solar charger controller
TRANSCRIPT
DESIGN AND CONSTRUCTION OF A SOLAR- POWERED
AUTOMATIC
STREET-LIGHTING SYSTEM
By
OKEKUNLE DAHUNSI JOHN
A Project Report submitted in the partial fulfillment
of the requirements for the degree of
Bachelor of Technology
(Electronic/Electrical Engineering)
in the Ladoke Akintola University of Technolgy, Ogbomoso, Oyo State,
Nigeria
2010
Supervised by:
Doctor Zachaeus K. Adeyemo
Engineer O. F. Oseni
© Okekunle Dahunsi John, 2010
To kind families and loyal friends.
ii
Acknowledgement
I am most grateful to God for the life, strength, diligence, and wisdom He has given
me to start and successfully complete this project work.
Much credit and deep appreciation must of necessity be given to my parents for their
financial and moral support.
My sincere gratitude goes the way of my supervisors, Dr. Z. K. Adeyemo and
Engineer O. F. Oseni for timely interventions in moments of difficulties, as well as their close
supervision and revisions. Thank you, sirs.
iii
Table of Content
Title page
Dedication……………………………………………………………………………………..ii
Acknowledgement…………..……………………………………………………………..…iii
Table of content………………………………………………………………………..……...iv
List of figures ………………………………………………………………………………..vii
Abstract…………………………………………………………………………………….viii
Chapter One
Introduction……………..……………………………………………………………………1
1.1 Preamble……...……………………………………………………………………….1
1.2 Aims and objectives……………………………………………………………….….2
1.2.1 Aims………………………………………………………….………………….……2
1.2.2 Objectives …………………………………………………………………………….2
1.3 Justification……………………………………………………………………………2
1.4 Scope of study…………………………………………………………………..……..3
Chapter Two
Literature Review ……………………………………………………………………………..4
2.1 Solar Energy……………………………………………………………………………….4
2.2 Solar panel……...……………………………………………...…………………………..5
2.3 Battery Type and Characteristics…………………………………...……………………..7
iv
2.4 Care and maintenance of Batteries………………………………………..……………….9
2.5 Operational Amplifiers…………………………………………………………………….9
2.6 Comparators…………………………………………………………………………..….12
2.7 Field Effect Transistors………………………………………………..…………………13
2.7.1 MOSFET………………………………………………………………...……………..15
Chapter Three
Design and Analysis………………………………………………………………...………..16
3.1 Solar Charging Controller Stage…………………………………………………………16
3.2 Dark Sensor Stage……………………………………………………………………..…18
3.3 The Oscillator Stage……………………………………………..……………………….21
Chapter Four
Construction and Testing…………………..………………………………………………....22
4.1 Construction…………………………………………………………………………...…22
4.2 Implementation……………………………………………………………………….….22
4.3 Soldering……………………………………………………………………………...….22
4.4 Casing and Boxing…………………………………………………...……….………….24
4.5 Testing……………………………………………………………………...…………….24
4.6 Problems Encountered…………………………………………………………...……….26
Chapter Five
v
21
Conclusions and Recommendations………..………………………………………….……28
5.1 Conclusion……………………………………………………………………...……….28
5.2 Recommendations…………………………………………………………...………….29
References …………………………………………………………………….……………30
vi
List of Figures
Fig 2.1: Picture of a typical solar panel ……………………………………………………….5
Fig 2.2: Basic op-amp………………………………………………………………………....9
Fig 2.3: Inverting constant gain amplifier ……………………………………………….........9
Fig 2.4: Unity follower…………………………………………………………………….....10
Fig 2.5: Summing amplifier………………………………………………………………….11
Fig 2.6: op-amp as a voltage comparator………………………………………………….…11
Fig 2.7: Circuit symbols of MOSFETs………………………………………………………15
Fig 3.1: Solar charging regulator…………………………………………………………..…18
Fig 3.2: Dark sensor stage……………………………………………………………………19
Fig 3.3: Light sensor……………………………………………………………………….…20
Fig 3.4: The oscillator stage of dark detector……………………………………………...…21
Fig 4.1a: Components layout on Vero-board 1………………………………………………24
Fig 4.1b: Component arrangement on Vero-board 2 ………………………………………..24
Fig 4.2: The isometric view of cased job…………………………………………………….25
Fig 4.3a: TL071 pin configuration…………………………………………………………...26
Fig 4.3b: BUZ100 pin configuration…………………………………………………………27
vii
Abstract
The scope of the project is to outline the procedures for the design and construction of
a solar powered automatic street lighting system.
