A to design a simple solar battery charging

Project Paper on Solar Battery Charger

Abstract- The main target of our project is
to design a simple solar battery charging circuit where a photovoltaic (PV)
panel is used to convert the solar energy into electrical energy and stored in
the rechargeable battery. The shunt regulator has also been used to prevent overcharging.
We have worked on the following circuit design.                     Fig.1: Solar   Battery  

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The demand of energy in
the world is very high. The continuing expansion of human population and
economic growth are the main reasons for such a huge demand of energy. A
non-renewable energy sources are being used since a long time to fulfill a
daily necessity of energy consumption in the world. The fossil fuels such as
coal, natural gas, petrol are the key sources of non-renewable energy. The demand
of fossil fuels is extremely high, but they are very limited in quantity. They
are not consistently accessible in the world. On other hand, there are many
disadvantages of using non-renewable energy. The fossil fuels are primarily
carbon based. The use of coal, oil and other natural gas produces huge quantity
of carbon dioxide and carbon monoxide, and these are the main causes for global
warming. They play a crucial role on destroying the ozon layer too. The oxides
produce from burning fossil fuels make a rain acidic which is very dangerous
for living creatures in the planet. To avoid the energy crises in future, the
creation and the implementation of other sustainable energy sources are
severely important and required. Sustainable energy is all about creating pure
and renewable sources of energy. It does not use any sources that are based on
fossil fuels. From few choices of sustainable energy, the solar energy is
considered the most effective and ideal form of sustainable energy. It is one
of the most common thing in the sector of renewable energy. Thermal energy and
the electrical energy are the two types of energy where solar radiation is
normally converted into. The energy in solar power is entirely obtained from
the power of the sun. Solar energy is a boundless, renewable energy source. Solar
energy can be applied in many implementations like irrigation, rural
electricity, and satellite communications. It is accessible to everybody in all
locations at impartially equal manner, whereas the fossil fuel sources are
obtainable only at certain locations. The solar energy does not produce any
harmful rays, so it does not cause any damage on our ecosystem. In short, solar
power is an extensive and inexhaustible form of energy.

Regarding our project,
we have designed a solar battery charging circuit which is entirely related
with solar power energy. The main purpose of our design is to charge a
rechargeable battery by using solar energy. 
In simple words, solar energy is converted into electrical energy and
stored in a rechargeable battery. Battery can be again recharged, after the battery
gets discharged.

            Components used:

–       17V
40W Solar Panel

–       Rechargeable
12V Battery

–       Resistors

–       Zener

–       Capacitor

–       Comparator

–       Darlington

–       Diode


Solar Panels are tools
that convert light into electricity. The solar panel is used as a device of a
larger photovoltaic system to produce and provide electricity for different
commercial and residential use. One solar panel can only generate a limited
quantity of power, so majority of applications use multiple panels. It is a
collection of solar cells. The solar cells are the fundamental building block
of solar panel. Solar cells are also called photovoltaic cells, which operate
to create electricity straightly from sunlight. The sun radiates a huge
quantity of energy every second. The solar cells are composed of silicon
semiconductors which absorb sunlight and transformed it into electricity. The
solar cell is located between n-type silicon and p-type silicon. The each cell
is designed with a positive and a negative layer to create an electric field,
just like in the battery. When sunlight hits solar cells, photons are absorbed
in the cell, and their energy causes electrons to become free. The electrons
move towards the bottom of the cell, and exit through the connecting wire. This
flow of electrons is considered as electricity. By combining solar cells in
photovoltaic panels, the required amount of electricity can be produced to
perform a specific job.

