Winning the Global Race for Solar Silicon

Transcription

1 Winning the Global Race for Solar Silicon David Lynch Professor of Materials Science & Engineering, University of Arizona & Chief Technical Officer, Solar Technology Research Corporation, Tucson, AZ 1

2 Topics Market Conditions for Photovoltaics New Routes for Producing Low Cost Solar Silicon The Solar Technology Research Corporation s Approach to Refining Silicon 2

3 The Future for Renewable Energy Generation C & E News, Feb

4 Photovoltaics are not only modular, they are also mobile. ARCO Magazine cells produced by NAPS 4

5 Although the role of silicon in photovoltaics is expected to decline, it is still expected to be a growth industry. 5

6 Predicted Installed PV Capacity GW GW % Annual Growth Rate of Installed Capacity % PV Capacity 2005 Germany 1.42 GW Japan 1.41 GW USA 0.48 GW Installed PV Capacity (MW) World Installed Capacity in IEA Reporting Countries Year

7 electronic solar "high purity" metallurgical 2N 3N 4N 5N 6N 7N 8N 9N Impurity content (ppmw) 7

8 Photovoltaics: The Production Path Metallurgical Si - $ 3 per kg Electronic Si - $ per kg SiO 2 Red. Silgrain TCS Dist CVD Cryst Wafers Etch. Missing Link Scrap Si - $ 25 per kg Solar Grade Aim $ per kg Remelt/Cryst Wafers Solar Cells Metallurgical Si Si Purification Siemens Ingot/Wafers Cells/Panels $ 2 $ 25 $ 40 $ 100 8

9 Is there a pot of gold at the end of the race for solar silicon? Stock Value (C$ per share) Stock Value of Timminco Prior to March 2007 Timminco produced metallurgical-grade silicon, and magnesium. March 2007, Timminco announces it has low cost process for producing solar-grade silicon, and has signed a purchase and sales agreement. 0 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 Date (mm/dd/yy) 9

10 Only if you get it right! Stock Value (C$ per share) Stock Value of Timminco Prior to March 2007 Timminco produced metallurgical-grade silicon, and magnesium. March 2007, Timminco announces it has low cost process for producing solar-grade silicon, and has signed a purchase and sales agreement. 0 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 1/1/09 Date (mm/dd/yy) 10

11 Some of the Players in the Race Tech. Company Tech. Company Integrated Reduction of Silica to s-si Solsilk/FESIL Solarvalue??? Elkem Solar Siemens TCS Hemlock, Wacker, Tokuyama, MEMC, & numerous new entrants Silane REC Silicon Up-grade m-si Elkem Solar, Dow Corning, Fluid Bed TCS Hemlock & Wacker Solarvalue, JFE, Nippon Steel. Timminco, STRC & others Silane REC Silicon 11

12 C SiO 2 General Approach of Metallurgical Processes for Producing Solar Silicon Silicon Submerged Arc Furnace m-si The primary issues is removal of B and P before directional solidification. hp-si hp-si Acid Treatment (Silgrain) hp-si Directional Solidification Refining B & P reduced-si solar - Si Solsilk/FESIL SolarValue Elkem Solar Dow Corning Nippon Steel JFE Timminco STRC 12

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14 Boiling Point Temp. (K) Impurity Element Expected to Report to Product Crater Temperature Top Bed Temperature Filter Temperature W Mo Zr B Expected Variation in Distribution of Trace Element V Co Ni Fe Sc Cr Sn Cu Al Mn Ba Pb Sb Bi Ca Sr Mg Zn Na Cd K Se As S Hg P Impurity Elements Impurity Elements Expected to Report to Silica Fume Off-Gas Percent W Mo Zr B V Co Ni Fe Sc Cr Sn Cu Al Mn Ba Pb Sb Bi Ca Sr Mg Zn Na Cd K Se As S Hg P product silica fume filtered off-gas Impurity Elements 14

15 Division Between Outer Reaction Zone Inner Reaction Zone cavity electrode bed(silica & coke/coal) 10.0 l T = 2273 K k e SiC Si arc p SiO (bar) 1.0 m SiO SiC = Si+SiO(g) + CO(g) T (K) 15 Si 0.1 i g j P T = 1 bar T = 2084 K d h P T = 10 bar T = 2188 K Si + SiO 2 = 2SiO(g) q p SiO : p CO 3:1 SiO(g) + SiC = 2Si + CO(g) SiC + 2SiO 2 = 3SiO(g) + CO(g) p o Ratios for P T = 1 bar 2:1 1:1 f n 2CO(g) 2C SiO 2 Outer Reaction Zone SiO(g) + 2C = SiC + CO(g) SiO(g) & CO(g) SiC Inner Reaction Zone