A solar panel is an arrangement of photovoltaic cells in series for voltage output, (or
parallel for current output) to a dc battery. The solar power harnesses the power from the sun
during the day, and with its characteristic of photovoltaic conversion generates a voltage
which is used up in charging the battery for a later operation during the night. The amount of
charge is limited by a charger-controller circuit.
The effectiveness of the automation of the solar powered street lighting depends on a
light-detecting circuit which is made up of Light-Dependent Resistors (LDRs), Integrated
Circuits (ICs), and some common electronic components like resistors, capacitors and
transistors. The light detecting circuit cuts off the supply to the illuminating lamp during the
day and switches it on when it detects darkness.
The automatic solar-powered street lighting system provides an alternate means of
powering a street light and eliminates the use of a fifth wire, thereby reducing the load on the
supply grid. In addition to these advantages, the automatic solar-powered street lighting
system reduces the risk of electric shock and does not require personnel to switch on or off.
The initial cost is however quite exorbitant and poses a major challenge to a wider spread of
use.
viii
Chapter one
Introduction
1.1 Preamble
Nature, in its complexity, has always been harnessed and used by man to solve
problem either spontaneously or gradually. Chemical elements contained in man’s
surroundings have been extracted and turned into drugs, plastic and other complex
structures. The metallic ores buried in the soil have been extracted and refined by man to
give metals of different properties which suits comfortably into different purposes, the
non-metallic materials underneath the earth surface have been uncovered by man to make
important materials like fuel (fossil) and thee most stunning of all, solid state materials,
like GaAs and Graphene.
The sun provides for us visible light that enables vision. Once again, man has risen up
not only to harness the energy possessed by the light (photon), but to find ways of
utilizing it when the sun is no more. This energy possessed by the light produced by sun
rays is called solar energy. The solar energy will be used to generate voltage level that
will be used to power bulbs on our streets. This process incorporates other components
which shall be discussed in details in the body of the project.
Nigeria a few years back had witnessed the issue of street lighting going to the falls as
inadequate maintenance and dwindling power generation has greatly affected the system.
Monitored by the Power Authority, the street lights got their supplies from the grid and
each electric street lights used a sodium pressure bulb of at least 200W, therefore electric
street lighting was substantially affecting the household power consumption; the bulky
network of wires and cables, flying and running underground in between each pole
1
employed in the construction of those lights was the reason for very high cost of
construction and maintenance of the lights. Moreover, no automatic system of switching
on or off was employed and the yellow light from has a poorer color rendition than the
white lights from LED bulbs.
The fore mentioned de merits in electric street lighting have called the attention of
communities to be shifted to solar electric lighting. Making use of solar cells or
photovoltaic cells (PV) as they may be interchangeably used, has made street lighting an
environmental system.
1.2 Aims and Objectives
1.2.1 Aim
The aim of this project is to comprehensively outline the procedures for the design
and construction of solar powered automatic street lighting system.
1.2.2 Objectives
The objectives of this project are:
1. To identify the various components, devices and processes that could suitably be
adopted for this purpose.
2. To study the characteristics of the devices to be employed.
3. To design and construct an automatic dark detector switching for the dusk-to-
dawn lighting
4. To analyze what the project will bring to the society.
1.3 Justification
In these times of heightened environmental awareness when issues like global
warming, accidents and energy conservation are burning, the energy sector is going
through a fire test! Energy loss needs to be reduced (energy loss in heat), systems giving
2
out hazardous needed to be re engineered and most importantly the energy consumed by
systems needs to be minimized. Electric street lighting is rightly regarded as an enormous
consumer of electricity, at a vast financial and environmental cost. However, because of
the safety and security benefits which result from a good lighting system, communities
everywhere are keen to implement cost effective, low power consuming and
environmental friendly lights.
The situation now is that streetlights powered by solar energy can be simply and
rapidly installed, giving the potential of many years of trustworthy use, with a minimum
of maintenance required. The solar cell converts energy received from sunlight to dc
voltage which is directly stored in a battery and a dark-detector circuit closes the dc LED
bulb to the battery when it is dark and remove it when it is dawn.
1.4 Scope of Study
The project design can be used on streets only and will therefore not incorporate the use
of sun-tracker system.
Its limitation is for use on perimeter lighting only is a function of its simplicity because
home lighting systems are more complex and expensive than the street lighting system due to
the introduction of devices like inverters and circuit breakers. Therefore the project will only
make use of a dark detector switch to control the cutting in and out of the battery since the
goal is to provide a lasting dusk-to-dawn lighting.
