fyp report final

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SOLAR BASED LED WALKWAY LIGHTS

B.E ELECTRONICS ENGINEERING

FINAL YEAR PROJECT REPORTFALL - 2010


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DEPARTMENT OF ELECTRONICS ENGINEERING

FINAL YEAR PROJECT REPORT

ON

SOLAR BASED LED WALKWAY LIGHTS

In the partial fulfillment of the requirements for the Bachelors Degree in Electronics

Engineering.

Submitted By:

Salman Shahid Sheikh 5039 [email protected]

Raza Arshad 4728 [email protected]

AzeemAftab 4727 [email protected]

Naseem-ul-Aziz 5052 naseem_ul@hotmail

Syed Zain Mir 4510 [email protected]

Muhammad Shariq Sami 5054 [email protected]

Shahzad Ahmad 4479 [email protected]

KARACHI, PAKISTAN

2010


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CERTIFICATE

This is to certify that the work carried out by Mr. Salman Shahid, Mr. Raza Arshad, Mr.

AzeemAftab, Mr. Naseem-ul-Aziz, Mr. Zain Mir, Mr. Shahzad Ahmad, and Mr. Muhammad

Shariq Sami for the project entitled Solar Based LED Walkway Lights for the award of the

degree of Bachelors of Electronics Engineering of this institute is based upon their authentic

work. We have the pleasure in forwarding their project. The project was carried out under our

supervision and all the materials included as well as the designing product is the result of their

full year authentic work-effort.

---------------------------------Engr. Kamran Raza

Electronics & TelecommunicationEngineering Department,

Iqra UniversityMain Campus.

(Project Supervisor)

---------------------------------Engr. Ashad Mustafa

Electronics & TelecommunicationEngineering Department,

Iqra UniversityMain Campus.

(Project Coordinator)

---------------------------------

Engr. Muhammad KhalidElectronics & Telecommunication

Engineering Department,Iqra University

Main Campus.(Project Mentor)


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DECLARATION

The project documented in this report was carried out by seven below mentioned final year

undergraduate students as project group members of the Department of Electronics

Engineering for the partial fulfillment of the requirements for the Bachelor Degree of

Engineering. This report and the whole project may be freely referred for any kind of

constructive engineering purposes.

------------------------------------

Mr. Salman Shahid Sheikh(Project Leader)

---------------------------------Mr, Raza Arshad

---------------------------------Mr. AzeemAftab

---------------------------------Mr. Syed Zain Mir

November, 2010

---------------------------------Mr. Naseem-ul-Aziz

---------------------------------Mr. Shahzad Ahmad

---------------------------------

Mr. MuhammadShariq Sami


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ACKNOWLEDGEMENT

We are indebted to Engr. Kamran Raza(Dean of Engineering Department) at Iqra University

for guiding us to develop the system and for helping us to perform the knowledge engineering

task.

We are grateful to Engr. Ashad Mustafaour project coordinator at Iqra University for helping

and guiding us in implementing a real time project. We also thank him for providing us a lot of

time and initiating our communication with other professionals who helped us in making our

project.We are grateful to the team of Engineers at the R&D Department for helping us

inengineering domain to implement our project, providing us time and for coordinating with

us.

We are equally grateful to Engr. Muhammad Khalidfor his encouragement and his promise

to help us throughout the project development.

We are equally grateful to Mr. NisarMohaniat R&D Lab Iqra University for helping us in

designing part of our project.

We are also grateful to Mr. Mukhtarfor his suggestions and acceptance of our request letter to

help us during the installation of our project.


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ABSTRACT

Solar lights work by drawing energy from the sun with the help of a panel or collector. They

capture that energy, and through an intricate process, turn it into the outdoor lighting you need.

The concept of solar energy is not a new one. Solar panels are often installed in houses as a

way to help the homeowner save money on electricity bills. There are, however, some things

about solar panels, even the ones used on lights like these, which can frustrate homeowners.

The primary problem is that solar power does not work in every geographical location. For

instance, if you live in an area that experiences a heavy winter season, you may see a decrease

in the energy collected during the winter months. As a result, you may not be able to enjoy the

lights during the winter months. The good news is that the solar panels are a lot more efficient

at converting the suns light into solar energy. When they first came out they were at 4% now

they are at 30%.

There are two different kinds of solar lights. The first uses the energy it gained from the sun to

power regular bulbs. The second uses the energy to power LED bulbs. LEDs are better at

placing light in a single direction than incandescent or fluorescent bulbs. Because of their

directional output, they have unique design features that can be exploited by clever designs.

LED strip lights can be installed under counters, in hallways, and in staircases; concentrated

arrays can be used for room lighting. LEDs can also be considered for applications such as

gardens, walkways, and decorative fixtures outside garage doors to be the most cost-efficient.

LED lights are more rugged and damage-resistant than compact fluorescents and incandescent

bulbs. LED lights don't flicker. They are very heat sensitive; excessive heat or inappropriate

applications dramatically reduce both light output and lifetime. LEDs provide the best energy

efficiency when compared to CFL and incandescent bulbs. LED fixtures can easily provide

color tenability; i.e. the same bulb can give warm white light or cool white light, or any color

in the spectrum. CFLs cannot do that today. LED fixtures can also be more intelligent through

communication capabilities, enabling them to perform better control, diagnostics, and

automation of functions.


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INTRODUCTION:

Background:

The idea of solar energy started over 100 years ago, but the technology hasn't been as great as it

is until today. With companies finding new ways to use renewable energy resources, solar energy

is going to be more important. Solar energy is one of the best renewable energy sources because

it is so abundant. We'll never have a sun drought, we'll never have to wait for the sun to pick up

nor will we have to drill into earth like with many of the other renewable energy resources.

