photovoltaic effect arises when a junction between a metal and a semiconductor or two opposite
polarity semiconductors is exposed to electromagnetic radiation, usually in the range near ultra violate
to infrared. A forward voltage appears across the illuminated junction and power can be delivered
from it to an external circuit. The p-n junction of whom the cell consists has a relatively large surface
area and relatively high efficiency (10.... 15 per cent). Solar cells are fabricated mainly from silicon,
gallium arsenide, selenium-cadmium sulphide, and thin-film cadmium sulphide. As part of theradiation is reflected by the surface of the cell, an anti-reflect layer is incorporated to minimize
reflection. The absorption coefficient is large for short wavelengths, and smaller for longer
wavelengths. The efficiency of solar cells reduces by about one half per cent for each degree
centigrade rise in their body temperature, so that most cells must be suitably cooled. Note, however,
that this depends to a large extent on the material; gallium arsenide/gallium phosphide, for instance,
has optimum efficiency at well over 100C . The spectral response curve of a silicon cell indicates a
useful range of wavelengths between 0.5m and 1.0m, peaking at about 800m.
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Chapter 1
Introduction
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Motivation for the Research
Probably the biggest concern with conventional energy sources is the amount of pollutants that are
released into the atmosphere. These growing concerns over the environmental changes caused by
power generation with conventional energy sources has lead to the need for developing an alternative
energy source; one that is highly efficient and pollution free.
The most common method of electrical power generation uses fossil fuels such as coal. However, the
burning of fossil fuels releases CO gas which has been directly 2 associated with global warming
due to the greenhouse effect. Photovoltaics represent one of the few energy generation options that do
not create pollutants or hazardous wastes [2].
Other factors that increase the appeal of solar energy as an alternative energy source are the high
reliability of solar cells, the steadily improving performance and decreasing manufacturing costs of
solar cells, and the fact that there is no fuel cost for the cells.
Justification for the Research
Before solar energy can be used as an alternative source of energy for the worlds everincreasing requirements, the efficiency of solar cells must be increased. Currently the average
efficiency of a normal sized solar (photovoltaic) cell is only adequate enough to power small
commercial devices, eg. calculators and toys. In order to supply enough power to operate larger
devices, larger solar cell arrays are required. These are typically too large, and therefore
unfeasible, for the application.
Instead of increasing the size of the array, it is more beneficial to increase the performance of
the solar cell. The overall performance (amount of solar power that can be collected) of solar
cells can be attributed to these two main factors: 1) the efficiency of the cell and 2) the intensity
of the source radiation on the cell.
The materials used in the manufacture of solar cells are the biggest factors that limit the cell
efficiency. This makes it difficult to improve the efficiency of the cell, and hence restricts the
overall performance of the cell. However, it is an easier process to increase the amount of source
radiation that is received at the cell.
There are three methods that can be implemented to increase the intensity of solar radiation
received by a solar array. These are:
Focusing the suns incident rays onto a rigid array
Tracking the suns path using fixed control algorithms Tracking the suns path using a dynamic tracking system
Sun-Tracking Techniques
When tracking objects, which are moving in the sky, there is a number of tracking techniques that can
be used. The two most common techniques which can be used for tracking objects, such as the sun, are
the:
Fixed control algorithm method
Dynamic methodThe main difference between these two methods is the way the position of the sun is determined. The
fixed control algorithm method determines the path of the sun by referencing an algorithm that
calculates, for each time period, the position of the sun.
This method does not actually find the sun in the sky, but instead works out the position of the sun
from specific, given data. This data is usually the current time, day,month and year.
The dynamic method is a system that actually finds the position of the sun based on sensory input. That
is, data from light sensitive sensors is used such that the system can actively find the sun. Since the
sensory data is continuous, the system can follow (track) the suns movement across the sky.
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Definition of the Research Project
The definition of this thesis is the design of a Sun-Tracking Solar Cell Array System .The concise
definition of the system is a microprocessor-controlled array that actively tracks the suns movement,
such that maximum power is received at the array at all times. This is achieved by using light sensitivesensors to determine the position of the sun, and then using motors, controlled by a 68HC11
microprocessor, to align the array such that all incident rays strike normal to the arrays surface.
Previous Work in this Area
This thesis is the continuation of the work performed by Elliot Larard in 1998. Larards design was
focused towards the development of a dynamic tracking system, ie. One that actively finds the sun
by use of light sensitive sensors. On the whole, the work performed by Larard was of a solid standard,
with a working prototype being developed (on breadboard) by the end of 1998. However, there were a
number of design flaws in his system that effected the overall performance (both efficiency andaccuracy of the system).
The previous system worked on the principle of two independent motors controlling the position of the
array. As can be seen from Figure 1.1 Larards system used the 1 st motor to control the tilt of the
array, while the 2 nd motor controlled the rotation of the array.
Figure
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The design of the sensor array was particularly good. The design consisted of a four sided pyramid
structure, which had a solar cell mounted on each side, to determine the position of the sun. Figure 1.2
shows the final design.
Aim of the PROJECT New Work in this Area
As mentioned in the previous section, the performance (efficiency and accuracy) of the system designed
by Larard (1998) was not up to optimal standard. The aim of the thesis this year (1999) is to redesign
aspects of the previous dynamic system such that the performance of the system is increased.
Throughout this report the term system performance includes the following:
The accuracy of positioning the array such that the suns rays strike
normal to the array.
The efficiency of the code which controls the positioning system.
The efficiency of solar cells as sensory devices.
Power consumption of the system.
Probably the biggest flaw of the previous system was the design of the positioning section. Larards
system ( Figure 1.1 ) used a two motor technique to position the array. The 1 st motor was used to
control the tilt of the array, while the 2 nd motor controlled the rotation of the array. As will be
discussed in the Chapter 3 (Methodology and Design) this method was plagued with problems
concerning the rotation axis. These problems effected the accuracy in which the array could be aligned.
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Introduction
To avoid these problems and increase the accuracy of the system a new positioning technique has
been utilised. This system will use the 1 motor to tilt the array in oneplane of movement, and
the 2 motor to tilt the array in the other plane of movement nd( Figure 1.3 ).
