The Sun Seeker-Final

7/31/2019 The Sun Seeker-Final

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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}

Documents

The Sun Seeker-Final