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CHAPTER 1

HYBRID CAR

1.1 WHAT MAKE A HYBRID

Any vehicle is a hybrid when it combines two or more sources of power.

Many people have probably owned a hybrid vehicle at some point. For example, a

mo-ped (a motorized pedal bike) is a type of hybrid because it combines the power

of a petrol engine with the pedal power of its rider. Giant trucks and pulling trains

are diesel electric hybrid. Submarines are also hybrid vehicles. Some are nuclear-

electric and some are diesel-electric. Any vehicle that combines two or more

sources of power that can directly or indirectly provide propulsion power is a

hybrid. The gasoline electric hybrid car is just a cross between a gasoline-powered

car and an electric car.

1.2Types of Hybrid Car

1.2.1 Gasoline powered car

The figure shows a schematic representation of gasoline-powered car. It

consists of a fuel tank, an engine and transmission. The fuel from the fuel tank

helps the running of engine. The power produced is transmitted to the transmission

system and it turns the road wheels.

ENGINE TRANSMISSION FUEL TANK

Figure 1.2.1.1: Gasoline powered car

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ENGINE

TRANSMISSION

Fig. 1.2.1.2: Gasoline car

1.2.2 PROBLEMS WITH GASOLINE POWERED CAR

To be useful for a car must meet certain requirements. A car should be able

to

a) Drive at least 300 miles between refueling.

b) Refueled quickly and easily.

c) Keep up other traffic on the road.

A gasoline car meets these requirements but produces a relative large

amount of pollution and generally gets poor mileage. On the other hand

the electric car produces almost no pollution but it can only go up to 100 miles

between charges and the problem is that it is very slow and Inconvenient to

recharge.

When driver for quick acceleration causes a car to be much less efficient

than they could be. Less powerful engine gets better mileage than an identical car

with a more power engine. The amusing thing is that most of what we require a car

to do uses a small percentage of its hybrid power when driving along the freeway

at 60 mph.

2.3 EVOLUTION OF HYBRID

The hybrid is a compromise. It attempts to significantly increase the mileage and

reduce the emissions of a gas-powered car while overcoming the shortcomings of

an electric car. It is wonder that while any one would build such a complicated

machine when most people are perfectly happy with their gasoline-powered car.

FUEL TANK

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The reason is two told that is to reduce tail pipe emission and to improve the

mileage.

1.2.3 ELECTRIC POWERED CAR

The figure shows a typical electric car. It consists of a set of batteries,

electric motor and transmission. The batteries provide power to electric motor and

the motor turns the transmission.

MOTOR TRANSMISSION BATTERY

Fig. 1.2.3.1: Electric powered car

Fig. 1.2.3.2: Electric Powered Car

BATTERY

ELECTRIC

MOTOR

TRANSMISSION

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CHAPTER 2

HYBRID STRUCTURE

2. HYBRID STRUCTURE

Two power sources found in a hybrid car in different ways. It has a fuel

tank, which supplies gasoline to the engine and set of batteries that supplies power

to an electric motor. Both the engine and the electric motor can turn the

transmission at the same time, and the transmission then turns the road wheels. The

different ways in which the power sources found in a hybrid car are describe as

follows.

i) Parallel Hybrid

ii) Series Hybrid

2.1 PARALLEL HYBRID CAR

The figure shows a typical parallel hybrid. You'll notice that the fuel tank

and gas engine connect to the transmission. The batteries and electric motor also

connect to the transmission independently. As a result, in a parallel hybrid, both

the electric motor and the gas engine can provide propulsion power.

BATTERY FUEL TANK

ENGINE

TRANSMISSION

ELECTRIC MOTOR

Fig.2.1.1: Parallel Hybrid Car

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BATTERY

ELECTRIC

MOTOR

Fig.2.1.2: Parallel hybrid

2.2 SERIES HYBRID CAR

The figure shows a series hybrid. The gasoline engine turns a generator,

and the generator can either charge the batteries or power an electric motor that

drives the transmission. Thus, the gasoline engine never directly powers the

vehicle. Take a look at the diagram of the series hybrid, starting with the fuel tank,

and 4- cylinder engine, Generator, Battery, Electric motor and transmission.

GENERATOR

TRANSMISSION FUEL TANK

ELECTRIC BATTERY

MOTOR ENGIN Fig.2.2.1: Series Hybrid Car

FUEL

TANK ENGINE

TRANSMISSION

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FUEL TANK ENGINE

GENERATOR

BATTERY

ELECTRIC MOTOR

TRANSMISSION

2.3 HYBRID COMPONENTS

Hybrid car contains the following parts.

i) Gasoline engine

The hybrid car has a gasoline engine much like the one you will find on

most cars. However, the engine on a hybrid is smaller and uses advanced

technologies to reduce emissions and increase efficiency.

ii) Fuel tank

The fuel tank in a hybrid is the energy storage device for the gasoline

engine. Gasoline has a much higher energy density than batteries do. For example,

it takes about 1,000 pounds of batteries to store as much energy as 7 pounds of

gasoline.

iii) Electric motor

The electric motor on a hybrid car is very sophisticated. Advanced

electronics allow it to act as a motor as well as a generator. For example, when it

needs to, it can draw energy from the batteries to accelerate the car. But acting as a

generator, it can slow the car down and return energy to the batteries.

iv) Generator

The generator is similar to an electric motor, but it acts only to produce

electrical power. It is used mostly on series hybrids.

v) Batteries

The batteries in a hybrid car are the energy storage device for the electric

motor. Unlike the gasoline in the fuel tank, which can only power the gasoline

engine, the electric motor on a hybrid car can put energy into the batteries as well

as draw energy from them

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vi) Transmission

The transmission on a hybrid car performs the same basic function as the

transmission on a conventional car.

2.4 USES OF HYBRID CAR

California emissions standards announced how much of each type of

pollution a car is allowed to emit in California. The amount is usually specified in

gm/mile of carbon monoxide. The key thing here is that the amount of pollutions

allowed does not depend on the mileage a car gets. But a car that burns twice as

much fuel to go a mile will generate approximately twice as much pollution. The

pollution will have to be reduced by the emission control equipment on the car. So

decreasing the fuel consumption of the car is one of the surest ways to decrease

emission. Carbon dioxide is another type of pollution a car produce it cause global

warming. So the hybrid cars are used to reduce the air pollution. They produce

very less Amount of exhaust gases like carbon dioxide and carbon monoxide with

respect to the other vehicles. The pollutants in this type of gas are very less and are

in a controlled manner

2.5 HYBRID MILEAGE TIPS

You can get the best mileage from a hybrid car by using the same kind of

driving habits that give you better mileage in your gasoline-engine car:

i) Drive slower

The aerodynamic drag on the car increases dramatically the faster you

drive. For example, the drag force at 70 mph (113 kph) is about double that at 50

mph (81 kph). So, keeping your speed down can increase your mileage

significantly.

ii) Maintain a constant speed

Each time you speed up the car you use energy, some of which is wasted

when you slow the car down again. By maintaining a constant speed, you will

make the most efficient use of your fuel.

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iii) Avoid abrupt stops

When you stop your car, the electric motor in the hybrid acts like a

generator and takes some of the energy out of the car while slowing it down. If you

give the electric motor more time to slow the vehicle, it can recover more of the

energy.

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CHAPTER 3

SOLAR SYSTEM

3. SOLAR CELLS

A device which gets heated by the sun’s energy is called solar heating

device. All the solar heating devices are designed in such a way that they help in

collecting as much sunlight as possible. The solar heating devices such as solar

cooker, solar water h eater and solar cells have greatly helped in solving the energy

problem, its consumption and future energy demands of our country. Solar energy

also reduces our dependence on fossil fuel.

3.1SOLAR CELL

It is a device which converts solar energy directly into electricity. Since

solar energy is a light energy so we can say, “Solar cell is a device which converts

light energy into electrical energy.”

Solar cells are made by a semiconductors such as silicon and galium. Those

solar devices which convert the solar radiation into electricity are called Solar

Cells. Before we discuss the solar Cells, we should know the meaning of semi-

conductors.

3.2 SEMI-CONDUCTORS

i) Semi-conductors are those substances which have very low electrical

conductivity.

ii) They are neither bad conductors nor good conductors of electricity.

iii) They are not good conductors., but unlike an insulator, they allow Some

current to pass through them.

iv) Two common semi-conductor are (1) Silicon, (2) Galium.

3.3 PROCESS OF TRANSFORMATION OF SOLAR ENERGY INTO

ELECTRICAL ENERGY

Solar energy is transformed in the form of electromagnetic radiations of

different wavelength. These radiations comprise visible light and invisible light

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(infra red) Solar cells can transform light energy into electrical energy which can

also be converted into mechanical energy.

The conductivity of solar cells, that is ability to conduct electricity of semi

conduct electricity of semi-conductors increases if certain impurities like Boron

and Arsenic are added to them. These can be explained from following Fig. 1.

Collection

Electric Current

Solar Raditions

Fig.3.3.1:Flow of Electrons

3.4 USE OF SEMI-CONDUCTORS IN SOLAR CELLS

Due to use of semi-conductors materials for making solar cells, efficiency

of solar cells has increased tremendously. The efficiency of Solar cells has

increased tremendously. The efficiency of solar cells, made from silicon, galium

and germanium is limited upto 10% to 15% that is they can convert about 10% to

15% of solar energy into electrical energy. Efficiency of modern solar cells mode

from selenium is upto 25% which is quite high.

3.5 CONSTRUCTION OF SOLAR CELLS

These days solar cells are usually made from semi-conductors like silicon,

galium and selenium. To make solar cells, wafer (think layer) of semi-conductor

materials is arranged in such a way that when the light falls on them, a potential

difference is produced between the two regions of wafer (See Fig. 2). When the

sunlight falls on wafer of selenium, it is converted into electricity due to emission

of electrons.

Solar Radiations Ctric Current

Borona Major impurity Flow of Electrons Arsenic Major impurity

Fig.3.5.1: Construction of solar cell

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Potential difference produced by a single solar cell of 4 sq cm size is about 0.4

volts and generates current of 0 milli-amperes.

3.6 SOLAR CELL PANEL

A lot of electricity is required for working of various device such as

artificial satellites, water pumps, street lighting, etc. No single cell can provide

such energy. But by joining a large number of solar cells in a particular way, we

can obtain any amount of electrical energy at any desired voltage. A solar cell

panel contains large number of solar cells joined together in a definite pattern. The

solar panel converts solar energy into electricity during day. The energy so

produced is stored in condensers and is used during nights. A solar panel can

provide much more electric power than a single solar cell.

3.7 ADVANTAGES OF SOLAR CELL PANEL

i) Solar cell panel provide a large amount of electricity than a single cell. The

electricity provided by it is used to run electric motors and lift water from deep

wells.

ii) The electric power required for working of artificial satellites stationed in

outer space. Street lighting in remove areas and running of irrigation water pumps,

etc., is obtained with the help of a solar cell panel.

iii) Solar cell panel is very helpful to overcome energy crises in the modern

times. In Fig. 3 solar energy is being used for running a water pump for irrigation

with the help of solar cell panel.

iv) There is also a solar cell panel ‘S’ in which hundreds of solar cells are

joined together. The electricity produced by solar panel is stored in battery ‘B’.

This battery runs the electric motor M and finally motor M drives the pump P,

which pumps out the underground water.

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3.8 APPLICATIONS OF SOLAR CELLS

i)The uses of solar cells have been very effective in providing electric power to

remote inaccessible and isolated places.

ii)Solar cells are used for providing electricity in artificial satellites and space

probes depend mainly on the electricity generated by solar panels. In India, solar

cells are being used for street light, for running water pumps and for operating

radio and televisions sets in remote areas.

iii)Solar cells are used for providing electricity to light houses situated in the sea

and to off shore oil drilling rig platforms Solar cells are used for operating

electronic watches and calculators. Solar cells have gained a lot of importance in

the last few decade because they are being used increasingly for providing

electricity to artificial satellites and space probes, for providing electricity to

remote areas and for operating modern instruments, like electronic watches and

calculators.

iv)In India, efforts are being made to harness solar energy on a large scale to meet

its ever-increasing needs for energy.

v)The department of Non-conventional Energy Sources (DNS) of Government of

India and similar departments of the State level are making all efforts to popularise

use of solar cells of generating electricity. Solar cells and solar panels are available

to the public at highly subsidised rates. In order to harness solar energy on a

commercial scale, many solar energy parks are being established in India.

vi)The greatest advantage of solar energy cells is that they make use of ever-lasting

solar energy and their use does not produce any environmental pollution.

3.8 SOLAR PANEL

A solar cell or photovoltaic cell is a device that converts solar energy into

electricity by the photovoltaic effect. Photovoltaics is the field of technology and

research related to the application of solar cells as solar energy. 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 source is unspecified.

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Assemblies of cells are used to make solar modules, which may in turn be linked

in photovoltaic arrays. Solar cells have many applications. Individual cells are used

for powering small devices such as electronic calculators. Photovoltaic arrays

generate a form of renewable electricity, particularly useful in situations where

electrical power from the grid is unavailable such as in remote area power systems,

Earth-orbiting satellites and space probes, remote radiotelephones and water

pumping applications. Photovoltaic electricity is also increasingly deployed in

grid-tied electrical systems.

Fig.3.8.1:Solar Panel

A solar cell, made from a monocrystalline sil

3.9 History

3.9.1 Timeline of solar cells

The term "photovoltaic" comes from the Greek φώς:phos meaning "light",

and "voltaic", meaning electrical, from the name of the Italian physicist Volta,

after whom the measurement unit volt is named. The term "photo-voltaic" has been

in use in English since 1849.

The photovoltaic effect was first recognized in 1839 by French physicist

Alexandre-Edmond Becquerel. However, it was not until 1883 that the first solar

cell was built, by Charles Fritts, who coated the semiconductor selenium with an

extremely thin layer of gold to form the junctions. The device was only around 1%

efficient. Russell Ohl patented the modern solar cell in 1946 (U.S. Patent

2,402,662 , "Light sensitive device"). Sven Ason Berglund had a prior patent

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concerning methods of increasing the capacity of photosensitive cells. The modern

age of solar power technology arrived in 1954 when Bell Laboratories,

experimenting with semiconductors, accidentally found that silicon doped with

certain impurities was very sensitive to light.

