Solar-powered Streetlight _published_

(1)

LAUTECH SOLAR-POWERED PROJECTS: THE DEPT. OF ELECTRONIC/ELECTRICAL ENGINEERING

DESIGN & CONSTRUCTION

OF AN AUTOMATIC

SOLAR-POWERED STREETLIGHT

By

Morakinyo Ayodeji, Amusan Olusola,

Sekoni Seun & Adebunmi Femi

January 12, 2011.

www.lautech.edu.ng

[In this project, a solar panel is used to convert sunlight into direct current electricity which charges a battery during the day. At night, a dark detector employing a photoconductive cell senses darkness and this activates the circuit. The circuit then powers the load (lamps) to give required illumination.]

(2)

CERTIFICATION

This is to certify that this project work was carried out by the following students: MORAKINYO, Ayodeji James (051217); AMUSAN, Olusola Samson (050976); SEKONI, Oluwaseun Adeyemi (053652); ADEBUNMI, Oluwafemi Solomon (050736) in the Department of Electronic and Electrical Engineering, Faculty of Engineering and Technology, Ladoke Akintola University of Technology, Ogbomoso.

(3)

DEDICATION

This project work is dedicated to the Almighty God, the giver of life and talent for every academic work. Without him, this project could not have been a success.

We also dedicate this work to every great legend in the field of electrical and electronic engineering. We have only succeeded in this work because we built on the foundations they have laid.

(4)

ACKNOWLEDGEMENT

Firstly, we acknowledge our heavenly father and creator. It is by Him that we are enabled, equipped and empowered to reach this point in our academic journey.

With great joy, true respect and deep gratitude, we appreciate our supervisor Engr. I. A. Adeyemo, for every piece of advice, each session of counsel and every other form of support he gave us during the project process.

Finally, we would also like to express our gratitude to our parents (Mr & Mrs S.O Morakinyo, Mrs Amusan, Mr & Mrs Sekoni and Mr & Mrs Adebunmi) for their financial, emotional and spiritual support. But for them, we would not be here today.

MORAKINYO A.J AMUSAN O.S SEKONI O.A ADEBUNMI O.S January, 2011.

(5)

This publication is a scholastic property of Morakinyo A.J, Amusan O.S, Sekoni, et al. ©2011 TABLE OF CONTENTS TITLE PAGE i CERTIFICATION ii DEDICATION iii ACKNOWLEDGEMENTS iv LIST OF FIGURES v TABLE OF CONTENTS vi

LIST OF TABLES viii

ABSTRACT ix

CHAPTER ONE: INTRODUCTION

1.1 PREAMBLE 1

1.2 AIMS & OBJECTIVES 1

1.3 SIMILAR WORK 2

1.4 SIGNIFICANCE OF STUDY 2

1.5 SCOPE OF STUDY 2

CHAPTER TWO: LITERATURE REVIEW

2.1 SOLAR ENERGY 4

2.2 SOLAR PANEL 5

2.3LIGHT DEPENDENT RESISTOR 7

2.4 RESISTORS & LIGHT EMITTING DIODES 7

2.5 OPERATIONAL AMPLIFIERS 10

2.6 CONSTANT VOLTAGE REGULATOR 12

2.7 BIPOLAR JUNCTION TRANSISTOR 12

2.8 RELAYS 13

(6)

CHAPTER THREE: DESIGN & CONSTRUCTION

3.1 BASIC DESIGN

16

3.2 CHARGE CONTROLLER 17

3.3 CHOOSING SOLAR PANEL 19

3.4 PARAMETERS FOR CHOOSING A BATTERY 19

3.5 DARK OPERATED SENSOR AND SWITCHING CIRCUIT 20

CHAPTER FOUR: DESIGN IMPLEMENTATION &

INSTALLATION

4.1 METAL FRAMEWORK 23 4.2 WELDING 26 4.3 SCREWING 27 4.4 INSTALLATION 27 4.5 TESTING 29 4.6 OBSERVATIONS 30 4.7 PRECAUTIONS 30 4.8 BILL OF QUANTITY 31

CHAPTER FIVE: CONCLUSION & RECOMMENDATION

5.1 CONCLUSION 33

(7)

LIST OF FIGURES

Figure

Title

Page

2.1 Schematic Symbol for a Photovoltaic Cell 5

2.2 Array of Photovoltaic Cells 6

2.3 Circuit Symbol of a Photo-resistor 7

2.4 Circuit Symbols for Fixed and Variable Resistors 8

2.5 Non-inverting Amplifier 10

2.6 Schematic Diagram of LM324N OP-AMP 11

2.7 Circuit Symbol of a Relay Switch 14

3.1 Block Diagram of a Solar-powered Street Light

(Automatic)

16

3.2 Block Diagram of Charge Controller Unit 17

3.3 Circuit Diagram of a Charge Controller 18

3.4 Sensor and Switching Circuit 21

4.1 Solar-powered Street Light 24

4.2 Wiring Block Diagram of Automatic Solar-powered

Street Light

29

(8)

Table Title Page

2.1 Resistor Tolerance Band Values 8

2.2 Tolerance Colour Band Values 8

(9)

ABSTRACT

This project work is concerned with the design and construction of an automatic solar-powered street light.

In this project, a solar panel is used to convert sunlight into direct current electricity which charges a battery during the day. At night, a dark detector employing a photoconductive cell senses darkness and this activates the rectifier circuit. The rectifier circuit then powers the load (lamps) to give required illumination.