Figure 1.3: Two Axis Tilt Method of Alignment
The efficiency of the system code and the power consumption of the system are interlinked design
aspects. While it would be advantageous to design the system such that it operated off the solar power
collected from the array, at the present stage of the project this would be an unobtainable goal. At the
moment the project is mainly focused on obtaining optimal positioning performance, however, some
power saving techniques will be designed into the positioning code. The Larard (1998) design
continuously updated its position, thus needing more power for operation. Since it has been observed
(see Section 2.2.3 ) that the sun can move 3 degrees before there is a noticeable change in voltage and
current output, the system code can be designed to factor in a time delay for alignments.
The final design improvements are concerned with the efficiency of the solar cells and the amplifier
circuits used in the system. Larard (1998) had found that the efficiency of the cells used in his design
varied greatly with the temperature conditions of the particular day. If the individual solar cells, which
are used as sensors, were all affected by different magnitudes, then the performance of the system would
have suffered. The research this year will incorporate some aspects to limit the effect of varying heat
conditions on the system.
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CHAPTER 2
Theory Of Operation
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Working
The light sensors(l.d.r) are mounted on a board attach to a stepper motor which is capable of changing
its position corresponding to the changes in the position of the sun. The board thus moves along with
sun and their by help in absorbing maximum solar energy by the solar panel. So this project aims toseek the position of the sun and hence the name,sun seeker.
The operation starts by giving the power supply from the main(240v ac) which feed into two
transformers(1.12v dc,500 mA. 2.5v dc,300 mA). The first transformer gives the power to the stepper
motors windings and the second transformer give the power supply to the micro controller circuit
board,now the l.d.r arrangement(5 l.d.r)sends the riding to the comprators(2 comprators)for comparing
the maximum intensity of light detected by them,now the compared signal is send to micro
controller(89s51)which is pre programmed to generate codes(binary codes)which are indected by
L.E.Ds(8 in total,1-glow,0-off)which are feed to optical isolators which generate a signal given to
power transriators allowing the power supply to the stepper motor bindings which result in the
movement of the motor.
Thus the whole arrangement achives the primary objective of roatating the solar panal from east to westand north to south direction,in steps of 1.80 their by changing the position of the solar panel w.r.t the
position of sun in earths orbit.
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CHAPTER 3
BLOCK DIAGRAM
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BLOCK DIAGRAM
POWER
SUPPLY TRANSFORMER
TRANSFORMER
RECTIFIER COMPARATOR
L.D.R
RECTIFIER
MICROCONTROLLER
LED
OPTICAL ISOLATORPOWER TRANSISTOR
STEPPER
MOTOR
STEPPER
MOTOR
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Solar Cell Theory
Properties of Solar Cells
As the Sun continues to produce nuclear fusion reactions on its surface, the Earth will continue to receive
an almost limitless source of energy. In fact the amount of the Suns energy that reaches the Earth every
minute is greater than the energy that the worlds population consumes in a year [6].
Currently the solar (or photovoltaic) cell is the most efficient method of converting this solar energy into
a useable form (electricity). The solar cell is fabricated from a wide
variety of semiconductor materials, using numerous device configurations and structures. The most
commonly used semiconductor material for fabrication of solar cells is silicon. Non-silicon materials are
also being used for photovoltaic devices, however, they are either too expensive for this type of
application, or they are inexpensive but have a low efficiency. For the purposes of this thesis only silicon
solar cells were considered.
6
Crystalline, or single-crystal, silicon is one of the best materials for solar cells. It has a very highsolar cell efficiency (approx. 23 %) under unconcentrated sunlight, and a workable band-gap of
1.1. However, single-crystal silicon cells are expensive and have low absorptivity.
A cheaper version of crystalline silicon is polycrystalline silicon. Polycrystalline silicon has the
same band-gap, is cheaper, but has a lower efficiency. Polycrystalline silicon is used in many low
cost products that do not require much energy to function.
The last variation of silicon used in solar cells is amorphous silicon. It is relatively cheap and has
a much higher absorptivity than its silicon counterparts. Its main drawbacks are that it has a low
efficiency rate (approx. 13%), and its band-gap energy (1.7) is not ideal [6].
The following sections of theory are based on the p-n junction cell, as it acts as a reference
device for all other cells. The solar cell has a bandgap: E as shown in Figure g2.1 . In general, materials with band gaps between 1 and 1.8 eV can be used in solar cells.
When a photon of light is absorbed, an electron is released, creating both a free electronand a hole where it had been. The electric field pushes electrons to one side and holes to
another, moving the charge carriers. When an external circuit is attached, the electrons
can flow from the n-layer through the circuit and back to the p-circuit, where the
electrons recombine with the holes so they can repeat the process. Without an external
circuit, the charge carriers would simply collect at the ends of the cell [6].
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7
The idealised equivalent circuit of the cell is shown in
Figure 2.2 . A constant-current
source is in parallel with the junction, the source I results from the excitation of excessL
carriers by solar radiation, I is the diode saturation current and R is the load resistance.S L
Position of Solar Cell to Maximise Power
While theoretically the values of the current and voltage obtained from solar cells are always greatest
when the suns incident rays strike normal to the cells surface, it was necessary to prove this result
experimentally. In order to accomplish this, a stationary light source (luminance of 362) was used to
shine light onto a solar cell.
After considering the above data, it can be seen that to maintain maximum power output from a solar
cell, the angle of incidence must be held at zero degrees. That is, the suns rays must strike normal to thecell.
Sensitivity Analysis
Another important aspect of solar cells that needed to be considered was the cells sensitivity.
From the table above it can be seen that there is no change in the voltage received until the cell is at an
angle of incidence of 3.5 . Therefore, it is possible that the array can be 0 3 degrees out of phase and still
receive maximum power. This factor is of great importance when selecting motors for the positioning
system. To be accurate in receiving maximum energy from the sun, when a new alignment occurs the
array will need to move no more then 3 degrees. If the motors rotate more than this the array will not be
able to line up accurately to receive maximum energy.