This resulted in the production of the first practical solar cells with a sunlight

energy conversion efficiency of around 6 percent. Russia launched the first

artificial satellite in 1957, and the United States' first artificial satellite was

launched in 1958 using solar cells created by Peter Iles in an effort spearheaded by

Hoffman Electronics. The first spacecraft to use solar panels was the US satellite

Explorer 1 in January 1958. This milestone created interest in producing and

launching a geostationary communications satellite, in which solar energy would

provide a viable power supply. This was a crucial development which stimulated

funding from several governments into research for improved solar cells.

In 1970 the first highly effective GaAs heterostructure solar cells were created by

Zhores Alferov and his team in the USSR. Metal Organic Chemical Vapor

Deposition (MOCVD, or OMCVD) production equipment was not developed until

the early 1980's, limiting the ability of companies to manufacture the GaAs solar

cell. In the United States, the first 17% efficient air mass zero (AM0) single-

junction GaAs solar cells were manufactured in production quantities in 1988 by

Applied Solar Energy Corporation (ASEC). The "dual junction" cell was

accidentally produced in quantity by ASEC in 1989 as a result of the change from

GaAs on GaAs substrates to GaAs on Germanium (Ge) substrates. The accidental

doping of Ge with the GaAs buffer layer created higher open circuit voltages,

demonstrating the potential of using the Ge substrate as another cell. As GaAs

single-junction cells topped 19% AM0 production efficiency in 1993, ASEC

developed the first dual junction cells for spacecraft use in the United States, with

a starting efficiency of approximately 20%. These cells did not utilize the Ge as a

second cell, but used another GaAs-based cell with different doping. Eventually

GaAs dual junction cells reached production efficiencies of about 22%. Triple

Junction solar cells began with AM0 efficiencies of approximately 24% in 2000,

26% in 2002, 28% in 2005, and in 2007 have evolved to a 30% AM0 production

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efficiency, currently in qualification. In 2007, two companies in the United States,

Emcore Photovoltaics and Spectrolab, produce 95% of the world's 28% efficient

solar cells.

3.10 Three generations of solar cells

The first generation photovoltaic cell consists of a large-area, single-

crystal, single layer p-n junction diode, capable of generating usable electrical

energy from light sources with the wavelengths of sunlight. These cells are

typically made using a diffusion process with silicon wafers. First-generation

photovoltaic cells (also known as silicon wafer-based solar cells) are the dominant

technology in the commercial production of solar cells, accounting for more than

86% of the terrestrial solar cell market.

The second generation of photovoltaic materials is based on the use of thin

epitaxial deposits of semiconductors on lattice-matched wafers. There are two

classes of epitaxial photovoltaics - space and terrestrial. Space cells typically have

higher AM0 efficiencies (28-30%) in production, but have a higher cost per watt.

Their "thin-film" cousins have been developed using lower-cost processes, but

have lower AM0 efficiencies (7-9%) in production and are questionable for space

applications. The advent of thin-film technology contributed to a prediction of

greatly reduced costs for thin film solar cells that has yet to be achieved. There are

currently (2007) a number of technologies/semiconductor materials under

investigation or in mass production. Examples include amorphous silicon,

polycrystalline silicon, micro-crystalline silicon, cadmium telluride, copper indium

selenide/sulfide. An advantage of thin-film technology theoretically results in

reduced mass so it allows fitting panels on light or flexible materials, even textiles.

The advent of thin GaAs-based films for space applications (so-called "thin cells")

with potential AM0 efficiencies of up to 37% are currently in the development

stage for high specific power applications. Second generation solar cells now

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comprise a small segment of the terrestrial photovoltaic market, and approximately

90% of the space market.

Third-generation photovoltaics are proposed to be very different from the

previous semiconductor devices as they do not rely on a traditional p-n junction to

separate photogenerated charge carriers. For space applications quantum well

devices (quantum dots, quantum ropes, etc.) and devices incorporating carbon

nanotubes are being studied - with a potential for up to 45% AM0 production

efficiency. For terrestrial applications, these new devices include

photoelectrochemical cells, polymer solar cells, nanocrystal solar cells, Dye-

sensitized solar cells and are still in the research phase.

3.11 Applications and implementations

3.11.1 Photovoltaic array

Solar cells are often electrically connected and encapsulated as a module.

PV modules often have a sheet of glass on the front (sun up) side , allowing light

to pass while protecting the semiconductor wafers from the elements (rain, hail,

etc.). Solar cells are also usually connected in series in modules, creating an

additive voltage. Connecting cells in parallel will yield a higher current. Modules

are then interconnected, in series or parallel, or both, to create an array with the

desired peak DC voltage and current.

The power output of a solar array is measured in watts or kilowatts. In

order to calculate the typical energy needs of the application, a measurement in

watt-hours, kilowatt-hours or kilowatt-hours per day is often used. A common rule

of thumb is that average power is equal to 20% of peak power, so that each peak

kilowatt of solar array output power corresponds to energy production of 4.8 kW·h

per day.

To make practical use of the 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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Fig.3.11.1.1:Laminated Cell

Polycrystalline PV cells laminated to backing material in a PV module

3.12 Theory

Fig.3.12.1: Solar Panel

i) Photons in sunlight hit the solar panel and are absorbed by semiconducting

materials, such as silicon.

ii) Electrons (negatively charged) are knocked loose from their atoms, allowing

them to flow through the material to produce electricity. The complementary

positive charges that are also created (like bubbles) are called holes and flow in the

direction opposite of the electrons in a silicon solar panel.

iii) An array of solar panels converts solar energy into a usable amount of direct

current (DC) electricity.

3.13 Optionally:

i) The DC current enters an inverter.

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ii) The inverter turns DC electricity into 120 or 240-volt AC (alternating current)

electricity needed for home appliances.

iii) The AC power enters the utility panel in the house.

iv) The electricity is then distributed to appliances or lights in the

house.

v) The electricity that is not used will be re-routed and used in other

facilities.

3.14 Photogeneration of charge carriers

When a photon hits a piece of silicon, one of three things can happen:

i) The photon can pass straight through the silicon — this (generally) happens for

lower energy photons,

ii) The photon can reflect off the surface,

iii) The photon can be absorbed by the silicon, if the photon energy is higher than

the silicon band gap value. This generates an electron-hole pair and sometimes

heat, depending on the band structure.

When a photon is absorbed, its energy is given to an electron in the crystal

lattice. Usually this electron is in the valence band, and is tightly bound in covalent

bonds between neighboring atoms, and hence unable to move far. The energy

given to it by the photon "excites" it into the conduction band, where it is free to

move around within the semiconductor. The covalent bond that the electron was

previously a part of now has one fewer electron — this is known as a hole. The

presence of a missing covalent bond allows the bonded electrons of neighboring

atoms to move into the "hole," leaving another hole behind, and in this way a hole

can move through the lattice. Thus, it can be said that photons absorbed in the

semiconductor create mobile electron-hole pairs.

A photon need only have greater energy than that of the band gap in order

to excite an electron from the valence band into the conduction band. However, the

solar frequency spectrum approximates a black body spectrum at ~6000 K, and as

such, much of the solar radiation reaching the Earth is composed of photons with

energies greater than the band gap of silicon. These higher energy photons will be

19

absorbed by the solar cell, but the difference in energy between these photons and

the silicon band gap is converted into heat (via lattice vibrations — called

phonons) rather than into usable electrical energy.

3.15 Charge carrier separation

There are two main modes for charge carrier separation in a solar cell:

i) Drift of carriers, driven by an electrostatic field established across the device

ii) Diffusion of carriers from zones of high carrier concentration to zones of low

carrier concentration (following a gradient of electrochemical potential).

In the widely used p-n junction solar cells, the dominant mode of charge

carrier separation is by drift. However, in non-p-n-junction solar cells (typical of

the third generation of solar cell research such as dye and polymer thin-film solar

cells), a general electrostatic field has been confirmed to be absent, and the

dominant mode of separation is via charge carrier diffusion.

3.16 The p-n junction

3.16.1Semiconductor

The most commonly known solar cell is configured as a large-area p-n

junction made from silicon. As a simplification, one can imagine bringing a layer

of n-type silicon into direct contact with a layer of p-type silicon. In practice, p-n

junctions of silicon solar cells are not made in this way, but rather, by diffusing an

n-type dopant into one side of a p-type wafer (or vice versa).

If a piece of p-type silicon is placed in intimate contact with a piece of n-

type silicon, then a diffusion of electrons occurs from the region of high electron

concentration (the n-type side of the junction) into the region of low electron

concentration (p-type side of the junction). When the electrons diffuse across the

p-n junction, they recombine with holes on the p-type side. The diffusion of

carriers does not happen indefinitely however, because of an electric field which is

created by the imbalance of charge immediately on either side of the junction

which this diffusion creates. The electric field established across the p-n junction

creates a diode that promotes current to flow in only one direction across the

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junction. Electrons may pass from the n-type side into the p-type side, and holes

may pass from the p-type side to the n-type side. This region where electrons have

diffused across the junction is called the depletion region because it no longer

contains any mobile charge carriers. It is also known as the "space charge region".

3.17 Connection to an external load

Ohmic metal-semiconductor contacts are made to both the n-type and p-

type sides of the solar cell, and the electrodes connected to an external load.

Electrons that are created on the n-type side, or have been "collected" by the

junction and swept onto the n-type side, may travel through the wire, power the

load, and continue through the wire until they reach the p-type semiconductor-

metal contact. Here, they recombine with a hole that was either created as an

electron-hole pair on the p-type side of the solar cell, or swept across the junction

from the n-type side after being created there.

3.18 Equivalent circuit of a solar cell

To understand the electronic behavior of a solar cell, it is useful to create a

model which is electrically equivalent, and is based on discrete electrical

components whose behavior is well known. An ideal solar cell may be modelled

by a current source in parallel with a diode; in practice no solar cell is ideal, so a

shunt resistance and a series resistance component are added to the model.[5] The

resulting equivalent circuit of a solar cell is shown on the left. Also shown, on the

right, is the schematic representation of a solar cell for use in circuit diagrams.

Fig.3.17.1: The equivalent circuit of a solar cell

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Fig.3.17.2: The schematic symbol of a solar cell

3.18 Circuit Equations defining solar cell

The equations which describe the I-V characteristics of the cell are

1. I = I_L - I_o \left( e^{q \left( V + I \times R_s \right) / nkT} - 1 \right)

2. I_L = I_{L \left( T_1 \right)} \left( 1 + K_o \left(T - T_1 \right) \right)

3. I_{L \left( T_1 \right)} = G \times I_{sc \left( T_1 \right) }

4. K_o = \left( I_{ sc \left(T_2 \right) } - I_{sc \left( T_1 \right) } \right) / \left(

T_2 - T_1 \right)

5. I_o = I_{ o \left( T_1 \right) } \times {\left( T / T_1 \right)}^{3/n} * e^{ -q *

V_g / nk * \left( 1/T - 1/T_1 \right)}

6. I_{ o \left( T_1 \right) } = I_{ sc \left( T_1 \right) }/ \left( e^{ q*V_{ oc \left(

T_1 \right) } / nkT_1 } - 1 \right)

7. R_s = - { \left( \tfrac{dV}{dI} \right) }_{ V_{oc} } - 1 / X_v

8. X_v = I_{ o \left( T_1 \right) } \times q / nkT_1 \times e^{ q*V_{ oc \left(

T_1 \right) } / nkT_1 }

where

* k is Boltzman's constant

* q is charge on an electron

* Vg is band gap voltage

* n is diode quality factor

* Rs is series resistance of cell

* Rsh is shunt resistance

* T1 and T2 are reference temperature in Kelvin

* T is working temperature of cell in Kelvin

* Voc is open circuit voltage

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* Isc is short circuit current

* Io is reverse saturation current of diode

* I is the current through Rs

* IL is current produced by the cell

in many sources IL is also known as Iph.

3.19 Solar cell efficiency factors

3.19.1 Energy conversion efficiency

A solar cell's energy conversion efficiency (η, "eta"), is the percentage of

power converted (from absorbed light to electrical energy) and collected, when a

solar cell is connected to an electrical circuit. This term is calculated using the ratio

of the maximum power point, Pm, divided by the input light irradiance (E, in

W/m²) under standard test conditions (STC) and the surface area of the solar cell

(Ac in m²).

\eta = \frac{P_{m}}{E \times A_c}

STC specifies a temperature of 25°C and an irradiance of 1000 W/m² with

an air mass 1.5 (AM1.5) spectrum. These correspond to the irradiance and

spectrum of sunlight incident on a clear day upon a sun-facing 37°-tilted surface

with the sun at an angle of 41.81° above the horizon.[6][7] This condition

approximately represents solar noon near the spring and autumn equinoxes in the

continental United States with surface of the cell aimed directly at the sun. Thus,

under these conditions a solar cell of 12% efficiency with a 100 cm2 (0.01 m2)

surface area can be expected to produce approximately 1.2 watts of power.

The losses of a solar cell may be broken down into reflectance losses,

thermodynamic efficiency, recombination losses and resistive electrical loss. The

overall efficiency is the product of each of these individual losses.

Due to the difficulty in measuring these parameters directly, other

parameters are measured instead: Thermodynamic Efficiency, Quantum

Efficiency, VOC ratio, and Fill Factor. Reflectance losses are a portion of the

Quantum Efficiency under "External Quantum Efficiency". Recombination losses

make up a portion of the Quantum Efficiency, VOC ratio, and Fill Factor.

23

Resistive losses are predominantly categorized under Fill Factor, but also make up

minor portions of the Quantum Efficiency, VOC ratio.

3.20 Thermodynamic Efficiency Limit

Solar cells operate as quantum energy conversion devices, and are therefore

subject to the "Thermodynamic Efficiency Limit". Photons with an energy below

the band gap of the absorber material cannot generate a hole-electron pair, and so

their energy is not converted to useful output and only generates heat if absorbed.

For photons with an energy above the band gap energy, only a fraction of the

energy above the band gap can be converted to useful output. When a photon of

greater energy is absorbed, the excess energy above the band gap is converted to

kinetic energy of the carrier combination. The excess kinetic energy is converted to

heat through phonon interactions as the kinetic energy of the carriers slows to

equilibrium velocity.