This lightening system is highly suitable in Nigeria where power supply is erratic; it thus offers the advantage of reliability compared to the lightening system powered by electricity received from utility company. Except for the initial high cost of installation, the system is easy to maintain since the original source of power (sunlight) is free.

(10)

CHAPTER ONE

INTRODUCTION

1.1 PREAMBLE

Light is crucial in everyday activity for the continuity of normal life. From plants to animals, from human beings to domestic insects, from technology to science, nothing seems to maximise its existence without the availability of light. Even the human eye requires some amount of light to function well (Blurtit, 2010). Light from the sun is natural and it is called sunlight. This sunlight can serve as a source of solar power which is converted to electric power for both household and industrial utilization.

Solar power is the generation of electricity from sunlight. This can be direct as with photovoltaic (PV) or indirect as with concentrating solar power (CSP) where the sun’s energy is focused to boil water which is then used to provide energy. Solar power is a predictably intermittent energy source, meaning that while solar power is not available at all times, we can predict with a very good degree of accuracy when it will not be available (Wikipedia, 2010). One area of application of solar energy is found in the construction of solar-powered street lights, an equipment that is paramount to meeting the security needs of every community in the 21st century.

Solar street lights are beneficial in that the day to day running and maintenance costs are reduced (Solar Street Lightning, 2010). Instead of the manually operated street lights, making use of power generated by the utility company, it is interesting that lead-acid battery and photovoltaic cells or solar modules can be used as the power source for the street lightning system. And with the use of a Light Dependent Resistor (LDR), automatic control can be included in the equipment.

This vital use of light gives rise to the idea of using solar energy to power street lights as an alternative to electricity. These solar-powered street lights can then be used for the provision of illumination on roads at night to enhance security and prevent accidents that may otherwise occur due to poor visibility.

(11)

1.2 AIM & OBJECTIVES

The aim is to design, construct and install a street light that charges in daytime, and discharges in the evening, without the need for a utility power source.

OBJECTIVES

1. To design a workable solar powered street light that does not utilize an inverter circuit

2. To eliminate the necessity for manual switching in the operation of community street light

3. To design and construct a charge controller for the battery

4. To install the solar-powered street light with two wings providing illumination

1.3 SIMILAR WORK

Previously, under the Department of Electronic/Electrical Engineering at the Ladoke Akintola University of Technology, Ogbomoso, a Solar-powered Street Lightning System was discussed by Akinola A.S & Odubola A., “Automatic Solar-powered Street Lightning System” Unpublished B.Tech thesis, Department of Electronic and Electrical Engineering, Ladoke Akintola University of Technology, Ogbomoso, (2004). In their dissertation, they indicated that their work involved design and construction. But, they did not specify whether or not their work included installation of the equipment.

1.4 SIGNIFICANCE OF STUDY

The use of solar modules with Lead acid battery to serve as power source for energy saving appliances is efficient and most reliable where there is erratic power supply. Therefore, the renewable property of energy makes it easier to use solar as a natural source of power through energy conversion process.

In a country such as Nigeria where the availability of uninterrupted power supply remains a major challenge, street lights powered by electricity from utility companies have repeatedly failed to provide consistent illumination but the proposed project seeks to amend this inadequacy. The lightning system operates through the

(12)

combination of a dark operated automatic switching circuit and the energy saving lamp made from LED array to give a stress-free operation and save more energy.

1.5 SCOPE OF STUDY

This project is focused at using a Light Dependent Resistor (LDR) which responds resistively to light for the automatic control process. This is planted on the equipment at a position where it is exposed to light from the atmosphere. The LDR senses light and differentiates daytime from night time, and then the sensor circuit triggers the switching circuit.

A comparator is used in the charge controlling circuit to sense the charging voltage of the battery so as to prevent it from overcharging.

(13)

CHAPTER TWO

LITERATURE REVIEW

2.1 SOLAR ENERGY

Solar energy (energy from the sun) travels to Earth through space in discrete packets of energy called photons (which are particles of light energy, or energy that is generated by moving electric charges). The amount of light that reaches any particular point on the ground depends on the time of day, the day of the year, the amount of cloud cover, and the latitude at that point. The solar intensity varies with the time of day, peaking at solar noon and declining to a minimum at sunset. The total radiation power (1.4 Kilowatts per square meter, called the solar constant) varies only slightly, about 0.2 percent every 30 years.

Energy from the sun can be directly or indirectly collected. Approximately 30 percent of the solar power reaching the Earth is consumed by the continuous circulation of water, a system called the water cycle or hydrologic [Holladay, April. "Solar Energy." Microsoft® Student 2008 DVD]. The oceans also collect and store solar energy while radiant energy from the Sun is transformed to the potential energy of water in streams and rivers. The power stored in the water cycle can be tapped by directing the flowing waters through modern turbines. Power produced in this way is called hydroelectric power. Earth's atmosphere, oceans, and plant life, for example, collect solar energy that can be extracted to power technology.

There are two main types of artificial collectors to directly capture and utilize solar energy: flat plate collectors and concentrating collectors. Since just a little amount of the Sun’s energy reaches the Earth’s surface, both types of collectors require large surface areas exposed to the Sun. The first type which is called the Flat plate collector is made of typically flat, thin boxes with a transparent cover that are mounted on rooftops facing the Sun. The Sun heats a blackened metal plate inside the box, called an absorber plate, that in turn heats fluid (air or water) running through tubes within the collector.