Solar panels are important to the evolution of the society. It is important for countries, such as

Pakistan, to move away from the dependency on foreign oil and to use energy resources that are

readily available. No one can deny the sun isn't a steady resource. Even on cloudy days, there

should be enough light and leftover energy to power homes through the day. More countries

have to discover ways to use solar panels as part of everyday life. The problem is it is still

cheaper to use fossil fuels in the short term. In the long run, solar panels will be everywhere

making energy cheaper than before.

Objectives:

Following were main objectives of the project:

1. To develop a solar based expert system and install it at Iqra University Main Campus.2. To initiate and to give idea how solar energy can be useful for our university.3. To take first step towards making our campus a zero energy building by using different

renewable energy resources.

Project Overview:

This project is about a solar based system that takes energy from the sun to produce electricity. It

comprises of a Solar panel, LEDs, Battery and a charging circuit. Solar panels, which produce

electricity when sunlight falls uponthem, are mounted in the sunniest area. In order to operate

efficiently, the panels are tilted at around 20-50 degree angle. Once properly mounted, the solar


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panels will start gathering energy from sunlight and transform it into DC power. The generated

solar power is then saved in a large battery to supply power to the LEDs during night. The smart

and efficient working of the charging circuit makes sure to turn on the LEDs as soon as the sun

sets.The picture below shows how the system has been implemented.


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LITERATURE REVIEW:

SOLAR ENERGY:

Solar energy is energy that comes from the sun. Every day the sun radiates, or sends out, an

enormous amount of energy. The sun radiates more energy in one second than people have used

since the beginning of time.

All this energy comes from within the sun itself. Like other stars, the sun is a big gas ball made

up mostly of hydrogen and helium. The sun generates energy in its core in a process called

nuclear fusion. During nuclear fusion, the sun's extremely high pressure and hot temperature

cause hydrogen atoms to come apart and their nuclei (the central cores of the atoms) to fuse or

combine. Four hydrogen nuclei fuse to become one helium atom. But the helium atom weighs

less than the four nuclei that combined to form it. Some matter is lost during nuclear fusion. The

lost matter is emitted into space as radiant energy.

It takes millions of years for the energy in the sun's core to make its way to the solar surface, and

then just a little over eight minutes to travel the 93 million miles to earth. The solar energy

travels to the earth at a speed of 186,000 miles per second, the speed of light.

Only a small portion of the energy radiated by the sun into space strikes the earth, one part in two

billion. Yet this amount of energy is enormous. Every day enough energy strikes the United

States to supply the nation's energy needs for one and a half years.

About 15 percent of the sun's energy that hits the earth is reflected back into space. Another 30

percent is used to evaporate water, which, lifted into the atmosphere, produce's rain-fall. Solar

energy also is absorbed by plants, the land, and the oceans. The rest could be used to supply our

energy needs.

SOLARCELLS:

A solar cell is a device that converts the energy of sunlight directly into electricity by the

photovoltaic effect. The term solar cell is reserved for devices designed specifically to capture


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energy from sunlight while the term photovoltaic cell is used when the light source is

unspecified. Assemblies of cells are used to make solar modules, also known as solar panels. The

energy generated this from solar modules, referred to as solar power, is an example of solar

energy. Photovoltaics is the field of technology and research related to the practical application

of photovoltaic cells in producing electricity from light, though it is often used specifically to

refer to the generation of electricity from sunlight.

SOLARCELL EFFICIENCY FACTORS:

Maximum-power point:

A resistive load on an irradiated cell from zero (a short circuit) to a very high value (an open

circuit) one can determine the maximum-power point, that is the maximum output electrical

power that a cell can deliver at that level of irradiation. Vm.Im = Pm in watts.

Energy Conversion Efficiency:

A solar cells energy conversion efficiency (, eta), is the percentage of power converted (from

absorbed light to electrical energy) and collected, when a solar cell is connected to electrical

circuit. This term is calculated using the ratio of Pm, divided by the input light irradiance under

standard test conditions (E, in W/m) and the surface area of the solar cell (Acin m).

As solar noon on a clear March or September equinox day, the solar radiation at the equator is

about 1000 W/m. Hence, the standard solar radiation (known as the air mass 1.5 spectrum)

has a power density of 1000 watts per square meter. Thus, a 12% efficiency solar cell having 1

m of surface area in full sunlight at solar noon at the equator during either the March or

September equinox will produce approximately 120 watts of peak power.


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Fill Factor:

Another defining term in overall behavior of a solar cell is the fill factor (FF). This is the rate of

the maximum power point divided by the open circuit voltage (Voc) and the short circuit current

(Isc):

Quantum Efficiency:

Quantum efficiency refers to the percentage of absorbed photons that produce electron-hole pairs

(or charge carriers). This is a term intrinsic to the light absorbing material, and not the cell as a

whole (which becomes more relevant for thin-film solar cells). This term should not be confused

with energy conversion efficiency, as it does not convey information about the power collected

from the solar cell.

Comparison of energy conversion efficiencies:

Silicon solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 40.7%

with multiple-junction research lab cells. Solar cell energy conversion efficiencies for

commercially available multicrystalline (mc-Si) solar cells are around 14-16%. The highest

efficiency cells have not always been the most economical for example a 30% efficient

multijuction cell based on exotic materials such as gallium arsenide or indium selenide and

produced in low volume might well cost one hundred times as much as an 8% efficient

amorphous silicon cell in mass production, while only delivering about four times the electrical

power.

To make practical use of solar-generated energy, the electricity is most often fed into the

electricity grid using inverters (grid-connected PV systems); in stand-alone systems, batteries are

used to store the energy that is not needed immediately.