Solar cells with multiple band gap absorber materials are able to more

efficiently convert the solar spectrum. By using multiple band gaps, the solar

spectrum may be broken down into smaller bins where the thermodynamic

efficiency limit is higher for each bin.

3.21 Quantum efficiency

As described above, when a photon is absorbed by a solar cell it is

converted to an electron-hole pair. This electron-hole pair may then travel to the

surface of the solar cell and contribute to the current produced by the cell; such a

carrier is said to be collected. Alternatively, the carrier may give up its energy and

once again become bound to an atom within the solar cell without reaching the

surface; this is called recombination, and carriers that recombine do not contribute

to the production of electrical current.

Quantum efficiency refers to the percentage of photons that are converted

to electric current (i.e., collected carriers) when the cell is operated under short

circuit conditions. External quantum efficiency is the fraction of incident photons

24

that are converted to electrical current, while internal quantum efficiency is the

fraction of absorbed photons that are converted to electrical current.

Mathematically, internal quantum efficiency is related to external quantum

efficiency by the reflectance of the solar cell; given a perfect anti-reflection

coating, they are the same.

Quantum efficiency should not be confused with energy conversion

efficiency, as it does not convey information about the power collected from the

solar cell. Furthermore, quantum efficiency is most usefully expressed as a spectral

measurement (that is, as a function of photon wavelength or energy). Since some

wavelengths are absorbed more effectively than others in most semiconductors,

spectral measurements of quantum efficiency can yield information about which

parts of a particular solar cell design are most in need of improvement.

3.22 VOC ratio

Due to recombination, the open circuit voltage (VOC) of the cell will be

below the band gap voltage of the cell. Since the energy of the photons must be at

or above the band gap to generate a carrier pair, cell voltage below the band gap

voltage represents a loss. This loss is represented by the ratio of VOC divided by

VG

3.23 Maximum-power point

A solar cell may operate over a wide range of voltages (V) and currents (I).

By increasing the resistive load on an irradiated cell continuously from zero (a

short circuit) to a very high value (an open circuit) one can determine the

maximum-power point, the point that maximizes V×I; that is, the load for which

the cell can deliver maximum electrical power at that level of irradiation. (The

output power is zero in both the short circuit and open circuit extremes).

A high quality, monocrystalline silicon solar cell, at 25 °C cell temperature,

may produce 0.60 volts open-circuit (Voc). The cell temperature in full sunlight,

even with 25 °C air temperature, will probably be close to 45 °C, reducing the

open-circuit voltage to 0.55 volts per cell. The voltage drops modestly, with this

25

type of cell, until the short-circuit current is approached (Isc). Maximum power

(with 45 °C cell temperature) is typically produced with 75% to 80% of the open-

circuit voltage (0.43 volts in this case) and 90% of the short-circuit current. This

output can be up to 70% of the Voc x Isc product. The short-circuit current (Isc)

from a cell is nearly proportional to the illumination, while the open-circuit voltage

(Voc) may drop only 10% with a 80% drop in illumination. Lower-quality cells

have a more rapid drop in voltage with increasing current and could produce only

1/2 Voc at 1/2 Isc. The usable power output could thus drop from 70% of the Voc

x Isc product to 50% or even as little as 25%. Vendors who rate their solar cell

"power" only as Voc x Isc, without giving load curves, can be seriously distorting

their actual performance.

The maximum power point of a photovoltaic varies with incident

illumination. For systems large enough to justify the extra expense, a maximum

power point tracker tracks the instantaneous power by continually measuring the

voltage and current (and hence, power transfer), and uses this information to

dynamically adjust the load so the maximum power is always transferred,

regardless of the variation in lighting.

3.24 Fill factor

Another defining term in the overall behavior of a solar cell is the fill factor

(FF). This is the ratio of the maximum power point divided by the open circuit

voltage (Voc) and the short circuit current (Isc):

FF = \frac{P_{m}}{V_{oc} \times I_{sc}} = \frac{\eta \times A_c \times

E}{V_{oc} \times I_{sc}}

3.25 Comparison of energy conversion efficiencies

3.25.1 Photovoltaics

At this point, discussion of the different ways to calculate efficiency for

space cells and terrestrial cells is necessary to alleviate confusion. In space, where

there is no atmosphere, the spectrum of the sun is relatively unfiltered. However on

earth, with air filtering the incoming light, the solar spectrum changes. To account

26

for the spectral differences, a system was devised to calculate this filtering effect.

Simply, the filtering effect ranges from Air Mass 0 in space, to approximately Air

Mass 1.5 on earth. Multiplying the spectral differences by the quantum efficiency

of the solar cell in question will yield the efficiency of the device. For example, a

Silicon solar cell in space might have an efficiency of 14% at AM0, but have an

efficiency of 16% on earth at AM 1.5. Terrestrial efficiencies typically are greater

than space efficiencies.

Solar cell efficiencies vary from 6% for amorphous silicon-based solar

cells to 40.7% with multiple-junction research lab cells and 42.8% with multiple

dies assembled into a hybrid package.[9] Solar cell energy conversion efficiencies

for commercially available multicrystalline Si solar cells are around 14-19%[10].

The highest efficiency cells have not always been the most economical — for

example a 30% efficient multijunction 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.

However, there is a way to "boost" solar power. By increasing the light

intensity, typically photogenerated carriers are increased, resulting in increased

efficiency by up to 15%. These so-called "concentrator systems" have only begun

to become cost-competitive as a result of the development of high efficiency GaAs

cells. The increase in intensity is typically accomplished by using concentrating

optics. A typical concentrator system may use a light intensity 6-400 times the sun,

and increase the efficiency of a one sun GaAs cell from 31% at AM 1.5 to 35%.

A common method used to express economic costs of electricity-generating

systems is to calculate a price per delivered kilowatt-hour (kWh). The solar cell

efficiency in combination with the available irradiation has a major influence on

the costs, but generally speaking the overall system efficiency is important. Using

the commercially available solar cells (as of 2006) and system technology leads to

system efficiencies between 5 and 19%. As of 2005, photovoltaic electricity

generation costs ranged from ~0.60 US$/kWh (0.50 €/kWh) (central Europe) down

to ~0.30 US$/kWh (0.25 €/kWh) in regions of high solar irradiation. This

27

electricity is generally fed into the electrical grid on the customer's side of the

meter. The cost can be compared to prevailing retail electric pricing (as of 2005),

which varied from between 0.04 and 0.50 US$/kWh worldwide. (Note: in addition

to solar irradiance profiles, these costs/kwh calculations will vary depending on

assumptions for years of useful life of a system. Most c-Si panels are warrantied

for 25 years and should see 35+ years of useful life.)

The chart at the right illustrates the various commercial large-area module

energy conversion efficiencies and the best laboratory efficiencies obtained for

various materials and technologies.

Reported timeline of solar cell energy conversion efficiencies (from National

Renewable Energy Laboratory (USA)

Reported timeline of solar cell energy conversion efficiencies (from National

Renewable Energy Laboratory (USA)

3.26 Watts peak

Since solar cell output power depends on multiple factors, such as the sun's

incidence angle, for comparison purposes between different cells and panels, the

measure of watts peak (Wp) is used. It is the output power under these conditions

known as STC

i) Insolation (solar irradiance) 1000 W/m²

ii) solar reference spectrum AM (airmass) 1.5

iii) cell temperature 25°C

3.27 Solar cells and energy payback

In the 1990s, when silicon cells were twice as thick, efficiencies were 30%

lower than today and lifetimes were shorter, it may well have cost more energy to

make a cell than it could generate in a lifetime. In the meantime, the technology

has progressed significantly, and the energy payback time of a modern

photovoltaic module is typically from 1 to 4 years [13] depending on the type and

where it is used (see net energy gain). With a typical lifetime of 20 to 30 years, this

28

means that modern solar cells are net energy producers, i.e they generate much

more energy over their lifetime than the energy expended in producing them.

3.28 Light-absorbing materials

All solar cells require a light absorbing material contained within the cell

structure to absorb photons and generate electrons via the photovoltaic effect. The

materials used in solar cells tend to have the property of preferentially absorbing

the wavelengths of solar light that reach the earth surface; however, some solar

cells are optimized for light absorption beyond Earth's atmosphere as well. Light

absorbing materials can often be used in multiple physical configurations to take

advantage of different light absorption and charge separation mechanisms. Many

currently available solar cells are configured as bulk materials that are

subsequently cut into wafers and treated in a "top-down" method of synthesis

(silicon being the most prevalent bulk material). Other materials are configured as

thin-films (inorganic layers, organic dyes, and organic polymers) that are deposited

on supporting substrates, while a third group are configured as nanocrystals and

used as quantum dots (electron-confined nanoparticles) embedded in a supporting

matrix in a "bottom-up" approach. Silicon remains the only material that is well-

researched in both bulk and thin-film configurations. The following is a current list

of light absorbing materials, listed by configuration and substance-name:

3.29 Bulk

These bulk technologies are often referred to as wafer-based

manufacturing. In other words, in each of these approaches, self-supporting wafers

between 180 to 240 micrometers thick are processed and then soldered together to

form a solar cell module. A general description of silicon wafer processing is

provided in Manufacture and Devices.

3.30 Silicon

3.30.1 Polysilicon, Silicon, and list of silicon producers

29

Fig.3.30..1.1: Basic structure of a silicon based solar cell and its working mechanism.

By far, the most prevalent bulk material for solar cells is crystalline silicon

(abbreviated as a group as c-Si), also known as "solar grade silicon". Bulk silicon

is separated into multiple categories according to crystallinity and crystal size in

the resulting ingot, ribbon, or wafer.

i) monocrystalline silicon (c-Si): often made using the Czochralski process.

Single-crystal wafer cells tend to be expensive, and because they are cut from

cylindrical ingots, do not completely cover a square solar cell module without a

substantial waste of refined silicon. Hence most c-Si panels have uncovered gaps

at the corners of four cells.

ii) Poly- or multicrystalline silicon (poly-Si or mc-Si): made from cast square

ingots — large blocks of molten silicon carefully cooled and solidified. These cells

are less expensive to produce than single crystal cells but are less efficient.

iii) Ribbon silicon: formed by drawing flat thin films from molten silicon and

having a multicrystalline structure. These cells have lower efficiencies than poly-

30

Si, but save on production costs due to a great reduction in silicon waste, as this

approach does not require sawing from ingots.

3.31 Thin films

The various thin-film technologies currently being developed reduce the

amount (or mass) of light absorbing material required in creating a solar cell. This

can lead to reduced processing costs from that of bulk materials (in the case of

silicon thin films) but also tends to reduce energy conversion efficiency, although

many multi-layer thin films have efficiencies above those of bulk silicon wafers.

3.32 CdTe

Cadmium telluride is an efficient light-absorbing material for thin-film

solar cells. Compared to other thin-film materials, CdTe is easier to deposit and

more suitable for large-scale production. Despite much discussion of the toxicity

of CdTe-based solar cells, this is the only technology (apart from amorphous

silicon) that can be delivered on a large scale[citation needed]. The perception of

the toxicity of CdTe is based on the toxicity of elemental cadmium, a heavy metal

that is a cumulative poison. However it has been shown that the release of

cadmium to the atmosphere is lower with CdTe-based solar cells than with silicon

photovoltaics and other thin-film solar cell technologies.

3.33 Copper-Indium Selenide

The materials based on CuInSe2 that are of interest for photovoltaic

applications include several elements from groups I, III and VI in the periodic

31

table. These semiconductors are especially attractive for thin film solar cell

application because of their high optical absorption coefficients and versatile

optical and electrical characteristics which can in principle be manipulated and

tuned for a specific need in a given device. CIS is an abbreviation for general

chalcopyrite films of copper indium selenide (CuInSe2), CIGS mentioned below is

a variation of CIS. CIS films (no Ga) achieved greater than 14% efficiency.

However, manufacturing costs of CIS solar cells at present are high when

compared with amorphous silicon solar cells but continuing work is leading to

more cost-effective production processes. The first large-scale production of CIS

modules was started in 2006 in Germany by Wuerth Solar.

When gallium is substituted for some of the indium in CIS, the material is

sometimes called CIGS , or copper indium/gallium diselenide, a solid mixture of

the semiconductors CuInSe2 and CuGaSe2, often abbreviated by the chemical

formula CuInxGa(1-x)Se2. Unlike the conventional silicon based solar cell, which

can be modelled as a simple p-n junction (see under semiconductor), these cells are

best described by a more complex heterojunction model. The best efficiency of a

thin-film solar cell as of March 2008 was 19.9% with CIGS absorber layer. Higher

efficiencies (around 30%) can be obtained by using optics to concentrate the

incident light. The use of gallium increases the optical bandgap of the CIGS layer

as compared to pure CIS, thus increasing the open-circuit voltage. In another point

of view, gallium is added to replace as much indium as possible due to gallium's

relative availability to indium. Approximately 70% of indium currently produced

is used by the flat-screen monitor industry. Some investors in solar technology

worry that production of CIGS cells will be limited by the availability of indium.

Producing 2 GW of CIGS cells (roughly the amount of silicon cells produced in

2006) would use about 10% of the indium produced in 2004.[20] For comparison,

silicon solar cells used up 33% of the world's electronic grade silicon production in

2006. Nanosolar claims to waste only 5% of the indium it uses. As of 2006, the

best conversion efficiency for flexible CIGS cells on polyimide is 14.1% by Tiwari

et al, at the ETH, Switzerland. Conversion efficiency values on metallic flexible

32

foils were reported by AbuShama et al in the proceedings of the IEEE 4th World

Conference on Photovoltaic Energy Conversion 2006 in Hawaii, USA.

That being said, indium can easily be recycled from decommissioned PV

modules. The recycling program in Germany would be is an example that

highlights the regenerative industrial paradigm: "From cradle to cradle".

Selenium allows for better uniformity across the layer and so the number of

recombination sites in the film are reduced which benefits the quantum efficiency

and thus the conversion efficiency.

