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Abstract—. Vedic literatures in India even state the use of
flying machines which were powered using the sun. Coming
21st century, we have come a long way in developing solar cells
which are the devices powering our future, converting sun’s
energy into electricity. This work is about using non
conventional energy i.e. solar energy for mobile battery
charging. Solar chargers are simple, portable and ready to
use devices which can be used by anyone especially in remote
areas. Solar panels don’t supply regulated voltage while
batteries need so for charging. Hence, an external adjustable
voltage regulator is used to have the desired constant voltage.
INTRODUCTION
Though the years, technology has allowed the cellular
phone to shrink not only the size of the ICs, but also the
batteries. However, as technology has advanced and made
our phone smaller and easier to use we still have one of the
original problem that we must plug the phones into the
walls in order to recharge the battery. Most people accept
the reality as there is no other option to this problem so they
carry extra batteries with them. Every time it is not possible
to charge mobile batteries everywhere at any time so we
design this mobile charger from which we can charge the
mobile battery anywhere at any time. In this project we are
using the concept of energy harvesting by using solar
energy for battery charging purpose. By using this we can
charge our mobile battery in remote areas where there is a
problem of electricity. Cost of this circuitry can be reduced
to certain extend so that common man can easily purchase
that and get benefit from that.
We will give the wide scope to this project by making
certain modifications and we can use this charger for
different handsets. Also modification to this project will be
applying to any battery operated devices like laptop. This
project can be divided into two main parts which are
hardware and software development. The hardware
development includes the solar panel connection, charging
and control circuit and microcontroller. The software
developments include the microcontroller programming.
THEORETICAL BACKGROUND
A. How are Solar Panels Made
Solar energy has long been grabbing attention of the
scientists and researchers as true alternate solution to fossil
fuel energy. Noticing the enormous abundance of sunlight
available to us as a blessing from our sun, it is not unusual
to wish to tap this energy which has been there since the
beginning of time and use it drive our engines and homes.
However the solar energy even though it is available in
abundance, the efforts to use this energy and transfer it into
a usable form and drives our day to day appliances has been
in vain. That is why solar energy has not become our prime
source of our energy requirements. We are either relying on
hydroelectric power which in turn causes environmental
disaster or we burn coal or use nuclear energy to generate
electricity. The main reason why we are not able to use the
solar energy is our solar panels are not able to tap more than
20% of its energy. This results in huge investment cost but
low return of investment. This makes the investment in
solar energy unattractive and therefore is becoming less and
less popular. However researchers all round the world have
been able to develop solar panels that will tap this solar
energy more efficiently. In order to understand how this is
possible we need to understand how solar panels are made.
There are two basic types of solar panels, first is the
crystalline solar panels made of crystalline silicon and other
is amorphous silicon panel which is made from amorphous
silicon.
In order to make Crystalline solar panels, thin disks are cut
from silicon in its crystalline form which are .8 cm thick.
These disks are then subjected to a careful polishing and
repairing process to ensure that no damage occurred during
the cutting process has remained unattended. The thickness
of these disks is so less that they appear to be wafer like
disks which gives them the name “silicon wafers”. Now for
the main part of the process, adding the “dopants”. Dopants
are materials that are added to these silicon wafer disks so
that they get electrically charged. The positive and the
negative charges are added accordingly in these silicon
disks and then are joined together so that electrons when
subjected to sunlight can flow and conduct electricity.
These disks now with the dopants in them are aligned
horizontal and vertical manner to form a matrix pattern
forming a solar panel. These solar panels are then covered
with glass plate in order to protect them from any physical
damage or scratches. The solar energy that our panels
receive has two types of energy light and heat energy. These
solar panels are then fitted with a special type of cement.
This is conductive cement which transfers the thermal
energy from the solar panels this preventing the solar
panels from the heat. This method of manufacturing solar
panels is quite traditional and has been used by many solar
panel manufacturers.
The amorphous silicon solar panels are made quite
differently. The manufacturing process of amorphous
silicon panels involves depositing silicon alloys in various
layers. The solar cells made by this process are far more
efficient and are capable of absorbing a wider range of solar
spectrum. This type of panel manufacturing is now
becoming very popular and is fast growing into an industry.