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Peak Watt (OR WATT PEAK):

Since solar cell output power depends on multiple factors, such as the suns incidence angle, for

comparison purposes between different cells and panels, the peak watt (Wp) is used. It is output

power under these conditions:

1. Solar irradiance 1000 W/m2. Solar reference spectrum AM (air mass) 1.53. Cell temperature 25C

SolarCells & Energy Payback:

There is a common conception that solar cells never produce more energy than it takes to makethem. While the expected working lifetime is around 40 years, the energy payback time of a solar

panel is anywhere from 1 to 20 years (usually under five) depending on the type and where it is

used (see net energy gain). This means solar cells can be net energy producers and can

reproduce themselves (from just over once to more than 30 times) over their lifetime.

SOLAR PANEL:

A solar panel (photovoltaic module or photovoltaic panel) is a packaged interconnected assembly

of solar cells, also known as photovoltaic cells. The solar panel is used as a component in a

larger photovoltaic system to offer electricity for commercial and residential applications.

Because a single solar panel can only produce a limited amount of power, many installations

contain several panels. This is known as a photovoltaic array. A photovoltaic installation

typically includes an array of solar panels, an inverter, batteries and interconnection wiring.


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Solar panels generate free power from the sun by converting sunlight to electricity with no

moving parts, zero emissions, and no maintenance. The solar panel, the first component of an

electric solar energy system, is a collection of individual silicon cells that generate electricity

from sunlight. The photons (light particles) produce an electrical current as they strike the

surface of the thin silicon wafers. A single solar cell produces only about 1/2 (.5) of a volt.

However, a typical 12 volt panel about 25 inches by 54 inches will contain 36 cells wired in

series to produce about 17 volts peak output.

Several technologies are used in the manufacturing of solar cells. The most common is

crystalline silicon, and can be either monocrystalline or polycrystalline.Amorphous silicon can

be cheaper but is less efficient at converting solarenergy to electricity. With a reduced life

expectancy and a 6 to 8% transformation efficiency, amorphous silicon is typically used for lowpower equipment,such as portable calculators. New solar technologies, such as silicon ribbonand

thin film photovoltaics, are currently under development. These technologiespromise higher

efficiencies but are not yet widely available.

TYPES OF SOLAR PANELS:

There are three basic types of solar panels

yMonocrystalline

y Polycrystalliney Amorphous

Monocrystalline solar panels:

The most efficient and expensive solar panels are made with Monocrystalline cells. These solar

cells use very pure silicon and involve a complicated crystal growth process. Long silicon rods

are produced which are cut into slices of .2 to .4 mm thick discs or wafers which are then

processed into individual cells that are wired together in the solar panel.


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Polycrystalline solar panels:

Often called Multi-crystalline, solar panels made with Polycrystalline cells are a little less

expensive & slightly less efficient than Monocrystalline cells because the cells are not grown in

single crystals but in a large block of many crystals. This is what gives them that striking

shattered glass appearance. Like Monocrystalline cells, they are also then sliced into wafers to

produce the individual cells that make up the solar panel.

Amorphous solar panels:

These are not really crystals, but a thin layer of silicon deposited on a base material such as metal

or glass to create the solar panel. These Amorphous solar panels are much cheaper, but their

energy efficiency is also much less so more square footage is required to produce the same

amount of power as the Monocrystalline or Polycrystalline type of solar panel. Amorphous solar

panels can even be made into long sheets of roofing material to cover large areas of a south

facing roof surface.


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THEORY AND CONSTRUCTION:

Solar panels use light energy (photons) from the sun to generate electricity through the

photovoltaic effect. The structural (load carrying) member of a module can either be the top layer

(superstrate) or the back layer (substrate). The majority of modules use wafer-based crystalline

silicon cells or a thin-film cell based on cadmium telluride or silicon. Crystalline silicon, which

is commonly used in the wafer form in photovoltaic (PV) modules, is derived from silicon, a

commonly used semi-conductor.

In order to use the cells in practical applications, they must be:

y Connected electrically to one another and to the rest of the systemy Protected from mechanical damage during manufacture, transport, installation and use (in

particular against hail impact, wind and snow loads). This is especially important for

wafer-based silicon cells which are brittle.

y Protected from moisture, which corrodes metal contacts and interconnects, (and for thin-film cells the oxide layer) thus decreasing performance and lifetime.

Most modules are usually rigid, but there are some flexible modules available, based on thin-film

cells.

Electrical connections are made in series to achieve a desired output voltage and/or in parallel to

provide a desired amount of current source capability.

Diodes are included to avoid overheating of cells in case of partial shading. Since cell heating

reduces the operating efficiency it is desirable to minimize the heating. Very few modules


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incorporate any design features to decrease temperature; however installers try to provide good

ventilation behind the module.

New designs of module include concentrator modules in which the light is concentrated by an

array of lenses or mirrors onto an array of small cells. This allows the use of cells with a very

high-cost per unit area (such as gallium arsenide) in a cost-competitive way.

Depending on construction, the photovoltaic can cover a range of frequencies of light and can

produce electricity from them, but sometimes cannot cover the entire solar spectrum

(specifically, ultraviolet, infrared and low or diffused light). Hence much of incident sunlight

energy is wasted when used for solar panels, although they can give far higher efficiencies if

illuminated with monochromatic light. Another design concept is to split the light into different

wavelength ranges and direct the beams onto different cells tuned to the appropriate wavelength

ranges. This is projected to raise efficiency by 50%. Also, the use of infrared photovoltaic cells

can increase the efficiencies, producing power at night.

Sunlight conversion rates (module efficiencies) can vary from 5-18% in commercial production,

typically lower than conversion of isolated cells. Panels with conversion rate of around 18% are

in development incorporating innovations such as power generation on the front and back sides.