The PV output power is
relied on solar irradiance and cell temperature. The following fig.2 has
displayed that the low irradiance results to low power, and high temperature
results in reducing in output power. The accuracy of the other components of
the entire system and environmental situations are other aspects which the
quantity of energy delivered by a PV module is dependent. Likewise, the rise in
sun power increase the output power of the solar cells, but simultaneously, the
increase of cell temperature impacts its electrical working capacity
negatively.   Fig.2:
P-V characteristics of a PV


For our design, we have
used 12V rechargeable battery. The battery is composed up of voltaic cells.
Batteries are very significant of any productive solar panel system. The energy
created by the sun and solar panels are stored in the batteries. It can be said
that in the absence of batteries, the system becomes totally ineffective.
Regarding a battery selection for our design, deep cycle battery has been
picked over shallow cycle battery. Deep cycle battery has designed to supply a
stable amount of current for a long duration of time phase where as shallow
cycle battery supply a very big amount of current for a very short duration of
time. Moreover, it can be said that a shallow cycle battery has a lot of
current available but at the same time it has a large amount of voltage drop.
Rechargeable type battery has its electrochemical reactions electrically
reversible where as a non-rechargeable type battery generates electricity using
an electrochemical reaction. Lead-acid batteries are most often used for small
PV charging system, and the main reason for this is because of their capacity
to supply a substantial amount of current. The different phases of charging
lead-acid batteries is very important because it limits how much current we can
send to the battery at different times. Our system only excess voltage from
reaching the battery, and does not regulate the amount of current sent to the
battery. The fig.3 below demonstrates a different charging phases of a
lead-acid battery. The constant-current charge, topping charge, and float charge
are three main charging stages of lead acid batteries. Moreover, different
chemical compositions might need more complex charging phases.

Charge stages of a lead cycle battery


A resistor is an
electronic device that controls or regulates the flow of electrical current in
a circuit. The current travelling via a resistor is directly proportion to the
voltage across the resistor’s terminals. If a resistance is high in a circuit,
then it can be determined that the flow of current is small for a given voltage,
where as if the resistance in low, then the flow of current is high for a given
circuit. The resistivity of resistor is affected by the temperature of a
resistor. If the resistor gets heated, then it is going to be more resistance
to current flow. Resistor is also used to add a required voltage for an active device.


Comparator circuits are
commonly operational amplifier based. They compare two or multiple inputs and
signal an output to let it know about which input is either greater or smaller.
The outcome of this comparison is denoted by the output voltage. They usually
compare voltage or current levels as inputs. While comparing the inputs, if one
is higher than the other one, then the comparator circuit output stays in one
condition, but when the inputs state are reversed, then the output of the
comparator switches. The comparator can also be used for identifying if an
arbitrary varying input signal hits reference level or a defined threshold
level. The different components such as diodes, op-amps can be used to
construct the comparator. Moreover, the comparators can be spotted in various
electronic implementations which may be used to drive logic circuit.  The comparators are extensively being used in
automatic switching devices, environment monitoring devices, analog to digital
converters.   Basically, in both accepting and outputting
case op-amp deals with analog signal, but the comparator only produces output
as digital signal.

our circuit, comparator is used to bias the Darlington pair amplifier when the
solar panel outputs excessive voltage. The potentiometer is used to control
when the amplifier turns on, which sets the maximum charging voltage for the
battery. In the following LT spice model, the use and implementation of
comparator in our circuit has been shown.

Comparator in LT spice model

The following fig.5 has demonstrated the performance
of comparator in our circuit. Looking at this figure, it can be said that when
V+ is greater than or equal to V-, the op-amp turns on, and here it is
represented by the pink and teal spikes.

Comparator performance


The Darlington pair is
a very essential circuit configuration for various electronic circuits
implementation. It gives numerous benefits that other structures of transistor
circuits are not capable to provide, and this is the main reason of its used in
various sectors of electronics scheme. In many implementation and application,
a single transistor might not be able to transfer enough current needed by the
load, which means the amount of input current accessible to switch on the
transistors is very less, so in this case, Darlington pair can be very
effective to use because it consists of two transistors but behaves as a single
transistor with a very high current gain. It provides very high input impedance
for overall circuit. Darlington is also called Super Alpha Pair.

the following LT spice model, the functioning and implementation of Darlington
Pair in our circuit has been shown.