3.34 Gallium arsenide (GaAs) multijunction

3.34.1 Multi junction photovoltaic cell

High-efficiency cells have been developed for special applications such as

satellites and space exploration. These multijunction cells consist of multiple thin

films produced using molecular beam epitaxy. A triple-junction cell, for example,

may consist of the semiconductors: GaAs, Ge, and GaInP2. Each type of

semiconductor will have a characteristic band gap energy which, loosely speaking,

causes it to absorb light most efficiently at a certain color, or more precisely, to

absorb electromagnetic radiation over a portion of the spectrum. The

semiconductors are carefully chosen to absorb nearly all of the solar spectrum, thus

generating electricity from as much of the solar energy as possible.

GaAs multijunction devices are the most efficient solar cells to date,

reaching a record high of 40.7% efficiency under solar concentration and

laboratory conditions. These devices use 20 to 30 different semiconductors layered

in series.

This technology is currently being utilised in the Mars rover missions.

Solar arrays made with a material which contains gallium arsenide GaAs

and germanium Ge is seeing demand rapidly rise. In just the past 12 months

(12/2006 - 12/2007), the cost of 4N gallium metal has risen from about $350 per

kg to $680 per kg. Additionally, germanium metal prices have risen substantially

to $1000-$1200 per kg this year. Although some Chinese producers of these

materials may be able to offset some of the price increases with their lower labor

33

costs. Those materials include gallium (4N, 6N and 7N Ga), arsenic (4N, 6N and

7N) and germanium, pyrolitic boron nitride (pBN) crucibles for growing crystals,

and boron oxide, these products are critical to the entire substrate manufacturing

industry.

Triple-junction GaAs solar cells were also being used as the power source

of the Dutch four-time World Solar Challenge winners Nuna in 2005 and 2007.

3.35 Light-absorbing dyes

3.35.1Dye-sensitized solar cells

Typically a ruthenium metalorganic dye (Ru-centered) is used as a

monolayer of light-absorbing material. The dye-sensitized solar cell depends on a

mesoporous layer of nanoparticulate titanium dioxide to greatly amplify the

surface area (200-300 m²/g TiO2, as compared to approximately 10 m²/g of flat

single crystal). The photogenerated electrons from the light absorbing dye are

passed on to the n-type TiO2, and the holes are passed to an electrolyte on the

other side of the dye. The circuit is completed by a redox couple in the electrolyte,

which can be liquid or solid. This type of cell allows a more flexible use of

materials, and is typically manufactured by screen printing, with the potential for

lower processing costs than those used for bulk solar cells. However, the dyes in

these cells also suffer from degradation under heat and UV light, and the cell

casing is difficult to seal due to the solvents used in assembly. In spite of the

above, this is a popular emerging technology with some commercial impact

forecast within this decade.

3.36 Organic polymer solar cells

Organic solar cells and Polymer solar cells are built from thin films

(typically 100 nm) of organic semiconductors such as polymers and small-

molecule compounds like polyphenylene vinylene, copper phthalocyanine (a blue

or green organic pigment) and carbon fullerenes. Energy conversion efficiencies

achieved to date using conductive polymers are low at 6% efficiency[24] for the

34

best cells to date. However, these cells could be beneficial for some applications

where mechanical flexibility and disposability are important.

3.37 Silicon

Silicon thin-films are mainly deposited by chemical vapor deposition

(typically plasma-enhanced (PE-CVD)) from silane gas and hydrogen gas.

Depending on the deposition's parameters, this can yield:

i) Amorphous silicon (a-Si or a-Si:H)

ii) protocrystalline silicon or

iii) Nanocrystalline silicon (nc-Si or nc-Si:H).

These types of silicon present dangling and twisted bonds, which results in

deep defects (energy levels in the bandgap) as well as deformation of the valence

and conduction bands (band tails). The solar cells made from these materials tend

to have lower energy conversion efficiency than bulk silicon, but are also less

expensive to produce. The quantum efficiency of thin film solar cells is also lower

due to reduced number of collected charge carriers per incident photon.

Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon

(c-Si) (1.1 eV), which means it absorbs the visible part of the solar spectrum more

strongly than the infrared portion of the spectrum. As nc-Si has about the same

bandgap as c-Si, the two material can be combined in thin layers, creating a

layered cell called a tandem cell. The top cell in a-Si absorbs the visible light and

leaves the infrared part of the spectrum for the bottom cell in nanocrystalline Si.

Recently, solutions to overcome the limitations of thin-film crystalline

silicon have been developed. Light trapping schemes where the incoming light is

obliquely coupled into the silicon and the light traverses the film several times

enhance the absorption of sunlight in the films. Thermal processing techniques

enhance the crystallinity of the silicon and pacify electronic defects.[citation

needed

A silicon thin film technology is being developed for building integrated

photovoltaics (BIPV) in the form of semi-transparent solar cells which can be

35

applied as window glazing. These cells function as window tinting while

generating electricity.

3.38 Nanocrystalline solar cells

These structures make use of some of the same thin-film light absorbing

materials but are overlain as an extremely thin absorber on a supporting matrix of

conductive polymer or mesoporous metal oxide having a very high surface area to

increase internal reflections (and hence increase the probability of light

absorption).

3.39 Concentrating photovoltaics (CPV)

Concentrating photovoltaic systems use a large area of lenses or mirrors to

focus sunlight on a small area of photovoltaic cells.[25] If these systems use single

or dual-axis tracking to improve performance, they may be referred to as Heliostat

Concentrator Photovoltaics (HCPV). The primary attraction of CPV systems is

their reduced usage of semiconducting material which is expensive and currently

in short supply. Additionally, increasing the concentration ratio improves the

performance of general photovoltaic materials[26]. Despite the advantages of CPV

technologies their application has been limited by the costs of focusing, tracking

and cooling equipment. On October 25, 2006, the Australian federal government

and the Victorian state government together with photovoltaic technology

company Solar Systems announced a project using this technology, Solar power

station in Victoria, planned to come online in 2008 and be completed by 2013.

This plant, at 154 MW, would be ten times larger than the largest current

photovoltaic plant in the world.

3.40 Silicon solar cell device manufacture

36

Fig.3.39.1:Solar powered scientific calculator

Because solar cells are semiconductor devices, they share many of the

same processing and manufacturing techniques as other semiconductor devices

such as computer and memory chips. However, the stringent requirements for

cleanliness and quality control of semiconductor fabrication are a little more

relaxed for solar cells. Most large-scale commercial solar cell factories today make

screen printed poly-crystalline silicon solar cells. Single crystalline wafers which

are used in the semiconductor industry can be made into excellent high efficiency

solar cells, but they are generally considered to be too expensive for large-scale

mass production.

Poly-crystalline silicon wafers are made by wire-sawing block-cast silicon

ingots into very thin (180 to 350 micrometer) slices or wafers. The wafers are

usually lightly p-type doped. To make a solar cell from the wafer, a surface

diffusion of n-type dopants is performed on the front side of the wafer. This forms

a p-n junction a few hundred nanometers below the surface.

37

Antireflection coatings, which increase the amount of light coupled into the

solar cell, are typically next applied. Over the past decade, silicon nitride has

gradually replaced titanium dioxide as the antireflection coating of choice because

of its excellent surface passivation qualities (i.e., it prevents carrier recombination

at the surface of the solar cell). It is typically applied in a layer several hundred

nanometers thick using plasma-enhanced chemical vapor deposition (PECVD).

Some solar cells have textured front surfaces that, like antireflection coatings,

serve to increase the amount of light coupled into the cell. Such surfaces can

usually only be formed on single-crystal silicon, though in recent years methods of

forming them on multicrystalline silicon have been developed.

The wafer then has a full area metal contact made on the back surface, and

a grid-like metal contact made up of fine "fingers" and larger "busbars" are screen-

printed onto the front surface using a silver paste. The rear contact is also formed

by screen-printing a metal paste, typically aluminium. Usually this contact covers

the entire rear side of the cell, though in some cell designs it is printed in a grid

pattern. The paste is then fired at several hundred degrees Celsius to form metal

electrodes in ohmic contact with the silicon. After the metal contacts are made, the

solar cells are interconnected in series (and/or parallel) by flat wires or metal

ribbons, and assembled into modules or "solar panels". Solar panels have a sheet of

tempered glass on the front, and a polymer encapsulation on the back. Tempered

glass cannot be used with amorphous silicon cells because of the high temperatures

during the deposition process.

3.40 Current research on materials and devices

3.40.1 Timeline of solar cells

There are currently many research groups active in the field of

photovoltaics in universities and research institutions around the world. This

research can be divided into three areas: making current technology solar cells

cheaper and/or more efficient to effectively compete with other energy sources;

38

developing new technologies based on new solar cell architectural designs; and

developing new materials to serve as light absorbers and charge carriers.

Silicon processing

One way of reducing the cost is to develop cheaper methods of obtaining

silicon that is sufficiently pure. Silicon is a very common element, but is normally

bound in silica, or silica sand. Processing silica (SiO2) to produce silicon is a very

high energy process - at current efficiencies, it takes over two years for a

conventional solar cell to generate as much energy as was used to make the silicon

it contains. More energy efficient methods of synthesis are not only beneficial to

the solar industry, but also to industries surrounding silicon technology as a whole.

The current industrial production of silicon is via the reaction between

carbon (charcoal) and silica at a temperature around 1700 degrees Celsius. In this

process, known as carbothermic reduction, each tonne of silicon (metallurgical

grade, about 98% pure) is produced with the emission of about 1.5 tonnes of

carbon dioxide.

Solid silica can be directly converted (reduced) to pure silicon by

electrolysis in a molten salt bath at a fairly mild temperature (800 to 900 degrees

Celsius). While this new process is in principle the same as the FFC Cambridge

Process which was first discovered in late 1996, the interesting laboratory finding

is that such electrolytic silicon is in the form of porous silicon which turns readily

into a fine powder, (with a particle size of a few micrometres), and may therefore

offer new opportunities for development of solar cell technologies.

Another approach is also to reduce the amount of silicon used and thus

cost, is by micromachining wafers into very thin, virtually transparent layers that

could be used as transparent architectural coverings. The technique involves taking

a silicon wafer, typically 1 to 2 mm thick, and making a multitude of parallel,

transverse slices across the wafer, creating a large number of slivers that have a

thickness of 50 micrometres and a width equal to the thickness of the original

wafer. These slices are rotated 90 degrees, so that the surfaces corresponding to the

faces of the original wafer become the edges of the slivers. The result is to convert,

39

for example, a 150 mm diameter, 2 mm-thick wafer having an exposed silicon

surface area of about 175 cm² per side into about 1000 slivers having dimensions

of 100 mm x 2 mm x 0.1 mm, yielding a total exposed silicon surface area of about

2000 cm² per side. As a result of this rotation, the electrical doping and contacts

that were on the face of the wafer are located the edges of the sliver, rather than the

front and rear as is the case with conventional wafer cells. This has the interesting

effect of making the cell sensitive from both the front and rear of the cell (a

property known as bifaciality). Using this technique, one silicon wafer is enough to

build a 140 watt panel, compared to about 60 wafers needed for conventional

modules of same power output.

3.42 Thin-film processing

Thin-film solar cells use less than 1% of the raw material (silicon or other

light absorbers) compared to wafer based solar cells, leading to a significant price

drop per kWh. There are many research groups around the world actively

researching different thin-film approaches and/or materials, however it remains to

be seen if these solutions can generate the same space-efficiency as traditional

silicon processing.

One particularly promising technology is crystalline silicon thin films on

glass substrates. This technology makes use of the advantages of crystalline silicon

as a solar cell material, with the cost savings of using a thin-film approach.

Another interesting aspect of thin-film solar cells is the possibility to deposit the

cells on all kind of materials, including flexible substrates (PET for example),

which opens a new dimension for new applications.

3.43 Polymer processing

The invention of conductive polymers (for which Alan Heeger, Alan G.

MacDiarmid and Hideki Shirakawa were awarded a Nobel prize) may lead to the

development of much cheaper cells that are based on inexpensive plastics.

However, all organic solar cells made to date suffer from degradation upon

exposure to UV light, and hence have lifetimes which are far too short to be viable.

40

The conjugated double bond systems in the polymers, which carry the charge, are

always susceptible to breaking up when radiated with shorter wavelengths.

Additionally, most conductive polymers, being highly unsaturated and reactive, are

highly sensitive to atmospheric moisture and oxidation, making commercial

applications difficult.

3.44 Nanoparticle processing

Experimental non-silicon solar panels can be made of quantum

heterostructures, eg. carbon nanotubes or quantum dots, embedded in conductive

polymers or mesoporous metal oxides. In addition, thin films of many of these

materials on conventional silicon solar cells can increase the optical coupling

efficiency into the silicon cell, thus boosting the overall efficiency. By varying the

size of the quantum dots, the cells can be tuned to absorb different wavelengths.

Although the research is still in its infancy, quantum dot-modified photovoltaics

may be able to achieve up to 42 percent energy conversion efficiency due to

multiple exciton generation(MEG).

3.45 Transparent conductors

Many new solar cells use transparent thin films that are also conductors of

electrical charge. The dominant conductive thin films used in research now are

transparent conductive oxides (abbreviated "TCO"), and include fluorine-doped tin

oxide (SnO2:F, or "FTO"), doped zinc oxide (e.g.: ZnO:Al), and indium tin oxide

(abbreviated "ITO"). These conductive films are also used in the LCD industry for

flat panel displays. The dual function of a TCO allows light to pass through a

substrate window to the active light absorbing material beneath, and also serves as

an ohmic contact to transport photogenerated charge carriers away from that light

absorbing material. The present TCO materials are effective for research, but

perhaps are not yet optimized for large-scale photovoltaic production. They require

very special deposition conditions at high vacuum, they can sometimes suffer from

poor mechanical strength, and most have poor transmittance in the infrared portion

41

of the spectrum (e.g.: ITO thin films can also be used as infrared filters in airplane

windows). These factors make large-scale manufacturing more costly.

A relatively new area has emerged using carbon nanotube networks as a

transparent conductor for organic solar cells. Nanotube networks are flexible and

can be deposited on surfaces a variety of ways. With some treatment, nanotube

films can be highly transparent in the infrared, possibly enabling efficient low

bandgap solar cells. Nanotube networks are p-type conductors, whereas traditional

transparent conductors are exclusively n-type. The availability of a p-type

transparent conductor could lead to new cell designs that simplify manufacturing

and improve efficiency.

