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Professor Humayun A MughalChairman, Akhter Group PLC
Photovoltaic Technology.
The answer toGlobal Warming?
Global Warming – a Reality
Energy Production – major Contributor
Growing Demand for Electricity – no Going back
Green Energy – is The Only Option
The PHOTOVOLTAIC technology – is the Green Option
PV is the ANSWER to our needs - Economic, Environmentally friendly and Renewable
Key Issues
Warming World A
t-a-glan
ce: Clim
ate chan
ge - evid
ence an
d p
redictio
ns
Long Term High A
t-a-glan
ce: Clim
ate chan
ge - evid
ence an
d p
redictio
ns
At-a-g
lance: C
limate ch
ang
e - eviden
ce and
pred
iction
s
Sea Level Rise
Growing Emissions A
t-a-glan
ce: Clim
ate chan
ge - evid
ence an
d p
redictio
ns
Cows are guilty of speeding up Global Warming.
QuickClimate
Quiz
B - FalseA - True
Methane is the second most significant greenhouse gas and cows are one of the greatest methane emitters. Their grassy diet and multiple stomachs cause them to produce methane, which they exhale with every breath.
A - True
D - UAEC - Kuwait
B - CanadaA - Australia
Which country has the highest CO2 emissions per capita?
The Carbon Dioxide Information Analysis Center figures:UAE - 6.17 metric tonnes of carbon per capita
Kuwait - 5.97, US - 5.4, Australia - 4.91, UK - 3.87.If total greenhouse gas emissions are compared, some analysts say Australia comes out higher than the US.
QuickClimate
Quiz
D - UAEE - USA
The big CO2 emitters
ENERGY USE WorldWide Energy Consumption 1980-2030
Where does ourenergy come from? Share of total Primary
Energy Supply in 2002
10,376 Mtoe IEA Energy Statistics
35.6%
41.6%
Increasing percentage of Total World Energy used for Electricity Generation
Quadrillion BTU
Electricity is
becoming more
important
Electricity How much do we use?
1999 2020
Total kwhrs 13 Trillion 22 Trillion
Population 6,004m 7,541m
Per capita kwhrs 2,165 2,917Electricity Use: International Energy Outlook 2002Population: US Census Bureau
Focus on
ElectricityWorld Electricity Generation by Fuel
Coal
• Easy to find, cheap, but high emissions• Steps toward increased efficiency:• New Super-critical plant
designs• Gas turbine exhausts to heat boiler feedwater
• Increase in biomass co-firing• Improvements in thermal efficiency
Technically exploitablecapability (TWh/yr)
1999 generation(TWh)
Hydropower - Regional Distribution
Hydro
• Potential in 150+ countries
• Proven, advanced technology
• Often integrated with other developments
• Low operating costs, long plant life
• Extremely efficient conversion
Nuclear
• Little pollution
• Virtually 0 greenhouse gas• Environmentally benign plants
Nuclear shares of national electricity generation - 2005
Natural GasAir Pollution from the Combustion of Fossil Fuels kg of emission per TJ of energy consumed
Nat. Gas
Oil Coal
Nitrogen Oxides 43 142 359
Sulphur Dioxide 0.3 430 731
Particulates 2 36 1 333Sources: U.S. Environmental Protection Agency; American Gas Association
• A Low CO2 emitter
• Hydrogen fuel cells
• Steps toward increased efficiency:• Combined-cycle power
plants• Acid gas re-injection
OilElectricity generation by:
• Conventional Steam
• Combustion Turbine
• Combined-cycle
• Air, land and water pollution
• Solid waste burden
Solar Energy
How much is available?The sun’s rays provide enough energy to supply 10,000 timesthe TOTAL energy requirementof mankind.
So, how do we harness it?• Solar
Thermal• Photovoltaic
The ULTIMATE source.