LIGHT EMITTING DIODE (LED):

Almost everyone is familiar with light-emitting diodes (LEDs) from their use as indicator lights

and numeric displays on consumer electronic devices. The low output and lack of coloroptions of

LEDs limited the technology to these uses for some time. New LED materials andimproved

production processes have produced bright LEDs in colors throughout the visiblespectrum,

including white light. With efficacies greater than incandescent (and approachingthat of

fluorescent lamps) along with their durability, small size, and light weight, LEDs arefinding theirway into many new applications within the lighting community. These newapplications have

placed increasingly stringent demands on the optical characterization ofLEDs, which serves as

the fundamental baseline for product quality and product design.


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Characteristics of LEDs, including physical size, flux levels, spectrum and spatial

distribution,separate them from typical element sources, which are generally employed and

measuredfor photometric and radiometric quantities. With an LED, it is often difficult to

achievea high level of photometric or radiometric measurement accuracy due to

uncertaintieswithin the measurement equipment and improper test setup. In addition,

traditionalphotometers, because of their inability to simulate the response of the human eye at

theends of the visible spectrum generate significantly flawed data when testing red, blue,

andsome styles of white LEDs.

LEDs are solid-state (p-n junction semiconductor) devices that convert electrical energydirectly

into light (electroluminescence). LED "cold" generation of light leads to highefficiency because

most of the energy radiates in the visible spectrum. In comparison,incandescent bulbs convert

about 5 percent of their power into visible light, while LEDs approach 15 to 20 percent

Incandescent lamps radiate much of their energy in thenon-visible spectrum, generating heat as

well as light. For example, the package of anLED may be 10 to 25 C hotter than ambient, but

under the same conditions, theenvelope of an incandescent bulb can be several hundred degrees

C hotter.

DEVICE PHYSICS AND PACKAGE DESIGN:

An LED in its simplest form is semiconductor p-n junction devices (chip) that, when forward

biased, emits photons (light) as the electrons and holes recombine near the junction. The energy

of the photons is determined primarily by the energy band gap of the semiconductor where the

recombination occurs. Since the eye is only sensitive to light with photon energy from 3.1 eV to

1.6 eV (0.40 to 0.78 m), compound semiconductor materials composed of column III and V

elements are the materials of choice for LEDs because they have the direct band gap properties

and energies necessary for efficiently producing visible photons.

To convert the wavelength () in microns to photon energy, the relationship = 1.24 / eV can be

used. Figure 2.0 shows the semiconductors of interest with their corresponding photon energies,

wavelengths, and the relative response of the human eye.


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The energy gap of a semiconductor is the minimum energy separating the valence band and the

conduction band. Each band contains the possible combinations of energy and momentum for

one type of carrier thevalence band for the carriers of positive charge (holes) and the

conduction band for negative charge carriers (electrons). An LED's internal quantum efficiency

is the number of photons generated divided by the number ofminority carriers (electrons)

injected into the p-doped region. When an injected electron combines with a hole through

radiative recombination, a photon is produced. There are other kinds of transitions that

competewith radiative recombination, but these transitions fail to produce photons. These

transitions occur at crystal imperfections of various sorts and dissipate their energy into the

crystal lattice as heat. For those photons that aregenerated, there can still be loss through

absorption within the LED material, reflection loss when light passes from a semiconductor to

air due to differences in refractive index and total internal reflection of light at angles greater

than the critical angle defined by Snell's law, lowering the overall quantum efficiency of the

LED.


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Figure 2.2 depicts a diagram of a typical LED lamp. An LED lamp contains an LED chip and an

epoxy molded lens encapsulate. The lens is used to change the direction and control the

distribution of light rays (spatial distribution pattern) or colored to serve as an optical filter to

enhance contrast. The epoxy encapsulates and lead frame occupy most of the volume. Presently

the most common LED is the 5mm LED package (or T 1-3/4).

ELECTRICAL PROPERTIES:

Operation at constant current:

The drive current through an LED must be controlled. High current densities within the junctionof the chip cause partial overheating which damages the crystalline structure of the LED die. At

these areas are so called dark line defects, where light ceases to be generated. This should not be

confused with the maximum junction temperature of the LED, which is related to the higher

temperature at which the optical grade epoxy starts to expand rapidlyand increases the risk of

catastrophic failures, such as broken wires or lifted LED dies. To produce light, an LED must be

operated in the forward-bias regime. The emitted light is a function of the forward voltage Vf

and the forward current If. In the lab, LEDs are usually operated in a forward bias direction from

a constant current DC power supply. At low currents, the slope of the radiant power (luminous

flux) verses time rises faster than the slopeof the electrical power (start-up range) verses time. At

high currents, the slope becomes flatter (saturation area), which is mainly caused by heating of

the LED chip. Under normal operating conditions (between the start-up range and saturation

area), the optical radiation emitted by LEDs is strongly correlated to the electrical current, which

is why constant current is recommended for measurements intended to characterize the optical

properties of an LED.

Modulated or Multiplexed Operation:

One efficient method of driving LED devices is to pulse them (usually 100Hz to 1000Hz) with a

high peak current for short durations on a low duty factor. This technique is frequently used to

multiplex a number of individual LED lamps. The advantage is high light output at low time


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average power consumption. LED operation under these non-steady-state conditions can create

temperature fluctuations at the junction and forward voltage instability, which modifies the

characteristic values obtained for the LED under test. Fortunately, these values are strongly

correlated to the values for steady-state operations, so that the true characteristics of the LED

under test can be calculated once the correlation is derived.

Single-Shot Operation:

During production, the measurements commonly made to characterize an LED are often carried

out under single-shot operations where the LED under test is pulsed with a DC current equaling

that of normal operations but only lasting tens of milliseconds. Similar to modulated operations,

the LED fails to reach steady-state conditions, but the correlation between single-shot and

steady-state conditions can be established by a few supplementary measurements.