For applications such as air conditioning, central power generation, and many industrial heat requirements, flat plate collectors cannot provide carrier fluids at temperatures high enough to be effective so, more complex and expensive

(14)

concentrating collectors must be used (John Perlin, 1999). Concentrating collector types reflect the Sun’s rays from a large area and focus it onto a small, blackened receiving area. Concentrating solar energy is the least expensive way to generate large-scale electrical power from the Sun’s energy and therefore has the potential to make solar power available at a competitive rate. An example is the popularly known solar panel.

2.2 SOLAR PANEL

A Solar panel or photovoltaic cell is a type of photo electric cell that uses the photovoltaic effect to generate electrical energy using the potential difference that arises between materials when the surface of the cell is exposed to electromagnetic radiation. Photovoltaic effect is simply the creation of a voltage in a material upon exposure to electromagnetic radiation. Illumination of the materials results in the creation of an electric current as excited electrons and the remaining holes are swept in different directions by the built-in electric field of the depletion region.

Fig 2.1 Schematic Symbol for a Photovoltaic Cell

Solar cells are often electrically connected and encumbered as a module. Photovoltaic modules often have a sheet of glass on the front facing the sun, allowing the light from the sun to pass while protecting the semiconductor wafers from the elements, rain, hail, etc (Timothy J. Maloney, 1996). Solar cells are usually connected in series in modules, creating an additional voltage of 12Volts. When cells are connected in parallel, they yield an additional current. Power output is measured in watts or kilowatts. In order to calculate the typical energy needs of the application, a measurement in Watt-hours, Kilowatt-hours or Kilowatt-hours per day is often used. Average power according to the rule of thumb is that average power equals 20% of

(15)

peak power, so that each peak kilowatt of solar array output power yields energy of 4.8KWh per day (24hours x 1kw x 20% = 4.8KWh).

Fig 2.2 Array of Photovoltaic Cells

A solar cell’s energy conversion efficiency is the percentage of power converted from absorbed light to electrical energy and collected when a solar cell is connected to an electric circuit.

There are three types of solar cells.

Monocrystalline silicon cells

Multicrystalline silicon cells

Amorphous silicon cells

Monocrystalline silicon cells are the most efficient, with a very high cost of production.

Multicrystalline silicon cells are less efficient, compared to the Monocrystalline silicon cells. They have a relatively less cost of production compared to the Monocrystalline silicon cells.

Amorphous silicon cells are also very efficient, but the Monocrystalline silicon cells have been found to be the most efficient of the three.

(16)

2.3 LIGHT DEPENDENT RESISTOR (LDR)

This is a special type of resistor whose resistance value depends on the brightness of light which is falling on it. It is also called a photo-resistor (from the Greek word, “photo”) because to operate as desired, it requires the presence or absence of light.

Fig 2.3 Circuit Symbol of a Photo-resistor (LDR)

The LDR needs an external voltage source to produce current which is controlled by the variable resistance of a photosensitive material that it is made of (Cadmium compounds as Cadmium sulphide and Cadmium Selenide). In the dark, the resistance of the LDR is very high, typically around 1M ohm. In bright light it is low, typically 1K ohm. The continuous power dissipation is 80mW and the maximum voltage which can be applied to it is 100V. The snake like track on the face of the LDR is a Cadmium Sulphide (CdS) film. On each side is a metal film which is connected to the terminal leads (A.K. Theraja & B.L. Theraja, 2005). LDRs are very useful especially in light/dark activated circuits when coupled with a variable resistor such that the LDR’s sensitiveness can be adjusted by this variable resistance. For instance, when the light dependent resistor and a variable resistor are used to form a voltage divider with bias applied to a transistor, a connected relay can be automatically activated.

2.4 RESISTORS & LIGHT EMITTING DIODES (LEDs)

RESISTORS: are passive circuit components which are bilateral in function. They can also be referred to as electronic components that offer resistance to the flow of electric current in a circuit. They are always applied in circuits for the following reasons:

1. To limit current

(17)

3. To dissipate heat Types of Resistors

(i) Fixed resistors which have fixed values

(ii) Variable resistors whose values can be varied.

Fig. 2.4 Circuit Symbols for Fixed and Variable Resistors.

Resistor values: the resistance values of a resistor is either stamped on it or

determined by colour codes. The last of the four colour bands indicates the tolerance values of the resistor.

Colour Tolerance Value

Gold ±5%

Silver ±10%

No colour ±20%

Table 2.1 Resistor Tolerance Band Values

Note that the third band colour indicates the value of the multiplier. For example, resistor value = AB x 10c. Where A is the first band value, B is the second band value and C, the third band value.

Band Colour Code

Black 0

Brown 1

Red 2

Orange 3

(18)

Table 2.2 Resistor Colour Band Values

LAMPS: are lamps made from semiconductor materials in the similitude of light emitting diodes such that several light emitting diodes are combined to yield an LED lamp. Since the output of an individual unit in terms of power is small compared to incandescent and compact fluorescent lamps, the most recent of these lamps possess internal circuits that make them operate from standard AC voltage. However, for the sake of this project, DC lamps are to be used. LED lamps offer long life and high efficiency, but with initial high costs compared to fluorescent tubes or lamps. LED units naturally emit light in a very small band of wavelengths, thereby producing strongly coloured lights. The colour is characteristic of the energy band gap of the semiconductor material used in manufacturing it. Creating white light from LED units require the use of a phosphor to convert some of the light to other colours. The only major shortcoming with LED bulb is the high cost of manufacture. The following are the characteristics of LED lamps:

Long life expectancy.