16 Oxi-Nitride Slag STRC Oxide Slag Timminco Elkem Solar Solarvalue 16

17 orthosilicate composition Refining with an Oxide Slag, B Removal X SiO2 L B 0.6 X O 2- X i or L B 0.4 (K 8 ' ) 1/4 assumed = CaO/SiO 2 molar ratio ( ) 17 slag 3Si( ) 2 3 3SiO 2( slag) + 6O ( slag) + 4B( l) = 4BO3 + l

18 Refining with an Oxide Slag, B Removal Process Slag: Si Mass Ratio Batch 17 2 orthosilicate X i or L B Counter Current X SiO2 (K 8 ' ) 1/4 assumed = orthosilicate composition L B X O 2- Distribution Coefficient for B acid Suzuki & Sano 10 th E.C. PV Solar Energy Conference, April SiO 2 + 6O 2- +4B = 4BO Si base CaO/SiO 2 molar ratio CaO/SiO 2 molar ratio 18

19 Refining with an Oxi - Fluoride Slag, B Removal Phosphide P + ( O ) = ( P ) + Phosphate 3 4 O 5 P + ( O ) + O2 ( g) = ( PO Log (%PO 4 3-)/(P P2 ) 1/2 or Log (%P 3- )/(P P2 ) 1/ ) a SiO2 = 0.01 Si(l) - SiO 2 (l) equilibrium CaO(sat.) - CaF 2 Melts T = 1773 K (PO 4 3- ) a SiO 2 = 0.1 a SiO 2 = 1 (P 3- ) maximum p O Log P O2 After Tabuchi and Sano

20 STRC Approach Technical Approach Remove B and P by replacing those elements with other impurities that can be easily removed down stream. Oxidative refining Silgrain Directional Solidification Patent Application, US 2007/ A1 Business Approach Modular Units at 600 metric tons per year PV producer financed for guarantied price Estimated production cost: $12-$14 per kg (pre directional solidification) With projected process improvement, cost estimated at $8 to $10 per kg. 20

21 STRC / UA Research Laboratory 21

22 STRC Technical Approach to Refining for B SiO 2 Al 2 O 3 minimum anticipated value for γ BN Si 2 N 2 O Si 3 N 4 Liquid L + Si 2 N 2 O + βss B A Liq. + β ss β ss % equivalent Al C D % equivalent O AlN mass oxi-nitride melt to mass of Si refined (Si 3 N 4 ) + 4B = 4(BN) + 3Si(l) T = 1700 K 30 ppma to 0.1 ppma B a Si = 1 a Si3 N 4 = 0.01 a Si3 N 4 = 0.1 a Si3 N 4 = 1 target γ BN 22

23 STRC Technical Approach to Refining for B SiO 2 Al 2 O 3 Liquid C 25 L + Si 2 N 2 O + βss A Liq. + β ss Si 2 N 2 O D % equivalent O 20 as received m-si target mass oxi-nitride melt to mass of Si refined Si 3 N B (Si 3 N 4 ) + 4B = 4(BN) + 3Si(l) T = 1700 K 30 ppma to 0.1 ppma B a Si = 1 % equivalent Al β ss minimum anticipated value for γ BN a Si3 N 4 = 0.01 a Si3 N 4 = 0.1 AlN a Si3 N 4 = 1 target γ BN ppmw B in Si Starter Slag 27.7% Al 2 O 3 8.5% MgO 17% SiO 2 16% CaO 15.8% CaF 2 15% Si 3 N 4 bench mark 1 ppmw mass slag / mass Si refined 23

24 SiO 2 Liquid C Al 2 O 3 STRC Technical Approach to Refining for P L + Si 2 N 2 O + βss A Liq. + β ss D % equivalent O 0.6 minimum anticipated value for γ AlP Si 2 N 2 O Si 3 N 4 B % equivalent Al β ss AlN mass oxi-nitride melt to mass of Si refined a Al2 O 3 / a SiO2 = 3 (Al 2 O 3 ) + 2P + 1.5Si(l) = 2(AlP) + 1.5(SiO 2 ) T = 1700 K 30 ppma to 0.1 ppma P a Si = 1 a Al2 O 3 / a SiO2 = 6 a Al2 O 3 / a SiO2 = 30 a Al2 O 3 / a SiO2 = 60 target γ AlP 24

25 Conclusions For Si photovoltaics to compete in the market there must be cost compression all along the cost chain. Opportunity exists to significantly reduce the cost of silicon for photovoltaics through metallurgical refining practice. Si Photovoltaics are expected to remain a growth area, even though market share will decline. 25