OPTICAL CHARACTERISTICS OF LEDs:

The radiation from an LED can be characterized by radiometric and spectroradiometric

quantities. If the LED emits visible radiation, then photometric and colorimetric quantities are

also required to quantify its effect on the human eye. Note that for every radiometric quantity

there is a photometric analog. The only difference is that, for radiometric quantities the radiation

is evaluated in energy units, while for photometric quantities the radiation isweighted against the

photopic response of the human eye.

Spectral Properties of Light Emitting Diodes:

The spectral distribution of the optical radiation emitted by LEDs distinguishes them from

typical element sources. The radiant power is neither monochromatic (as emitted by lasers), nor

broadband (as found with incandescent lamps), but rather something between the two. The light

output of a typical LED has a narrowband spectral bandwidth between 20nm and 50nm and a

peak wavelength somewhere in the near UV, the visible, or near infrared regions of the spectrum.

Typical relative spectral distributions are shown in Figure 3.0. The spectral properties of an LED

are important to aid manufacturers in their design efforts and process control. End-users use


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these values in determining the correct LED for their application. An overview of the spectral

parameters of an LED is listed below:

Peak Wavelength p:

Wavelength at the maximum spectral power (ReferenceFigure 3.0). The peak wavelength has

little significance forpractical purposes since two LEDs may have the same peakwavelength but

different color perception.

Full Width Half Max (FWHM):

The spectral bandwidth at half peak0.5 is calculated fromthe two wavelengths'0.5 and ''0.5 on

either side ofp.0.5 = '0.5 - ''0.5 (Reference Figure 3.0).

Center Wavelength m:

The center wavelength is the wavelength halfway between the half-wavelength'0.5 - ''0.5.

Centroid Wavelength c:


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The centroid wavelength is the center of moment or the mean of the spectral powerdistribution.

Dominant Wavelength:

The dominant wavelength is determined from drawing a straight line through thecolorcoordinates of the reference illuminant (usually arbitrarily chosen as illuminant E) andthe

measured chromaticity coordinates of the LED in the International Commission onIllumination

(CIE) 1931 chromaticity diagram. The intersection of this straight line on the boundary of the

chromaticity diagram gives the dominant wavelength. It is a measureof the hue sensation

produced in the human eye by the LED.

Purity:

Purity is defined as the ratio of the distance from reference illuminant (usually arbitrarilychosen

as Illuminant E) to the measured chromaticity coordinates and the distance fromreference

illuminant to the intersection with the boundary of the chromaticity diagram.Most LEDs are

narrow band radiators, with a purity of nearly 100%, i.e. the color cannotbe distinguished from a

monochromatic beam. Polychromatic sources have low purityapproaching zero.

Full Width Half Max Angle, Viewing Angle or Beam Angle:

The total cone apex angle in degrees encompassing the central, high luminous intensity portion

of a directional beam, from the on-axis peak out to the off-axis angles in both directions at which

the source's relative intensity is 1/2.

Half-Angle:

The included angle in degrees between the peak and the point on one side of the beam axis at

which the luminous intensity is 50% of maximum or half of the beam angle. Note: PeakWavelength, Full Width Half Max, Center Wavelength, and Centroid Wavelength are all plotted

on a scale of (power / ) vs. ().

Color & Dominant Wavelength:


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Often used for determining the color of an LED, dominant wavelength is actually a measure of

the hue sensation produced in the human eye. Hue designates the basic color being referenced;

such as, red, yellow or blue-green. The hue refers to the color impression that a sample makes.

Two LEDs can have the same hue, but it is possible for one to appear washed out. For example,

one can look red and one can look pink.

In order to guarantee a match in color from one LED to another both dominant wavelength and

purity should be referenced. Purity is a characteristic of chroma (also referred to as saturation),

which is the degree of color saturation, or the amount of pure color added to obtain the sample.

The purer colors of a particular hue sample are placed nearer to the boundary of the chromaticity

diagram.

In order to calculate the color properties of an LED, the spectral properties of the LED must be

known. Therefore, a photometer cannot be used. In choosing a spectroradiometer with which to

calculate these values, it should be noted that the optical bandwidth of a spectroradiometer

artificially broadens the spectral shape of any source. For LEDs, this can introduce errors,

especially in the calculated chromaticity coordinates and dominantwavelength.

On the other hand, error contributions on color for spectroradiometers with bandwidths of 5nm

have been documented to be less than about 0.002 in x,y (0.001 in u',v') and 0.2nm in dominantwavelength. Bandwidths of 1nm or less have no appreciable error contribution. In choosing a

spectroradiometer one should be aware of these errors. Spectroradiometers with bandwidths of

5nm or less are accepted for most practical measurements of LEDs of all colors.

BATTERY:

An electrochemical battery - or, more precisely, a "cell" - is a device in which the reaction

between two substances can be made to occur in such a way that some of the chemical energy isconverted to useful electricity. When the cell can only be used once, it is called a "primary" cell.

When the chemical reaction can be reversedrepeatedly by applying electrical energy to the cell,

it is called a "secondary" cell and can be used in an accumulator or "storage" battery.


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Certain cells are capable of only a few charge-discharge cycles and are, therefore, technically

"secondary" cells. Such is the case with certain silver oxide-zinc batteries. These batteries are not

capable of the repeated cycling required of a satellite battery system, and are, therefore,

considered to be "rechargeable primary" rather than storage batteries.

To define a battery in another way, it is an arrangement whereby an "electrochemical" reaction

can be made to take place so that the "electrical" part of the reaction proceeds via the metallic

path of the external circuit, while the "chemical" part of the reaction occurs via ionic conduction

through electrolyte.

The type of chemical reaction that can be used in an electrochemical cell is known as an

"oxidation-reduction" reaction - a reaction in which one chemical species gives electrons to

another. By separating the two species and controlling the flow of ions between them, battery

engineers make devices in which essentially allof these electrons can be made to flow through

an external circuit, thereby converting most of the chemical energy to electrical energy during

the discharge of the cell.

