final term paper from my views 123

8/6/2019 Final Term Paper From My Views 123

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Micro Thermo-Photovoltaic

Power Generation

Submission for Term paperleading to Thesis

Supervised by

Prof. Ranjan Ganguly

and

Prof. Amitava dutta

Submitted by

Ankit Kumar Jain

001011502011

M.E., (Power Engg.)


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ACKNOWLEDGEMENT

My deepest thanks to Prof. Amitava Dutta and Prof. Ranjan Ganguly

(joint guides of the project) for guiding and correcting various documents of mine

with attention and care. They have taken pain to go through the paper and make

necessary correction as and when needed.

I heart fully hope to have the support of all the above

mentioned dignitaries for successful completion of this project

term paper.


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CONTENTS: PAGE NO.

INTRODUCTION 4

PRINCIPLE OF TPV SYSTEM 5

CONTENTS OT TPV 5-6

EFFICIENCY AND ADVANTAGE OF TPV 7-8

MICRO TPV DEVICE 8-9

DESIGN AND STUCTURE OF MICRO TPV 9-14

FABRICATION OF PV CELL ARRAY 14-17

SHORT-CIRCUIT CURRENT AND OPEN CIRCUIT VOLTAGE OF PV CELL 18-19

FILL FACTOR 20-21

DIFFERENT LOSSES 21-26

SYSTEM EFFICIENCY AND POWER OUTPUT AT DIFFERENT CONFIGUR. 27

APPLICATION 27-28


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Introduction

Traditional batteries have failed to satisfy the increased needs and demand for

smaller scale and higher densities power sources. A relatively new concept, micro

power has been developed to satisfy the growing trend of miniaturization of

electro-mechanical devices. A detailed review of such a technology can make

room for further improvements. There is a need to improve the efficiency of such

miniature devices , as not many but quite few of the micro power devices has been

developed. Practicing methods to improve such a technology can greatly enhancethe development of micro power devices. [1]

Potential Applications:

1. Portable electronics

a. Cellular phones, Notebook, Computer PDAs/Palmtops, various hand-held

devices.

2. Wireless equipments

a. Sensors and communication systems, remote control.

3. Miniature rocket for micro satellite, micro unmanned aerial vehicle, micro

rovers, micro air and space vehicle.

4. Military and security, portable cells for soldiers (signal sets, radio sets, etc),

Micro scouting vehicle, remote alarms.

5. Micro climate control.

6. Micro : - robots, motors, turbines, thrusters, automobiles.[2]


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Principle of TPV System:

The basic principle of thermo photo-voltaic (TPV) is the direct conversion of

thermal energy into electricity without involving any moving parts [3,4]. The TPV

system basically consists of four essential components. They are [1]

The heat source,

A selective emitter,

A filter system and

A low band gap photovoltaic converter.

When the heat source generates heat energy from either combustion, solar or

nuclear, this heat energy will be absorbed by the selective emitter. When the


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emitter is heated to a sufficiently high temperature, it will emit photons. Thus, the

selective emitter is used to convert heat from the source into radiation. The emitter

can be made from broadband materials such as,

1. Silicon carbide (SiC),

2. Selective emitting materials such as Er3Al5O12 (erbia),

3. Co/Ni (cobalt/nickel) doped MgO (magnesium oxide),

4. Yb2O3 (ytterbia).

The spectrums of broadband emitters operate at temperatures around 10001600

K. When the photons emitted from the emitter are impinging on the PV array, they

evoke free electrons and produce electrical power output. Thus, the photovoltaic

converter functions to convert heat radiation into electricity.

However, only those photons radiated by the emitter having energy greater than the

band gap (e.g. for GaSb cells, it is 0.72 eV, corresponding to a wavelength of1.7Um) of the photovoltaic cell can be converted into electricity. Those photons

with a wavelength longer than 1.7 Um cannot generate free electrons and produce

electricity when impinging on the photovoltaic cell. If these photons are not

stopped, they will be absorbed by the PV cells and subsequently result in a

destructive heat load on the system components, which will lower the conversion

efficiency of the system [5,6].