3
Chapter Two
Literature review
2.1 Solar Energy
Solar energy, energy directly from the sun, is one of the most important non-
conventional energy sources available for man’s use. Solar energy is incident on the earth at
the rate of about2.0 × 1015𝑘𝑊/𝑑𝑎𝑦. Nigeria is in the high solar radiation belt of the world.
It receives an annual average of about 3.5𝑘𝑊/𝑚2 a day in the coastal latitudes and about
7.0𝑘𝑊/𝑚2 a day in the far north of the country.
This is a vast amount of energy. It is clean, renewable, inexhaustible and non-
polluting. Man can harness the energy for useful purpose by means of some active and
passive devices such as flat plate connectors, concentrators, photo-thermals, photocells, etc.
Solar energy is captured by being converted to other forms of energy. This can be done either
by thermal technology or photovoltaic system. Of these alternatives, photovoltaic system has
received the most attention and development. In solar thermal technology, solar energy as
electromagnetic waves is first converted into heat energy. The heat energy may then be used
either directly as heat or converted into other forms of energy. Typical applications are in
drying, cooking, cooling etc.
In solar photovoltaic technology, the solar energy is directly converted to electricity
using semiconductor devices called solar cells. The photovoltaic technology is an internal
form of photoelectric effect, in that pairs of charge carriers (electrons and holes) are liberated
within the bulk of a semiconductor material (solar cells) by the absorption of sufficient
energetic photons. Photovoltaic systems are made up of a number of solar cells as the
smallest unit. Solar cells are made of various shapes and form different materials. Common
solar cells are circular in shape, about 0.1mm diameter. Almost all solar cells have been of
4
the p-n junction silicon variety about 250µm thick. Depending on the material used, the area
of the cell and the brightness of the sun (incident solar intensity), a typical solar cell in full
sun generates a direct voltage of about 0.45V and direct current of approximately 0.28A. This
gives a nominal power of 126W on a clean sunny day.
2.2 Solar Panels
Using solar panels is a great way to generate clean and renewable electricity to power
remote appliances, or even the average home. Solar (or photovoltaic) cells, are a very useful
way of providing electricity to remote areas (as mentioned earlier), where the use of
electricity may be important, yet the laying of high voltage cable may not be viable. The best
example of the importance of solar energy to provide electricity in remote locations can be
found on satellites. For many years, satellites have been using solar panels to catch the sun’s
rays, in order to provide power to the equipment on board.
Figure 2.1: picture of a typical solar panel
Photovoltaic cells can be aligned as an array, as shown in figure 2.1. There are many
advantages of using a solar cell array, with various panels fitted along a mounting system.
One of the main advantages is that we are able to combine various numbers of cells to
provide a greater output of electricity, and this method makes solar electricity a viable option
to power small homes and businesses.
5
The increasing efficiency of solar energy technologies means we are able to purchase and
install panels, knowing we are likely to receive an efficient way of harnessing energy from
the sun’s rays to turn into electricity for use in our homes.
It is quite possible for a household to run completely off photovoltaic electricity from the use
of solar panels, yet this is unlikely in most cases. The costs involved with supplying a whole
house with electricity from solar energy would be quite high for the average homeowner.
However, the use of solar electricity in the average home is still able to provide a substantial
amount of electricity, reducing future energy bills.
2.3 Battery Type and Characteristics
The battery being the sole energy source is a critical aspect of the design, hence a very
reliable battery charger is required to enable proper charge and discharge cycles. Though the
battery is a bought out part in every sense of it, yet selecting a good one for the solar powered
automatic street light requires a lot of technical considerations. For proper selection and
maintenance of the battery to take place, the factors affecting battery reliability have to be
considered. These include;
1. Temperature: The natural problems that cause battery ageing are strongly affected by
temperature. Manufacturing data indicates that the battery life is reduced by 10% of every
additional 100F. For this reason it is not only necessary that the solar powered automatic
street light design should be such that the batteries are kept as cool as possible at all time, but
also that a battery with wide operating temperature range should be selected.
2. Battery voltage: Batteries are made of individual cells. To make up a battery of voltage
higher than that of a cell, individual cell must be connected in series. When batteries are kept
7
on constant charge as they are in the solar powered automatic street light system, the
individual cells are charged in series. Slight manufacturing variation in battery cells can cause
some cell to take a larger percentage of charging voltage than the others. This causes
premature ageing of those cells. The series connected group of cells is only as strong as its
weakest link, so when any individual cell becomes weak the whole battery is weakened. It
has been proved that the magnitude of this ageing problem is directly related to the number of
cell in the string and therefore increases as the battery voltage increases.
