SOLAR POWERED BATTERY CHARGER WITH STATE OF CHARGE
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TABLE OF CONTENTS
CHAPTER TITLE PAGE
1 INTRODUCTION 1
1.1 Introduction
1.2 Project Background 1
1.3 Problem Statement 2
1.4 Objectives 3
1.5 Scope of Project 3
2 LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Solar Energy 5
2.3 Solar Energy as a Power Source 6
2.4 Benefits of Solar Energy 7
2.5 Solar Cell 8
2.6 History of the Solar Cell 8
2.7 How a solar cell works 10
2.8 Battery Charger 12
2.9 Solar Powered Battery Charger Development 14
3 METHODOLOGY 17
3.1 Introduction 17
3.2 Flowchart 17
3.3 Method 18
4 CONCLUSION 21
4.1 Conclusion 35
4.2 Recommendation
Eng ridwaan Farhan
A report submitted in partial fulfilment of the
requirements for the award of the
Bachelor of Electrical Engineering (Power Systems)
Faculty of Electrical & Electronic Engineering
University Hargeisa somaliland
OCTOBER, 2018
https://en.wikipedia.org/wiki/Battery_charger
https://en.wikipedia.org/wiki/Battery_charger
ABSTRACT
Solar energy is one of the many forms of renewable energy on earth. This
energy can be harnessed by using a solar cell or photovoltaic cell which converts
sunlight directly into electricity. Solar power can also be used in many small
electrical devices such as battery chargers. In this project, a solar powered
battery charger with a state of charge indicator circuit is developed to charge AA
batteries and to show indication to the user when the batteries reach a fully
charged state. The primary benefit of using a solar powered battery charger is
that it is one of the cheapest forms of recharging batteries. Apart from this, s olar
powered battery chargers are fast gaining popularity as they have been proven to
be handy in many situations especially in the outdoors, being portable and user
friendly. In this project, a constant current source is provided to the batteries in
order to recharge it and the state of charge indicator circuit is developed with an
adjustable precision Zener shunt regulator. Once the batteries are fully charged,
an LED will light up to show the user that the batteries can now be used reused.
CHAPTER 1
INTRODUCTION
1.1 Introduction
The introduction to this thesis can be divided into four major parts. Each
sub section will discuss the background of the project, problem statement,
objectives and scope of the project.
1.2 Project background
There are many forms of renewable energy on earth. Solar energy is one
of this many form. The earth receives about IXIO12 MW of energy from the sun
every year. This amount is enough to cover the Earth's energy demand for over
1000 times. Capturing sunlight and turning them into electricity for daily usage is
a very good way to minimize expenditure and pollution. Solar energy has proven
to be a clean and safe form of energy for our daily living and is made available
naturally around most parts of the world.
Solar energy can be harnessed by using a solar cell or photovoltaic cell to
convert sunlight directly into electricity. Since the development of early
photovoltaic cells, the very first photovoltaic system has been applied in
Malaysia in early 1980s. The applications of photovoltaic system were mainly
concentrated on stand-alone systems, especially for rural electrification program. 2
However, lately we find that solar power can be used in many devices
such as water heaters, home lighting systems and even calculators. Furthermore,
smaller electrical appliances such as garden lights and street lights are also
powered by solar energy. Due to the introduction of solar energy to power small
electrical appliances, we now find that battery chargers can also utilise this
source of power. In fact, one of the cheapest forms of recharging batteries is by using a solar cell as it is simple to construct and the energy obtained from the sun
is free. Solar powered battery chargers are fast gaining popularity as they have
been proven to be handy in many situations especially in the outdoors.
Furthermore, this battery charger is quite portable and user friendly too as it is
simple to handle. These attractive features are further enhanced by the fact that
this type of battery charger is cheap to construct and has many added advantages.
The solar powered battery charger is environmentally safe too as it
purely uses renewable energy and reduces chemical waste because it allows
alkaline batteries to be reused for a certain amount of times before being
disposed. This type of battery charger also has a longer life cycle as it requires
minimal maintenance and can directly convert energy from the sun to produce
electricity.
1.3 Problem statement
We tend to use many batteries powered electrical devices in our daily lives
especially when we are outdoors during hikes, camping, road trips and vacations.
These electrical devices such as torch lights, radios and walkie talkies are
essential items when we are outdoors. When these electrical devices run out of
battery charge, we usually find ourselves in a lurch in locating a suitable power 3
source to recharge the batteries. Hence, in this situation, a solar powered battery
charger would be a more practical solution to charge these batteries.
1.4 Objectives
There are two objectives in this project. They are as the following
(i) To develop a solar powered battery charger.
(ii) To develop a state of charge, (SOC) circuit to indicate the charging level
of the batteries.