These photons should be sent back to the emitter in order

to improve the system. Thereby, a filter is often employed in the design of

conventional TPV systems. It serves to recycle and reflect back all the sub-band

gap photons with too low energy and transmits all convertible to the PV array.


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However, in the micro-TPV system, the existence of a filter will complicate the

fabrication and enlarge the volume of the system.

Thermophotovolatic schematic Author: [User:Fdu.uiuc],wikipedia[20]

Efficiency:

The overall efficiency of a conventional thermo photovoltaic (TPV) system is

given as follows [5,6]:

TPV = RS F pv

where the subsystem efficiencies are defined as follows:

RS is the net radiation power emitted by emitter,

F the radiation power absorbed in PV cell

pv is the electrical output power/radiation power absorbed in PV cell.


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The net radiated power is defined as the total emission minus the radiation returned

and absorbed in the emitter. The PV efficiency depends not only on the quality of

the cell itself, but also on the shape and power density of the spectrum absorbed in

it.

Advantages of thermo photovoltaic system: there are many advantages of

photovoltaic systems some of them are[5,6]:

1. Its a clean and quiet source of electrical power with no moving parts.

2. It has high power density.

3. We can use different type of energy source.4. In fabrication and manufacturing it is easy.

5. Reliable and low maintenance cost.

6. Inexpensive and convenience production.

So the thermo photovoltaic system has such a large advantages and has good

potential to replace the traditional batteries.

A micro thermo photovoltaic power device:

A micro power device is based on the principle of Thermo photovoltaic (TPV)

system. The concept and theory of the TPV method of power Generation has been

implemented into the design, development And fabrication of the micro-TPV

power generator. Each individual component of the device will be looked into.

This includes the[1]

1. Heat source (micro-combustor),

2. SiC emitter,


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3. Dielectric filter

4. GaSb photovoltaic (PV) cell array and

5. The cooling fins.

Other major issues concerning the design of the micro-TPV power generator such

as combustion in the micro-cylindrical combustor, effect of wall thickness of micro

combustors (on the performance of the system), and the effect of step height (of the

micro-combustor) on wall temperature is also considered.

The layout of TPV system

Energy band gap diagram


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Design and structure of the micro thermo photovoltaic device[1,7]:

The design of the micro-TPV power device comprises mainly of four main

components:

(1) A heat source;

(2) A micro-flame tube combustor (the wall of the micro-combustor will be a

broad band emitter);

(3) A simple dielectric filter;

(4) A PV cell array.

[6]

All these components are integrated together to form the general structure of the

micro power device. The schematic layout of the micro-TPV power device is

shown in Fig. Operating principle of micro TPV :The micro-thermo photovoltaic

(micro-TPV) system is a Micro power generator which uses photovoltaic (PV)


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cells to convert heat radiation (from the combustion of hydrocarbon fuel)into

electricity.

The general operating principle of the device is as follows: hydrocarbon fuel first

mixes with compressed air in the micro-mixer. The mixture then enters a

cylindrical micro combustor, where the combustion takes place. As the wall of the

micro-combustor is heated to a sufficiently high temperature, it emits a lot of

photos (as radiation) from a broadband emitter. The broadband emitter is on the

wall of the micro-combustor. The micro-combustor is peripherally enclosed by

arrays of photovoltaic (PV) cells, so that the Radiative heat from the wall of the

micro-combustor can be absorbed by the PV cells. The radiated photons interact

with the electrons in the PV cells by imparting their energy to the electron as

kinetic energy, which consequently produces an electric current. Hydrogen will be

used as the hydrocarbon fuel for combustion[8,9].

the cross-sectional schematic layout of micro thermo photovoltaic devic [21,1]


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Micro-combustor:

The most important components of the micro-TPV power system, the micro-

combustor. Compared to conventional combustors, a micro-combustor is more

highly constrained by inadequate residence time for complete combustion and high

rates of heat transfer from the combustor. Some of the major challenges and

problems with micro-scale combustion.. For micro-TPV applications, the desired

output is a high and uniform temperature along the wall of the micro combustor.