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Motor And Motor Driver Theory
Introduction
For both of the tracking techniques discussed in the previous chapter, the control
methods for positioning the solar array are similar. Both tracking systems would need to
consist of two motors, which control the position of the array, and a control circuit
(either analog or digital) to direct these motors. The following sections discuss somepossible types of motors that could be used for this type of application.
DC Motors
Figure 2.4: Inner Workings of a DC Motor
Figure 2.4 shows the inner workings of a basic DC motor. The outside section of the motor is
the stator (stationary part), while the inside section is the rotor (rotating part). The stator is
comprised of two (or more) permanent magnet pole pairs, while the rotoris comprised ofwindings that are connected to a mechanical commutator. The opposite polarities of the energised
winding and the stator magnet attract each other. When this occurs the rotor will rotate until
perfect alignment with the stator is achieved. When the rotor reaches alignment, the brushes
move across the commutator contacts (middle section of rotor) and energise the next winding.
There are two other types of dc motors: series wound and shunt wound. These motors also use
a similar rotor with brushes and a commutator. However, the stator uses windings instead of
permanent magnets. The basic principle is still the same. A series wound dc motor has the stator
windings in series with the rotor. A shunt wound dc motor has the stator windings in parallel with
the rotor winding [1].
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DC Servomotors
By itself the standard DC motor is not an acceptable method of controlling a sun-tracking array.
This is due to the fact that DC motors are free spinning and subsequently difficult to position
accurately.
Even if the timing for starting and stopping the motor is correctly achieved, the armature does not
stop immediately. DC motors have a very gradual acceleration and deceleration curves, therefore
stabilisation is slow. Adding gearing to the motor will help to reduce this problem, but overshoot
is still present and will throw off the anticipated stop position. The only way to effectively use a
DC motor for precise positioning is to use a servo .
The servomotor is actually an assembly of four things: a normal DC motor, a gear reduction unit,a position-sensing device (usually a potentiometer), and a control circuit. The function of the
servo is to receive a control signal that represents a desired output position of the servo shaft ,
and apply power to its DC motor until its shaft turns to that position. It uses the position-sensing
device to determine the rotational position of the
shaft, so it knows which way the motor must turn to move the shaft to the commandedposition. The shaft typically does not rotate freely round and round like a DC motor.
Stepper Motors
The main difference between stepper motors and standard DC motors is that they cannot run freely by
themselves. The basic operational characteristic of stepper motors is that they do as their name suggests;
they "step" a little bit at a time. Also, the torque-speed relationship for stepper motors is different to that
of DC motors. DC motors are not very good at producing high torque at low speeds, where as, stepper
motors produce the highest torque at low speeds. Stepper motors also have a characteristic known as
holding torque . Holding torque allows a stepper motor to hold its position firmly when not turning. In
applications where the motor is not constantly running (ie.starting/stopping) this is very beneficial, as it
eliminates the need to incorporate a braking device.
Stepper motors fall into two basic categories: permanent magnet and variablereluctance . Permanent
magnet stepper motors are available in a wide variety: Unipolar,Bipolar, and Multiphase. There are also
hybrid motors, which are controlled in the same manner as permanent magnet motors. Variable
reluctance motors usually have three (sometimes four) windings, with a common return. Permanent
magnet motors however, have two independent windings with or without centre taps. Centre-tapped
windings are used in unipolar permanent magnet motors. These windings need to be energised in the
correct sequence in order for the motor's shaft to rotate clockwise. Reversing the order of the sequence
will cause the motor to rotate counter-clockwise.
When choosing stepper motors for specific applications the following motor characteristics should be
considered.
Voltage
Stepper motors usually have a voltage rating. This is either printed directly on the unit, or is specified inthe motor's datasheet. Exceeding the rated voltage is sometimes necessary to obtain the desired torque
from a given motor, but doing so may produce excessive heat and/or shorten the life of the motor.
ResistanceResistance-per-winding is another characteristic of a stepper motor. This resistance will determine
current draw of the motor, as well as affect the motor's torque curve and maximum operating speed
[3].Degrees-per-step This is often the most important factor in choosing a stepper motor for a given
application. This factor specifies the number of degrees the shaft will rotate for each full
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step. Half step operation of the motor will double the number of steps/revolution, and cut the degrees-
per-step in half. For unmarked motors, it is often possible to carefully count, by hand, the number of
steps per revolution of the motor. The degrees per step can be calculated by dividing 360 by the number
of steps in 1 complete revolution. Common degree/step numbers include: 0.72, 1.8, 3.6, 7.5, 15, and
even 90. Degrees-
per-step is often referred to as the resolution of the motor. As in the case of an unmarked motor, if a
motor has only the number of steps/revolution printed on it, dividing 360 by this number will yield the
degree/step value [3].
Variable Reluctance Stepper Motors
Variable reluctance stepper motors are the easiest to control over other types of stepper motors. In order
to rotate this motor continuously, the common wire is connected to the positive supply and each winding
is energised in sequence (see Figure 2.5 ). Positive
logic is assumed, ie. 1 means turning on the current through a motor winding. This type of motor feels
like a DC motor when the shaft is spun by hand; it turns freely and you cannot feel the steps. This is
because it is not permanently magnetised like its unipolar and bipolar counterparts.
Figure 2.5: Variable Reluctance Stepper Motor and Drive Pattern
In order to control this type of stepper motor, some form of drive circuitry must be utilised. The
type of circuitry needed has to focus on the switching of current on and off in each motor
winding.
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Figure 2.6 shows some switching devices that may be used for
this application.
Figure 2.6: Drive Switches for Variable Reluctance Stepper Motors
Both of these switches are compatible with TTL input. The 5 volt supply used for the logic, including
the 7407 open-collector driver, should be well regulated. The motor power on the other hand needs
only minimal regulation. Power Darlington transistors with a current gain over 1000 have been used to
switch a few amps through the motor winding. Also, the high-voltage open collector driver is used to
protect the logic circuitry if the transistor fails. The 2 switching circuit is able to handle inductive nd
spikes without the help of protection diodes if it is attached to a large heat source. If diodes are used
then they must be fast, since the IRL540 transistor has a very fastswitching time.