1.5 Scope of project
Scope of this project can be narrowed down into two main areas. They
are as the following
(i) To use supply purely from a solar cell.
The battery charger is expected to be powered using a 20 V 10 W solar
panel. This solar panel will function as the power supply to the entire
circuit with a supply current of around 0.5A when the solar panel is able
to perform at its maximum level.
(ii) Battery charger has an output of 1.5-3 V.
The battery charger is expected to have an output of 1.5-3 V of charging
voltage. The charging unit is expected to be able to produce a charging 4
current of around 83 mA. This current will then be capable of charging
one or two alkaline batteries each with the output voltage of 1.5 V.
CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
The literature review of this thesis is divided into three parts. The first
part of the literature review begins with an introduction to solar power as a form
of renewable energy. It also concentrates on the benefits that can be obtained
from using solar energy as a power source. The second part of the literature
review gives a history of the solar cell and its chemical composition. This part
also dwells on how a solar cell works. The third part is a summary of the
benefits of a battery charger in particular the solar battery charger. It also
explains how solar powered battery charger can be developed.
2.2 Solar Energy
Solar energy is be categorized as energy in the form of heat and light
from the sun. Energy from the sun travels to the earth in the form of
electromagnetic radiation with a wide spectrum of frequency range. Available
solar energy is often expressed in units of energy per time per unit area, such as
watts per square meter (W/m2 ) or watt hours per square meter (WHIm
2 ). The amount of energy available from the sun outside the Earth's atmosphere is
approximately 13 67 W/m 2[1]. no
At any particular time, the available solar energy is primarily dependent
upon how high the sun is in the sky and current cloud conditions. On a monthly
or annual basis, the amount of solar energy available also depends upon the
location. In general, useable solar energy is depends upon available solar energy,
other weather conditions, the technology used, pollution or geographical position
and the application involved [2,3].
2.2.1 Solar Energy as a Power Source
Electricity generation using solar cells has been of particular interest for a
long time and is fast gaining popularity among countries that lie across the
Equator. Malaysia, as a country close to the Equator, possesses a daily peak
solar hours more than 4 hours. This is higher than those in Japan. Germany and
USA where solar energy, as an alternative energy, has been strongly supported
by their governments. The availability of solar energy in Malaysia makes it an
ideal source for power generation.
Energy substitution is not a recent innovation as many forms of
renewable or alternative energy have been explored to date [4]. Solar energy
demand has grown at about 25% per annum over the past 15 years. This form of
energy has been accepted worldwide as a high potential alternative energy as
current research and markets have shown that solar photovoltaics (PV) is
amongst the fastest growing and most promising forms of renewable energy for
electricity generation [2].
To understand how solar energy can be fully utilized, we first need to
understand and useful way by utilizing an old, well-known physical
phenomenon, the photovoltaic effect, whereby some of the sun's light is
transformed directly into electricity [4]. 7
A photovoltaic solar cell is essentially a semiconductor which can
generate as electric potential when ionized by radiation. In other words, a solar
cell can convert the radiant energy of sunlight directly into electricity with high
reliability and long life cycle.
2.2.2 Benefits of Solar Energy
cells have been used to charge various solar batteries for applications in
aerospace industry, electric vehicles, communication equipment and remote
motor supplies [5]. Many different applications of PV systems are possible and
vary from water pumps to total electrification of remote villages, serving
multiple loads [4, 6] and satellite power systems [7]. In Malaysia, the potential
of solar energy has begun to be utilised in a wide range of applications such as
heating, lighting and other forms of agricultural uses as well a wide range of
applications in remote and urban areas [8].
There are many benefits to be gained from using solar energy as a power
source. Photovoltaic technology has been proven to be a new and exciting energy
source as its conversion method is both novel and unique. Photovoltaic power
systems do not contain any moving parts which may wear out, do not contain any
fluids or gasses which could leak and can operate at moderate temperatures.
Furthermore, no fuel is needed to activate this system, making it a non-polluting
and quick responding as well as almost maintenance free power source [1].
Solar energy does not give rise for environmental concern as some other
conventional energy sources which contribute dangerous chemical emissions [8].
On the plus side, photovoltaic array can be made from silicon, a common
element found on earth. Recent technological developments in thin-film 8
.photovoltaic, such as amorphous silicon and hybrid die sensitized/photovoltaic
(PV) cells, are leading to new generations of consumer portable solar arrays.
These new arrays are lightweight, durable, and flexible and have been reported to
achieve power efficiencies of up to 10%.
Commercial-off-the-shelf arrays already exist, that have panels embedded
in fabric that can be folded to dimensions of less than 12" x 12", yet are able to
produce up to 50 Watts of power at 12 V. These new products make solar power
available to hikers, campers, soldiers-on-the-move, etc., since the arrays can now
be easily carried in backpacks [9].