The major challenge in the micro-combustor design is to keep an optimum balance

between sustaining combustion and maximizing the heat output . A high surface-

to-volume ratio is very favorable to the output power density per unit volume.

However, a high heat output will affect the stable combustion in the micro

combustor[1,7]

Sic emitter:

The emitter is another most important component in the design of the micro-TPV

power device. The emitter is the wall of the micro combustor and it functions to

convert heat energy from the combustion into radiation by emitting photons. There

are basically two different types of emitters, namely broadband emitters and

selective emitters. Blackbody is a typical broadband radiation materials, its

emission behavior can be approximated by graphite or a soot-covered surface.

However, a broadband radiating material of practical importance is silicon carbide

(SiC) with an emissivity SiC 0.9. While a selective emitter exhibits a high

emittance in the spectral range usable for the PV cells, and a low emittance

elsewhere. There are several methods have been developed to fabricate selective

emitters. One of them is to use oxides of rare earth materials such as[10].


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Er2O3 (erbia) and Yb2O3 (ytterbia)

Another way is micro-structuring the surface of the emitters. a new thermally

Excited Co/Ni (cobalt/nickel)-doped MgO (magnesium oxide) matched emitter.

This kind of emitters exhibits a better spectral efficiency .The prototype micro-

TPV power generator uses silicon carbide (SiC) as the material for the emitter .SiC

has been selected due to its good emissivity and high temperature reliability..

Furthermore, compared with other selective emitters such as micro-machining

tungsten and rare earth oxide, it is easier to fabricate into a cylindrical shape. The

SiC emitter is a typical broadband emitter and the spectrum of broadband emitters

generally operates at temperature of about 10001600 K .As part of an effort to

develop a suitable material for the emitter, carried out a series of experiments to

test the performance of prototype micro-TPV power generator with different

emitting materials. The efficiency of the micro-combustor can be improved by

replacing the SiC emitter with other selective emitters, which will consequently

lead to a higher overall efficiency for the micro-TPV power generator.

Dielectric filter:

The another component in the design of the micro-TPV power device is a simple

nine-layer dielectric filter. the SiC emitter is a typical broadband emitter. The

spectrum of broadband emitters operating at temperatures in the range of 1000

1600K contains a significant proportion of photons with energies not sufficient

enough to generate charge carriers in the PV cells. only those photons radiated bythe emitter having energy greater than the band gap (e.g. for GaSb cells, it is0.72

eV, corresponding to a wavelength of 1.7um) of the photo voltaic cell can be

converted into electricity. So we can say, those photons with a wavelength longer

than 1.7 micro m. cannot generate free electrons and produce electricity when


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impinging on the photovoltaic cell. These photos are called sub-band gap

photons .If this portion of energy is being absorbed by the PV cells, it will result in

a destructive heat load on the generator components, subsequently lowering the

conversion efficiency of the system.

To improve the overall efficiency of the micro-

TPV system, it is very important to recycle these photons. Therefore, a filter is

required in the micro-TPV system (to filter out photons with wavelength longer

than 1.7 um). The filter is able to recycle the energy emitted in the range of 1.83.5

_m mid-wavelength band, thereby improving the overall efficiency of the

system .The reflectance of the dielectric filter[9] . The reflectance is measured with

a customized in-house built optical test system done by the commercial fabricator

(with an uncertainty of less than 3%). Ideally, the filter should be able to reflect all

non-convertible photons back to the emitter and transmit all convertible photons to

the PV cell array. However, this is very difficult to achieve in actual practice.

Photovoltaic cell array:

The function of photovoltaic cell (converter) is to convert the heat radiation into

electricity (dc). The photons emitted from the emitter impinge on the photovoltaic

array, they stimulate (evoke) free electrons and produce electrical power output.