The material cost of such solar panel is also cheap. The
solar cells made from with this process have special ability
to continue giving the same output even when the entire
array of cells has come under shade. This prevents the
circuit from being breaking and thus maintains the same
energy output.
B. Solar Energy Compared to Other Alternative Energy
Sources
We have to switch to clean an energy source, which is for
sure after realizing the consequences of using the fossil
fuels and destroying the environment. The big question is
how? Millions around the world depend on the vast energy
reserves available deep down the earth. The reserves are
depleting and will dry out soon. On the other hand the
demand and the consumption rate are not going down. This
is why we have to find out an energy source which will not
only be free of pollution and eco friendly but also be able to
produce enough energy to power our needs? So the question
is whether there exist and energy source that can meet our
needs or not. Let us discuss three alternative energy
solutions that are available and find out whether that can be
the one or not. These changes in the temperature and
pressure occur due to the difference in the amounts of heat
energy received by different areas from the sun depending
on the earth’s rotation. This energy in the form of wind can
be converted into electrical or chemical energy, stored in
the batteries. The devices used to tap this wind energy are
windmills, as the wind blows the rotational energy of
turbines is converted into electrical energy by generators.
The process is clean, eco friendly and also renewable. One
wind mill can produce enough energy to power a house.
However the electrical energy that is produced from the
turbines is not enough compared to the energy produced
from the fossil fuels. The disadvantage is that it is costly
and not completely renewable; therefore a better way needs
to be discovered to produce energy completely clean and eco
friendly. As the wind does not blow at a constant speed and
there is no certainty about the wind direction and therefore
the output is not efficient as it should be. Also, the wind
mills subjected to a severe damage when struck by heavy
rains and lightning storms can be subjected to heavy
damage. The second is the biomass.
Biomass is a true renewable source of energy. This is
because the substance used to produce energy is the excretal
waste and remains of plants and animals, also human
waste. Basically any organic material can produce bio
energy. This therefore includes agricultural wastes, organic
wastes, waste paper and waste from the food processing
industries. Since this type of waste keeps getting produced
everyday and in tons, there is no chance that the biomass
energy such as bio fuel can get exhausted. The cons are similar to the wind power, very expensive therefore not
enough energy output. Apart from these constraints, a bi
product is created nitrogen oxide which is not good for the
atmosphere if produced in large amounts.
Next is the solar energy, out of all the three energy sources
this one is the most diversified form of renewable energy.
Sun’s heat energy can be used for various purposes which
make it versatile. Through technological advancement, we
have the capability to tap solar energy and produce energy
and then store it. We also have developed devices that can
harness the sun’s heat energy for different purposes such as
distilling water, boiling water for bathing or drinking etc.
the cons is that the sunlight only remains for sometime
during the day and therefore our solar panels should be
efficient enough to absorb enough energy that can take us
through the day. But as mentioned above efficient panels
have been built and there is hope that we will be able to
create solar panels powerful enough to absorb more energy
and become self sufficient. Therefore solar energy seems to
be the true alternative energy source which we can use it.
The principle used to generate electricity from the solar
panels is the same as that used to generate electricity from
the chemical reaction using a standard battery. The basic
working of solar panels depends on the semi conductor
property of silicon. The silicon is a unique substance that
has revolutionized the way electronic appliances work. This
property is used to generate electricity from the solar
panels. In order to understand how solar panels work we
need to understand how silicon works at an atomic level.
