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Solar Cell(Photovoltaics)
: 20075418 Ju Dae-Hyun
Solar Cell (PV)
Light Electricity
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Nonrenewable Enargy
(Renewable Energy)
(Nonrenewable Energy)
Renewable
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What is a Solar Cell?
A structure that converts solar energy directly to DC electricenergy.
It supplies a voltage and a current to a resistive load (light,battery, motor).
Power = Current x Voltage=Current2 x R= Voltage2/R
It is like a battery because it supplies DC power.
It is not like a battery because the voltage supplied by the cellchanges with changes in the resistance of the load.
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Basic Physics of Solar Cells
Silicon (Si) is from group 4 of the periodtable. When many Si atoms are in closeproximity, the energy states form bands offorbidden energy states.
One of these bands is called the bandgap(Eg) and the absorption of light in Si isa strong function of Eg.
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The Sun daily provides about 10 000 times more energy tothe Earth than we consume
Photovoltaic technology directly converts solar energy intoelectricity
No moving parts
no noise
no emissions
long lifetime Large industrial potential - cost reductions needed
Feedstock for PV industry is silicon - the second most abundant element in the crust of the Earth
The Sun as Energy Source
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Solar Energy status
Market is exploding
The solar industry is very profitable
Lack of highly purified silicon (polysilicon)
Cost of solar electricity is too high, R&D focus
on reducing cost and increasing efficiency
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Actual Growth vs. Historic Forecasts
Actualmarket
development
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Solar Energy status
Market is exploding
The solar industry is very profitable
Lack of highly purified silicon (polysilicon)
Cost of solar electricity is too high, R&D focus
on reducing cost and increasing efficiency
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159
435
857
1705
2454
0
200
400
600
800
1000
1200
1400
1600
1800
2001 2002 2003 2004 2005
(MNOK)
- Gross revenue development
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Solar Energy status
Market is exploding
The solar industry is very profitable
Lack of highly purified silicon (polysilicon)
Cost of solar electricity is too high, R&D focus
on reducing cost and increasing efficiency
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Solar Grade Silicon Supply-Demand
(MT/year)
0
5 000
10 000
15 000
20 000
25 000
2002 2003 2004 2005 2006 2007 2008 2009 2010
SOG Polysilicon supply SOG Polysilicon demand
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Solar Energy status
Market is exploding
The solar industry is very profitable
Lack of highly purified silicon (polysilicon)
Cost of solar electricity is too high, R&D fo
cus on reducing cost and increasing effici
ency
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Cost reductions existing technologies
Thinner wafers
- Wire sawing
- Laser cutting and etching Higher efficiencies
- Semiconductor technologies on single
crystal wafers (examples Sanyo / SunPower) Thin film technologies (flat panel display)
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Public incentives are important
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Cost goals for third generation solar cells
Efficiency and cost projections for first-, second- and third generation photovoltaic
technology (wafers, thin-films, and advanced thin-films, respectively)Source: University of New South Wales
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Next generation technology
Silicon nanostructures
Bandgap engineering of silicon.
Applications could be tandem solar cells and energy selective contacts for hot carrier solar cells.
Fabrication of silicon nanostructures consisting o
f quantum well and quantum dot super lattices toachieve band gap control
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Understanding cell efficiency
SOLAR SPECTRUM AM 1,5
(1000 watt/m2)
0
2
4
6
8
10
12
14
16
18
200 300 400 500 600 700 800 900 1000 1100 1200 1300
wavelength, nm
Irradiance,
watt/m2
Irradiation AM 1,5
Useful irradiation (c-Si)
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Hot carrier Cells
This concept tackles the major PV loss mechanism of thermalisationof carriers.
The purpose is to slow down the rate of photoexcited carrier coolingcaused by phonon interaction in the lattice to allow time for the carriers to be collected whilst they are still hot, and hence increasing the voltage of a cell.
Next generation technology (cont.)
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Thermoelectric solar cells
Application of the concept of energyselective elec
tron transport used in hot carrier solar cells, to develop thermo electrics and thermo-ionics devices.
Next generation technology (cont.)
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Polysilicon Wafer Solar Cell Solar Module
Chemical Process
(purification)
Casting
Cutting
Surface Treatment Assembly
Systems
Installation
Operation
The PV Value Chain (multi-crystalline)
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Prices are actually increasing
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How does solar energy work?
Solar Electric or Photovoltaic Systems convert some of the energy in
sunlight directly into electricity. Photovoltaic (PV) cells are made
primarily of silicon, the second most abundant element in the earth'scrust, and the same semiconductor material used for computers. When
the silicon is combined with one or more other materials, it exhibits
unique electrical properties in the presence of sunlight. Electrons are
excited by the light and move through the silicon. This is known as the
photovoltaic effect and results in direct current (DC) electricity. PV
modules have no moving parts, are virtually maintenance-free, and
have a working life of 20 - 30 years.
Silicon Solar cell
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PhotovoltaicsMost current solar cells are photovoltaicTypically made from silicon or amorphous silicon.
Typical efficiency ~ 12%.Best efficiency ever in laboratory: ~30%.Theoretical maximum, including concentrating light: 43%
Generic design: doped pnjunction.Photons come in and photoionize donors.Built-in electric field at junction causes carriers to flow,building up a potential (voltage) btw the pand nsides.Clearly one can play with different band gap systems toarrive at materials with different absorption spectra.
Also, good mobility of charge essential for this to work well -trapping of charge or poor mobility will kill efficiency.
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Principle p-n Junction Diode.
Silicon Solar cell
Ref. Soft Condensed Matter physics group in
univ. of Queenland
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p n
p
n
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:Si ingot 330m 2cm x 2cmSurface cleaning
Texturing :chemical v-groove
p-n junction :
POCl3(900C)
ITOincreasing minorty carrier correction, ARC
Poly-Si Solar cell Making process
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Back Surface FieldDeposition Al and Ag ohmic-contact
Forward surface Electrode
Anti-reflection coating(ARC) TiO2
deposition
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H2 diffusiondangling bond H2 bonding Decreasing recombination
Measure
H2 H2 H2 H2
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- An individual PV cell typically produces between 1 and 2 watts
Solar Cell, Module, Array
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decrease the area of solar cell material being used in a system
Concentrator collectors
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Uses for Solar Energy
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Solar Home Systems
Space
Water
PumpingTelecom
Main Application Areas Off-grid
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Residential Home
Systems (2-8 kW)PV Power Plants
( > 100 kW)
Commercial Building
Systems (50 kW)
Main Application Areas
Grid Connected
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Solar energy will become the most important and cost-efficient energy source in the future.
The present lack of silicon feedstock is promoting a rapid development of next generation technology.
Immediate actions are taken to cut thinner wafers and increase cell efficiencies for crystalline silicon.
New thin film technologies are being developed
Stronger influence from semiconductor industry will accelerate thedevelopment of better technologies
Nanosilicon and other third generation technologies may offer a long-term solution for the future solar energy technology.
Conclusions