There are some typical low band gap PV cells developed for TPV applications are:

1. gallium antimonite( GaSb)

2. gallium indium arsenide(GaInAs)

3. InGaAsSb etc.


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The prototype micro-TPV power generator employs a GaSb PV cell array for the

micro-TPV system corresponding to the dielectric filter. The GaSb cell array is

able to respond the photons with wavelength 1.8 um

http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current

"science.nasa.gov ... Science@NASA Headline News 2002[22]
http://www.google.com/url?url=http://science.nasa.gov/science-news/science-at-nasa/&rct=j&sa=X&ei=6svkTaGpLsG8rAe35-GjBg&ved=0CCYQ6QUoADAB&q=band+gap+of+pv+cell&usg=AFQjCNHp-tgV0B5CHhhsGDhpfU5eBYPlww&cad=rjahttp://www.google.com/url?url=http://science.nasa.gov/science-news/science-at-nasa/&rct=j&sa=X&ei=6svkTaGpLsG8rAe35-GjBg&ved=0CCYQ6QUoADAB&q=band+gap+of+pv+cell&usg=AFQjCNHp-tgV0B5CHhhsGDhpfU5eBYPlww&cad=rja


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Fabrication of the GaSb photovoltaic cell array:

The technology used for to form the pn-junction is based on a Zn vapor diffusion

process into an N-doped GaSb substrate thus expensive epitaxial growth of this

A semiconductor layer is successfully avoided. The Zn vapor diffusion process is

Performed. The diffusion source is a mixture of Zn and antimony.

So there are different process of fabrication which are as follows [10]:

1. Silicon nitrate diffusion (SiN) over an n-type GaSb wafer doped with Te.

2. Photolithography is used to open holes in the dielectric.

3. Front side pattern of the wafer is then protected with photo resist.

4. Etch nitrate and diffused Zn.

5. Backside nonselective etch and metallization.

6. Then front side metallization area is standard lift-off photolithography

7. Metallization and lift-off the front side area.

8. Matching of the emitter.

9. Depositions of an anti-reflection (AR) coating are performed to maximize

photocurrent.


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Fabrication process:


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The outline of the GaAb fabrication process[10]

Cooling fins:


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The operation temperature of the PV cells affects the overall power output of the

GaSb TPV cell on band gap and reverse the saturation current. As the operating

temperature increases, the conversion efficiency of the TPV cell will decrease.

Therefore, effective cooling would be necessary in a GaSb TPV system. Arrays of

cooling fins are attached on the back of the PV cells to remove the sink heat from

the PV cells. The cooling fins[1,21] can be made of highly conductive materials

such as aluminum or copper. The fin surfaces can be manufactured by extruding or

welding. The array of cooling fins will enhance the rate of heat transfer from the

surface of the GaSb PV cells by several folds, by exposing a larger surface area to

convection and radiation.

The array of cooling fins attached to a prototype micro-TPV power generator .

array of cooling fins attached to the back side of PV cell.[1,21]

Short-circuit current of photovoltaic cell:


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The short-circuit current is the current through the photovoltaic cell when

the voltage across the solar cell is zero (i.e., when the PV cell is short

circuited). It is written as ISC. The short-circuit current is due to the

generation and collection of light-generated carriers. For an ideal

photovoltaic cell at most moderate resistive loss mechanisms, the short-

circuit current and the light-generated current are identical. Therefore, the

short-circuit current is the largest current which may be drawn from the PV

cell.

http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current

The short-circuit current depends on a number of factors which

are as follows:

the area of the solar cell. To remove the dependence of the PV cell area, it

is more common to list the short-circuit current density ( mA/cm2) rather

than the short-circuit current;

the number of photons (i.e., the power of the incident light source). Isc

from a solar cell is directly dependant on the light intensity.
http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-currenthttp://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current


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the spectrum of the incident light.

the optical properties (absorption and reflection) of the photovoltaic cell .

the collection probability of the PV cell, which depends on the surface

passivation and the minority carrier lifetime in the base.