Relatively low energy consumption, since they are energy-saving bulbs.

Good reflection of lights with small reflectors or lenses.

They do not have glass tubes that can break, while internal parts are rigidly supported, making them resistant to impact, vibration, and all other forms of mechanical stress.

They are dimmable over a wide range of voltage for AC transmission 85V and 240V. However, the brand of bulbs to be used, 12V, 5watts rated DC bulbs is the specification for the project.

(19)

One of the major advantages of LED bulbs is that it is good for spotlighting or floodlighting because it tends to be directional. Also, LED screw-in bulbs offer either low levels of light at a moderate cost or moderate levels of light at a high cost.

2.5 OPERATIONAL AMPLIFIER (LM324N)

Operational amplifiers are popularly known as OP-AMP. They are also called differential voltage amplifiers due to their ability to amplify the difference in the voltage between the two inputs. The output voltage is simply the difference between the inverting and non-inverting inputs multiplied by the gain.

If the non-inverting input (+) is more positive than the inverting input voltage (-), the output will be positive. If it is more negative in value than the inverting input, then output becomes more negative (Jones L, 1996).The output voltage changes in phase as that of the non-inverting input.

Where, RA and RB are Resistances.

Characteristics of Op-Amp

It has a very high open loop voltage gain.

A very high input impedance

A large common mode reflection ratio

A low output impedance

The typical LM324N OP-AMP used in this project is a quad comparator of two inputs with an output each. They are always incorporated in circuits meant for

(20)

sequential switching or voltage comparison. They can be used for amplifying signals in different modes. The general arrangement is to fix or reference one of the input voltages, either by using a zener diode, a regulator or a potential divider network.

Fig 2.6 Schematic Diagram of the LM324N OP-AMP

PINs Function 1, 8, 14 Output 2, 6, 9, 13 Inverting Input 3, 5, 10, 12 Non-inverting Input 4 Vcc+ 11 GND

Table 2.3 LM324N Pins and their Functions

2.6 CONSTANT VOLTAGE REGULATOR (LM 7808)

The linear LM7808 is an integrated circuit linear positive regulator with three terminals. It offers a fixed output despite the amount of voltage supplied to its input. However, care must be taken not to supply excessive voltage to its input terminals otherwise, the IC would be damaged. The minimum input voltage must be 3Volts higher than the regulated output voltage. The 7800 series (i.e. 05, 06, 08, 10, 12, 15, 18, or 24) provides up to 1A load current and has on-chip circuitry to shut down the

(21)

regulator if any attempt is made to operate it outside its safe operating area. But if this happens, the solution is to let the chip cool down and then attach the heat sink.

Its features include:

Output current of 1.5A

Output voltage tolerance of 5%

Internal thermal overload protection

Operating voltage range: 10.5 volts – 23 volts

No external component

Output voltage of 8Volts

Also offered in plastic package of TO – 220

Its applications are found in post regulator for switching DC/DC converter and in bias supply for analog circuits.

2.7 BIPOLAR JUNCTION TRANSISTOR (BJT)

This is a three layered, three terminal semiconductor device which is used in electronic circuits either as a switch or for amplification purpose. It was invented by Schockley, Bardeen and Brattain at Bell Labs in 1947 and today, it has revolutionised the way we live. A BJT works based on the principle that certain materials, such as Silicon, can be made to perform as “solid state" devices. Any material is only conductive in proportion to the number of "free" electrons that are available. Silicon has very few free electrons but if "impurities" such as Arsenic are introduced in a controlled manner then the free electrons or conductivity is increased.

By adding other impurities such as Gallium, an electron deficiency or hole is created. As with free electrons, the holes encourage conductivity and the material is called a semi-conductor. Semiconductor material which conducts by free electrons is called n-type material while material which conducts by virtue of electron deficiency is called p-type material.

There are two types of BJTs: the more common NPN type and the PNP type.

In PNP type, the emitter is made positive with respect to both the collector and base and the collector is made negative with respect to both the emitter and base in normal operation. The reverse is the case for the NPN type.

(22)

The bipolar junction transistor can also function in 3 different configurations:

a) The common emitter (CE) circuit uses emitter as its common electrode. The input signal is applied to the base and the amplified output is taken from the collector. This is the one generally use because it has the best combination of current gain and voltage gain.

b) The common base (CB) circuit uses base as its common electrode. The input signal is applied to the emitter and the amplified output is taken from the collector. The relatively high emitter current compared to the base current results in very low input impedance value. For this reason, the CB circuit is seldom used.

c) The common collector (CC) circuit uses collector as its common electrode. The input signal is applied to the base and the amplified output is taken from the emitter. This circuit is also called an emitter follower. This name means that the output signal voltage at the emitter follows the input signal at the base with the same phase but less amplitude. The voltage gain is less than 1 and is usually used for impedance matching. It has high input at the base as a load for the preceding circuit and low output impedance at the emitter as a signal source for the next circuit.

2.8 RELAYS

They are electromechanical switches which operate based on electromagnetic principles. They could also be used as electromagnetic switches that are triggered by an electronic switch, such as transistors which switch from one point to another. Relay Terminologies:

Nominal Coil Voltage (Rated Coil Voltage): the voltage intended by design to be applied to the coil to operate it.