3. Battery charger: The charging condition of a battery has a major effect on the battery life
span. The battery’s life span is maximized if the battery is always powered from a constant
voltage. This is because maintaining the battery under a continuous charge arrests some of
the battery’s natural ageing processes. Another important aspect of the battery is the battery
type. For use in electronic equipment, the possible choices are
(a) Nickel- Cadmium (Wet cell rechargeable battery)
(b) Sealed lead-acid battery
Nickel cell provide 1.2V, and generally available in the 100mAH – 200AH range and wok
down to 200C (and up to 45
0C). Lead- acid battery provides 2V per cell, and is generally built
to provide 1 – 20AH and work down to 650C (and up to 65
0C). Both types have relatively flat
discharge curves. Lead acid batteries have low self discharging rate and are claim to retain
two third of their charge after a quick storage at room temperature; NiCad batteries have
relatively poor charge retention, typically losing half their charge in four months.
There life span depend on their charge and discharge cycle both NiCad and lead acid
batteries claiming to be good for 250 – 1000 charge or discharge cycles (more if they are only
partially discharge each time; less if completely discharge or rapidly discharged). NiCad have
8
an overall life expectancy of 2 – 4 years if held at a constant trickle charge current, the
comparable life for sealed lead acid batteries is claimed to be 5 – 10 years.
Due to obvious fewer advantages of lead acid batteries over the NiCad in terms of ampere
hour rating, life expectance, charge retention, operating temperature and number of cells in
series for a given voltage, the sealed lead acid battery is often recommended for battery
performance.
2.4 Care and Maintenance of Batteries
For maximum performance to be achieved, the battery has to be serviced from time to
time. Servicing the battery involves;
(a) Regular check and topping of the acid level.
(b) Cleaning of corroded terminals to ensure proper contact.
(c) Charging of acid when concentration falls below average level.
(d) Ensuring that the battery voltage is appropriate to prevent over charging of the
battery.
2.5 Operational Amplifiers.
An operational amplifier, or op-amp, is a very high gain differential amplifier with
high input impedance and low output impedance. Typical uses of the operational amplifier
are to improve voltage amplitude changes (amplitude and polarity), oscillators, filter circuits
and many types of instrumentation circuits. An op-amp contains a number of differential
amplifier stages to achieve a very high voltage gain.
Figure 2.2 shows a basic op-amp with two inputs and one output as would result using a
differential amplifier input stage. Each input results in either the same or opposite polarity (or
9
phase) output, depending on whether the signal is applied to the plus (+) or the minus (-)
input, respectively.
+
-
Input 1
Input 2
Output
VCC
GND
Fig 2.2: Basic op-amp
The op-amp can be connected in a large number of circuits to provide various operating
characteristics. Most common of these circuits connections include:
Inverting amplifier
This connection provides a constant gain amplifier circuit as shown in figure 2.3.
+
-
VCC
GND
RF
R1
V1
V0 = RF × V1
R1
Fig 2.3: inverting constant gain amplifier
10
The output is obtained by multiplying the input by a fixed or constant gain, set by the input
resistance R1 and feedback resistor Rf. The output obtained is inverted from the input. The
inverting amplifier connection is more widely used because it has better frequency stability.
Unity Follower
This circuit connection as shown in figure 2.4 provides an operational amplifier with
unity (1) gain without phase or polarity reversal.
+
-
VCC
GND
R1
V1V0
Fig 2.4 unity follower
With this circuit connection the output obtained is the same polarity and magnitude as the
input.
Mathematically,
V0 =V1
Summing Amplifier
This circuit connection provides the means of algebraic summing (adding) of signals.
Figure 2.5 shows a three-input summing amplifier circuit which provides a means of adding
three voltages, each multiplied by a constant-gain factor.
11
+
-
VCC
GND
R1
V1
V0
R2
R3
V2
V3
Figure 2.5: summing amplifier.
2.6 Comparators
In electronics, a comparator is a device which compares two voltages or currents,
and switches its output to indicate which is larger. More generally, the term is used to refer to
a device that compares two items of data.
A standard op-amp can be used as a comparator as indicated in the following diagram.