Open circuit voltage of photovoltaic cell:

The open-circuit circuit voltage, VOC, is the maximum voltage available from a

photovoltaic cell, and this occurs at zero current. The open-circuit voltage[11]

corresponds to the amount of forward bias on the PV cell due to the bias of the

PV cell junction with the light-generated current.

http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current[11]

fill factor:


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The short-circuit current and the open-circuit voltage are the maximum

current and voltage respectively from a photovoltaic cell. However, at both

of these operating points, the power from the solar cell is zero. The "fill

factor", more commonly known by its abbreviation "FF", is a parameter

which, in conjunction with Voc and Isc determines the maximum power

from a solar cell. The FF is defined as the ratio of the maximum power from

the pv cell to the product of Voc and Isc. So fill factor[12] is given by

FF= Vm x Im / Voc x Isc

http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current[12]

Table for the description of FF, Voc, Isc:


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Performance of GaSb PV circuits incorporated with filters

s.no. FF Voc(V) Isc(amp) Vmax(V) Imax(amp) Pmax(watt)

1. .750 2.84 2.25 2.36 2.03 4.80

2. .761 2.81 2.15 2.24 2.05 4.60

3. .738 2.79 2.15 2.32 1.91 4.42

4. .752 2.84 2.25 2.36 2.03 4.80

5. .757 2.82 2.23 2.36 2.01 4.75

Losses in photovoltaic cell:

1. Reflection losses

2. Thermal losses

3. Recombination losses

1. surface recombination loss

2. depletion region recombination

3. bulk recombination

4. recombination at metal semiconductor contacts

4. Series resistance losses

1. emitter resistance losses

2. metal semiconductor contact

3. metal fingers and bus-bars

1. Reflection losses:

The reflection losses occur from top surface of the photovoltaic cells which

Receives the light (photons). Reflection losses [13] affect the Isc short circuit


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current of the photovoltaic cell. Reflection reduces the absorbed carriers and hence

the Isc. It is necessary to improve the absorption and reduce reflection to improve

short circuit current. For a Si these losses account for more than 30%.

2. Thermal losses:

A major portion of loss in photovoltaic cell is a due to heat. Heat radiation

absorbed by the PV cells has excess energy than that required for generation of

electron hole pair (band-gap energy Eg). This excess energy is released in the form

heat .This thermal energy causes rise of temperature of cell. The parameters that

are affected by the temperature of the cell are band gap energy, diffusion length,minority carrier lifetime, intrinsic carrier density. The increases in diffusion length

and minority carrier concentration and intrinsic carrier concentration and decrease

in band gap energy causes the increases in the reverse saturation current Io . The

increase in Io reduces the open circuit voltage.

3. Recombination loss:

Photon incident on the PV cell generates electron hole pairs; these generated pairs

are called as carriers. Generated carriers need to be separated before they

recombine, with emission of energy. Recombination [14] causes loss of carrier and

affects the performance of the cell. Open circuit voltage Voc of the cell is affected

by recombination of carriers. As recombination increases the Voc reduces. Various

techniques are used to reduce the recombination in the PV cells and improve Voc.

Generation of carriers is in the entire volume of the PV cell material. The carriers

generated near depletion region are separated out very quickly as they get swept

away by the electric field present in the depletion region. Were as the carriers

which are generated away from the depletion region that is in the bulk region, on


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the surface, or at the back surface have less probability of getting separated. These

carriers will be lost and would not contribute to current flow if they recombine.

These losses account for major portion total input power. Different

recombination losses that occur at different regions of the PV cells are:

1. Surface recombination.

2. Bulk recombination.

3. Depletion region recombination.

4. Recombination at metal Semiconductor contact.

1. Surface recombination:

Surface recombination is high in Si due to the presence of incomplete

bonds. The incomplete bonds traps the generated carriers and get recombined [14].

2. depletion region combination:

Recombination occurring in the depletion region is less significant as compared

to the surface recombination due to the presence of electric field. Charge

carriers generated in depletion region are separated by electric field very

quickly avoiding any chance of recombination. Any recombination occurring in

the depletion region is mostly by the band to band recombination.