Pick-Up Voltage: the voltage on an un-operated device is increased, the value at or above which all contacts must function.

Drop-Out Voltage: the voltage on an operated device is decreased, the value at or below which all contacts must revert to their un-operated position.

Maximum Continuous Voltage: the maximum voltage that can be applied continuously to the coil.

Nominal Operating Current: the current flow in the coil when nominal voltage is impressed on the coil.

Nominal Operating Power: the power used by the coil at nominal voltage. DC coils (watts); AC coils (VA).

(23)

Relays usually consist of three contacts of connection. Namely;

Common contact ( C )

Normally open contact ( NO )

Normally closed contact ( NC )

There are various ranges of relay ratings. They range from 5Amps, 10Amps, 15Amps, 20Amps, 30Amps, etc.

Fig. 2.7 Circuit Symbol of a Relay Switch

2.9 BATTERY

A Battery is an electric cell or a device that converts chemical energy into electricity. It consists of two or more cells connected in series or parallel, but the term is also used for single cells. All cells consist of a liquid, paste, or solid electrolyte and a positive electrode, and a negative electrode. The electrolyte is an ionic conductor; one of the electrodes will react, producing electrons, while the other will accept electrons. When the electrodes are connected to a device to be powered, called a load, an electrical current flows.

Batteries in which the chemicals cannot be reconstituted into their original form once the energy has been converted (that is, batteries that have been discharged) are called primary cells or voltaic cells. Batteries in which the chemicals can be reconstituted by passing an electric current through them in the direction opposite that of normal cell operation are called secondary cells, rechargeable cells, storage cells, or accumulators. The storage battery, or secondary cell, which can be recharged by reversing the chemical reaction, was invented in 1859 by the French physicist Gaston Planté.

The lead-acid battery, which consists of three or six cells connected in series, is used in automobiles, trucks, aircraft, and other vehicles. Its chief advantage is that it

(24)

can deliver a strong current of electricity for starting an engine; however, it runs down quickly. The electrolyte is a dilute solution of sulphuric acid; the negative electrode consists of lead, and the positive electrode of lead dioxide. In operation, the negative lead electrode dissociates into free electrons and positive lead ions. The electrons travel through the external electric circuit, and the positive lead ions combine with the sulphate ions in the electrolyte to form lead sulphate. When the electrons re-enter the cell at the positive lead-dioxide electrode, another chemical reaction occurs. The lead dioxide combines with the hydrogen ions in the electrolyte and with the returning electrons to form water, releasing lead ions in the electrolyte to form additional lead sulphate.

A lead-acid storage cell runs down as the sulphuric acid gradually is converted into water and the electrodes are converted into lead sulphate. When the cell is being recharged, the chemical reactions described above are reversed until the chemicals have been restored to their original condition. A lead-acid battery has a useful life of about four years. But, it is a good practice to utilize along with the battery, a suitable charge controller, as this will help the battery perform better and last longer. According to H.P. Garg and J. Prakash, overcharging of some batteries results in loss of electrolyte, corrosion, plate growth and loss of active material from the plates, causing reduction in battery life. Also, repeated failure to reach full charge leads to stratification of electrolyte. Thus, there is a need of charge regulators/controllers to optimize the battery life.

(25)

CHAPTER THREE

DESIGN & CONSTRUCTION

3.1 BASIC DESIGN

The design is such that the solar panel will be installed on the galvanized pole considering some specifications like angle of tilt and direction of sunlight. The fabricated pole will be bolted on a flat slab and its uprightness will be checked using a plum. The 12V dc battery that will power the LED bulbs will be connected to the solar panel via the charge controller for charging purpose. The pole will be constructed such that it will have two wings with each wing carrying one LED bulb or lamp. The automatic switching of the lamp (ON or OFF) will be performed by the light sensor circuit which consists of the light dependent resistor (LDR), relay, op-amp, transistor and some other electronic components.

Fig. 3.1 Block Diagram of a Solar-powered Street Light (Automatic)

The solar panel is tilted at an angle in the range of 15°≤x≤30° facing the geographical south. This is because Nigeria (wherein this project is being executed) is situated in the geographical north of the globe. The sun rises at the east and sets at the west and illumination is directed towards the geographical north. After erections have been made on the erected pole of about 18ft, the panel would be tightened up using bolts and nuts. The photovoltaic cells on the solar panel would generate voltage when it is well illuminated by light.

(26)

3.2 CHARGE CONTROLLER

The charge controller serves as an interface between the current generated by the module and the battery charging during the day. The battery is prevented from over-current or over-charging by the charge controller. The charge controller is an electronic circuit comprising an operational amplifier (connected in comparator mode), an electronic switch (transistor) and an electromechanical switch (relay). The block diagram of a charge controller is shown on figure below:

(27)

Fig 3.3 Circuit Diagram of a Charge Controller

When

When VCC = 14V, VP = 7V (which is less than the reference voltage). Hence, a

variable resistor will be ideal for R2.

Choosing VP = 9V for us to have a high output.

(28)

14R2 = 9 + 9R2

5R2 = 9

Preferred value, R2 = 5KΩ variable.

The comparator (LM 324) IC compares the non-inverting input voltage VP and

the non-inverting input voltage VN. There is usually a high output from the OP-AMP

if VP>VN which will switch on the transistor that will trigger the relay once the +VCC

on the battery rises to 14V in order to cut off the battery from charging throughout the photovoltaic supply. A freewheeling diode is connected across the coil terminals of the relay to protect the components from back emf from the inductive coil.