VS+
VS-
V+
V-
+
-
Vout
Fig 2.6: op amp as a voltage comparator
When the non-inverting input is at a higher voltage than the inverting input, the high gain of
the op-amp causes it to output the most positive voltage it can. When the non-inverting input
drops below the inverting, the op-amp outputs the most negative voltage it can. Since the
output voltage is limited by the supply voltage, for an op-amp that uses a balanced, split
supply, (powered by ±VS) this action can be written:
12
Vout = Vs sgn (V+- V-), Where sgn(x) is the signum function.
A dedicated voltage comparator chip, like the LM339, is designed to interface directly
to digital logic (such as TTL or CMOS), since the output is a binary state, and is often used to
interface real world signals to digital circuitry. The LM339 accomplishes this with an open-
collector output. When the inverting input is higher, the output of the comparator is
connected to the negative power supply. When the non-inverting input is higher, the output is
floating (has a very high impedance to ground). With a pull-up resistor and a 0 to +5 power
supply, for instance, the output takes on the 0 or +5, and can be interfaced to TTL logic.
When comparing a noisy signal to a threshold, the comparator may switch rapidly from state
to state as the signal crosses the threshold. If this is unwanted, a Schmitt trigger can be used
to provide a cleaner output signal. It uses hysteresis to increase the switching region from a
single point to a band.
2.7 Field Effect Transistors
The field-effect transistor (FET) is a transistor that relies on an electric field to control
the shape and hence the conductivity of a 'channel' in a semiconductor material. FETs are
sometimes used as voltage-controlled resistors. The concepts related to the field effect
transistor predated those of the bipolar junction transistor (BJT). Nevertheless, FETs were
implemented only after BJTs due to the simplicity of manufacturing BJTs over FETs at the
time.
All FETs except J-FETs have four terminals, which are known as the gate, drain,
source and body/base/bulk. Compare these to the terms used for BJTs: base, collector and
emitter. BJTs and J-FETs have no body. It is common in large FETs to connect the body and
source internally to simplify design. In most applications one would connect the source to the
13
body anyway. The voltage applied between the gate and source terminals modulates the
current between the source and drain terminals. A difference between the voltages of the
source and body will change the threshold voltage. This is known as the body effect and is
used primarily in digital circuits, although it is taken into account in high precision analog
circuits. There are two 'modes' of FET: enhancement, in which a voltage applied to the gate
increases the current flow from source to drain; and depletion, in which a voltage applied
decreases the current flow from source to drain. Thus enhancement FETs are normally off,
whereas depletion FETs are normally on.
Types of field-effect transistors
The FET is simpler in concept than the bipolar transistor and can be constructed from a wide
range of materials. The channel region of any FET is either doped to produce an N-type
semiconductor, giving an "N-channel" device, or with a P-type to give a "P-channel" device.
The doping determines the polarity of gate operation. The different types of field-effect
transistors can be distinguished by the method of insulation between channel and gate:
1. The MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) utilizes an
insulator (typically SiO2).
2. The JFET (Junction Field-Effect Transistor) uses a p-n junction as the gate.
3. The MESFET (Metal-Semiconductor Field-Effect Transistor) substitutes the p-n
junction of the JFET with a Schottky barrier; used in GaAs and other III-V
semiconductor materials.
4. Using band gap engineering in a ternary semiconductor like AlGaAs gives a HEMT
(High Electron Mobility Transistor), also called an HFET (heterostructure FET). The
fully depleted wide-band-gap material forms the isolation.
14
5. The MODFET (Modulation-Doped Field Effect Transistor) uses a quantum well
structure formed by graded doping of the active region.
2.7.1 MOSFET
The metal-oxide-semiconductor field-effect transistor (MOSFET) is by far the most common
field-effect transistor in both digital and analog circuits. MOSFET is composed of a channel
of n-type or p-type semiconductor material and is accordingly called an NMOSFET or a
PMOSFET.
Circuit symbols for MOSFETS
A variety of symbols are used for the MOSFET. The basic design is generally a line for the
channel with the source and drain leaving it at right angles and then bending back into the
same direction as the channel. Sometimes a broken line is used for enhancement mode and a
solid one for depletion mode, but the awkwardness of drawing broken lines means this
distinction is often ignored. Another line is drawn parallel to the channel for the gate.