3. recombination at metal semiconductor contacts:

Metal semiconductor contacts regions provide very large recombination sites.

Semiconductor and metal contact junctions are formed at both front and back side


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of the solar cell. Back side contact contributes more to the recombination [15] as it

has more contact area with the semiconductor. Surface recombination velocity is

also present at the rear contact and needs to be reduced.

4. series resistance losses:

Series resistance losses contribute to around less than 20% of the total input

Power. But these losses increases tremendously when PV cell is operated at high

intensities. The high intensity is obtained when a large amount of photons is

focused on the PV cells. Series resistance of the cell is combination of [16],

1. Emitter layer resistance

2. Metal-semiconductor contact

3. Metal bus-bars and fingers

4. Bulk semiconductor resistance.

The metal bus-bars and fingers, emitter layer and metal-semiconductor contact

resistance contribute in large magnitude to series resistance. Bulk resistance is low

due to its high conductivity.

1. Emitter resistance[17]:

Emitter resistance of solar cell is one of the most dominating components of series

resistance of PV cell. Sheet resistance is measure of emitter resistance and it is

desired to have sheet resistance value in the range of 80-100 ohm/square .Factors

affecting the emitter resistance are, thickness of the emitter layer, current direction

in the emitter region, current collection by the metal fingers and bus bars.


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1. metal semiconductor contact[18]:

The other main component of the series resistance is the semiconductor to metal

contact resistance. Metal contacts are required in the PV cells for collection of the

carriers and transport them to the load to deliver power.

2. metal fingers and bus bars[19]:

Metal fingers and bus bar resistance causes considerable loss of power in the

PV cells. Metal contacts are placed on the front surface and back surface of the

PV cells to collect carriers and pass them to the load. Front contact metal is in

the form of fine grid lines were as the back contact is a metal plate covering

entire back surface. Metals used for the contact resistance are Al; Ti; Pd; Ag ,

etc. Back contact metal is Al were as for front contact the finer grid lines are of

high conductivity metal usually Ag or paste of Ag; Pd or Ti is used. These

contacts are deposited on semiconductor by using various techniques such as

Photo-lithography, Evaporation, Sputtering, Screen printing, Electroplating.

The possible measures that can help to reduce the series resistance are as

follows,

1. High conductivity base (substrate) material.

2. Optimizing the junction depth for reducing the emitter resistance .Increasing

the thickness to reduce the sheet resistance.

3. Increasing the number of fingers by reducing the width increases the current

collection and reduces the metal semiconductor contact resistance.


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4. Electroplated metal contacts to reduce the resistance of the metal contacts by

increasing the metal density.

5. Different metallization techniques..

6. Use of different techniques for depositing metal contacts at the front and

back surface. . This can reduce the cost of deposition of metals.

input and output with losses[16]

System efficiency and power output on different configuration:


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Micro TPV device

configuration

Power output

density(w/cm2)

Predicted

elec.

Poweroutput(w)

Predicted

efficiency of

emitter(micro-combustor)

Predicted

effic.of PV

cells

Ove

effi

Sic emitter, GaSb PV

cells

.48 .92 21.4 3.08 .

Sic emitter,

GaInAsSb PV cells[5]

.78 1.45 21.4 4.80 1.

Co/Ni-doped Mgo

matched emitter,GaSb PV cells[23]

2.47 4.71 21.4 15.72 3.

Sic emitter, GaSb PV

cells, length

increased to

22mm[10]

.55 1.45 29.4 3.52 1.0

Co/Ni-doped Mgo

matched emitter,

GaSb PV cells length

increased to

22mm[10]

2.10 5.5 29.4 13.3 3.9

APPLICATION:

In spite of the high initial cost, photovoltaic systems are being used increase to

supply electricity for many applications where small amount of power is needed.

Their cost-effectiveness increases with the distance of the location where they are

to be installed from the main power grid lines. For example it is more easy and

economical to install a alone PV system instead of a transmission line to a village

having a load of 10kw, if the village is more than 40km from the grid lines. So


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there are various applications for which PV system have been developed , so some

of them are:

1. Pumping water for irrigation and drinking.

2. Electrification for remote villages for providing street lighting and other

community services.