3.3 CHOOSING SOLAR PANEL (RATINGS)

Using four of the 5W LED bulbs amounts to 20W of electrical power being dissipated at 12V rating, PSH = 5hrs (time of maximum illumination)

Current consumption of the 20W load = Power/Voltage = 20/12. Hence, IL = 1.67A.

Ampere hour needed per day (i.e. from 7p.m till 7a.m (12hours)) becomes:

(1.67 x 12) this yields approximately 20Ah. While current needed from the solar panel is:

Hence, a panel that could supply a current of 4A is needed. Preferred value is 4.2A per 50W panel.

3.4 PARAMETERS FOR CHOOSING A BATTERY

Ampere-hour of the battery needed = Amp-hr needed per day x number of days of autonomy /Depth of discharge.

Autonomy number is the number of days that could be cloudy that you want the system to work effectively. (e.g. 2days)

(29)

Depth of discharge (D.O.D.) of a battery is a measure of how much energy has been taken away from a battery. With the lead-acid dry cell battery in use for this project, a discharge of 50% or 0.5 is allowed for it without damage caused to it. Therefore,

:

Preferred value for battery is 60Ah to allow for losses.

3.5 DARK OPERATED SENSOR AND SWITCHING CIRCUIT

The light dependent resistor (LDR) senses the dark and daytime and responds correspondingly to changes in the weather by causing the resistance of the resistor to vary from about 1KΩ to 100KΩ and vice versa. The incorporated sensor and switching circuit is shown in the next page:

(30)

.

Fig. 3.4 Sensor and Switching Circuit

This change in resistance causes a change in the voltage levels or the value of the non-inverting input (VP). Assuming that VN is being regulated constantly by the

voltage divider between R1 and R2, we assume that R1 = R2, which in turn equals

10KΩ,

Then,

When LDR is at 1KΩ, (daytime);

(31)

When the LDR (Rλ) is at 100KΩ, (Dark time),

Then VP is

Here, VP>VN which in turn fulfills the condition for high output of the

comparator. The high output of the comparator would switch on the transistor and it conducts to trigger the relay which will switch on the LED bulbs at the dark time. A freewheeling diode is connected across the coil terminals of the relay for protection against back e.m.f.

The variable 10KΩ resistor is used to tune up the sensitivity of the dark operated sensor. The 1KΩ resistor connected in series with the LED indicator for the output serves as a current limiter for the light emitting diode. The maximum current of the LED is 10mA which is IF. The output voltage VCC is also known as the LED

operating voltage (VLED). This has a value of 12V.

(32)

CHAPTER FOUR

DESIGN IMPLEMENTATION & INSTALLATION

4.1 METAL FRAMEWORK

The metal framework upon which the circuitry, battery and luminaries

will be installed requires a suitable mechanical engineering design. Mechanical

design means the design of things and systems of a mechanical nature. For the

most part, mechanical design utilizes mathematics, the material science and the

engineering mechanics science (Charles R. Mischke, 2002). This comprises a

galvanized steel column, mild steel solar tray guide, base plate, light brace

support, battery and circuit container as well as a variety of suitable fasteners.

The two main types of metallic materials utilized are discussed in the following

paragraphs.

Galvanized Steel

According to William F. Hosford (2005), galvanized means zinc plated.

Because zinc is anodic to iron, galvanizing protects the steel from corrosion.

Galvanized steel is a form of steel that has gone through a chemical process to

keep it from corroding. During the process, the steel gets coated in layers of

zinc to prevent rust, since zinc is resistant to rust. Galvanized steel is an

essential fabrication component for outdoor applications as well as industrial

marine use. The major method of preventing steel from corrosion is by alloying

it with another metal such as zinc. The chemical reactions between the two

metals cause a bonding to occur. This action does not make zinc a paint or coat.

Instead, it becomes part of it on a permanent basis. Zinc protects the steel by

acting as a sacrificial layer. As such, if rust occurs on the surface of galvanized

steel, the zinc part of it gets corroded first, and this prevents the rust from

getting to the pure steel.

(33)

Galvanization process is termed hot dip galvanization. It is the process of

coating iron, steel or aluminium with a thin layer of zinc, by passing the metal

through a molten bath of zinc at a temperature of around 460˚C. The galvanic

process was discovered by Luigi Galvani in the 1700s when he invented the

galvanic cell. Galvanization is the name given to the electrochemical processes

in his honour. This however should not be confused with galvanizing steel,

because it is not an electrochemical process, though the result remains the

same.

Steel in galvanized form can be found everywhere as it has wide

applications. An advantage of this form of steel is its effectiveness. And above

all, it can be recycled and re-used multiple times. Galvanized steel is very

practicable in applications where this is high proximity to rust, and rust

resistance is required. Galvanized steel is also suitable for high temperature

applications of up to 200˚C. The use of galvanized steel at temperatures above

this will result in peeling of the zinc at inter-metallic layer. Hot dip galvanized

steel can be referred to as galvanized iron. It is used in heating and cooling duct

systems in building.

Mild Steel

Also referred to as low carbon steel, mild steel is weldable and hard. It is

malleable when heated, and as such can be forged. These properties are due to

the presence of minute quantity of carbon content for hardening. It has a low

content of carbon, up to (0.3%), and is neither extremely brittle nor ductile. It is

used where large amount of steel has to be formed such as structural steel.