Some of the components common to all cells are:

1. The "cathode" or "positive" electrode, which consists of a mass of "electron-receptive"chemical held in intimate contact with a metallic "plate" through which the electrons

arrive from the external circuit.

2. The "anode" or "negative" electrode, which consists of another chemical which readilygives up electrons - an "electron donor" - similarly held in close contact with a metallic

member through which electrons can be conducted to the external circuit.

3. The "electrolyte," usually a liquid solution that permits the transfer of mass necessary tothe overall reaction. This movement takes place by "migration" of "ions" - positively or

negatively charged molecular fragments - from anode to cathode and from cathode to

anode.


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A schematic diagram of these basic cell elements is shown above. The cell is shown connected to

a load representing the discharge reaction. Charging is accomplished by connecting an electrical

source in place of the load, thereby reversing the entire process.

CATEGORIES OF BATTERIES:

Batteries are classified into two broad categories, each type with advantages and disadvantages.

y Primary Batteryy Secondary Battery

Primary Battery:

Primary batteries permanently transform chemical energy to electrical energy. When the initial

supply of reactants is exhausted, energy cannot be readily restored to the battery by electrical

means.

Primary batteries can produce current immediately on assembly. Disposable batteries are

intended to be used once and discarded. These are most commonly used in portable devices that

have low current drain, are only used intermittently, or are used well away from an alternative

power source, such as in alarm and communication circuits where other electric power is onlyintermittently available. Disposable primary cells cannot be reliably recharged, since the

chemical reactions are not easily reversible and active materials may not return to their original

forms. Battery manufacturers recommend against attempting to recharge primary cells. Common

types of disposable batteries include zinc-carbon batteries and alkaline batteries. Generally, these

have higher energy densities than rechargeable batteries, but disposable batteries do not fare well

under high-drain applications with loads under 75 ohms (75 ).

Secondary Battery:

Secondary batteries can be recharged; that is, they can have their chemical reactions reversed by

supplying electrical energy to the cell, restoring their original composition.


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Secondary batteries must be charged before use; they are usually assembled with active materials

in the discharged state. Rechargeable batteries or secondary cells can be recharged by applying

electric current, which reverses the chemical reactions that occur during its use. Devices to

supply the appropriate current are called chargers or rechargers.

BATTERY CELL TYPES:

There are many general types of electrochemical cells, according to chemical processes applied

and design chosen. Two main types are:

y Wet Celly Dry Cell

Wet Cell:

A wet cell battery has a liquid electrolyte. The wet battery filled with electrolyte and charged

when it is built. During storage, a slow chemical reaction will cause self-discharge. Periodic

discharging is required. Wet cells may be primary cells (non-rechargeable) or secondary cells

(rechargeable).Wet cells are still used in automobile batteries and in industry for standby power

for switchgear, telecommunication or large uninterruptible power supplies, but in many places

batteries with gel cells have been used instead. These applications commonly use lead-acid or

nickel-cadmium cells.

DryCell:

A dry cell has the electrolyte immobilized as a paste, with only enough moisture in the paste to

allow current to flow. As opposed to a wet cell, the battery can be operated in any random

position, and will not spill its electrolyte if inverted. While a dry cell's electrolyte is not truly

completely free of moisture and must contain some moisture to function, it has the advantage of

containing no sloshing liquid that might leak or drip out when inverted or handled roughly,

making it highly suitable for small portable electric devices. By comparison, the first wet cells

were typically fragile glass containers with lead rods hanging from the open top, and needed

careful handling to avoid spillage. An inverted wet cell would leak, while a dry cell would not.


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Lead-acid batteries would not achieve the safety and portability of the dry cell until the

development of the gel battery

LEAD ACID BATTERY:

Lead-acid batteries are the oldest type of rechargeable battery. Despite having a very low energy-

to-weight ratio and a low energy-to-volume ratio, their ability to supply high surge currents

means that the cells maintain a relatively large power-to-weight ratio. These features, along with

their low cost, make them attractive for use in various places to provide the high current.

CELL THEORY:

A lead-acid cell works by a simple principle, when twodifferent metals are immersed in an acid

solution, a chemical reaction creates an electrical pressure. One metal is brown-colored lead

dioxide (Pb02). It has a positive electrical charge. The other metal is gray colored sponge lead

(Pb). It has a negative electrical charge. The acid solution is a mixture of sulfuric acid (H2SO4)

and water(H20). It is calledelectrolyte. If a conductor and a load are connected between the two

metals, current will flow. This discharging will continue until the metals become alike and the

acid is used up. The action can be reversed by sending current into the cell in the opposite

direction. This charging will continue until the cell materials are restored to their original

condition.


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ELECTROCHEMICAL REACTIONS:

A lead-acid storage battery can be part ially discharged and recharged many times.There are four

stages in this discharging/charging cycle.

y Chargedy Dischargingy Dischargedy Charging

Charged:

A fully charged battery contains anegative plate of sponge lead (Pb), a positive plate of lead

dioxide (Pb02), and electrolyte of sulfuric acid (H2SO4) and water (H20).

Discharging:

As the batter y is discharging, the electrolyte becomes diluted and the plates become sulfated.

The electrolyte divides into hydrogen (H2) and sulfate (S04). The hydrogen (H2) combines with

oxygen (0) from the positive plate to form more water (H20). The sulfatecombines with the lead

(Pb) inboth plates to form lead sulfate (PbS04).


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Discharged:

In a fully discharged battery, bothplates are covered with lead sulphate (PbSO4) and the

electrolyte is diluted to mostly water (H2O).

Charging:

During charging, the chemical action is reversed. Sulphate (S04) leaves the plates and combines

with hydrogen (H2) to become sulphuric acid (H2SO4). Free oxygen (02) combines with lead (Pb)

on the positive plate to form lead dioxide (Pb02). Gassing occurs as the battery nears full charge,

and hydrogen bubbles out at the negative plates, oxygen at the positive.