3. Telecommunication for the post and telegraph and railway communication

network.

[ prof. sukhatme IIT Mumbai]

Future work:

After some consideration we can say there are some work that has to do before it

can be established for commercial application. There are still some possibilities for

improvement in the micro TPV system.

Some of the future works that can be carried out are as follows:

1. More needs to optimization of the micro-combustor by numerical and

experimental studies. This will further develop or improve the system.

2. There are some other issues for predicting the efficiency of micro-TPV systems

such as, micro-combustor temperature, photon losses, non-uniformity of photon

flux. Apart from this some other issues like mismatched performance of individual

cells. So future work should work should be done in these areas.


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3. Development of new micro-combustors, so that we can achieve the stable

combustion and high wall temperature.

4. There should some work to investigate the possibilities of develop or integrate

the TPV system with a gas turbine to recover the exhaust heat, that could improve

the efficiency.

References:

[1] W.M. Yang, S.K. Chou, C. Shu, A.W. Li, H. Xue, Int. J. Comput.Eng. Sci.4 (2003) 481484.


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[2] W.M. Yang, S.K. Chou, C. Shu, H. Xue, Z.W. Li, J. Phys. D: Appl.Phys.37 (2004) 10171020.

[3] H. Sai, Y. Kanamori, H. Yugami, PowerMEMS 2003International Workshop,December, 2003, pp. 118121.

[4] Z. Chen, P.L. Adair, M.F. Rose, Proceedings of the 31stIntersociety EnergyConversion Engineering Conference, Part 2 (of 4),Washington, DC,USA, August 1116, 1996, pp. 10131017.

[5] W.M. Yang, S.K. Chou, C. Shu, Z.W. Li, H. Xue, Sol. Energy

Mater. Sol.Cells 80 (2003) 95104.

[6] H. Xue, W.M. Yang, S.K. Chou, C. Shu, Z. Li, MicroscaleThermophys.Eng. 9 (2005) 8597.

[7] W.M. Yang, S.K. Chou, C. Shu, H. Xue, Z.W. Li, J.F. Pan, EnergyConvers.Manage. 44 (2003) 26252634.

[8] Z.W. Li, S.K. Chou, C. Shu, W.M. Yang, J. Micromech. Microeng.15(2004) 207212.

[9] W. Yang, S.K. Chou, C. Shu, Z.W. Li, H. Xue, Appl. Thermal Eng.22(2002) 17771787.

[10] W.M. Yang, S.K. Chou, C. Shu, H. Xue, Z.W. Li, J.

Microelectromech.Syst. 13 (2004) 851855.

[11] Kerr, M.J.,A. Cuevas, and R.A. Sinton generalized analysis ofquasi-steady-state and transient decay open circuit voltagemeasurement journal of applied physics,vol. 91,issue 1,pp.399,2002.


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[12] Green, M.A. Solar cell fill factors: General graph andempirical expression, solid-state electronics,vol.24,issue8,pp.788-789,1981.

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[14] S.M.Sze. Physics of Semiconductor Devices. John Wiley and Sons, 1969

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http://www.google.com/url?url=http://science.nasa.gov/science-news/science-at-nasa/&rct=j&sa=X&ei=6svkTaGpLsG8rAe35-GjBg&ved=0CCYQ6QUoADAB&q=band+gap+of+pv+cell&usg=AFQjCNHp-tgV0B5CHhhsGDhpfU5eBYPlww&cad=rjahttp://www.google.com/url?url=http://science.nasa.gov/science-news/science-at-nasa/&rct=j&sa=X&ei=6svkTaGpLsG8rAe35-GjBg&ved=0CCYQ6QUoADAB&q=band+gap+of+pv+cell&usg=AFQjCNHp-tgV0B5CHhhsGDhpfU5eBYPlww&cad=rja

final term paper from my views 123

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