Other advantages of using mild steel include relative cheapness, availability of

wide variety with different properties, high degree of stiffness and magnetic

property.

Mild steel also has wide applications, as it is the most common form of

steel. It has got a relatively low price while it has properties that are acceptable

for many useful applications. Carbon steels that have about 0.3% require

(34)

special precautions. Relative to stainless steel, there are fewer problems

associated when welding mild steel. It has poor corrosion resistance, implying

that it rusts easily. Hence, it should not be used in corrosive environment unless

a provision for protective coating is made.

4.2 WELDING

It is a process of permanently joining two or more metal parts by

melting both materials. Welding may be considered to be a fabrication

technique. In welding, two or more parts are joined to form a single piece when

one-part fabrication is expensive or inconvenient (William D. Callister, 1997).

The molten materials cool quickly and the two metals are permanently bonded.

Higher content or alloy steels tend to form hard welds that are brittle and could

crack. This unsuitable tendency can be reduced by tempering. When low

carbon steel is used, the surface-cleaning process which is becomes necessary

when aluminium is used can be easily avoided, preventing further cost.

Materials that are similar in composition cannot be welded by spot welding

method due to different melting properties and terminal conductivities. Steel

that is plated can be assumed to take the characteristics of its coating. Nickel

and chrome plate steels are relatively easy to weld by spot welding, whereas

aluminium, zinc and tin need special preparation to be able to weld them.

Arc welding

This is a type of welding that uses a welding power supply to create an

electric arc between an electrode and the base material, thereby melting the

metal at the welding point. They use either direct current or alternating current

consumable or non-consumable electrodes. The welding region is sometimes

protected by some type of inert gas known as a shielding gas. This method of

welding is widely used because of its low capital and running cost.

(35)

The welding of galvanized steel is done in the same way as the welding

of base steel of the same composition. The difference between welding

galvanized steel and uncoated steel is a result of low vaporization temperature

of the zinc coating. The successful welding of galvanized steel is so widely

accepted that there is little mechanical property that compares uncoated and

galvanized weld. Weld toughness, porosity control, corrosion resistance, etc are

much more complex that the strength of the weld.

4.3 SCREWING

Screwing is another method of joining metals. It consists of proper

cleaning of the parts to be joined, and then using the appropriate joining pieces.

They are made of iron, brass, bronze or steel and have heads of various shapes,

half-round heads, counter sunk heads, cheese heads, half round and counter

sunk combined. All screws used for metals are known as tapped screws or

metal thread screws, which distinguishes them from screws used for wood.

Screws are made in various pitches. The pitch of screw is the distance it will

move in the direction of its axis in one revolution through a fixed nut. Also,

screws can be identified by their diameter standard, shape of head metal and

length under head. In screwing work together, the part that takes the head of the

screw has a clearing hole in it, while the other part has to have a tapping hole,

and this is known as the core diameter. This enables the work to be drawn

tightly together.

4.4 INSTALLATION

The automatic solar-powered street light is installed with a twin arm

lighting kit to operate in a dusk-to-dawn operation mode using an automatic

ON/OFF feature. The lighting kit does not utilize an inverter circuit but instead,

four 15Watt D.C. bulbs powered by D.C. supply from the battery are

employed.

(36)

Installation of Solar Panel

Attach the solar panel tray guide or carrier upon the pole and slightly fasten its

bolts and nuts. Fix the solar panel into the tray guide and tighten the

appropriate screws effectively. Connect the 6mm cables from the panel

terminals to the battery and also, from the battery to the electronic circuit unit.

Ensure that the standard polarities are observed i.e. black for negative (labelled

–ve) and red for positive (labelled +ve). Adjust the solar panel’s direction and

angle to obtain optimal performance, and fasten the bolts and nuts tightly.

Installation/Erection of Pole

An anti-skid unloaded metal pole having a square base is erected on a

concreted square-shaped foundation. This base of the pole then fastened to the

foundation by means of rag bolts. Consequently, the pole is made to stand

uprightly.

Installation of the Lighting Kits & the Battery

Carefully secure the lighting kits into the lamp holders and fix the

luminaries. Then connect the wires to the controller as shown in the associated

wiring diagram of this project. Also, put the battery in the box attached to the

erected pole, ensuring appropriate connection of cables unto it with battery

clips.

Installation of the Charge Controller of the Automatic Switch

Since circuitry of this design incorporates both a charge controller unit

and a dark-operated sensor switch together as a kit, both units are installed on

the same electronic board and planted in the same enclosure together with the

battery. The battery, lighting lamps and the solar panel are connected

(37)

appropriately to the charge controller/automatic switch as shown in the block

wiring diagram as shown below.

SOLA R P

ANEL

4.2 Wiring Block Diagram of Automatic Solar-powered Street Light

(38)

After the installation process has been completed, an act of testing and if

necessary, a troubleshooting session must be executed. Testing is the act of

examining of the normal working operation, seeking to know the

characteristics of the equipment and noting where appropriate changes can be

made. On the other hand, troubleshooting is the art of isolating problem areas

and using a variety of techniques and experience to solve it. These are done to

ensure that the fabricated lightning equipment is in optimal working condition.

If any performance deviation is observed, the operation of the equipment must

be troubleshooted in order to isolate the problem and fix the fault.

At night, the streetlight operated by itself, switching on the luminaries

and by dusk, it switched off the lamps by itself. Therefore, the characteristics of

the equipment were normal and there is no need for further changes. This

project has been tested ok.