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Unipolar Stepper Motors
Unipolar motors are straightforward to control. A simple counter circuit can generate the proper
stepping sequence, and drivers as simple as 1 transistor per winding are possible. Unipolar
stepper motors are characterised by their centre-tapped windings. In use, the centre taps of thewindings are typically wired to the positive supply, and the two ends of each winding are
alternately grounded to reverse the direction of the field provided by that winding. Since the
number of phases is twice the number of coils (each coil is divided in two), the diagram below
( Figure 2.7 ), which has two centre- tapped coils, represents the connection of a 4-phase unipolar
stepper motor.
Figure 2.7: Unipolar Stepper Motor Coil Setup and 1-Phase Drive Pattern
To rotate the motor continuously, power is applied to the two windings in sequence. Positive
logic is assumed, ie. 1 means turning on the current through a motor winding. It should also be
observed that the two halves of each winding are never energized simultaneously.
In addition to the standard drive sequence, high-torque and half-step drive sequences are also
possible. In the high-torque sequence, two windings are active at a time for each motor step. This
two-winding combination yields around 1.5 times more torque than the standard sequence, but it
draws twice the current. Half-stepping is achieved by combining the two sequences. First, one of
the windings is activated, then two, then one, etc. This effectively doubles the number of steps the
motor will advance for each revolution of the shaft, and it cuts the number of degrees per step in
half [3].
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A "H-bridge" circuit ( Figure 2.10 ) is used to drive bipolar stepper motors. For each coil of the stepper
motor one H-bridge driver circuit is needed. Typical bipolar steppers have 4 leads, connected to two
isolated coils in the motor.
Figure 2.10: A Typical H-Bridge Circuit
A note worthy characteristic of H-bridge circuits is that they have electrical braking mechanisms.
These brakes can be used to slow, or even stop, the motor from spinning freely when not moving under
control by the driver circuit. This is accomplished by essentially shorting the coil(s) of the motor
together, causing any voltage produced in
the coils by during rotation to "fold back" on itself and make the shaft difficult to turn. The faster the
shaft is made to turn, the more the electrical "brakes" tighten.
Multiphase Stepper Motors
Figure 2.11: Multiphase Stepper Motor Coil Setup
A less common class of permanent magnet stepping motor is wired with all windings of the motor in a
cyclic series, with one tap between each pair of windings in the cycle. The most common designs in this
category use 3-phase and 5-phase wiring. The control requires 1/2 of an H-bridge for each motorterminal, but these motors can provide more
torque from a given package size because all, or all but one, of the motor windings are energised at every
point in the drive cycle [4].
It is common for 5-phase motors to have high resolutions ; up to the order of 0.72 degrees per step. With
a 5-phase motor, there are 10 steps per repeat in the stepping cycle
Here, as in the bipolar case, each terminal is shown as being either connected to the positive or negative
bus of the motor power system. It should also be noted that at each step only one terminal changes
polarity. As mentioned above, multiphase stepper motors utilise the H-Bridge driver circuitry.
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Hardware
Sensor Design
Since the system is required to track the sun, an effective sensor design must be developed. The sensor
design involves the position of the sensors, the type of sensors and the amplifier circuit that converts the
voltage readings into a more useable form.
Position of Sensors
The sensor design of Larard (1998) was a very effective way of locating the position of the sun. This
design incorporates a four sided pyramid structure with solar cells mounted on each side. The solar
cells, which are acting as sensors, are positioned so they are orthogonal to the opposing sensor. While
the design from Larard (1998) was kept, the size of the pyramid structure was increased to
accommodate the larger solar panels used as sensors.
Choice of Sensors
Since this thesis is based on a sun-tracking application is seemed appropriate that the sensors be
solar cells. While other light sensitive sensors would have been effective, by using solar cells
future applications (such as running the device of its own collected solar power) may benefit
from the extra cells in the array.
Amplifier Circuit
Although the new cells provided more voltage then the cells used by Larard (1998), the readings from
the sensors were still less then 1 volt (under normal light conditions).Since comparisons between the
sensors is considerably hard with these low levels, an amplifier circuit had to be developed. By using
an amplifier circuit these voltage readings could be increased to a more appropriate range (0-5 volts).
The amplifiers used were LM358 low-power dual operational amplifiers. These amplifiers are robust,
easy to work with and do not require complicated circuitry. The only feature of the circuit ( Figure 3.5 )
which requires explanation is the variable 10k resistor. This resistor is used for calibration of the fourpyramid sensors. By utilising a variable resistor instead of a fixed resistor the sensors can be adjusted
such that they read the same value when the pyramid is directly pointed at the sun. Also, if light
conditions are weaker on a particular day then the resistor can be adjusted to allow for greater voltage
readings.
Positioning Design
Once the position of the sun has been located it is necessary to accurately position the array such
that the suns rays strike normal to the array. The key aspects to this design are the method of
alignment, the choice of positioning motors and the motor gearing system.
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Method of Alignment
Probably the biggest flaw in the previous system designed by Larard (1998) was in the positioning
method. While the system did function, the accuracy was affected by his final design. The biggest flaw
with his design concerned the rotation motor and axis.
Testing of his system showed that the gearing mechanism, for the rotation axis, was extremely
inefficient. The height needed for the sensor tower, combined with the greater weight of the sensor
pyramid at the top of the tower, caused unstable movement of the array when rotated. This caused the
teeth of the gearing cogs to not engage accurately, and subsequently caused jerky, inaccurate
movement. Also, while it was observed that clockwise rotation was available (although jerky) the
gearing mechanism could not handle counter-clockwise rotation.
Since the aim of this project is to design a more efficient and accurate system, a new technique for
positioning the array had to be implemented. This method will still utilize two motors, however, the 1
motor will be used to control the tilt of the array in one st plane, while the 2 motor will control the tilt
of the array in the other plane. This nd method will allow greater accuracy and freedom of movement,
and overcome the problems associated with the tilt and rotate method previously employed.