N-type
enchancement
mode
P-type
enchancement
mode
S
D
G
S
D
G
N-type depletion
mode
P-type depletion
mode
G
S
DD
S
G
Figure 2.7: circuit symbols of MOSFETS
15
Chapter Three
Design and Analysis
3.1 Solar Charging Controller
In a self-contained solar power installation that can provide electrical energy even when the
weather is bad or it’s dark outside, an energy reservoir in the form of a lead-acid battery is
indispensable. In order to prevent the battery from being discharged via the solar panel when
the terminal voltage of the panel drops below the actual level of the battery voltage, reverse
current protection is necessary. In its most rudimentary form, such a ‘solar current valve’ is
just a simple diode. A Schottky diode, which has a low forward voltage drop, is normally
used to minimize losses.
Unfortunately, the terminal voltage of a 12-V solar panel is significantly higher than its
nominal rated voltage when it is illuminated by strong sunlight, so it is not possible to avoid
exceeding the fully-charged (terminal charge) voltage of the battery using only this single
diode. If the voltage applied to the battery is too high, it produces gas, which reduces the
lifetime of the battery and can also be dangerous, since the gas is explosive. A regulator
circuit is thus necessary, in addition to the reverse-current protection diode, to limit the
terminal charge voltage of the battery to 2.30 V per cell (equivalent to 13.8 V for a 12-V
battery). The regulator circuit presented here fulfils these two tasks — reverses current
protection and voltage regulation — in an elegant manner.
In the circuit diagram of the regulator, shown in Figure 2.8, it’s easy to identify the reverse-
current protection. If the terminal voltage of the battery is higher than that of the solar panel,
the Schottky diode D3 prevents any current from flowing from the positive terminal of the
battery to the positive terminal of the solar panel, independent of the state of the rest of the
circuit. In the reverse situation, the charging current has free access to the battery. The
voltage drop across the diode is 0.43 V at a current of 3 A.
16
However, the solar panel current can also flow through D4 and T2 when transistor T2 is
switched on. The transistor is driven by the op-amp IC1, which is wired as a comparator.
Transistor T1 and potentiometer P1 provide a reference voltage, which is filtered by capacitor
C1. This voltage is set to roughly half of the terminal charge voltage of the battery. The op-
amp compares the reference voltage to the voltage at the junction of R1 and R2, which is half
of the battery voltage less the 0.6-V drop of diode D2. The exact values are shown in the
circuit diagram. If the battery voltage is less than the terminal charge voltage, the output of
the op-amp remains low and T2 is cut off. Led D1 is thus off, which indicates that the full
solar panel current is flowing into the battery. If the battery voltage rises above the terminal
charge voltage, the comparator output changes to high (D1 on) and switches on T2, so that
the output of the solar panel is short circuited. Since a solar panel represents a current source,
which can deliver only a limited current even when it is strongly illuminated by the sun, this
otherwise brutal form of shunt regulation is fully acceptable. Nevertheless, an additional
measure is used to minimize the power dissipation in T2 and D4, and thus avoid the need for
a large heat sink. This is provided by capacitor C4, which produces a brief positive feedback
pulse (lasting around 4 ms) to the op-amp whenever it changes state. This significantly
improves the switching behavior of the op-amp, so that the edges of the output signal are
distinctly steeper.
The power dissipated by an n-channel MOSFET (such as the BUZ100) is the lowest when it
is either fully on or fully cut off, or in other words when it passes either a high current or no
current at all. In the ‘analogue’ region between these two extreme states, the power
dissipation is much greater. The edges of the drive signal should therefore be as steep (and
thus as short) as possible. This is precisely what C3 achieves. When the charging current to
the battery drops due the short-circuiting of the solar panel, the battery voltage also drops
17
slightly. This causes the comparator to switch states and allow the battery to be charged
again. In practice, this means that the fuller the battery is, the faster the LED blinks.
T1
T2
BF256B
BUZ10
D3
D4
PBYR745
PBYR745
D2
1N4148
R1
150kΩ
R2150kΩ
P1
500kΩ C1
2.2µF
C2
10nFC3
100nF
C4
100µF
R3
4.7kΩ
R4
4.7kΩ
R5
100kΩ
D1
TL071
3
2
4
7
6
BATT +ve
SOLARP +ve
BATT -ve
SOLARP -ve
13.8V13.2V
11.9V1
1.4
V
6.5V
6.6V
red
Figure 3.1: Solar charging regulator.