2.3 Solar Cell
The solar panel, sometimes called solar cell or photovoltaic cell is a
device that converts light directly into electricity by the photovoltaic effect.
Sometimes the term solar cell is reserved for devices intended specifically to
capture energy from sunlight, while the term photovoltaic cell is used when the
light source is unspecified. Assemblies of cells are used to make solar pan els,
solar modules, or photovoltaic arrays. These arrays are then used during energy conversion.
2.3.1 History of the Solar Cell
observed that the action of shining light on an electrode submerged in a
conductive solution would create an electric current. Forty years later the first
solid state photovoltaic device was created as the photoconductivity of selenium
was discovered. In 1894, Charles Fritts prepared the first large area solar cell by
pressing a layer of selenium between gold and another metal. This paved the way
for observing early cells which were thin film Schottky barrier devices where a
semitransparent layer of metal deposited on top of the semiconductor top
provides photovoltaic action [10].
However, it was not the photovoltaic properties of materials like selenium
that was further researched on but its photoconductivity was given importance.
The fact that the current produced was proportional to the intensity of the
incident light and related to the wavelength of light in a definite way meant that
photoconductive materials were ideal for photographic light meters. This meant
that the light meter could operate without a power supply. It was not until the
1950's however that through the development of good quality silicon wafer;
potentially useful quantities of power were produced by photovoltaic devices in
crystalline silicon [10].
Further development in silicon electronics lead to the manufacturing ofpn junctions
in silicon. The first silicon solar cell was reported in 1954 and was
recorded to have converted sunlight with an efficiency of six times higher than
selenium. This early silicon cell introduced the possibility of power generation
in remote locations where fuel could not easily be delivered. It was also used in
satellite development where the requirement for reliability and low weight made
silicon solar cells widely developed for space application.
In the 1970's, the crisis in energy supply paved the way to a sudden
growth of interest in alternative sources of energy. Photovoltaics became a
subject of intense interest during this period of time and strategies for producing
cheaper photovoltaic devices and materials were explored.
Routes to lower cost included photo electrochemical junctions and
alternative materials such as polycrystalline silicon, amorphous silicon, other 10
'thin film' materials and organic conductors. This interest continued to expand
in the 1990's, along with the growing awareness of the need to secure sources of
electricity alternative to fossil fuels.
At present, the majority of PV modules currently in use are based on
monocrystalline and polycrystalline silicon. Crystalline means that the material
in the PV has a regular ordered internal structure within each grain. The
electrical properties of the crystalline PV are affected by the boundaries between
grains. The PV modules made from monocrystalline silicon offer the highest
efficiencies because they have no grain boundaries, but are also most expensive
to manufacture. To contrast, the poly-crystalline PV modules are somewhat less
efficient, but are cheaper to produce. Currently two types of PV modules have
very similar cost of per watt electricity. In comparison with the crystalline silicon
PV, thin film technology holds the promise of reducing the module cost through
low material and energy consumption during the fabrication [2].
During this current period, the economics of photovoltaics is
continuously expanding and has become competitive with conventional
electricity supply for remoter low power applications such as navigation,
telecommunications and rural electrification as well as for enhancement of supply
in grid- connected loads during peak usage.
2.3.2 How a Solar Cell Works
Solar photovoltaic conversion is a one-step conversion process which
generates electrical energy from light energy. This explanation relies on ideas
from quantum theory. Light is made up of packets of energy, called photons,
whose energy depends only upon the frequency or colour of light. The energy of
metal
1 1%1 1irh* I icihf I
visible photons is sufficient to excite electrons, bound into solids up to higher
energy levels where they are freer to move [10].
Normally, when light is absorbed by matter, photons are given up to
excite electrons to higher energy states within the material, but the excited
electrons quicidy relax back to their ground state.
This action can be described further through Figure 2.1. The diagram on
the left (a) shows the photoelectric effect where ultraviolet light liberates
electrons from the surface of a metal [10].
(a) figure 2.1 Comparison between (a) Photoelectric effect in metal, and
(b) Photovoltaic effect in a solar cell
However, in a photovoltaic device, as seen on the right, (b) in Figure 2. 1,
when electrons are knocked loose from their atoms, there is some built in
symmetry which pulls away the excited electrons before they can relax and feeds
them to an external circuit, thus allowing them to flow through the material to produce electricity. Due to the special composition of solar cells, the electrons
are only allowed to move in a single direction.
12
The extra energy of the excited electrons generates a potential difference
or electromotive force (emf). This force is then converted into a usable amount
of direct current (DC) electricity as shown further in Figure 2.1 and drives the
electrons through a load in the external circuit to do electrical work.