4.6 OBSERVATIONS

The following observations were made:

• To enhance the sensitivity of the LDR and hence, improve the

performance of the streetlight, the potentiometer was removed from

inside the circuitry’s container and be put on the outside the casing.

• Measured charging current and optimal or average output voltage of PV

cell were respectively.

At the testing stage, the proper charging of the battery from the solar

panel was checked and noticed to be appropriate. Also, since this street light is

meant to work without the need for manual switching, it was observed to have

worked from dusk to the early hours of the morning.

Lastly, it was noticed that the charging current increases with

illumination received by the panel from the sun. In other words, the charging

rate is directly proportional to the illumination received from the sun.

(39)

4.7 PRECAUTIONS

Considering the socio-economic and quality control factors involved in

this project work, certain cautions must be taken at the fabrication stage.

Factors such as cost and quality of materials, environmental condition of

installation location and affordability of finished product must be checked

when planning, fabricating and criticizing the work done. The following should

be considered when executing this project work:

• The materials used for the project must be carefully selected to ensure a

balance between cost and quality thereby making finished product

affordable and reproducible. High quality galvanized steel (expensive)

was coupled with moderate quality mild steel (relatively inexpensive) in

fabricating this project work. Also, D.C. bulbs were utilized instead of

the more common LED array lamps to ensure that high cost of

production does not hinder the successful completion of the project.

When implementing this kind of project on a commercial scale, cost and

quality must be well balanced to ensure that finished equipment does not

become too expensive or be of poor quality.

• The battery should be connected first to the circuit unit to prevent

unwanted oscillation of the relay.

• The LDR must be well exposed to an atmosphere where light intensity

can be properly sensed.

4.8 BILL OF ENGINEERING MATERIALS & EVALUATION

(BEME)

It is the bill of materials identifying and listing the components of a

finished engineering product. It itemizes the raw materials, subassemblies, and

even the intangibles that contribute to the costs of manufacturing a product. See

next page for the associated BEME.

(40)

S/N DESCRIPTION MAKE/BUY

PRICE QUANTITY (Naira)

1 Base Plate Make 1

2 Stud & Rag Bolt Buy 4

3 Steel Column Buy 1

4 Positioner Locknut Buy 2

5 Split Positioner Make 1

6 Bulb Holder Buy 2

7 Light Brace Suppport Make 2

8 Battery & Circuit Container Make 1

9 Solar Panel Tray Guide Make 1

10 Weldering Cost N/A N/A

11 Battery Buy 1

12 Bulbs Buy 4

13 Solar Panel Buy 1

14 Logistics & Transport N/A N/A

15 10KΩ Resistor Buy 3

16 470µF Capacitor Buy 2

17 C945 Transistor Buy 6

18 1KΩ Resistor Buy 6

19 10KΩ Variable Resistor Buy 2

20 5KΩ Variable Resistor Buy 2

21 92XX Series Diode Buy 3

22 Red LED Buy 2

23 Green LED Buy 2

24 LM 324N Buy 2

2 30A, 12V Relay Buy 2

26 Soldering Lead Buy 3

27 Veroboard Buy 1

28 Jumper Wire Buy 2

29 LDR Buy 1

30 LM 7808 Buy 2

31 Battery Clip Buy 2

32 IC Socket Buy 1

33 10mm Copper Wire Buy 6

34 5mm Copper Wire Buy 6

35 Casing Buy 1

36 Cement Buy 1

37 Bricklayer's Labour Cost N/A N/A

(41)

CHAPTER FIVE

CONCLUSION & RECOMMENDATION

5.1 CONCLUSION

The solar-powered streetlight was designed and constructed such that the conventional need for inverter or utility power source is eliminated. Also, the equipment was fabricated along with a switching circuit and charge controller unit that prevents the battery from overcharging. The main improvement of this project has been the elimination of a dc to ac inverter unit.

5.2 RECOMMENDATION

It is recommended that LED array lamps be utilized instead of DC bulbs in order to achieve greater efficiency and luminosity. It should however be noted that the use of such lamps implies a higher cost of production for the project implementers.

Also, the services of skilled and seasoned labourers should be employed for the mechanical and civil aspects of this project. This is to ensure proper balance between the cost, quality and durability of the metal framework and the concrete slab.

(42)

REFERENCES

Array of Photovoltaic Cells. Microsoft Student 2008 Edition, USA, Microsoft Corporation.

Callister, W. (1997) Materials Science and Engineering: an Introduction, Canada, John Wiley & Sons Inc.

Garg, H.P. & Prakash J. (2000), Solar Energy: Fundamentals and Applications. New Delhi, Tata McGraw-Hill Publishing Company Ltd.

Holladay, A. (2008) "Solar Energy", Microsoft Encarta 2008 Edition, USA, Microsoft Corporation.

Hosford, W. (2005) Physical Metallurgy. Florida, CRC Press.

Maloney, T (1996) Modern Industrial electronics, 3rd Edition, USA, Prentice-Hall Inc.

Mischke C. R. & Shigley J. E. (2002) Mechanical Engineering Design, USA, McGraw-Hill Inc.

Perlin, J. (1999) From Space to Earth: The Story of Solar Electricity, USA, Aatec Publishers.

http://www.blurtit.com/q856738.html

http://www.solar-street-lighting.com

http://www.ciras.iastate.edu/publications/CIRASNews/fall97/bom.html http://www.wikipedia.com