3.46 Silicon wafer based solar cells

Despite the numerous attempts at making better solar cells by using new

and exotic materials, the reality is that the photovoltaics market is still dominated

by silicon wafer-based solar cells (first-generation solar cells). This means that

most solar cell manufacturers are equipped to produce these type of solar cells.

Therefore, a large body of research is currently being done all over the world to

create silicon wafer-based solar cells that can achieve higher conversion efficiency

without an exorbitant increase in production cost. The aim of the research is to

achieve the lowest cost per watt solar cell design that is suitable for commercial

production.

3.47 Manufacturers

Solar cells are manufactured primarily in Japan, Germany, USA, and

China, though numerous other nations have or are acquiring significant solar cell

production capacity. While technologies are constantly evolving toward higher

efficiencies, the most effective cells for low cost electrical production are not

necessarily those with the highest efficiency, but those with a balance between

low-cost production and efficiency high enough to minimize area-related balance

of systems cost. Those companies with large scale manufacturing technology for

coating inexpensive substrates may, in fact, ultimately be the lowest cost net

42

electricity producers, even with cell efficiencies that are lower than those of single-

crystal technologies.

43

CHAPTER 4

WIND ENERGY

4. INTRODUCTION

The Earth is unevenly heated by the sun, such that the poles receive less

energy from the sun than the equator; along with this, dry land heats up (and cools

down) more quickly than the seas do. The differential heating drives a

global atmospheric convection system reaching from the Earth's surface to

the stratosphere which acts as a virtual ceiling. Most of the energy stored in these

wind movements can be found at high altitudes where continuous wind speeds of

over 160 km/h (99 mph) occur. Eventually, the wind energy is converted through

friction into diffuse heat throughout the Earth's surface and the atmosphere. The

total amount of economically extractable power available from the wind is

considerably more than present human power use from all sources. The most

comprehensive study as of 2005 found the potential of wind power on land and

near-shore to be 72 TW, equivalent to 54,000 MToE (million tons of oil

equivalent) per year, or over five times the world's current energy use in all forms.

The potential takes into account only locations with mean annual wind speeds ≥

6.9 m/s at 80 m. The study assumes six 1.5 megawatt, 77 m diameter turbines per

square kilometer on roughly 13% of the total global land area (though that land

would also be available for other compatible uses such as farming).

Large-scale wind farms are connected to the electric power

transmission network; smaller facilities are used to provide electricity to isolated

locations. Utility companies increasingly buy back surplus electricity produced by

small domestic turbines. Wind energy, as an alternative to fossil fuels, is

plentiful, renewable, widely distributed, clean, and produces no greenhouse gas

emissions during operation. However, the construction of wind farms is not

universally welcomed because of their visual impact but any effects on the

environment are generally among the least problematic of any power source.

44

Wind energy is the one of the renewable means of electricity generation

that is part of the worldwide discussion on the future of energy generation and

use and consequent effect on the environment. We believe that there should be

wider participation in this important debate, including technocrats like us. There

are many research problems that could be attracted by physicists including e.g.

Material for turbine vanes(limit wind turbine size),semiconductor materials and

power electronics for electric power conditioning. In this report we discuss basic

technical and some economic aspects of wind energy and hope to provide a helpful

guide to some important issues and literature relevant to this technology.

45

4.1 WORKING PRINCIPLE

Wind energy is the kinetic energy of the air in motion. Total wind energy

flowing through an imaginary area A during the time t is:

E = A . v . t . ρ . ½ v2,

where v is the wind velocity and ρ is the air density. The formula presented is

structured in two parts: (A . v . t) is the volume of air passing through A, which is

considered perpendicular to the wind velocity; (ρ . ½ v2) is the kinetic energy of

the moving air per unit volume.

P = ½ * air density * Area Swept by Rotor * Wind Speed3

P = E / t = ½ . ρ .A . v3

i) Power in the wind is correlated 1:1 with area and is extremely sensitive to wind

speed (the cubic amplifies the power significantly)

ii) If the wind speed is twice as high, it contains 23 = 2 x 2 x 2 = 8 times as much

energy

iii) A site with 16 mph average wind speed will generate nearly 50% more

electricity and be more cost effective than one with 14 mph average wind

speed (16*16*16) / (14*14*14) = 1.4927

iv) Therefore, it “pay$” to hunt for good wind sites with better wind speeds

v) Wind speed increases with height above the ground

vi) Energy in the wind increases as height increases (theoretically)

V2/V1 = (H2/H1)1/7

46

Fig.4.1.1: Wind Energy Graph

4.2 WIND TURBINE:

A wind turbine is a device that converts kinetic energy from the wind

into mechanical energy. If the mechanical energy is used to produce electricity, the

device may be called a wind generator or wind charger. If the mechanical energy is

used to drive machinery, such as for grinding grain or pumping water, the device is

called a windmill or wind pump. Developed for over a millennium, today's wind

turbines are manufactured in a range of vertical and horizontal axis types. The

smallest turbines are used for applications such as battery charging or auxiliary

power on sailing boats; while large grid-connected arrays of turbines are becoming

an increasingly large source of commercial electric power.

Fig.4.2.1: Wind Turbine Schematic diagram

47

4.3 TYPES OF WIND TURBINE:-

a) Horizontal-axis

i) Horizontal-axis wind turbines (HAWT)

ii) Downwind turbine HAWT

iii) Upwind turbine HAWT

iv) Counter Rotating HAWT

v) Modern wind turbines

b) Vertical-axis

i) Vertical-axis wind turbines (or VAWT)

4.4 HORIZONTAL-AXIS WIND TURBINES (HAWT):

Horizontal-axis wind turbines (HAWT) have the main rotor shaft

and electrical generator at the top of a tower, and must be pointed into the wind.

Small turbines are pointed by a simple wind vane, while large turbines generally

use a wind sensor coupled with a servo motor. Most have a gearbox, which turns

the slow rotation of the blades into a quicker rotation that is more suitable to drive

an electrical generator. Since a tower produces turbulence behind it, the turbine is

usually positioned upwind of its supporting tower. Turbine blades are made stiff to

prevent the blades from being pushed into the tower by high winds. Additionally,

the blades are placed a considerable distance in front of the tower and are

sometimes tilted forward into the wind a small amount.

Fig.4.4.1: HAWT

48

DOWNWIND TURBINE UPWIND TURBINE

Fig.4.5.1: Turbine Type

a) Upwind turbines are used mostly.Because wind velocity increases at higher

altitudes, the backward force and torque on a horizontal axis wind turbine

(HAWT) blade peaks as it turns through the highest point in its circle. The

tower hinders the airflow at the lowest point in the circle, which produces a

local dip in force and torque. These two effects combine to produce a

cyclic twist on the main bearings of a HAWT. The combined twist is worst

in machines with an even number of blades, where one is straight up when

another is straight down. To improve reliability, teetering hubs are used

which allow the main shaft to rock through a few degrees, so that the main

bearings do not have to resist the torque peaks.

b) MODERN WIND TURBINES:- Turbines used in wind farms for

commercial production of electric power are usually three-bladed and

pointed into the wind by computer-controlled motors. These have high tip

speeds of over 320 kilometres per hour (200 mph), high efficiency, and low

torque ripple, which contribute to good reliability. The blades are usually

colored light gray to blend in with the clouds and range in length from 20

to 40 metres (66 to 130 ft) or more. The tubular steel towers range from 60

to 90 metres (200 to 300 ft) tall. The blades rotate at 10-22 revolutions per

minute. A gear box is commonly used for stepping up the speed of the

generator, although designs may also use direct drive of an annular

generator. Some models operate at constant speed, but more energy can be

49

collected by variable-speed turbines which use a solid-state power

converter to interface to the transmission system. All turbines are equipped

with protective features to avoid damage at high wind speeds,

by feathering the blades into the wind which ceases their rotation,

supplemented by brakes.

ii) COUNTER ROTATING TURBINES

Fig.4.5.2: Counter rotating Turbine

Counter rotating turbines can be used to increase the rotation speed of the

electrical generator. When the counter rotating turbines are on the same side of the

tower, the blades on the one in front are angled forwards slightly so as to never hit

the rear ones. They are either both geared to the same generator or, more often, one

is connected to the rotor and the other to the field windings. Counter rotating

turbines geared to the same generator have additional gearing losses. Counter

rotating turbines connected to the rotor and stator are mechanically simpler; but,

the field windings need slip rings which adds complexity, wastes some electricity

and wastes some mechanical power. As of 2005, no large practical counter-rotating

HAWTs are commercially sold. Counter rotating turbines can be on opposite sides

of the tower. In this case it is best that the one at the back be smaller than the one

at the front and set to stall at a higher wind speed. This way, at low wind speeds,

50

both turn and the generator taps the maximum proportion of the wind's power. At

intermediate speeds, the front turbine stalls; but, the rear one keeps turning, so the

wind generator has a smaller wind resistance and the tower can still support the

generator. At high wind speeds both turbines stall, the wind resistance is at a

minimum and the tower can still support the generator. This allows the generator

to function at a wider wind speed range than a single-turbine generator for a given

tower. To reduce sympathetic vibrations, the two turbines should turn at speeds

with few common factors, for example 7:3 speed ratio. Overall, this is a more

complicated design than the single-turbine wind generator, but it taps more of the

wind's energy at a wider range of wind speeds.

iii) VERTICAL-AXIS WIND TURBINES ( VAWT)

Vertical-axis wind turbines (VAWTs) have the main rotor shaft arranged

vertically. Key advantages of this arrangement are that the turbine does not need to

be pointed into the wind to be effective. This is an advantage on sites where the

wind direction is highly variable, for example when integrated into buildings. The

key disadvantages include the low rotational speed with the consequential

higher torque and hence higher cost of the drive train, the inherently lower power

coefficient, the 360 degree rotation of the aerofoil within the wind flow during

each cycle and hence the highly dynamic loading on the blade, the pulsating torque

generated by some rotor designs on the drive train, and the difficulty of modelling

the wind flow accurately and hence the challenges of analysing and designing the

rotor prior to fabricating a prototype.

With a vertical axis, the generator and gearbox can be placed near the ground,

hence avoiding the need of a tower and improving accessibility for maintenance.

Drawbacks of this configuration include (i) wind speeds are lower close to the

ground, so less wind energy is available for a given size turbine, and (ii) wind

shear is more severe close to the ground, so the rotor experiences higher loads. Air

flow near the ground and other objects can create turbulent flow, which can

introduce problems associated with vibration, such as noise and bearing wear

51

which may increase the maintenance or shorten the service life. However, when a

turbine is mounted on a rooftop, the building generally redirects wind over the roof

and this can double the wind speed at the turbine. If the height of the rooftop

mounted turbine tower is approximately 50% of the building height, this is near the

optimum for maximum wind energy and minimum wind turbulence. It should be

borne in mind that wind speeds within the built environment are generally much

lower than at exposed rural sites.

Fig.4.5.3:VAWT

4.5 TURBINE DESIGN AND CONSTRUCTION

Wind turbines are designed to exploit the wind energy that exists at a

location. Aerodynamic modeling is used to determine the optimum tower height,

control systems, number of blades and blade shape.

i) One of the best construction materials available (in 2001) is graphite-fibre in

epoxy. Graphite composites can be used to build turbines of sixty meters radius,

enough to tap a few megawatts of power. Smaller household turbines can be made

of lightweight fiberglass, aluminum, or sometimes laminated wood.

ii) Wood and canvas sails were originally used on early windmills. Unfortunately

they require much maintenance over their service life. Also, they have a relatively

52

high drag (low aerodynamic efficiency) for the force they capture. For these

reasons they were superseded with solid airfoils.

iii) Wind power intercepted by the turbine is proportional to the square of its

blade-length. The maximum blade-length of a turbine is limited by both the

strength and stiffness of its material.

iv) The wind blows faster at higher altitudes because of the drag of the surface (sea

or land) and the viscosity of the air. The variation in velocity with altitude, called

wind shear is most dramatic near the surface. Typically, the variation follows the

1/7th power law, which predicts that wind speed rises proportionally to the seventh

root of altitude. Doubling the altitude of a turbine, then, increases the expected

wind speeds by 10% and the expected power by 34%. Doubling the tower height

generally requires doubling the diameter as well, increasing the amount of material

by a factor of eight.

v) For HAWTs, tower heights approximately twice the blade length have been

found to balance material costs of the tower against better utilisation of the more

expensive active components.

vi) Although turbines can be built with any number of blades, there are many

constraints. There are a number of vibration modes that increase in peak intensity

as the number of blades decreases. Some of these vibrations, besides causing wear

on the machine, are also audible. Thus, noise and wear considerations point to

larger numbers of blades, generally at least 3.Many small scale wind turbines, such

as the Whisper 175, use 2 blades because such turbines are easy to construct as

they avoid the need for using a hub with linkages to individual blades, and the

blade(s) can be shipped easily in one long package. Three-bladed turbines, which

are much more efficient, and more quiet, require more complicated onsite

assembly

4.6 NEED OF ROTATIONAL CONTROL

The speed at which wind turbines rotate must be controlled for several reasons:

53

i) Maintenance:- because it is dangerous to have people working on a wind turbine

while it is active, it is sometimes necessary to bring a turbine to a full stop.

ii) Noise reduction:- As a rule of thumb, the noise from a wind turbine increases

with the fifth power of the relative wind speed (as seen from the moving tip of the

blades). In noise-sensitive environments (nearly all onshore installations), noise

limits the tip speed to approximately 60 m/s. High efficiency turbines may have tip

speed ratios of 5-6, which, for onshore turbines, limits high efficiency operation to

winds of just 10 m/s.

iii) Centripetal force reduction:- as the rotational speed increases, so does the

centripetal force working on the central hub or axis. When it exceeds safe limits

blades could snap off, and the turbine would fail dramatically.

iv) Compatible with wind speed and direction:-On a pitch controlled wind turbine

the turbine's electronic controller checks the power output of the turbine several

times per second. When the power output becomes too high, it sends an order to

the blade pitch mechanism which immediately pitches (turns) the rotor blades

slightly out of the wind. Conversely, the blades are turned back into the wind

whenever the wind drops again. (Passive) stall controlled wind turbines have the

rotor blades bolted onto the hub at a fixed angle. The geometry of the rotor blade

profile, however has been aerodynamically designed to ensure that the moment the

wind speed becomes too high, it creates turbulence on the side of the rotor blade

which is not facing the wind as shown in the picture on the previous page. This

stall prevents the lifting force of the rotor blade from acting on the rotor. An

increasing number of larger wind turbines (1 MW and up) are being developed

with an active stall power control mechanism. Technically the active stall

machines resemble pitch controlled machines, since they have pitchable blades. In

order to get a reasonably large torque (turning force) at low wind speeds, the

machines will usually be programmed to pitch their blades much like a pitch

controlled machine at low wind speeds. (Often they use only a few fixed steps

depending upon the wind speed).