3.2 Dark Sensor Stage
The dark sensor stage employs a light dependent resistor (LDR) to detect when the
environment is dark. The dark sensor stage is shown in figure xxx
18
R1
R2
R3
R4
R5LDR1
VR1
NE555P
D1
Q1
V+
1
3
7
2
6
8 4
Q2
C1
1kΩ
1kΩ
4.7kΩ
2.2kΩ10kΩ
4.7kΩ
100µF
BC337
BC337
Figure 3.2: Dark sensor stage
The LDR is a device which changes its resistance according to the amount of light falling on
it. In bright sunlight it has a resistance of about 100 ohms or less. In total darkness its
resistance is more than 100 kilo-ohms. The LDR acts as a variable resistor, which alters its
resistance when the level of light alters. The LDR works thus:
Brightness = Low resistance
Darkness = High resistance
R1
LDR1
1kΩ
Vout
VR11kΩ
Figure 3.3: Light sensor
19
When in bright light,
The voltage output from the dark sensor stage,
𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛 𝑅2
𝑅1 + 𝑅2
𝑉𝑖𝑛 = 12𝑉,𝑅1 = 𝑅1 + 𝐿𝐷𝑅 = 1000 + 100 = 1100Ω, R2 = 1000Ω
𝑉𝑜𝑢𝑡 = 12 × 1000
1100 + 1000
𝑉𝑜𝑢𝑡 = 5.751𝑉
Here, the transistor employed is connected in the common emitter mode to amplify and invert
the Vout. Thereby the LOW signal is fed into the logic inverter which inverts it to a HIGH.
The high input to the oscillator stage would not trigger the oscillator and the switching stage
is not powered and the street lights won’t come on.
In the dark,
The voltage output from the dark sensor stage,
𝑉𝑜𝑢𝑡 = 𝑉𝑖𝑛 𝑅2
𝑅1 + 𝑅2
𝑉𝑖𝑛 = 12𝑉,𝑅1 = 𝑅1 + 𝐿𝐷𝑅 = 1000 + 100000 = 101000Ω, R2 = 1000Ω
𝑉𝑜𝑢𝑡 = 12 × 1000
101000 + 1000
𝑉𝑜𝑢𝑡 = 0.117𝑉
Here, a HIGH signal is fed into the logic inverter which inverts it to a LOW. The low input to
the oscillator stage would trigger the oscillator and the switching stage becomes powered and
the street lights would come on.
20
3.3 The Oscillator Stage
The oscillator stage is employed to provide a switching signal that biases the
transistor every time the oscillator is triggered. The oscillator stage is implemented using the
popular NE555 timer/ oscillator IC.
NE555P
V+
1
3
7
2
6
8 4
R4
10kΩ
C1
100µF
From dark
sensor stage
To transistor
switching stage4.7kΩ
R5
Fig 3.4: The oscillator stage of the dark detector.
The oscillator output a timed pulse determined by
𝑇 = 1.1𝑅𝐶𝑠
𝑤𝑒𝑟𝑒,𝑅 = 10𝑘Ω,𝐶 = 100𝜇𝐹
𝑇 = 1.1 × 10,000 × 100 × 10−6
𝑇 = 0.1 sec (𝑓𝑜𝑟 𝑓𝑎𝑠𝑡 𝑠𝑤𝑖𝑡𝑐𝑖𝑛𝑔)
The fast switching time of 0.1s is used to ensure that the lamps are continually on as long as it
is dark.
21
Chapter Four
Construction and Testing
4.1 Construction
The physical realization of the project is very vital. This is where the fantasy of the whole
idea meets reality. Here the paper work is transformed into a finished hardware. After
carrying out all the paper design and analysis, the project was implemented, constructed and
tested to ensure its working ability. The construction of this project was done in three
different stages.
1. The implementation of the whole project on a solder-less experiment board (bread
board).
2. The soldering of the circuits on Vero-boards.
3. The coupling of the entire project to the casing.
4.2 Implementation
The implementation of this project was done on the breadboard. The power supply
was first derived from a bench power supply in the school electronics lab to confirm the
workability of the stages in the design before the power supply stage was soldered. The
implementation of the project on bread board was successful and it met the desired design
aims with each stage performing as designed.
4.3 Soldering
The various circuits and stages of this project were soldered in tandem to meet desired
workability of the project. The solar charge controller was first soldered before the dark
sensor stage was done. The soldering of the project was done on a Vero- board, and was
soldered on two Vero boards.
22
The first Vero board contains the solar charge controller circuit and the second Vero board
contains the dark sensor stage with the relay switching stage.
Figure 4.1a -b below shows the soldering and component arrangement on the various Vero
boards.
Vero-board 1 has solar charge controller circuit.
Figure 4.1a components layout on Vero-board 1.
Vero-board2 has the dark sensor stage with the relay switching stage.
Figure 4.1b component arrangement on veroboard2.