Photovoltaic Possible materials to make PV cells
• CiGs Copper Indium Gallium Diselenide
• Polymers
• CdTe Cadmium Telluride
• Silicon Amorphous Thin Film
Mono crystalline Multi crystalline
0%
10%
20%
30%
40%
50%
60%
Other Am. Silicon Ribbon/SheetCrystalline
Mono Crystalline Multi Crystalline
Solar power market share by technology
The Chain
Metallurgical
Grade Silicon
Electronic Grade Chunks
Ingot
Bars
Wafers
Modules
“Sand”
Strings
Cells
Manufacturing ProcessLet’s start on the beach!
• It’s not good enough! We need 99.999999% purity.
• Chemical companies produce metallurgical grade (99%) silicon.
• The starting point is mined quartz sand, SiO2
Manufacturing ProcessMetallurgical Grade Silicon
Silicon Dioxide is mined from the earth's crust, melted, and taken through a complex series of reactions that occur in a furnace with temperatures from 1500 to 2000 oC to produce Metallurgical Grade Silicon (MG-Si).
Source - Wacker
Manufacturing ProcessHydrochlorination of Silicon
MG-Si is reacted with HCl to form trichlorosilane (TCS) in a fluidized-bed reactor. The TCS will later be used as an intermediate compound for polysilicon manufacturing. The TCS is created by heating powdered MG-Si at around 300 oC in the reactor. In the course of converting MG-Si to TCS, impurities such as Fe, Al and B are removed.
Si + 3HCl -----> SiHCL3 + H2
Manufacturing ProcessDistillation of Trichlorosilane
The next step is to distill the TCS to attain a high level of purity. At a boiling point of 31.8oC, the TCS is fractionally distilled to result in a level of electrically active impurities of less than 1ppba. The hyper-pure TCS is then vaporized, diluted with high-purity hydrogen, and introduced into a deposition reactor for the polysilicon manufacturing process.
Manufacturing ProcessPolysilicon Manufacturing
Conversion of hyper-pure TCS back tohyper-pure Silicon in poly deposition bells.Thin U-shaped silicon slimrods heated to ~1100 oC.Part of TCS is reduced to Silicon that slowly growsover the slimrods to a final diameter of 20cm or more.
Besides the reduction to Silicon, part of the TCS disproportions to the by-product SiCl4.
Polysilicon has typical metal contaminationof <1/100ppb and dopant impurities in the rangeof <1ppb. It is now suitable for further processing.
Manufacturing ProcessPolysilicon Manufacturing
The process focus shifts to the silicon’s atomic structure.
It must be tranformed into ingots with a singular crystal orientation (this is the primary purpose of Crystal Growing).
Before the Polysilicon can be utilized in the Crystal Growing process, it must be first mechanically broken into a chunks of 1 to 3 inches and undergo stringent surface etching and cleaning to maintain a high level of purity.
These chunks are then arranged into quartz crucibles which are packed to a specific weight; typically more than 100kg for 200mm crystals to be grown.
The next step is the actual crystal growing process.
Manufacturing ProcessCrystal Growing
The crystal growing process simply re-arranges silicon atoms into a specific crystal orientation.
The packed crucible is carefully positioned into the lower chamber of a furnace (right).
The polysilicon chunks are melted into liquid form, thengrown into an ingot.
As the polysilicon chunks reach their meltingpoint of 1420 oC, they change from solid to hotmolten liquid.
Heat Exchange Method (HEM) is used to formcrystalline structure.
Manufacturing ProcessCrystal Growing
Computer Simulation of HEM Process
Manufacturing ProcessIngot Sectioning
The process in the furnace will see the molten liquid formed into an ingot, using a directional solidification system (DSS), that may be sectioned into silicon bars.
Manufacturing ProcessIngot Sectioning
The Ingot bricks are cut down ….
Ingot sectioning saw Cropping saw
Bars
Manufacturing ProcessWafer Production
…. and sliced to create wafers.
Wire Saw
Wafers
Production line designed to produce photovoltaic
solar cells with as-cut p-type wafers for starting material.