On the whole, the effectiveness of a photovoltaic device depends upon the
choice of light absorbing materials and the way in which they are connected to
the external circuit.
2.4 Battery Charger
Battery chargers are generally used to recharge rechargeable batteries.
Some common types of rechargeable batteries are nickel cadmium (NiCd), nickel
metal hydride (NiMH) and lithium ion (Li-ion). However in some cases,
disposable alkaline batteries can also be recharged. The idea of recharging
alkaline batteries is not new. Although not endorsed by manufacturers, ordinary
alkaline batteries have been recharged in households for many years.
Recharging these batteries is only effective, however, if the cells have
been' discharged to less than 50 % of their total capacity. The number of times a
battery can be recharged depends on many factors. These include the
discharging drain load or depth of discharge, the frequency of use, the length of
time in a discharged state, charge temperature and conditioning With each
recharge, the amount of capacity the cell can hold is reduced.
Recharging batteries reduce the ecological impact as for a same quantity
of energy produced; rechargeable batteries have up to 32 times less impact on the
environment than disposable batteries. When batteries are improperly disposed
of in household and workplace waste, they can leak toxic heavy metals into the
13
environment as batteries leach heavy metals slowly into the soil and ground and
surface water. When batteries are incinerated, certain metals may be released
into the air or concentrated in the ash that has to be disposed.
Heavy metals from batteries can make it into the food chain where they
pose health impacts on humans. Mercury was phased out of certain batteries
starting in 1996 with the signing of the Battery Act, but other heavy metals such
as cadmium are still used, which are very toxic [11].
Recycling of batteries through the proper collection and disposal at a
municipal collection location will greatly reduce their impact on the
environment. Using rechargeable batteries reduces the manufacturing levels of
heavy metals and greatly reduces disposal requirements. It also lessens the
impact on air pollution, global warming, air acidification and water pollution. In
short, by recharging batteries, we are reducing waste [11].
Hence, when a battery charger is combined with a solar panel as its
power supply, it creates an environmental friendly battery charger. A solar
battery charger is also simple and inexpensive method for recharging batteries. It
may be applied for small power battery charging or for direct solar power
supplies such as in calculators, signs and lightings etc [5].
One obvious specialty of the solar battery charger is that we do not need a
power outlet for it to function. The solar battery charger fully relies on the sun
alone for its charging energy and can be used in any location where sunshine is
available. Since an external electrical source is not required to recharge
batteries, the solar battery charger offers freedom of movement. This type of
charger can be fully portable, lightweight and user friendly. 14
However, most solar chargers require a longer period of time to charge a
set of batteries compared to other conventional chargers [12]. This is because
even in bright sunlight, most solar cells currently in production are only about 10
percent efficient, which makes them slower than chargers that plug into a wall
outlet.
2.5 Solar Powered Battery Charger Development
A simple solar battery charger is generally made up of four parts. A
common solar powered battery charger is shown in Figure 1, with the various
possible subsystems that comprise it [2].
Solar ...........Voltage Energy
Loads
Figure 2.2 Subsystem of a solar powered battery charger
The solar PV array is the source which generates electricity when
exposed to sunlight, thereby producing DC power. The solar array is made with
multiples of solar cells. The solar cells are connected in a series-parallel
configuration to match the required solar voltage and power rating [7].
As shown in Figure 2.2, the solar PV array is then connected to the
voltage regulation subsystem. The voltage regulator maintains the system's
15
voltage between low and high voltage limits when power is available froni the
array and creates a constant-current constant-voltage charge.
To understand the concept of a constant-current constant-voltage charge,
we must first realize that there are several techniques used in the conventional
approach to charging a battery. The first and the most common in consumer products is the constant current trickle charge. These chargers provide a very
low, constant current rate to the battery and rely on the user to stop the charge
when the battery has returned to full capacity [13].
A deviation on the constant current charge approach is the constant—
current constant-voltage charge profile. Under this arrangement, a constant
current is applied until battery voltage rises to a predetermined value, at which
point the charging voltage is held constant and the current is reduced. When the
current has reached a minimum value, the charging stops [13].
In some applications, the solar battery charger is a stand-alone system
which includes a power converter which is used to control the solar array voltage
into desired voltage. This power controller is usually either a buck converter
which steps-down the input voltage or a boost converter that steps-up the
voltage. In short, the power converter plays an important role in the voltage
regulation of the charger [7].
The voltage from the regulator then is channeled to a diode as shown in
Figure 2.2. The blocking diode controls the direction of the flow of energy
between the array and the system to prevent discharge of the energy storage
system through the solar array and subsequent loss of energy or damage to the
array.
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