23
4.4 Casing and Boxing
The third phase of the project construction is the casing of the project. This project was
coupled to a plastic casing. The casing material being plastic designed with special
perforation and vents and also well labeled to give ecstatic value.
Figure 4.2: shows the isometric view of cased job.
4.5 Testing
Stage by stage testing was done according to the block representation on the breadboard,
before soldering of circuit commenced on Vero board.
The process of testing and implementation involved the use of some test and measuring
equipments stated below.
24
1. Bench Power Supply: This was used to supply voltage to the various stages of the
circuit during the breadboard test before the power supply in the project was soldered.
Also during the soldering of the project the power supply was still used to test various
stages before they were finally soldered.
2. Oscilloscope: The oscilloscope was used to observe the ripples in the power supply
waveform and to ensure that all waveforms were correct and their frequencies
accurate.
3. Digital Multi-meter: The digital multi-meter basically measures voltage, resistance,
continuity, current, frequency, temperature and transistor 𝑓𝑒 . The process of
implementation of the design on the board required the measurement of parameters
like, voltage, continuity, current and resistance values of the components and in some
cases frequency measurement. The digital multimeter was used to check the output of
the voltage regulators used in this project.
For proper understanding of how the project operates and to allow for troubleshooting, the
pin configuration of the ICs and other active components used are shown below.
Figure 4.3a shows the pin out of the TL071, op- amp which was used at the solar charging
controller stage in this project.
8
7
6
54
3
2
1 VCC
Invert input B
Output B
Non- invert input B
Output A
Invert input A
Non- invert input A
GND
TL071
Figure 4.2a: TL071 pin configuration.
25
Figure 4.3b shows the pin out of the BUZ100 which was used at the solar charging controller
stage in this project.
BUZ100
1 2 3
1 = Gate
2 = Drain
3 = source
Figure 4.3b: BUZ100pin configuration.
4.6 Problems Encountered
Like every research and practical engineering work, diverse kinds of problems are often
encountered. The problems encountered in this project and how they were solved and
maneuvered are listed below.
1. At the implementation stage of this project, the dark sensor stage was not working
properly. This problem was traced to wrong connection at the comparator stage. The
connection was corrected and the stage started working.
26
Chapter Five
Conclusion and Recommendations
5.1 Conclusion
The project which is the design and construction of a solar power street light was
designed considering some factors such as economic application, design economy,
availability of components and research materials, efficiency, compatibility and portability
and also durability. The performance of the project after test met design specifications.
Also the operation is dependent on how well the soldering is done, and the positioning of
the components on the Vero-board. If poor soldering lead is used the circuit might form dry
joint early and in that case the project might fail. Also if logic elements are soldered near
components that radiate heat, overheating might occur and affect the performance of the
entire system. Other factors that might affect performance include transportation, packaging,
ventilation, quality of components, handling and usage.
The construction was done in such a way that it makes maintenance and repairs an easy task
and affordable for the user should there be any system breakdown.
The project has really exposed me to digital and practical electronics generally which is one
of the major challenges I shall meet in my field now and in future. The design of the solar
power street light involved research in both digital and power electronics.
The project was quite challenging and tedious but eventually was a success.
I wish to thank the department, my supervisor and project co-coordinator for giving
me the opportunity to do this project. However, like every aspect of engineering there is still
28
room for improvements and further research on the project as suggested in the
recommendations written out in the section that follows in the paragraph below
5.2 Recommendations.
For the purpose of the future research, the project work can be improved upon. The following
areas were highlighted for this purpose.
1. The whole circuitry can be reduced by making use of integrated circuit with higher
scale of integration.
2. Moreover, it is recommended that students should be enlightened on new areas of
technology that are yet to be addressed in order to bring solution to the various
problems faced by man in his day to day activities.
29
References
1. Metha, V.K (2003); Principles of Electronics, S.Chand & Company Ltd (117-205,
transistors, and general references).
2. Boylestead, R L. and Nashelsky, L.(2002); Electronics Devices and Circuit Theory,
Prince-Hall. 8th Edition.
3. Maddock, R. J and Calcutt D. M, (1994); Electronics a course for engineers, Longman
Publishers (pages 341-349, IC timers, 249-263 counters, 290-293 decoder drivers).
4. Loveday, G. (1984); Essential Electronics (pages 241-244 transistors, general
references). Pitman
5. Hill, W. and Horowitz, P. (1989) The Art of Electronics, Second Edition, U.S.A.,
Cambridge University Press.
30