Manufacturing ProcessFrom Wafers
2. Texturing ……………………….
3. Junction formation …………….
1. Surface etch …………………...
4. Edge etch ………………………
5. Oxide Etch ……..……………...
6. Antireflection coating …….…...
7. Metalization ……………..……..
8. Firing ……..……………………..
9. Wafer/Cell Characterization
1
2
3
4
5
6
7
Manufacturing ProcessCell Production
.
Surface Etch Removes saw damage (about 12 m on all
sides).
Texturing Roughens surface to minimise light reflection
Manufacturing Process – Cell Production
.
Junction FormationPhosphorous diffused into wafer to form p-n junction
Diffusion Furnace
Manufacturing Process – Cell Production
.
Edge Etch Removes the junction at the edge of the wafer
Wafer Holder
Plasma Etch Station
Manufacturing Process – Cell Production
.
Oxide Etch Removes oxides from surface formed during diffusion
Wafer Etch Station
Manufacturing Process – Cell Production
.
Anti-Reflection CoatingA silicon nitride layer reduces reflection of sunlight and passivates the cell
Plasma PECVD Furnace
Manufacturing Process – Cell Production
.
MetalisationFront and back contacts as well as the back aluminum layer are printed
Screen Printerwith automaticloading and unloadingof cells
Manufacturing Process – Cell Production
.
FiringThe metal contacts are heat treated (“fired”) to make contact to the silicon.
Firing furnace to sinter metal contacts
Manufacturing Process – Cell Production
Module Production
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
2003 2004 2005 2006 2007 2008 2009 2010
Price TrendEstimate of global average solar module
prices
US$/watt
Cost Breakdown Produced in Low labour cost
area
10.5%
2.6%8.9%
78%
(Labour cost $2/hour)
The FutureIs Bright
Example of cost recovery on an installation amortised over 25 years.
Assumes an increase in fossil fuel costs of 5% pa.
PV generatedper kwh
Fossil generated
per kwh
Future DevelopmentsR&D is focused on increasing conversion efficiency and reducing cell manufacturing cost, to reduce electricity generation cost.
• Improved crystallisation processes for high quality, low-cost silicon wafers
• Advanced silicon solar cell device structures and manufacturing processes
• Technology transfer of high efficiency solar cell processes from the laboratory to high volume production
• Reduction of the silicon wafer thickness to reduce the consumption of silicon
• Stable, high efficiency thin-film cells to reduce semiconductor materials costs
• Novel organic and polymer solar cells with potentially low manufacturing cost
• Solar concentrator systems using lenses or mirrors to focus the sunlight onto small-area, high-efficiency solar cells
Laser Grooved Buried Contact Layer High Efficiency Si Cells Currently up to 19% Efficiency Production Efficiencies up to 17%
AKHTER Improved Cell Efficiency
AKHTER Solar Lens Development
Optical Design
• Polarisation effects and the effects of real draught angles and facet sizes.
• Lens Zones modelled as a series of annular cones.
Energy concentration achieved by new optical design onto a 20mm diameter detector, placed in the focal plane of the lens.
AKHTER Solar Lens Development
DETECTOR IMAGE: INCOHERENT IRRADIANCE
New optical design reaches82% efficiency with a power distribution on the solar cellwithin a factor of 3.
This reduces hotspot problems.
• Focal plane 135mm from back surface of lens.
• Lens 4mm thick with facets 2mm deep.
• 3 degree draft angle.
• Uses specialised optical materials
AKHTER Solar ConcentratorDesign Characteristics
Computer controlled Dual Axis Tracking System
Compatible with new concentrator technology
Independent of sensors which usually result in maintenance and operational problems
Plant operation may be monitored from anywhere in the world
AKHTER Tracking System
Space requirement – 500m x 600mProducing 18Million Kilowatt hours per yearEnough to meet needs of 10,000 Homes
AKHTER 10MW Solar Plant
Akhter Solar Concentrator Plant
Professor Humayun A MughalChairman, Akhter Group PLC
Thank you
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