Choice of Motors and Motor Drivers
To physically position the solar cell array two motors are required. After careful consideration of themotors discussed in Chapter 2 , unipolar stepper motors were chosen. Stepper motors were chosen
over DC motors since they are more effective in situations where controlled movement (ie. accurate
positioning) is needed. Stepper motors also have a holding torque which meant that complex motor
circuitry, such as in the case of servomotors, did not have to be developed. Finally, stepper motors are
known to be more reliable as they do not have contact brushes like DC motors.
Once the decision had been made to use stepper motors, it was now a matter of choosing which type of
stepper motor would best suit the projects needs. Unipolar stepper motors were chosen because they do
not require complex drive circuitry to control them, and because of their high reliability and robustness.
Since the aim of this project is to design a highly efficient and accurate sun-tracking system, it was
required that the stepper motors have a reasonably small degree-per-step ratio. However, the project is
also required to be a cost-effective solution. The smallest degree-per-step motor (0.72 ) seemed to be an
unnecessary expense when a wide range 0 of motors were already available.
Originally the design implemented two 9 volt, 3.6 0 per step motors. The choice of these motors was
based on the lower degree-per-step ratio and the lower power consumption then the other motors.
However, there were only two of these motors available and one proved to be faulty, so 12 volt 7.5 per
step motors were chosen instead.
The drive circuitry chosen for the unipolar stepper motors are simple Darlington transistor circuits. The
ULN2803A chip was used for the drive circuitry as it incorporates 8 Darlington transistors, since four
transistors are needed for each of the stepper motors.
The structure of the ULN2803A chip is exactly the same as the ULN2003 chip featured above, except
that it contains eight Darlington transistors instead of seven. Each Darlington transistor is matched, via
the base resistor, to standard bipolar TTL outputs [4], which is used to switch the current to each motor
winding on and off. This is used to supply the correct drive sequence to rotate the motors. The diode
shorting the emitter to the collector protects the transistor against any reverse voltages, while the diode
connecting the collector to VCC protects the transistor against any inductive spikes.
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Motor Gearing System
From the sensitivity analysis of the chosen solar cell (see Section 2.2.3 ) it was observed that for the
system to be 100% accurate (ie. always receiving maximum power from the sun) the motors would
have to rotate less than 3 degrees-per-step. If the number of degrees-per-step were any larger than this
then the array would never be able to line up accurately with the sun to receive maximum energy. Since
the chosen stepper motors have a 7.5 degree-per-step ratio, a gearing system had to be implemented.
The final design of the gearing system for each motor. A small cog is attached
to the shaft of the stepper motor, which in turn is linked to a larger cog, which is attached to the sensor
plane of movement. This gearing system effectively decreases the number of degrees-per-step from 7.5
to approximately 2.3. This is more then adequate to allow accurate positioning of the array.
Choice of Control Method
The best method for controlling an application such as this is to use complete software control. Under
complete software control, there is no need for a translator circuit external to the microcontroller. Also,
using software control greatly reduces the number and cost of components, and results in simpler board
design. However, it places the responsibility of generating all of the sequencing signals on the software.
If the microcontroller is not fast enough (due to code inefficiency or slow processor speed), or too
many motors are driven simultaneously, the system may slow down. Interrupts and other system events
can plague the control software more in this case.
Despite the downfalls of addressing a stepper motor directly in this manner, it is definitely the easiest
and most straightforward approach to controlling a stepper motor
Choice of Control Chip
By choosing software control the next decision that had to be made was what control chip would
be used. The main functions that were required of the chip included converting the analog
voltages from the four sensors into digital values that could be compared. Not only did the
controller have to handle inputs from the sensors, but also inputs from the user interface and
outputs to the stepper motors. The user interface required a control switch (manual/automatic
tracking) and four pushbuttons (inputs) to control the position of the array when in manual mode.
Each stepper motor required four data channels (outputs) for rotation to be controlled.
Taking into consideration all of the necessary design specifications, the 68HC11E2
microprocessor was chosen as the control chip. This was a reasonable choice for this
application as the device contains:
An in-built A/D converter
2K bytes of EEPROM
Five 8-bit I/O ports
These three factors cover the main functionality of the system. The in-built A/D converter is
needed for converting the analog sensor readings, three 8-bit I/O ports are required to handle the
sensor and pushbutton inputs and motor outputs, and there is more then enough program spacefor the system code. There are a number of other factors that makes the 68HC11E2 chip the most
reasonable choice for this system, however, these three were the deciding factors.
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Voltage Regulation
The stepper motors and op-amps do not require voltage regulation, however, the 68HC11E2
microprocessor does require a steady, regulated 5 volts. The LM7805 voltage regulator was used such
that a regulated 5 volt supply could be accomplished.
Figure: 3.12: Voltage Regulation Circuit
This circuit takes an unregulated supply (0-15 volts) and makes available from this a regulated 5 volt (
VCC ) supply, which is used for powering the microprocessor. Since the stepper motors require 12
volts for operation, this value was used as the input voltage to the regulator circuit. The reason for this
was that it limited the number of power rails to two (12V & 5V) in the PCB design. The stepper
motors are robust enough to run off an unregulated 12 volts, and the LM358 op-amps can run off
voltages up to 15 volts, so they fine running off an unregulated 12 volts as well.
Printed Circuit Board (PCB) Development
After the individual circuits had been devised and tested on breadboard, a printed circuit board (PCB)was developed. The software program Protel was used to draw the schematic diagram of the
circuitry ( Appendix A ), which was then transformed into a PCB file ( Appendix B ).
Choice of Programming Language
One of the first issues that had to be addressed was how the new system would be programmed. The
previous system had been programmed completely in assembly language. While using assembler was
an adequate way of programming the system, it was by no means the easiest or most efficient. This
year the system code has been developed using the programming language C.
The main reason for using C is because it is more flexible and has wider applicability then assembler.
One of the most attractive features is that the code size is smaller in C then assembler. This in turn
results in faster development time, improved efficiency and a reduction in debugging time. C also has
a tight casting error system that ensures the correct use of variables throughout the program. Finally, C
is easier to understand and modify, which is a benefit for any continuing work in this area in the
following years.