Darlington Pair Amplifier in LT spice

When the Darlington
Pair is biased through the R_Driver resistor by the comparator, the amplifier
is powered on. As the voltage from the comparator increases, the Beta value of
this amplifier sky rockets, and this causes a massive current rush through the
burn-off resistor. The burn-off resistor is exclusively used to dissipate any
excess power to battery through heat generation. The following fig.7 has
demonstrated the performance of Darlington Pair in our circuit. From the
figure, it can be concluded that, in our circuit, the Darlington Pair amplifies
the base current by nearly 7,000 times during peak power consumption.   Fig.7:
Darlington Pair performance


very few equations were used to verify the circuit.

Ohm’s law: V=I*R

Power: P=I*R

Voltage Divider: = * /

Transistor amplification:

= (?+1) *

Op-Amp Gain:=  / ( -)

Power Transmission Efficiency:


Here,  is the power going to the battery.


our model, the voltage source with a resistor does not exactly reflect the
constant current supplied by a solar panel; therefore the results are not
perfectly accurate. Moreover, using sine wave for this model is fairly
irregular. In reality, it looks more like a square wave. When adding white
noise, it really did not reproduce noise in the field. Overall, the power
efficiency was at a maximum of 70%, which explains that 80% of the power has
reached the battery directly.

some reason, the battery voltage in Fig.8 always stayed above 2V, even when the
supplied voltage was less than this. This leads to the asymptotes in Fig.9 for
the conversion ratio.  Fig.8: Solar panel voltage, charger voltage and charge
current over time.


 Fig.9: Power
output of solar panel and power input of battery over time. Power conversion
ratio over time also shown.


Solar battery charger
does not need any external electrical sources to get battery recharged, so it
can be said that this design has a benefit of freedom of movement. To charge
the battery at constant voltage, solar charger requires voltage regulator. On
the other hand, the voltage supplied by a solar panel can be varied
considerably depending with the time, climate situation, and irradiation from
the sun. The solar cells are the back bone of any electric circuit. For our
circuit, solar panels are used as a power supply and supply into a voltage
regulator in order to have a constant voltage charging for the battery.
Batteries are the most effective way to store solar energy. Consequently, solar
charger circuits target at charging batteries rather than driving components.
When the battery gets fully charged, it is very important to cut off charging.
This can be handled by using a zener diode. It switches on if there is a
cut-off voltage and supplies the current via the transistor. The solar battery
charger is one of the best examples of solar powered devices. The batteries can
be recharged and reused by using solar power. By implementing this design, the
non-renewable energy source can be conserved. This design can be taken as one
of the good example for how without spoiling the environment, the natural
energy sources can be used for the energy needs. The most vital thing to be
noticed is that by utilizing the solar power, the rate of consumption of
nonrenewable sources can be instantly minimized. Moreover, the solar energy is
getting more powerful as a renewable source because of its many beneficial features.
The solar energy needs collectors and different equipment to convert solar
energy into electrical energy, but it is always free and renewable. The solar
energy is sustainable source. The source of sustainable energy provides the
necessity of present generation without harming the capacity of upcoming
generations to meet their requirements. In simple word, solar energy is
referred as sustainable energy source because it can never be over consumed. The
solar energy is considered as an everlasting source of renewable energy where
as sources of fossil fuels are limited in quantity. After working on our
project, we have learned to explain the connection between the direction of
electrons flowing via a battery and the change in the battery’s voltage. The
technological improvements are steadily being done in the device and configuration
of solar power components, so as a result, the solar cells in the panel is
becoming more effective and powerful at converting solar energy into electrical
energy. In future, more exceptional technological renovation could happen, and
more effectiveness and benefits could be achieved from solar power energy.