54

v) Sensor:-It simply consists of a ball resting on a ring. The ball is connected to a

switch through a chain. If the turbine starts shaking, the ball will fall off the ring

and switch the turbine off. There are many other sensors in the nacelle, e.g.

electronic thermometers which check the oil temperature in the gearbox and the

temperature of the generator.

vi) Overspeed Protection :-It is essential that wind turbines stop automatically in

case of malfunction of a critical component.

vii) Aerodynamic Braking System: Tip Brakes The primary braking system for

most modern wind turbines is the aerodynamic braking system, which essentially

consists in turning the rotor blades about 90 degrees along their longitudinal axis

(in the case of a pitch controlled turbine or an active stall controlled turbine ), or in

turning the rotor blade tips 90 degrees (in the case of a stall controlled turbine ).

Aerodynamic braking systems are extremely safe.

vii) Mechanical Braking System :- The mechanical brake is used as a backup

system for the aerodynamic braking system.

4.7 DETERMINING FACTORS

Some of the factors determining the economics of the utility scale wind energy are:

i) Costs depend very much on the wind speed at that site since the power varies as

cube of the wind speed.

ii) Turbine design and construction: more than 60% of total costs are contributed

by the turbine costs.

iii) Rated capacity of the turbine: larger wind farms are known to be more

economical than small wind farms.

iv) Exact location and orientation of the turbine greatly affects the economics of

the wind energy.

55

v) Improvements of turbine design: for example, use of light weight material .

vi) Wind energy is a capital intensive source of energy.

vii) Assuming the same size project, the better the wind resource, the lower the

cost.

viii) Assuming the same wind speed of 8.08 m/s, a large wind farm is more

economical.

4.8 WIND PLANT CLASSIFICATION

a) OFFSHORE WIND POWER PLANT

Offshore wind power refers to the construction of wind farms in bodies of

water to generate electricity from wind. Better wind speeds are available offshore

compared to on land, so offshore wind power’s contribution in terms of electricity

supplied is higher. Offshore wind turbines are less obtrusive than turbines on land,

as their apparent size and noise is mitigated by distance. Because water has less

surface roughness than land (especially deeper water), the average wind speed is

usually considerably higher over open water. Capacity factors (utilisation rates) are

considerably higher than for onshore locations

ii) ADVANTAGES : higher wind speed results in low turbine height

iii) DISADVANTAGES: higher o&m costs due to harsh, corrosive environment

and tougher approach.

b) ON SHORE POWER PLANT

These are installed on hills/ridges. These turbine installations in hilly or

mountainous regions tend to be on ridgelines generally three kilometers or more

inland from the nearest shoreline. This is done to exploit the topographic

acceleration as the wind accelerates over a ridge. The additional wind speeds

56

gained in this way can increase the amount of energy produced because more wind

is going through the turbines. Great attention must be paid to the exact positions of

the turbines (a process known as micro-sitting) because a difference of 30 m can

sometimes mean a doubling in output.

i) ADVANTAGES: low o&m costs due to easy approach.

ii) DISADVANTAGES: relatively large turbine height

4.9 ADVANTAGES OF WIND POWER PLANT

a)Economic Advantages:

i) No delay in construction: wind turbines are easy to construct and does not

require long gestation periods.

ii) Low maintenance costs: maintenance costs are very small compared to

installation costs.

iii) Reliable and durable equipment: except for wind speeds greater than 30 mi/hr,

once installed, wind equipment last for more than 25 years.

iv) Farmers and ranchers earn additional income by leasing their land for wind

turbine.

v) Wind industry produces more jobs per unit energy produced than other forms

of energy.

vi) No hidden costs, which greatly reduces the environmental impacts

vii) Greater fuel diversity.

viii) Wind energy is big business turning over A$13 billion globally and

employing 100,000 people in 2003. By 2020, the industry is expected to employ

1.8 million people and be worth $A120 billion a year.

57

b) Additional advantages:

i) Clean,pollution free, renewable

ii) Price stability

iii) Energy independence from foreign fuel sources

iv) Can reduce green house effect if used in place of fossil fuel plants

4.10 TYPICAL CONCERNS AND THEIR REMEDIES

a) VISUAL IMPACT:

i) Off shore turbines

ii) Arrangement:

Aesthetic concerns may be addressed through the use of modern turbines --

tubular towers and sleek, minimalist features contribute to a more attractive

appearance. Avoiding construction of conspicuous roads and clearings, burying

transmission lines, and hiding buildings and structures behind ridges or vegetation

are also prudent steps. Finally, educating nearby communities prior to construction

about wind energy and its benefits can reduce opposition to visual effects

b) AVIAN CONCERNS

i) Suitable choice of site

ii) Using tubular towers instead of lattice tower.

For wind plants currently experiencing bird conflicts, the immediate task is to

find practical measures to reduce bird deaths and injuries. Mitigation proposals

include changing the color of wind turbine blades, using tubular towers with

diagonal stringers, eliminating places for birds to perch on the towers (especially

perches near uninsulated electricity transmission lines).

iii) Using radars

58

using radar to alert wind project operators to the passage of large flocks of birds.

Federal and state agencies and environmental organizations are collaborating on a

research program to address the bird issue.

b) NOISE

i) Varies as 5th

power of relative wind speed

ii) Streamlining of tower and nacelle

Streamlining (rounding or giving an aerodynamic shape to any protruding features

and to the nacelle itself) reduces any noise that is created by the wind passing the

turbine. Turbines also incorporate design features to reduce vibration and any

associated noise.

iii) Acoustic insulation of nacelle

The generator, gears, and other moving parts located in the turbine nacelle produce

mechanical noise. Soundproofing and mounting equipment on sound-dampening

buffer pads helps to deal with this issue.

iv) Specially designed gear box

Wind turbines use special gearboxes, in which the gear wheels are designed to flex

slightly and reduce mechanical noise. In addition, special sound-dampening buffer

pads separate the gearboxes from the nacelle frame to minimize the possibility that

any vibrations could become sound.

v) Use of upwind turbines

A wind turbine can be either "upwind" (that is, where the rotor faces into the

wind) or "downwind" (where the rotor faces away from the wind). A downwind

design offers some engineering advantages, but when a rotor blade passes the

"wind shadow" of the tower as the rotor revolves, it tends to produce an

"impulsive" or thumping sound that can be annoying. Today, almost all of the

commercial wind machines on the market are upwind designs, and the few that are

59

downwind have incorporated design features aimed at reducing impulsive noise

(for example, positioning the rotor so that it is further away from the tower).

1. Reducing angle of attack

2. Low tip speed ratios

c) CHANGES IN WIND PATTERNS

i) Reducing turbulence

d) INTERMITTENT

i) Coupling with hydro or solar energy

e) TV, MICROWAVE, RADAR INTERFERENCE

Switching from conducting material to non-conducting and composite material

4.11 POTENTIAL AND APPLICATION OF WIND ENERGY

4.11.1 WIND SECTOR IN INDIA:-

i) The development of wind power in India began in the 1990s, and has

significantly increased in the last few years. Although a relative newcomer to the

wind industry compared with Denmark or the US, domestic policy support

for wind power has led India to become the country with the fifth largest installed

wind power capacity in the world.

ii) As of December 2010 the installed capacity of wind power in India was

13,065.37 MW, mainly spread across Tamil Nadu (4132.72

MW), Maharashtra (1837.85MW), Karnataka (1184.45MW), Rajasthan (670.97

MW), Gujarat (1432.71 MW), Andhra Pradesh (122.45 MW), Madhya

Pradesh (187.69 MW), Kerala (23.00 MW), West Bengal (1.10 MW), other states

(3.20 MW) It is estimated that 6,000 MW of additional wind power capacity will

60

be installed in India by 2012. Wind power accounts for 6% of India's total installed

power capacity, and it generates 1.6% of the country's power.

4.12 INDIA’S LARGEST WIND PLANT:-

i) Commissioned by suzlon in dhule – satara,maharashtra.

ii) Asia’s largest with present capacity of 400 mw with 320turbines of 1.25mw .

iii) Soon its going to become world’s largest after commissioning 1000mw.

4.13 WORLD’S LARGEST WIND PLANTS:-

i) The Roscoe Wind Farm in Roscoe, Texas, owned and operated

by E.ON Climate & Renewables is the world's largest wind farm (as of October

2009) with 627 wind turbines and a total installed capacity of 781.5 MW.

4.14 CONCLUSION

Wind energy, as an alternative to fossil fuels, is plentiful, renewable, widely

distributed, clean, and produces no greenhouse gas emissions during operation,also

Wind energy has very good potential and it is the fastest growing energy source.

The future looks bright for wind energy because technology is becoming more

advanced and windmills are becoming more efficient. Also as a technocrat it is our

responsibility to make wind energy as a part of the worldwide discussion on the

future of energy generation and use and consequent effect on the environment.

61

CHAPTER 5

SHOCK ABSORBER SYSTEM

5. Shock Absorber System

The project here is all about Power-Generating Shock Absorber (PGSA).

The Power-Generating Shock Absorber (PGSA) converts kinetic energy into

electricity through the use of a Linear Motion Electromagnetic System (LMES).

There are at least two entities who have spent time/resources developing this

concept: Goldneretal and Oxenreider. An electromagnetic linear generator and

regenerative electromagnetic shock absorber is disclosed which converts variable

frequency, repetitive intermittent linear displacement motion to useful electrical

power. The innovative device provides for superposition of radial components of

the magnetic flux density from a plurality of adjacent magnets to produce a

maximum average radial magnetic flux density within a coil winding array. Due to

the vector superposition of the magnetic fields and magnetic flux from a plurality

of magnets, a nearly four-fold increase in magnetic flux density is achieved over

conventional electromagnetic generator designs with a potential sixteen-fold

increase in power generating capacity. As a regenerative shock absorber, the

disclosed device is capable of converting parasitic displacement motion and

vibrations encountered under normal urban driving conditions to a useful electrical

energy for powering vehicles and accessories or charging batteries in electric and

fossil fuel powered vehicles. The disclosed device is capable of high power

generation capacity and energy conversion efficiency with minimal weight penalty

for improved fuel efficiency.

5.1 Transformation of sound into electric energy

Sound energy is also a type of wave motion. We are heard by others when

we talk because of the sound energy we produce. It is due to the effect of the air

molecules vibrating when we talk. The vibrating molecules hit our eardrums,

62

which enable us to hear others talk. Sound energy may be converted into electrical

energy for transmission, and later the electrical energy can be converted back into

sound energy at the receiving end. An example of such transformations could be

seen in the microphone and the loudspeaker. Sound, like heat energy is easily

lost. The transformation of one form of energy into another may be accompanied

by losses in the form of sound and/or heat that are often not desirable.

5.2 COMPONENTS USED IN THIS HYBRID MODEL OF CAR

i) Stepper motor

ii) Induction braking coil

iii) Gears

iv) Resistances

vi) Capacitors

vii) Diode

5. 3 VOLTS MOTOR CYCLE BATTERY

We have used a motorcycle lead acid battery. This battery is of 6 volts. Power

of this battery is used for glowing tube light when the power supply is off.

Otherwise, the power supply keeps on charging the battery.

5.4 NEON LAMP

230 volts neon lamps are connected between 220 volts AC input and

transformer. This lamp is working as an indicator. It indicates whether the power is

on or off.

5.5 FLUORESCENT TUBE LIGHT

A fluorescent 20 watts tube is used as a source of light. The given circuit

operates it automatically.

63

Fig 5.5.1: Battery Types

5.7 CAPACITORS

It is an electronic component whose function is to accumulate charges and

then release it. To understand the

concept of capacitance,

consider a pair of metal plates which all are placed near to each other without

touching. If a battery is connected to these plates the positive pole to one and the

negative pole to the other, electrons from the battery will be attracted from the plate

connected to the positive terminal of the battery. If the battery is then disconnected,

one plate will be left with an excess of electrons, the other with a shortage, and a

potential or voltage difference will exists between them. These plates will be acting

as capacitors. Capacitors are of two types: - (1) fixed type like ceramic, polyester,

electrolytic capacitors-these names refer to the material they are made of aluminium

foil. (2) Variable type like gang condenser in radio or trimmer. In fixed type

capacitors, it has two leads and its value is written over its body and variable type

has three leads. Unit of measurement of a capacitor is farad denoted by the symbol

F. It is a very big unit of capacitance. Small unit capacitor are pico-farad denoted by

pf (Ipf=1/1000,000,000,000 f) Above all, in case of electrolytic capacitors, it's two

terminal are marked as (-) and (+) so check it while using capacitors in the circuit in

right direction. Mistake can destroy the capacitor or entire circuit in operational.

64

Fig 5.6.1: Types of Capacitors

5.7 crystal oscillators

Crystal oscillators are oscillators where the primary frequency determining

element is a quartz crystal. Because of the inherent characteristics of the quartz

crystal the crystal oscillator may be held to extreme accuracy of frequency

stability. Temperature compensation may be applied to crystal oscillators to

improve thermal stability of the crystal oscillator. Crystal oscillators are usually,

fixed frequency oscillators where stability and accuracy are the primary

considerations. For example it is almost impossible to design a stable and accurate

LC oscillator for the upper HF and higher frequencies without resorting to some

sort of crystal control. Hence the reason for crystal oscillators. The frequency of

older FT-243 crystals can be moved upward by crystal grinding. I won't be

discussing frequency synthesizers and direct digital synthesis (DDS) here. They

are particularly interesting topics to be covered later.

5.7.1 A practical example of a Crystal Oscillator

This is a typical example of the type of crystal oscillators which may be

used for say converters. Some points of interest on crystal oscillators in relation to

figure 1.