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Outline of the System
One of the aims of the thesis is that the system has to be able to run in either automatic or manual
mode. The automatic mode relies on sensory input from the pyramid structure to track the sun, while
the manual mode relies on input from the user interface to control the motors. One of the new features
that have been incorporated into the system is that both motors will be able to rotate simultaneously.
The previous system aligned one set of sensors (A1/A2) before aligning the second set (B1/B2). By
allowing both motors to rotate simultaneously the alignment time is decreased. The following
flowchart ( Figure 3.16) outlines the steps that the program will follow during operation.
Automatic Alignment
The main aspect of this thesis was to design an automatic sun-tracking device. In order to accomplish
this aspect the amplified, analog sensor voltages needed to be read into the A/D converter (Port E) of
the microprocessor. It should be noted that in setting up the 68HC11E2 microprocessor, the A/D
converter had to be supplied with high and low reference voltages (pins V and V ). For this
application the gains of the amplifiers RH RL
were adjusted so the sensors read 5 volts when the array was pointed directly at the sun (high
reference), and 0 volts when the sensors received no light (low reference).
Comparisons could then be made between opposite sensors, and the movement of the motorscontrolled. An example of this would be that if Sensor A1 ( Figure 3.17 ) has a greater voltage
reading then Sensor A2, then Motor A ( Figure 3.18 ) would be required to rotate clockwise until
both sensors read the same value. However, if Sensor A1 has a smaller voltage reading then A2, then
Motor A would be required to rotate counter- clockwise. The same technique applies for Sensors B1/
B2 and Motor B.
Figure 3.19: Unipolar Stepper Motor Coil Setup and 1-Phase Drive Pattern
The 1-phase drive pattern was chosen over both the half-step and high-torque drive patterns
mentioned in Chapter 2 . The motors already provide enough torque that the high-torque pattern is not
necessary, and the half-step pattern provides no improvement in positioning accuracy with an increase
in positioning time. Both methods also draw more current then the 1-phase pattern.
An added feature of the system, when in automatic mode, is that if all of the sensors read less then
250mV the system returns to its initial (set) position and enters stand-by mode. Stand-by mode
signifies that the sun has set (night) and there is no need to try and locate it. The initial position of
array is the position when the pyramid structure is pointing vertically up ( Figure 3.20 ). This ensures
that from no matter what angle the sun rises it will always be able to be located.
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Manual Alignment
The design also incorporates a manual alignment feature, which can be activated through a toggle
switch. The manual interface, which is connected to Port C, consists of the auto/manual toggle switch
and four pushbuttons for controlling the two motors.
The set-up of the pushbuttons is similar in nature to the set-up up of the sensors. For example, if
pushbutton A1 is pressed the microprocessor will receive a high signal and subsequently rotate Motor
A clockwise, however, if pushbutton A2 is pressed Motor A is rotated counter-clockwise. The same
technique applies for pushbuttons B1/B2 and Motor B. As with the automatic lignment method, the
drive sequence in was used.
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CHAPTER 4
CIRCUIT DIAGRAM
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POWER SUPPLY
In alternating current the electron flow is alternate, i.e. the electron flow increases to maximum in one
direction, decreases back to zero. It then increases in the other direction and then decreases to zero
again. Direct current flows in one direction only. Rectifier converts alternating current to flow in one
direction only. When the anode of the diode is positive with respect to its cathode, it is forward biased,
allowing current to flow. But when its anode is negative with respect to the cathode, it is reverse
biased and does not allow current to flow. This unidirectional property of the diode is useful for
rectification. A single diode arranged back-to-back might allow the electrons to flow during positive
half cycles only and suppress the negative half cycles. Double diodes arranged back-to-back might act
as full wave rectifiers as they may allow the electron flow during both positive and negative half
cycles. Four diodes can be arranged to make a full wave bridge rectifier. Different types of filter
circuits are used to smooth out the pulsations in amplitude of the output voltage from a rectifier. The
property of capacitor to oppose any change in the voltage applied across them by storing energy in the
electric field of the capacitor and of inductors to oppose any change in the current flowing through
them by storing energy in the magnetic field of coil may be utilized. To remove pulsation of the direct
current obtained from the rectifier, different types of combination of capacitor, inductors and resistors
may be also be used to increase to action of filtering.
NEED OF POWER SUPPLY
Perhaps all of you are aware that a power supply is a primary requirement for the Test Bench
of a home experimenters mini lab. A battery eliminator can eliminate or replace the batteries of solid-
state electronic equipment and the equipment thus can be operated by 230v A.C. mains instead of the
batteries or dry cells. Nowadays, the use of commercial battery eliminator or power supply unit has
become increasingly popular as power source for household appliances like transreceivers, record
player, cassette players, digital clock etc.
U SE OF DIODES IN RECTIFIERS:
Electric energy is available in homes and industries in India, in the form of alternating voltage. The
supply has a voltage of 220V (rms) at a frequency of 50 Hz. In the USA, it is 110V at 60 Hz. For the
operation of most of the devices in electronic equipment, a dc voltage is needed. For instance, a
transistor radio requires a dc supply for its operation. Usually, this supply is provided by dry cells. But
sometime we use a battery eliminator in place of dry cells. The battery eliminator converts the acvoltage into dc voltage and thus eliminates the need for dry cells. Nowadays, almost all-electronic
equipment includes a circuit that converts ac voltage of mains supply into dc voltage. This part of the
equipment is called Power Supply. In general, at the input of the power supply, there is a power
transformer. It is followed by a diode circuit called Rectifier. The output of the rectifier goes to a
smoothing filter, and then to a voltage regulator circuit. The rectifier circuit is the heart of a power
supply.
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RECTIFICATION
Rectification is a process of rendering an alternating current or voltage into a unidirectional one. The
component used for rectification is called Rectifier. A rectifier permits current to flow only during
the positive half cycles of the applied AC voltage by eliminating the negative half cycles or
alternations of the applied AC voltage. Thus pulsating DC is obtained. To obtain smooth DC power,
additional filter circuits are required.
