Sustainable Si production for solar cells
– a responsibility for Norway?
(or how can Norway contribute to the PV
industry in collaboration with China?)
Gabriella Tranell, Associate
Professor
The Norwegian University of Science
and Technology
1
Solar Energy –
What is driving the development globally?
USA, May 2009
Federal government: $467 million to
expand and accelerate the development
and use of solar and geothermal energy
China, July 2009
China announces plans to achieve
a solar power capacity of 2 GW by
2011, nearly 15 times up from 2009
India, August 2009
Indian government announces
goal of generating 20 GW of
solar energy by 2020
2 Billion people still without access to electricity from the grid….
2
Foreseen growth in the PV market will most likely again
bring increased demand of solar grade silicon…..
Corresponds
to ~176000
tons of SoGSi or 241100
tons MG-Si*
Source EPIA 2009
*100% cSi, 2007 mc-Si scenario,
Jungbluth, Tuchschmid and de
Wild-Scholten
3
Silicon in the solar cell production chain
Silicon cost, availability and production method is critical to
achieving competitive and sustainable solar electricity for the
international community!
Currently responsible for
~30% of total energy
consumption and
associated GHG emission
in SC production chain
4
Silicon
•
Silicon (Si) occurs in nature (earth) only in the
oxidized state as quartz or other silicate minerals
( Si4+ ). Any process aiming at elementary silicon
(Si0) involves necessarily some reduction steps
•
Silicon is not a metal but a metalloid: this implies
that efficient purification methods applied to
metallic compounds are not always efficient
when applied to silicon
•
High purity is however requested for silicon to act
as a semiconductor in photovoltaic cells
5
Routes Towards High Purity, SoG-Si (6N+ Purity)
Raw Materials (C + SiO2)
”MG-Si ”(Si = 98-99% )
Siemens/FBR-Si
SoG-Si
6N+
8-11N
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Production of Si as Si or FeSi World Wide*
•China
dominates the
market
Si and FeSi production in 2006
Total volume 4700.000 tons
•Norway has
worlds largest
and most
energy efficient
furnace
Others
22 %
US
3%
China
51 %
Brasil
5%
Norway
6%
Russia
13 %
Source:
USGS
* ~80% by weight of total is Si in FeSi. China produced ~550 kton of MG-Si.
Numbers do not include ~150 kton Si from the US
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The Industrial Carbothermic Process for MG-Si production
11-13MWh/ t Si
Overall reaction:
SiO2 + 2C → Si + 2CO
What do we need?
- Raw materials
- Electrical Energy
8
MG-Si Process “Outputs”
Emissions:
•”Electric Energy CO2”
•Fossile CO2 =4.3 t/t Si
•Biological CO2 = 1.8t/t Si
•SO2 = 13 kg/t Si
•NOx =11 kg/t Si
Energy:
Bi-product:
0,2-0,4 tons of SiO2/ ton Si
Heat content of gas ~
electric energy added
– with current
technology 30% may
be recovered
Product: Chemical composition of commercial MG
silicon
Too high for SoG-Si
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Si production and CO2 emissions
Electricity
source
Total spec. CO2
(kg CO2/kg Si)
Hydro/Nuclear
4.3
Gas Power
10.6
Coal power
17.7
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Polysilicon (TCS route)
“The Siemens process”
TCS (electronic grade)
MG-Si
Chemical Vapor
Deposition
HCl
Production of TCS
T ≈ 1100ºC
T ≈ 300ºC
Polysilicon
Si + 3HCl → HSiCl3 + H2
One or more
fractional distillations
H2
Recovery and
HSiCl3 + H2 → Si + 3HCl
regeneration
Energy consumption >120 MWh/t
Chemical waste
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So how does this relate to Norway and the solar
industry?
12
Silicon-based solar energy and offshore wind in Norway –
Why?
Natural Resource
Water Falls
Oil- and gas
resources
Industrial Utilisation
Metallurgical
industry
Oil- and gas
industry
New Innovation
Solar industry
Offshore wind
technology
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PV industry in Norway
Wafer-based technology
REC Wafer
Elkem Solar
System
REC Silicon
Panel
Metallurgical
Chemical
Cell/
Module
Wafer
Si (98%)
Raw
Materials
SoG-Si
REC Solar
Norsun
CruSiN
Metallkraft
Saint Gobain
Wash. Mills
Vetro Solar
Norsk
Solkraft
Umoe Solar
FeSil Sunergy
Prediktor
Innotech
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The Elkem Solar Route
Elkem Silicon Metal
Pyro-metallurgical
refining
Hydro-metallurgical
refining
Elkem Silicon SiMet is ideal
• Commercial quality
• Available on site
Pyro-metallurgical refining step
• Well known principles
• Large scale capability
• Run in industrial scale today
Hydro-metallurgical refining step
• Well known principles
• No scale constrains
• Run in industrial scale today
Final solidification refining step
• Well known principles
Directional Solidification
Final polishing
Solar Grade
Silicon Feedstock
•Status: In production. Ramping up towards targeted
3000t/year
•Can be used as blend or 100% mix – good results in
cell production
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The Solsilc Process –
the ”Pure Raw Materials Route”
7steps
1. Agglomeration of quartz, carbon black and
SiC-fines
2. Silicon Carbide. Formation of silicon carbide
(SiC) is an intermediate process in the reduction
furnace.
3. Reduction. The charge is agglomerates made of
quartz, SiC and carbon
4. Holding. Metal is tapped and processed
5. Filtering. With one or more filters
6. Casting/Directional Solidification
7. Clean and cut ingot
•Small scale test plant close to completion
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CO2- and energy account for PV-Si
kg CO2 og kWh/kg Si
200
180
CO2
160
kWh
140
120
100
80
60
40
20
0
Conventional Siemens
Best Practice Europe
Elkem Route
•Energy payback time now ~18 months, with UMG Si metal 2-4 months
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Renewable energy storage and multiplication
Hydrogen
Carbon
Energy Recovery!
WOOD
CO2-free
Electricity
Silicon
Bio-carbon
CO2
CCS
Quartz
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Solar cell
materials for
energy export,
20-40 x more
energy produced
than used !!
Challenges ahead –
Collaboration between China and Norway?
• Challenges/Opportunities
– Create trust and acceptance for non-Siemens metal in the market;
openness on specification, qualification
– Increased recovery of high- and low temperature heat/ chemical
energy
– New reductants for better GHG emission performance
– Utilisation of waste products and raw materials fines
– Recycling of PV silicon from process and end-of-life
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☼Energy efficient and environmentally friendly production of
silicon is one of the keys to a robust solar energy future
☼Norway and China are key players in this game and should
join forces in competence development for global impact!
“The future's so bright, I gotta’ wear shades”
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