Figure 5.7.1.1: schematic of a crystal oscillator

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The transistor could be a general purpose type with an Ft of at least 150 Mhz for

HF use. A typical example would be a 2N2222A. The turns ratio on the tuned

circuit depicts an anticipated nominal load of 50 ohms. This allows theoretical 2K5

ohms on the collector. If it is followed by a buffer amplifier (highly recommended)

I would simply maintain the typical 7:1 turns ratio. I have included a formula for

determining L and C in the tuned circuits of crystal oscillators in case you have

forgotten earlier tutorials. Personally I would make L a reactance of around 250

ohms. In this case I'd make C a smaller trimmer in parallel with a standard fixed

value.

5.8 RESISTANCE

Resistance is the opposition of a material to the current. It is measured in

conductor is 100% efficient. To control the electron flow (current) in a predictable

manner, we use resistors. Electronic circuits use calibrated lumped resistance to

control the flow of current. Broadly speaking, resistor can be divided into two

groups viz. fixed & adjustable (variable) resistors. In fixed resistors, the value is

fixed & cannot be varied. In variable resistors, the resistance value can be varied

by an adjuster knob. It can be divided into (a) Carbon composition (b) Wire wound

(c) Special type. The most common type of resistors used in our projects is carbon

type. The resistance value is normally indicated by colour bands. Each resistance

has four colours, one of the band on either side will be gold or silver, this is called

fourth band and indicates the tolerance, others three band will give the value of

resistance (see table). For example if a resistor has the following marking on it say

red, violet, gold. Comparing these coloured rings with the colour code, its value is

27000 ohms or 27 kilo ohms and its tolerance is ±5%. Resistor comes in various

sizes (Power rating). The bigger, the size, the more power rating of 1/4 watts. The

four colour rings on its body tells us the value of resistor value as given below.

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5.9 Colour Code

Colour Code

Black 0

Brawn 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

Fig 5.8.1: Type of Resistor

The first rings give the first digit. The second ring gives the second digit.

The third ring indicates the number of zeroes to be placed after the digits. The

fourth ring gives tolerance (gold ±5%, silver ± 10%, No colour ± 20%). Resistance

coils of different values are connected b/w the gaps. When the knob is rotated, the

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pointer also moves over the brass pieces. If a gap is skipped over, its resistance is

included in the circuit. If two gaps are skipped over, the resistances of both

together are included in the circuit and so on. A dial type of resistance box

contains many dials depending upon the range, which it has to cover. If a

resistance box has to read up to 10,000ohm, it will have three dials each having ten

gaps i.e. ten resistance coils each of resistance 10 ohm. The third dial will have ten

resistances each of 100 ohm. The dial type of resistance boxes is better because the

contact resistance in this case is small & constant.

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CHAPTER 6

PARKING SYSTEM

6. Easy Parallel Parking – Car Goes Sideways, Wheels Turn 90 degrees

It gives immense pleasure when a person rides a car and goes on a smooth

nice highway. On the other hand, the same person gets frustrated when he has

to make sharp manoeuvres to parallel park his car in closely packed parking spot

with front and rear car taking a portion of his parking space. I suggest a feature in

cars that may alleviate the pain. Let’s see the pain and the solution.

6.1 Parallel Parking

Parking on the streets, in apartment complexes and even some other

parking areas, requires one to Parallel Park a car. In Parallel parking of car, a

person needs to park his car lengthwise parallel to curb. There may be car ahead

and behind the parking spot where this car needs to be parked. The space provided

to park this car may be around 1.5 car length – 1 length for the car and 1/4 length

ahead of and 1/4 length behind the car.

6.2 Method

The recommended and easy way for parallel parking of a car is

i) Stop the car parallel to the car in front

ii) Turn steering wheel towards the curb and move the car backwards (reverse

gear)

iii) when car has entered around 80% length in the parking spot, turn steering

wheel away from the curb and continue moving

iv) Watch for the car in the back and the curb on side

v) Straighten the steering wheel and move the car to maintain equal distance

from car in front and back

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6.3 Drawback of parallel parking in conventional way

i) Parallel parking a car is a skill that one needs to learn and practice. One may not

perform parallel parking without first learning it. This is the reason, Department of

Motor Vehicles in USA

ii) Even with all the learning drivers do make some mistake while parallel parking

a car and the result is nicks on the bumper of car.

iii) Most of the time, parallel parking requires one vehicle to acquire 1.5 to 2 car

parking length so that the car can get in the parking spot and come out of it.

iv)Parallel parking requires a vehicle to move forward and then reverse causing it

to travel more distance than was really required.

a)More distance leads to more fuel consumption

b)More distance leads to more wear and tear of the car

c)More distance and parallel parking causes more time spent

d)Above point also causes more money spent to Parallel Park a car.

6.4 Available Solutions

i)Park Assist

ii)Parking sensors or vicinity sensors and rear view or back up camera

iii)Extreme parking skills

6.5 Your Venture

The available solutions, undoubtedly, seem fascinating but they are not

natural and some of the drawbacks still exist. My suggestion (your venture) may

supplement these solutions rather than replace it. Design axle and driving

mechanism of a car such that wheels can turn 90 degrees to park a car straight

away rather than making manoeuvres required for parallel parking. In other words.

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i) A car stops moving forward (or backward)

ii) All the wheels of the car turns 90 degrees

iii) The car moves to the left or right hand side i.e. the car moves sideways on

the instructions of driver.

Fig 6.5.1: Ways of Parking System

6.6Advantages

i) The mechanism is intuitive so a driver needs to spend very little time to

learn if such mechanism is implemented in a car.

ii) Cars can be parked very close to each other. This may save costly parking

space, lead to more parking fees to commercial parking spaces and

eventually passing on the benefit to drivers (reduction of parking fees).

iii) In congested apartment complexes where parking is limited, this

mechanism can be very helpful.

iv) This mechanism addresses all the drawbacks of parallel parking

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v) On a congested road, if the car in front breaks down and you have little

space to pass (overtake) that car then this feature may be very helpful.

6.6 Challenges

i) This solution is not in market for all this time cars/automobiles are there in the

world (200 to 400 years) implies this solution is extremely challenging.

ii) Axle and driving mechanism will need to be designed so that wheels can turn

90 degrees. There will be no precedence of such mechanism so one will need to

undergo all the Research and Design for this solution.

iii) The 2 wheel drive vehicles will need to be redesigned so that power can be

shifted to a front and rear wheel rather than to pair of front wheels or rear wheels.

Four wheel drive vehicles may have an advantage in this term.

iv) Sideways driving of car may be dangerous when passing a struck car in front.

Car’s signal mechanism will need to be designed to warn the driver coming from

behind that car is moving sideways.

v) The forward and reverse gears in current vehicles may not work well for

sideways movement. Sideways movement should be slower than forward and rear

movement.

vi) Mechanism will need to be made for a driver to stop the car completely before

he makes sideways movement.

vii) The cost of this mechanism once implemented may be high. One may

consider designing this solution for bigger and costlier car, which may derive

premium from wealthy customers, and the car’s bottom has more room to turn

wheels 90 degrees.

viii) The competition with Park Assist Technology and Backup Camera may be

steep even though these technologies can supplement our solution.

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CHAPTER 7

ANDROID SYSTEM

7. ANDROID SYSTEM

7.1 What is Robot?

Robot is a mechanical device that sometimes resembles a human and is

capable of performing a variety of often complex human tasks on command or by

being programmed in advance.

7.2Project is about

Here at this robot I have used a Bluetooth module to control the robot via 2

BO motors at 100RPM approx the robot is control by an android phone

application. Microcontroller used is AT89S52 form 8051 family to work in a serial

communication UART mode the communication is configured on 9800bps to

communicate it with the Bluetooth module. The Bluetooth module used is a HC-05

in smd package which works on a 3.3v and have a serial communication with any

device connected to it the communication speed can be configured on various

speed via AT Command. The BT module is a SPP supported profile so it can be

connected easily to any module or phone. In this profile the data can be sent and

receive to module. The BT module is connected to the RX pin of microcontroller.

The L293D is a motor driver IC to operate the motors in any direction required

dependent on the logic applied to the logic pins. A readymade compact size chassis

I have used to avoid the chassis assembly the chassis contains 2 decks the lower is

used for BO motors fitting the upper is used as a battery stack .on top the plate the

board is mounted by screw fitting.

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7.3 Block Diagram

Fig 7.3.1: Android System

Fig 7.3.2: Circuit Diagram for Bluetooth Module

BT

module

Motor 2

Motor 1 L293D

Motor

driver

AT89S52

Micro

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The reset circuit at pin 11 and KEY circuit at pin24 can be ignored to work

the module in communication mode.

Fig 7.3.3: Integrated Circuit

7.4 Motor driver circuit :

The pin 8 of IC should b connected to the 9v battery or 12v.

This pin8 is internally connected to the driver ckt inside the IC which helps the

motor to get the good supply which also helps the smooth functioning of motors

Fig.7.4.1: Motor Circuit

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5.5 The complete circuit:

The crystal circuit and the reset circuit is as common usually used in every

AT89S52 circuit. The leds connected to the motor indicates the flow of

current….the direction of the motor rotation.

Fig 7.4.2: Complete circuit of android system

7.5 The Bluetooth module:

The Bluetooth module used is a HC-05 based on SPP support

Features:

i)Wireless serial Bluetooth port.

ii) With free power adapter bottom board come with well power regulator. User

can connect 3.3 to 5VDC and connect TX and RX to your control IO (general 3.3

to 5V digital input output of MCU or IO is ok, or general TLL IO)

iii) Easy to connect this module with PC, just search and key "1234" pass code.

iv) With white SMD LED on the adapter board, can see the Bluetooth connection

status.

Step to connect:

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i) Connect the wiring, power up, while the device is not connected, the Bluetooth

module board has a white LED flashing

ii) At PC side, search Bluetooth device.

iii) Found name called "HC-05" device

iv) Connect it, and pass code is "1234"

v) While connection is ok, you can see the LED become always on

7.6 Usage:

i)Coupled Mode: Two modules will establish communication automatically when

powered.

ii)PC hosted mode: Pair the module with Bluetooth dongle directly as virtual

serial.

iii)Bluetooth protocol : Bluetooth Specification v2.0+EDR

iv)Frequency : 2.4GHz ISM band

v)Modulation : GFSK(Gaussian Frequency Shift Keying)

vi)Speed : Asynchronous: 2.1Mbps(Max) / 160 kbps, Synchronous:

1Mbps/1Mbps

vii)Security : Authentication and encryption

viii)Profiles : Bluetooth serial port

ix)CSR chip : Bluetooth v2.0

x)Wave band : 2.4GHz-2.8GHz, ISM Band

xi)Protocol : Bluetooth V2.0

xii)Voltage : 5V (3.6V-6V, NO more than 7V)

xiii)User defined Baud Rate : 4800, 9600, 19200, 38400, 57600, 115200,

230400,460800,921600 ,1382400.

7.7 Pin Definition:

i) PIO8 connects with LED cathodea with 470ohm series resistor in between. LED

NEGATIVE connects to ground. It is used to indicate the module state. After

powered on, flashing intervals differ in different states.

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ii) PIO9 is used to control LED indicating paring. It will be steady on when paring

is successful.

iii) PIO11, module state switching pin. HIGH -> response to AT command; LOW

or floating -> regular work status.

iv) With build-in reset circuit, reset is completed automatically after powered on.

v) Steps to set to MASTER:

vi) Set PIO11 HIGH with a 10K resistor in between.

vii) Power on, module comes into AT Command Response Status

Viii) Open HyperTerminal or other serial tool, set the baud rate 38400, 8 data bits,

1 stop bit, no parity bit, no Flow

7.8 At commands to check the Module:

i) Set PIO11 HIGH with a 10K resistor in between.

ii) Power on, module comes into AT Command Response Status

iii) Open HyperTerminal or other serial tool, set the baud rate 38400, 8 data bits, 1

stop bit, no parity bit, no Flow

iv) Now u r enter in AT commond mode.

Command AT

Response OK the module is connected successfully

Commond AT+ROLE?

Response +ROLE=0 the module is in slave mode

Commond AT+ROLE=1

Response OK the module is set in master mode

For more command refer data sheet ……;)

In slave mode the PC, Phone etc will search the module and pair with the module

In master mode the module will search for any PC, Phone etc

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CHAPTER 8

DC MOTORS

8.1 DC Motor

Faradays used oersteds discovered, that electricity could be used to produce

motion, to build the world first electric motor in 1821. Ten years later, using the

same logic in reverse, faraday was interested in getting the motion produced by

oersteds experiment to be continuous, rather then just a rotatory shift in position. In

his experiments, faraday thought in terms of magnetic lines of force. He visualized

how flux lines existing around a current carrying wire and a bar magnet. He was

then able to produce a device in which the different lines of force could interact a

produce continues rotation. The basic faradays motor uses a free-swinging wire

that circles around the end of a bar magnet. The bottom end of the wire is in a pool

of mercury. Which allows the wire to rotate while keeping a complete electric

circuit?

Fig.8.1.1: DC Motor

Although Faraday's motor was ingenious. It could not be used to do any practical

work. This is because its drive shaft was enclosed and it could only produce an

internal orbital motion. It could not transfer its mechanical energy to the outside

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for deriving an external load. However it did show how the magnetic fields of a

conductor and a magnet could be made to interact to produce continuous motion.

Faradays motor orbited its wire rotor must pass through the magnet’s lines of

force.

Fig.8.1.2: Magnetic Lines Of Forces

When a current is passes through the wire ,circular lines of force are

produced around the wire. Those flux lines go in a direction described by the left-

hand rule. The lines of force of the magnet go from the N pole to the S pole You

can see that on one side of the wire, the magnetic lines of force are going in the

opposite direction as a result the wire, s flux lines oppose the magnet’s flux line

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since flux lines takes the path of least resistance, more lines concentrate on the

other side of the wire conductor, the lines are bent and are very closely spaced. The

lines tend to straighten and be wider spaced. Because of this the denser, curve

field pushes the wire in the opposite direction. The direction in which the wire is

moved is determined by the right hand rule. If the current in the wire went in the

opposite direction. The direction of its flux lines would reverse, and the wire

would be pushed the other way.