A diode can be used as rectifier. There are various types of diodes. But, semiconductor diodes
are very popularly used as rectifiers. A semiconductor diode is a solid-state device consisting of two
elements is being an electron emitter or cathode, the other an electron collector or anode. Since
electrons in a semiconductor diode can flow in one direction only-from emitter to collector- the diode
provides the unilateral conduction necessary for rectification. Out of the semiconductor diodes, copper
oxide and selenium rectifier are also commonly used.
FULL WAVE RECTIFIER
It is possible to rectify both alternations of the input voltage by using two diodes in the circuit
arrangement. Assume 6.3 V rms (18 V p-p) is applied to the circuit. Assume further that two equal-
valued series-connected resistors R are placed in parallel with the ac source. The 18 V p-p appears
across the two resistors connected between points AC and CB, and point C is the electrical midpoint
between A and B. Hence 9 V p-p appears across each resistor. At any moment during a cycle of vin, if
point A is positive relative to C, point B is negative relative to C. When A is negative to C, point B is
positive relative to C. The effective voltage in proper time phase which each diode "sees" is in Fig.
The voltage applied to the anode of each diode is equal but opposite in polarity at any given instant.
When A is positive relative to C, the anode of D1 is positive with respect to its cathode. Hence
D1 will conduct but D2 will not. During the second alternation, B is positive relative to C. The anode
of D2 is therefore positive with respect to its cathode, and D2 conducts while D1 is cut off.
There is conduction then by either D1 or D2 during the entire input-voltage cycle.
Since the two diodes have a common-cathode load resistor RL, the output voltage across RL
will result from the alternate conduction of D1 and D2. The output waveform vout across RL,
therefore has no gaps as in the case of the half-wave rectifier.
The output of a full-wave rectifier is also pulsating direct current. In the diagram, the two equal
resistors R across the input voltage are necessary to provide a voltage midpoint C for circuit
connection and zero reference. Note that the load resistor RL is connected from the cathodes to this
center reference point C.
An interesting fact about the output waveform vout is that its peak amplitude is not 9 V as in the
case of the half-wave rectifier using the same power source, but is less than 4 V. The reason, of
course, is that the peak positive voltage of A relative to C is 4 V, not 9 V, and part of the 4 V is
lost across R.
Though the full wave rectifier fills in the conduction gaps, it delivers less than half the peak
output voltage that results from half-wave rectification.
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BRIDGE RECTIFIER
A more widely used full-wave rectifier circuit is the bridge rectifier. It requires four diodes
instead of two, but avoids the need for a centre-tapped transformer. During the positive half-cycle of
the secondary voltage, diodes D2 and D4 are conducting and diodes D1 and D3 are non-conducting.
Therefore, current flows through the secondary winding, diode D2, load resistor RL and diode D4.
During negative half-cycles of the secondary voltage, diodes D1 and D3 conduct, and the diodes D2
and D4 do not conduct. The current therefore flows through the secondary winding, diode D1, load
resistor RL and diode D3. In both cases, the current passes through the load resistor in the same
direction. Therefore, a fluctuating, unidirectional voltage is developed across the load.
Filtration
The rectifier circuits we have discussed above deliver an output voltage that always has the
same polarity: but however, this output is not suitable as DC power supply for solid-state circuits. This
is due to the pulsation or ripples of the output voltage. This should be removed out before the output
voltage can be supplied to any circuit. This smoothing is done by incorporating filter networks. The
filter network consists of inductors and capacitors. The inductors or choke coils are generally
connected in series with the rectifier output and the load. The inductors oppose any change in the
magnitude of a current flowing through them by storing up energy in a magnetic field. An inductor
offers very low resistance for DC whereas; it offers very high resistance to AC. Thus, a series
connected choke coil in a rectifier circuit helps to reduce the pulsations or ripples to a great extent in
the output voltage. The fitter capacitors are usually connected in parallel with the rectifier output and
the load. As, AC can pass through a capacitor but DC cannot, the ripples are thus limited and theoutput becomes smoothed. When the voltage across its plates tends to rise, it stores up energy back
into voltage and current. Thus, the fluctuations in the output voltage are reduced considerable. Filter
network circuits may be of two types in general:
CHOKE INPUT FILTER
If a choke coil or an inductor is used as the first- components in the filter network, the filter is
called choke input filter. The D.C. along with AC pulsation from the rectifier circuit at first passes
through the choke (L). It opposes the AC pulsations but allows the DC to pass through it freely. Thus
AC pulsations are largely reduced. The further ripples are by passed through the parallel capacitor C.
But, however, a little nipple remains unaffected, which are considered negligible. This little ripple
may be reduced by incorporating a series a choke input filters.
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CAPACITOR INPUT FILTER
If a capacitor is placed before the inductors of a choke-input filter network, the filter is called
capacitor input filter. The D.C. along with AC ripples from the rectifier circuit starts charging the
capacitor C. to about peak value. The AC ripples are then diminished slightly. Now the capacitor C,
discharges through the inductor or choke coil, which opposes the AC ripples, except the DC. The
second capacitor C by passes the further AC ripples. A small ripple is still present in the output of DC,
which may be reduced by adding additional filter network in series.
CIRCUIT DIAGRAM
MICROCONTROLLER INTERFACING
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STEPPER MOTOR INTERFACING
PRINTED CIRCUIT BOARD
Printed circuit boards are used for housing components to make a circuit, for comactness, simplicity of
servicing and ease of interconnection. Single sided, double sided and double sided with plated-
through-hold (PYH) types of p.c boards are common today.
Boards are of two types of material (1) phenolic paper based material (2) Glass epoxy material.
Both materials are available as laminate sheets with copper cladding.
Printed circuit boards have a copper cladding on one or both sides. In both boards, pasting thin
copper foil on the board during curing does this. Boards are prepared in sizes of 1 to 5 metre wide and
upto 2 metres long. The thickness of the boards is 1.42 to 1.8mm. The copper on the boards is about
0.2 thick and weighs and ounce per square foot.