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BATTERY CAPACITY:

The energy stored in a battery, called the battery capacity, is measured in either watt-hours (Wh),

kilowatt-hours (kWh), or ampere-hours (Ahr). The most common measure of battery capacity is

Ah, defined as the number of hours for which a battery can provide a current equal to the

discharge rate at the nominal voltage of the battery. The unit of Ah is commonly used when

working with battery systems as the battery voltage will vary throughout the charging or

discharging cycle.

In lead-acid batteries, there are three active components, the positive electrode active

material,the negative electrode active material and the electrolyte. One of these substances will

limit thecapacity. When one of the active substances is consumed the battery voltage will

collapse andthe battery is discharged. Most often, the positive electrode material is limited in a

new battery.The amount of that material will, as a result, determine the capacity.

Again it is practical to use an approximate value of the capacity of a battery called the Nominal

capacity. The nominal capacity of a battery is a measure given by the manufacturer for the

capacity guaranteed to be reached when a new battery is discharged according to a Standardized

test procedure.


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DEPTH OF DISCHARGE:

In many types of batteries, the full energy stored in the battery cannot be withdrawn (in other

words, the battery cannot be fully discharged) without causing serious, and often irreparable

damage to the battery. The Depth of Discharge (DOD) of a battery determines the fraction of

power that can be withdrawn from the battery. In addition to an overall DOD below which the

battery should not be discharged, many battery manufactures will specify a daily DOD, which

determines that maximum power that can be withdrawn from a battery in a single day.

BATTERY VOLTAGE CHARACTERISTICS

If you connect a voltmeter over the terminals of a 6-cell monoblock lead-acid battery at rest, it

will show about 12-13 volts. (During charge up to 15 volts may be acceptable and during very

rapid discharge down to 9 volts can be normal).

The theoretical voltage of a lead-acid battery cell depends on the chemical reactions inside it.

Under standard conditions it is 1.93 V (or 11.6V for a 6-cell monoblock battery).

In practice 2.0 V is used as a reference value for a single cell. This is called the nominalVoltage.

According to this a 6-cell battery is referred to as a 12 V battery.

CHARGE CONTROLLER:

Solar electric systems use charge controllers to manage the electrical power produced by the

modules, protect the batteries, and to act as a connection point for all the system components.

The charge controller, or regulator has three primary functions .First, it provides a central point

for connecting the load, the module and the battery. Secondly, it manages the system so that the

harvested electricity is effectively used, and so that components (especially batteries and lights)are protected from damage due to overcharge, deep discharge and changing voltage levels.

Thirdly, it allows the end user to monitorthe system and locate potential system problems.


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WHY CHARGE CONTROLLER?

The success of a solar electric lighting system depends, to a large extent, on the performance of

the batteries. For a system to operate well and have a long lifetime, the batteries must be kept in

as high a state of charge as possible. The energy entering the batteries during the day(i.e. the

solar charge), must be roughly equivalent to the energy being discharged from the batteries at

night by the load plus losses.

Any solar electric lightning system must be managed so that the energy flow from the batteries to

the load is not greater than the energy harvest, and so that the energy flow into the batteries from

the module is not so high that it will cause damage to the batteries. Solar Energy systems use

Charge Controller to manage the electrical power produced by the modules, protect the

batteries and to act as a connection point for all the system components.

SYSTEM CONNECTONS:

The charge controller should contain a properly installed junction box with fuses. Here the

battery, solar module and loads are fastened together by means of connector strips, and fuses are

incorporated to protect the equipment from damage by short circuit.

Fuses or miniature circuit breakers (MCBs) protect the major circuits in the system from short

circuit. Simple automotive type fuses or fuse wires areused. Ten amp fuses are sufficient for

systems below 50Wp, while 20 amp fuses (or larger) are necessary for larger systems.MCBs are

small switches that automatically break the circuit when there is a short circuit. They can be

switched back ON when the wiring problem is corrected. Both the charge wire from the solar

cell and the load wires (to the light and to other loads) should be fused or protected by an

MCB.Main circuit switches are often necessary to control certain loads from the centrally located

charge regulator using main circuit switches. For example, in a school, classroom lights may be

switched ON from the charge controller located in the office. This prevents misuse of lights by

students in the class rooms. In a home, the lights can be turned OFF from the main circuit switch

during the day to prevent the draining of the battery by lights accidently left ON.


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POWER MANAGEMENT:

Charge controller performs services that protect the system and notify the user as to whether the

system is functioning properly.

USER-ALERTS

Part of the work of charge controllers is to inform the user whether the system is properly

working, usually the LEDs. Beepers or alarms are used for such purposes

The solar charge LED indicates whether a current is flowing from the solar array to the battery. It

lights up when the array is charging the battery. If the solar charge light does not come ON when

the sun is out, the reason could be any of the following problems:

y A loose connection of a charge wire.y Bad fuse or disconnected circuit breaker.y Loose battery terminal.y Bad battery or cell.y Broken solar cell module.

The low battery LED notifies he user that the battery is in a low state of charging. Depending on

the set point it can be 11.0 to 11.9 volts.If this light comes ON. The user should completely stop,

or reduces as much as possible, the use of electric lights and appliances until the battery is in a

higher state of charge. Some controller use an alarm or beepers instead of an LED light. The low

battery light avoids the need to continually use a voltmeter or hydrometer to check the battery

state of charge. Some controller have three to five different LEDs , which each lights up at a

different state of charge, this give the user a better idea of the condition of a battery.

The battery full LED tells the user that the battery is fully charged, and with some controllers,

that he controller has reduced the battery charging current to a trickle charge.