8.2 Rules for motor action

The left hand rule shows the direction of the flux lines around a wire that is

carrying current. When the thumb points in the direction of the magnetic lines of

force. The right hand rule for motors shows the direction that a current carrying

wire will be moved in a magnetic field. When the forefinger is pointed in the

direction of the magnetic field lines, and the centre finger is pointed in the

direction of the current in the wire the thumb will point in the direction that the

wire will be moved.

FIG.8.2.1: TORQUE AND ROTATING MOTION

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In the basic action you just studied the wire only moves in a straight line and stops

moving once out of the field even though the current is still on. A practical motor

must develop a basic twisting force called torque loop. We can see how torque is

produced. If the loop is connected to a battery. Current flows in one direction

oneside of the loop, and in the opposite direction on the other. Therefore the

concentric direction on the two sides. If we mount the loop in a fixed magnetic

field and supply the current the flux lines of the field and both sides of the loop

will interact, causing the loop to act like a lever with a force pushing on its two

sides in opposite directions. The combined forces result in turning force, or torque

because the loop is arranged to pivot on its axis. In a motor the loop that moves in

the field is called an armature or rotor. The overall turning force on the armature

depends upon several factors including field strength armature current strength and

the physical construction of the armature especially the distance from the loop

sides to the axis lines. Because of the lever action the force on the sides are further

from the axis; thus large armature will produce greater torques.

Fig.8.2.2: Magnetic Poles

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Fig.8.2.3: Torque

In the practical motor the torque determines the energy available for doing useful

work. The greater the torque the greater the energy. If a motor does not develop

enough torque to pull its load it stalls.

8.3 Producing continuous rotation

The armature turns when torque is produced and torque is produced as long

as the fields of the magnet and armature interact. When the loop reaches a position

perpendicular to the field, the interaction of the magnetic field stops. This position

is known as the neutral plane. In the neutral plane, no torque is produced and the

rotation of the armature should stop; however inertia tends to keep a moving object

in the motion even after the prime moving force is removed and thus the armature

tends to rotate past the neutral plane. But when the armature continues o the sides

of the loop start to swing back in to the flux lines, and apply a force to push the

sides of the loop back and a torque is developed in the opposite direction. Instead

of a continuous rotation an oscillating motion is produced until the armature stops

in the neutral plane.

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Fig.8.3.1: Neutral Plane

84

To get continuous rotation we must keep the armature turning in the same

direction as it passes through the neutral plane .We could do this by reversing

either the direction of the current flow through the armature at the instant the

armature goes through the neutral pole. Current reversals of this type are normally

the job of circuit switching devices. Since the switch would have to be

synchronized with the armature, it is more logical to build it into the armature then

in to the field. The practical switching device, which can change the direction of

current flow through an armature to maintain continuous rotation, is called a

commutator.

8.4 The commutator

For the single-loop armature, the commutator is simple. It is a conducting

ring that is split into two segment with each segment connected to an end of the

armature loop. Power for the armature from an external power source such as a

battery is brought to the commutator segments by means of brushes. The

arrangement is almost identical to that for the basic dc generator. The logic behind

the operation of the commutator is easy to see in the figures. You can see in figure

A that current flows into the side of the armature closest to the South Pole of the

field and out of the side closest to the North Pole. The interaction of the two fields

produces a torque in the direction indicated, and the armature rotates in that

direction.

No torque is produced but the armature continues to rotate past the neutral plane

due to inertia. Notice that at the neutral position the commutator disconnects from

the brushes sides of the loop reverse positions. But the switching action of the

commutator keeps the direction of current flow through the armature the same as it

was in the figure. A. Current still flows into the armature side that is now closest to

the South Pole. Since the magnet’s field direction remains the same throughout the

interaction of fields after commutation keeps the torque going in the original

direction; thus the same direction of rotation is maintained. As you can see in

figure D, Inertia again carries the armature past neutral to the position shown in the

fig. A while communication keeps the current flowing in the direction that

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continues to maintain rotation. In this way, the commutator keeps switching the

current through the loop, so that the field it produces always interacts with the pole

field to develop a continuous torque in the same direction.

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Fig.8.4.1:ABCD For Commutator

8.5 THE ELEMENTRY DC MOTOR

At this point, you have been introduced to the four principal parts that

make up the elementary D.C motor. These parts are the same as those you met in

87

your study of the basic D.C generator .a magnetic field, a movable conductor, a

commutator and brushes. In practice, the magnetic field can be supplied by a

permanent magnet or by an electromagnet. For most discussions covering various

motor operating principles, we will assume that a permanent magnet is used at

other times when it is important for you to understand that the field of the motor is

develop electrically, we will show that an electromagnet is used. In either case, the

magnetic field itself consists of magnetic flux lines that form a closed magnetic

circuit. The flux lines leave the north pole of the magnet, extend across the air gap

between the poles of the magnet, enter the South Pole and then travel through the

magnet itself back to the north pole. The movable conductor, usually a loop, called

armature, therefore is in the magnetic field.

When D.C motor is supplied to the armature through the brushes and commutator,

magnetic flux is also build up around the armature. It is this armature flux that

interacts with the magnetic field in which the armature is suspended to develop the

torque that makes the motor operate.

Fig.8.5.1: Inertia

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Almost every mechanical movement that we see around us is accomplished

by an electric motor. Electric machines are a means of converting energy. Motors

take electrical energy and produce mechanical energy. Electric motors are used to

power hundreds of devices we use in everyday life. Motors come in various sizes.

Huge motors that can take loads of 1000’s of Horsepower are typically used in the

industry. Some examples of large motor applications include elevators, electric

trains, hoists, and heavy metal rolling mills. Examples of small motor applications

include motors used in automobiles, robots, hand power tools and food blenders.

Micro-machines are electric machines with parts the size of red blood cells, and

find many applications in medicine.

Electric motors are broadly classified into two different categories: DC (Direct

Current) and AC (Alternating Current). Within these categories are numerous

types, each offering unique abilities that suit them well for specific applications.

In most cases, regardless of type, electric motors consist of a stator (stationary

field) and a rotor (the rotating field or armature) and operate through the

interaction of magnetic flux and electric current to produce rotational speed and

torque. DC motors are distinguished by their ability to operate from direct current.

There are different kinds of D.C. motors, but they all work on the same principles.

In this chapter, we will study their basic principle of operation and their

characteristics. It’s important to understand motor characteristics so we can choose

the right one for our application requirement. The learning objectives for this

chapter are listed below.

8.6 Learning Objectives

Understand the basic principles of operation of a DC motor.

Understand the operation and basic characteristics of simple DC motors.

Compute electrical and mechanical quantities using the equivalent circuit.

Use motor nameplate data.

Study some applications of DC motors.

89

8.7 Electromechanical Energy Conversion

An electromechanical energy conversion device is essentially a medium of

transfer between an input side and an output side. Three electrical machines (DC,

induction and synchronous) are used extensively for electromechanical energy

conversion. Electromechanical energy conversion occurs when there is a change in

magnetic flux linking a coil, associated with mechanical motion.

8.8 Electric Motor

The input is electrical energy (from the supply source), and the output is

mechanical energy (to the load).

ELECTRICAL Electromechanical Energy Mechanical

ENERGY Conversion Device Energy

SOURCE Motor Load

8.9 Electric Generator

The Input is mechanical energy (from the prime mover), and the output is

electrical energy.

Mechanical Energy Electromechanical Energy Electrical

Conversion Device Energy

Source Generator Load

8.10 Construction

DC motors consist of one set of coils, called armature winding, inside another set

of coils or a set of permanent magnets, called the stator. Applying a voltage to the

coils produces a torque in the armature, resulting in motion.

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8.11 Stator

The stator is the stationary outside part of a motor.

The stator of a permanent magnet dc motor is composed of two or more

permanent magnet pole pieces.

The magnetic field can alternatively be created by an electromagnet. In

this case, a DC coil (field winding) is wound around a magnetic material

that forms part of the stator.

8.12 Rotor

The rotor is the inner part which rotates.

The rotor is composed of windings (called armature windings) which are

connected to the external circuit through a mechanical commutator.

Both stator and rotor are made of ferromagnetic materials. The two are

separated by air-gap.

8.13 Winding

A winding is made up of series or parallel connection of coils.

Armature winding - The winding through which the voltage is applied or

induced.

Field winding - The winding through which a current is passed to produce

flux (for the electromagnet)

Windings are usually made of copper.

8.14 DC Motor Basic Principles

8.14.1 Energy Conversion

If electrical energy is supplied to a conductor lying perpendicular to a

magnetic field, the interaction of current flowing in the conductor and the magnetic

field will produce mechanical force (and therefore, mechanical energy).

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8.15 Value of Mechanical Force

There are two conditions which are necessary to produce a force on the

conductor. The conductor must be carrying current, and must be within a magnetic

field. When these two conditions exist, a force will be applied to the conductor,

which will attempt to move the conductor in a direction perpendicular to the

magnetic field. This is the basic theory by which all DC motors operate. The force

exerted upon the conductor can be expressed as follows.

F = B i l Newton

where B is the density of the magnetic field, l is the length of conductor, and i the

value of current flowing in the conductor. The direction of motion can be found

using Fleming’s Left Hand Rule.

Figure 8.15.1: Fleming’s Left Hand Rule

The first finger points in the direction of the magnetic field (first - field),

which goes from the North Pole to the South Pole. The second finger points in the

direction of the current in the wire (second - current). The thumb then points in the

direction the wire is thrust or pushed while in the magnetic field (thumb - torque or

thrust).

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8.16 Principle of operation

Consider a coil in a magnetic field of flux density B (figure 4). When the

two ends of the coil are connected across a DC voltage source, current I flow

through it. A force is exerted on the coil as a result of the interaction of magnetic

field and electric current. The force on the two sides of the coil is such that the coil

starts to move in the direction of force.

Figure 8.16.1: Torque production in a DC motor

In an actual DC motor, several such coils are wound on the rotor, all of

which experience force, resulting in rotation. The greater the current in the wire, or

the greater the magnetic field, the faster the wire moves because of the greater

force created. At the same time this torque is being produced, the conductors are

moving in a magnetic field. At different positions, the flux linked with it changes,

which causes an emf to be induced (e = d /dt) as shown in figure 5. This voltage

is in opposition to the voltage that causes current flow through the conductor and is

Referred to as a counter-voltage or back emf.

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Figure 8.16.2: Induced voltage in the armature winding of DC motor

The value of current flowing through the armature is dependent upon the

difference between the applied voltage and this counter-voltage. The current due to

this counter-voltage tends to oppose the very cause for its production according to

Lenz’s law. It results in the rotor slowing down. Eventually, the rotor slows just

enough so that the force created by the magnetic field (F = Bil) equals the load

force applied on the shaft. Then the system moves at constant velocity.

8.17 Torque Developed

The equation for torque developed in a DC motor can be derived as

follows. The force on one coil of wire F =i l x B Newton

Note that l and B are vector quantities since B = /A where A is the area of the

coil, Therefore the torque for a multi turn coil with an armature current of Ia

T = K *fie *Ia

Where fie is the flux/pole in weber, K is a constant depending on coil geometry,

and Ia is the current flowing in the armature winding.

Note: Torque T is a function of force and the distance, equation (2) lumps all the

constant parameters (eg. length, area and distance) in constant K.

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The mechanical power generated is the product of the machine torque and the

mechanical speed of rotation, wm

Or, Pm = wm T

= wm K fie Ia

It is interesting to note that the same DC machine can be used either as a

motor or as a generator, by reversing the terminal connections.

95

CHAPTER 9

EFFICIENCY

9.1 HYBRID EFFICIENCY

Besides a smaller, more efficient engine, today's hybrids use many other tricks

to increase fuel efficiency. Some of those tricks will help any type of car get better

mileage, and some only apply to a hybrid.

9.2 Recover energy and store it in the battery

Whenever you step on the brake pedal in your car, you are removing energy

from the car. The faster a car is going, the more kinetic energy it has. The brakes

of a car remove this energy and dissipate it in the form of heat. A hybrid car can

capture some of this energy and store it in the battery to use later. It does this by

using "regenerative braking." That is, instead of just using the brakes to stop the

car, the electric motor that drives the hybrid can also slow the car. In this mode, the

electric motor acts as a generator and charges the batteries while the car is slowing

down.

9.3 Sometimes shut off the engine

A hybrid car does not need to rely on the gasoline engine all of the time

because it has an alternate power source -- the electric motor and batteries So the

hybrid car can sometimes turn off the gasoline engine.

9.4 It uses advanced aerodynamics

This is used to the air resistance. This helps the hybrid car to increase its

efficiency. A less power is required when the car is made in an aerodynamic

model.

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9.5 It uses small efficient engine

The engine in a hybrid weight only 56 kg and it is a small, 1 litre, three

cylinder that produces 67 HP and 5700 rpm. The additional power provide by the

small electric motor is able to accelerate the hybrid car from 0-60 mph in about 11

seconds.

9.6 ADVANTAGES OF HYBRID CAR

i) Decreasing fuel consumption while it turns reduces emission.

ii) Pollution is reduced considerably

iii) Improve mileage.

iv) Reduced tail pipe emission

v) Refueling problem reduced

vi) No need of more fuel consumption at the time of acceleration.

vii) Uses small engine and components their by reduces weight.

viii) Better performance.

9.7 WHAT’S AVAILABLE NOW

Three hybrid cars are now available in the United States – the Honda Civic

Hybrid, the Honda Insight and the Toyota Prius. We will be discussing the latter

two, and although both of these cars are hybrids, they are actually quite different in

character. The Honda Insight, which was introduced in early 2000 in the United

States, is designed to get the best possible mileage. The Insight is a small,

lightweight two-seater with a tiny, high-efficiency gas engine. The Toyota Prius,

which came out in Japan at the end of 1997, is designed to reduce emissions in

urban areas. It meets California's super ultra low emissions vehicle (SULEV)

standard. It is a four-door sedan that seats five, and the power train is capable of

accelerating the vehicle to speeds up to 15 mph (24 kph) on electric power alone.

The Prius was honoured as the 2004 North American Car of the Year.

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9.8 CONCLUSION

The hybrid car gives very good mileage and it produces less pollution. So in

the incoming years the hybrid car will become the most common vehicle in the

world. Hybrid car produces less pollution than gasoline powered car and good

mileage than electric car.

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