Silicon in its pure form i.e. when all the impurities have
been removed a silicon atom is bonded with another silicon
atom. Since the valency of silicon atom is 8 which means
that there are 8 electrons in its outermost orbit. However in
its natural state there are only 4 electrons bounded in the
outermost orbit. Hence these 4 electrons are able to bond
with another 4 electrons with 4 silicon atoms around it. The
4 free electrons that can move around throughout the
substance. During the absence of electric potential these
free electrons tend to remain close to their parent atoms so
that they are at minimum energy level. However when the
electric potential is applied across the substance these free
electrons receive energy and move direction of the potential
difference applied thus producing electric current. However
the current produced in a pure semiconductor is quite less because these free electrons wants to remain at minimum
energy level possible. Now let us take an example of a pure
silicon semiconductor and introduce a small amount of
phosphorus. Now this new atom has five electrons around
it. When it bonds with other 4 silicon atoms, its fifth
electron is free. But again during the absence of potential
difference, the fifth electron is bonded with the phosphorus
atom. In presence of potential, these free electrons can
move in the direction of the potential difference applied
hence generating electric current. This phosphorus atom is
negatively charged this makes the silicon/phosphorus plate
negatively charged. In the same way when another
substance such as boron is introduced in a pure silicon
plate, it becomes positively charged. This is because boron
has valency 3 and there is one space left in the boron atom
which is called “a hole”. Since this plate hence needs an
electron and hence it becomes positively charged, these two
positive and negatively charged plates when combined
together can now produce electricity. This is when the sun’s
energy comes into picture. The solar radiation coming from
the sun is used as a trigger to initiate a flow of electric
current from positive plate to the negative plate. Now what
exactly in the sun’s radiation causes the electrons to
agitate? The substance is photon. When this photon falls on
the negative plates of the solar panel it knocks off free
electrons on the plate. As this electron is loosely attached to
its parent atom is freed it can now move around the plate.
However this electron is attracted by the positively charged
plate and the electron is bounded again. In the same way
when more photons knock off electrons, electricity is
generated. The current produced by a single solar cell is
very less. However when this current is drawn by the wires,
it can power a small motor or other small electronic devices.
Many solar cells when combined together can produce
sufficient amount of electricity to power a house. However
the main disadvantage of this technology is that
manufacturing cost of these panels is very high, also you
need large amount of solar panels if your energy
requirement is very high. This is the reason why solar
panels and electricity produced through them have a very
high start up cost. The advantage is that when solar panel
are installed they can produce electricity virtually free.
III. FRAME WORK OF PROJECT
A. Proposed Work
Fig 1.shows block diagram & overview of the project.
There are three main input sources like AC input, input
from solar panel and last one is storage battery. Here we are
using PIC microcontroller 16F877A. There is a LCD
display which shows all information related to battery. A
buck converter was chosen because of its simplicity,
efficiency and low heat Dissipation .The PIC
microcontroller controls the buck converter through the use
of hardware PWM Module and an external current sense
resistor. The hardware PWM and current sense resistor
feedback are significant in providing an accurate and
repeatable charge methodology
APPLICATIONS
For low-power portable electronics, like calculators or
small fans, a photovoltaic array may be a reasonable
energy source rather than a battery.
In other situations, such as solar battery chargers,
watches, and flashlights the photovoltaic array is used to
generate electricity that is stored in batteries for later use.
By using over voltage protection circuit we can protect
our battery from over charging. Charge discharge control
circuit contain two-way Switch. It gets active when
voltage exceeds above threshold voltage level.
VI. ADVANTAGES
Cost Effective: Compared to the other mobile chargers,
the solar chargers are cost effective as it absorbs power
from the sun. It does not require electric power
Versatile: It is also known to be versatile as it can be used
for all types of mobile phones
Uninterrupted Power Supply: One of the greatest
advantages of solar mobile phone charger is that it can be
used to charge mobiles even during power outages.
Emergency Purposes: Another benefit is that it hardly
requires any electrical outlet. It can therefore be used
during emergencies and outdoor purposes.
Compact Design: Solar mobile phone chargers are
compact in size and easy to carry around.
VII. LIMITATIONS
Quite expensive: One of the most important drawbacks is
its price compared to the ordinary mobile phone
chargers, it is quite expensive as it utilizes solar energy
captivators.
Charging time large: Another significant drawback is the
time frame required by the chargers to charge mobile
phones. It can take six to eight hours to charge mobile
phones compared to the other.
VIII. CONCLUSION
Renewable energy is not a new concept, nevertheless at an
exponential growing population, the development and
improvement of them are essential to sustain world power
hunger. In 2050 the population expectation on earth is
about 9 billion people, where approximately 5 billion will
use mobile phones. The application of renewable energy at
portable devices starts to plays a significant role at global
energy saving. Solar chargers are simple, portable and
ready to use devices which can be used by anyone especially
in remote areas.