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LOW VOLTAGE DISCONNECTS:

The low voltage disconnect continuously measures the state of charge of the battery.If the battery

voltage drops below a certain level, the charge controller automatically disconnects the load from

the battery.This might happen during the cloudy season when the television is being used too

much, and there is not enough charge to bring the battery state of charge up. Usually a red LED

lights up to notify the user that the battery has been disconnected. The controller will not

reconnect the load until the battery voltage has returned to a suitable level (i.e. 12.3V) or, in the

case of some controller, until the user manually resets it.

Disconnect voltages are commonly set between 11.1 to 11.9V on commercially available

controllers. With some charge controllers, the level at which the controller cut off the load can be

adjusted. Before buying the charge controller check the disconnect voltage.

OVERCHARGE PROTECTION

Charge controller with this feature prevents the array from overcharging the battery. Like the low

battery disconnect, the controller monitors the battery state of charge. Depending on the type the

controller may reduce the current from the module to the trickle charge(i.e. a small current that

fills the battery without causing gassing) ant then stop charging altogether or it may turn the

charge OFF and ON over the period of time. The cut off voltage should be specified on the

controller.

OTHER FEATURES:

Controller may include other features to enhance the systems performance:

Load timers:

Load timers are switches that connect and disconnect loads after a certain amount of time. They

automatically turn loads ON, limit the amount of time that the loads are kept ON, and prevent

abuse of the battery. For example, in a school, a load timer might switch classroom lights so that

they come on at sunset, stay ON for three hours before automatically being turned OFF.


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Blocking diodes:

Blocking diodes prevent current from flowing from the batteries to the solar cell modules when

the modules are not producing current at night. A blocking diode is like a one-way gate that

allows current to enter the battery from the module but does not allow it to flow back.

Surge Protectors:

Surge protectors protect the system components and appliances against the rapid power increases

expected whenlightning strikes nearby. Amodule (and the other solar equipment) will probably

not survive a direct lightning strike but, if the lightning strike nearby, a surge protector would

prevent damage to the system. Surge protectors operate by absorbing high current flows through

the system from spikes or lightning strikes.

CHOOSING CHARGE CONTROLLER:

The selection and sizing of charge controllers and system controls in PV systems involves the

consideration of several factors, depending on the complexity and control options required. While

the primary function is to prevent battery overcharge, many other functions may also be used,

including low voltage load disconnect, load regulation and control, control of backup energy

sources, diversion of energy to and auxiliary load, and system monitoring. The designer must

decide which options are needed to satisfy the requirements of a specific application. The

following list some of the basic considerations for selectingcharge controllers for PV systems.

y System voltagey PV array and load currentsy Battery type and sizey Regulation algorithm and switching element designy Environmental operating conditionsy Mechanical design and packagingy System indicators, alarms, and metersy Overcurrent, disconnects and surge protection devicesy Costs, warranty and availability


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SIZING CHARGE CONTROLLERS:

Charge controllers should be sized according to the voltages and currents expected during

operation of the PV system. The controller must not only be able to handle typical or rated voltages

and currents, but must also be sized to handle expected peak or surge conditions from the PV array

or required by the electrical loads that may be connected to the controller. It is extremely important

that the controller be adequately sized for the intended application. If an undersized controller is

used and fails during operation, the costs of service and replacement will be higher than what

would have been spent on a controller that was initially oversized for the application.

Typically, we would expect that a PV module or array produces no more than its rated maximum

power current at 1000 W/m2 irradiance and 25C module temperature. However, due to possible

reflections from clouds, water or snow, the sunlight levels on the array may be enhanced up to

1.4 times the nominal 1000 W/m2 value used to rate PV module performance. The result is that

peak array current could be 1.4 times the nominal peak rated value if reflection conditions exist.

For this reason, the peak array current ratings for charge controllers should be sized for about

140% or the nominal peak maximum power current ratings for the modules or array.

The size of a controller is determined by multiplying the peak rated current from an array times

this enhancement safety factor. The total current from an array is given by the number ofmodules or strings in parallel, multiplied by the module current. To be conservative, use the short-

circuit current (Isc) is generally used instead of the maximum power current (Imp). In this way,

shunt type controllers that operate the array at short-circuit current conditions are covered safely.

The control of battery charging is so important that most manufacturers of high quality batteries

(with warranties of five years or longer) specify the requirements for voltage regulation, low

voltage disconnect and temperature compensation. When these limits are not respected, it is

common for batteries to fail after less than one quarter of their normal life expectancy, regardless

of their quality or their cost. A good charge controller is not expensive in relation to the total cost

of a power system.


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OPERATING PRINCIPLE AND DETAILED DESIGN:

SOLAR WALKWAY LIGHTS SYSTEM OPERATING PRINCIPLE:

SYSTEM OPERATION:

The solar LED walkway light system converts the sun energy into electricity and stores it to

provide white illumination.

Luminaries utilize High Power white LED with superior thermal management design. These

extremely durable fixtures are waterproof and designed for multiple applications including

indoor and outdoor.

Luminaries are supplied fully assembled and ready for either retrofit or new installations.

SOLAR SYSTEM BENEFITS:

y Easy Installation no wiring required.y Installation and moving is easy no more waiting for the utility company.y Proven technology. Theft-resistant components and hardware. All parts are corrosion

resistant.

y Low installation cost.y Easily and quickly deployed in almost every location.y No wiring run from the grid.y No cuts through existing roads, sidewalks and landscaping.y Very less maintenance.y No utility bill.y Maintenance free batteries.


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DESIGN OF SYSTEM:

SOLAR PV PANEL

POLE

LIGHT SOURCE AND

LAMP SHADE

BATTERY BOX &

CHARGE CONTROLLER

FOOTING CAGE

POLE ARM

Operation Scheme

SOLAR PV PANEL

CONTROLLER

LIGHT SOURCE

BATTERIES

Electrical Connection Scheme

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fyp report final

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