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CHAPTER 5
LIST OF COMPONENTS
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Transformers x1:9-0-9 step down transformer
Comparator
MicrocontrollerRectifier
LED
Registors
Voltage regulator
Optical isolator
Power resistors
Power transresistor NPN
Stepper motor:6v,200gmPower supply
Step down transformer
Diodes
Capacitor
Ressistor
LDR(light detecting resistor)
Crystal
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CHAPTER 6
TESTING AND ANALYSIS
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Introduction
During the design process the hardware and software aspects were broken down and designed in
smaller sections. This made testing of the system easier, as some of the smaller design components
could be combined such that individual aspects of the system could be tested. By testing smaller
aspects of the system, instead of the system as a whole, faults could easily be located and rectified.
Once any faults were fixed the system as a whole was tested.
Unexpected Problems with the Design
The initial testing of the completed design went reasonably well, with the system easily performing all
of the required functions. However one minor, unexpected problem arose
which needed to be addressed.
Due to the nature of the alignment method, great care had to be taken to reduce the effect the weight
of the motors had on Axis B ( Figure 4.1 ). Axis A was fine since Motor A only had to support the
weight of the sensor structure. Even when Motor A was not energised it was still able to support the
weight of the pyramid structure at any position. Motor B however was required to support the weightof itself, Motor A and the pyramid structure. Since the stepper motors are considerably heavy, they
were positioned as close as possible to the supporting tower of the array in order to minimize their
effect on Axis B.
The first series of tests involved using a portable floodlight, which was setup at different positions
around the array, such that a number of different voltage readings could be obtained. Values were
recorded for both the tracking array and the stationary (sensor pyramid always pointing vertically)
array. The aim of this series of tests was to simulate different positions of the sun and observe the
differences between the two systems.
The light source was set up at 16 positions (A-P) inside of a spherical area above the sensor structure (
Figures 4.5 and 4.6 ). Five different angles and four different heights were chosen that followed thecurved surface (radius = 46cm) above the array. It should be noted that the light source was only set
up in one half of the area that the system can track to. This prevented the pyramid structure from
blocking the light to the collection panel when taking readings for the stationary array. The following
table and graph provide the results of the tests.
From the results of this series of tests it is obvious that the sun-tracking system is more effective in
collecting solar energy. While the stationary system is able to obtain large amounts of solar energy
when the sun is reasonably overhead (light positions K-P), the values obtained for the first set of light
positions (A-E) are extremely small. The first set of light positions closely match where the sun would
be when rising and setting, so from the above results the stationary system has been proven inefficient
during these time periods.
Although the data obtained from the laboratory experiments has proven that the sun- tracking system
is more efficient then the stationary system, it is still beneficial to observe the system in a real world
situation. The following table and graph provide the data for a whole day test with the system.
The data obtained from the real world test closely matched the data that had been obtained from the
laboratory tests. As can be seen from the above graph, the sun- tracking system collects the maximum
amount of solar energy possible across the entire day, where as, the stationary system only collects
maximum energy when the sun is overhead. These findings matched what had been observed in the
laboratory tests with the only difference being that the laboratory tests did not factor in the decrease in
the amount of available solar energy at dawn and dusk. This factor accounts for the drop in the voltage
level at dawn and dusk for the sun-tracking system.
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CHAPTER 7
CONCLUSIONS
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Introduction
At the commencement of the research project a number of system specifications were
established that, if adhered to, would increase the overall performance of the system. These
specifications were that the system had to:
Locate the position of the sun through sensory devices Position the array, by use of motors, such that the suns rays always
strike the solar panel normal to its surface Be controlled by a software program that minimised the amount of
power used by the system.
Background research was conducted into solar cell theory, sensor setups, motor types and
positioning methods such that a basic system model could be theorised. This theory model had
to conform to all of the necessary specifications that had been previously set. From here the
model was expanded and developed section by section until a working prototype had been
devised. Once construction was completed, the sun-tracking system was tested along side astationary system to see which system received the most solar energy.
Conclusions Regarding the System
Upon examination of the results obtained from the tests with the stationary array and those obtained
from the sun-tracking array, it was obvious that the sun-tracking method is more effective in gathering
solar energy. This was the expected outcome of the research, with the current system meeting all of
the required goals set out. The system itself is a very effective solution to the initial problem posed.Although it is not the only solution available, it is however, the most efficient given the time, budget
and material restrictions involved with an undergraduate thesis.
Applications for the System
This sun-tracking system can be used, and implemented, into any application that currently uses
stationary solar panels for collecting energy from the sun. However, for small appliances such as
pocket calculators, which do not require large amounts of solar energy, this method would not be very
beneficial. In domestic applications it would be beneficial in solar hot water systems, as well as, in
larger household appliances. A future use could be having a solar battery charger inside households
for backup power usage. This backup power technique is currently gaining popularity within the
commercial areas of society.
Currently households in remote areas of the world utilise solar energy for all of their daily
requirements. In these situations extremely large solar arrays are needed such that enough power can
be collected. A sun-tracking array would be very beneficial in these places, as it would mean a
decrease in the array size, with an increase in the amount of power that can be received.
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Areas of Further Research
The most logical next-step in research in this area would be to minimise the amount of power that isrequired to operate the system. While not minimising the power used by the system, a solar battery
charger could be used to run the system. Solar energy could be used to charge a battery, which then
could be used to power the electronics and motors of the system. The benefit of this would be that the
array would not need to use an external power supply, thus being more power efficient. Other aspects
may include using different motors that require less power, and modifying the source code such that
power consumption is reduced.
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CHAPTER 8
BIBLOGRAPHY
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Following are the reference made with regard to the accumulation of the material in compilation of the
project report for the project Sun Seeker:
Books and Journals reffered
1. Berringer, K., Motors in Motion: DC Motors, 1997. [online].
{http://mot-sps.com/motor/mtrtutorial/prin/dc.html}
2. Carlson, D.E., The Merits and Advantages of Photovoltaic Systems for Electric
Utility Applications, IEA Executive Conference on Photovoltaic Systems for
Electric Utility Applications , pp. 61-68, 1990.
3. Johnson, J., Working with Stepper Motors, 1998. [online].
{http://eio.com/jasstep.htm}
4. Jones, D.W., Control of Stepper Motors: A Tutorial, 1998, [online].
{http://www.cs.uiowa.edu/~jones/step}