Solar Cell Operation
Beginnings of the PV Journey 1973 to 2013
Dick Swanson EE237, April 3, 2013
Outline • The Genesis and Growth of the PV Industry • History of SunPower • Importance of Efficiency • PV Today • Looking Forward • How Solar Cells Work
© 2013 SunPower Corporation
2
THE GENESIS AND GROWTH OF THE PV INDUSTRY
© 2013 SunPower Corporation
3
Commercial Solar Cell, ca 1960 Hoffman Electronics
~0.04 W ~8% Efficiency ~$400/W Cost © 2013 SunPower Corporation
44
The 1970s Oil Crises Sparked Interest in PV as a Terrestrial Power Source Don’t worry Mr. President, solar will be economical in 5 years!
I can’t believe he said that.
Sun Day, May 5, 1978, SERI 5
© 2013 SunPower Corporation
5
Situation in 1973; the beginnings of the terrestrial PV industry Wafered Silicon Process
Polysilicon
Ingot
Wafer
Solar Cell
Solar Module
Systems
$300/kg 3 inches in diameter Sawn one at a time 0.5 watts each $100/watt $200/watt © 2013 SunPower Corporation
6
1975 View Wafered Silicon Hopelessly Too Expensive
Breakthrough Needed
Thin Films
Remote Power
© 2013 SunPower Corporation
Concentrators
Solar Farms
7
What Actually Happened Wafered Silicon Emerges as the Dominant Technology
Breakthrough Needed
Thin Films
Remote Power
© 2013 SunPower Corporation
Concentrators
Solar Farms
DOE Wafered Silicon Program
Residential/ Commercial Grid connected
8
Historical PV Module Shipments
Japanese companies Japanese roof program
Entrepreneurial companies Early innovation Rapid growth German FIT
Oil companies
© 2013 SunPower Corporation
9
Historical Module Price Experience Curve
Module Price (2010 $/W)
60.00
81% Progress Ratio 1979 $33.69/W
Excess Capacity
6.00
Silicon Shortage
2012 $0.85/W
0.60 1
10
100
1000
10000
100000
Cumulative Production (MW) © 2013 SunPower Corporation
10
The Rollercoaster Ride
CSI
10000
Annual Shipments (MW)
Natural Gas Shortages PURPA
German FiT
1000
2nd Three Mile Island
oil crisis
Natural Gas Shortages
German FiT dead
100
Thin Films To take over
Natural Gas Glut Reagan
Thin Films don’t take over
Japan PV rooftop prog.
Chernobyl
10
German FiT Silicon GlutNot Dead
Financial Crisis
Silicon Shorage Natural Gas Glut, Fracing
1
© 2013 SunPower Corporation
11
Why Wafered Silicon Still Dominates
We never envisioned: • The dramatic cost reduction potential of wafered silicon • The early dominance of residential and commercial grid connected markets
© 2013 SunPower Corporation
12
HISTORY OF SUNPOWER FROM STANFORD UNIVERSITY TO GLOBAL LEADER
© 2013 SunPower Corporation
13
1985, Stanford University, Point Contact Cell 27% Efficiency at 100X
• Low Recombination • • • •
Minimal diffused regions Oxide/Alneal passivated surfaces Point arrangement of pn-junctions High injection operation
• High Generation • Zero grid obscuration • High-res, high-tau wafers • Good internal optics
• Low Parasitics • Rear electrodes • Double level metallization
• High-tau FZ wafers • Multiple High-tau Tube Diffusions • Photolithographic Features
Photo from M.A. Green, CLEAN ELECTRICITY FROM PHOTOVOLTAICS, eds Mary D Archer & Robert Hill (Imperial College Press, 2001)
© 2013 SunPower Corporation
14
1980, My Stanford solar research group visits PG&E
© 2013 SunPower Corporation
15
1990: SunPower begins operations
© 2013 SunPower Corporation
16
Concentrator Cells for Solar Systems, Pty.
© 2013 SunPower Corporation
17
1993, Honda Dream
© 2013 SunPower Corporation
18
Winning 1993 World Solar Challenge
© 2013 SunPower Corporation
19
1996, NASA/AeroVironment Helios
100,000 feet Record Altitude for an airplane © 2013 SunPower Corporation
20
1999, Project Mercury: Develop a low-cost back-junction cell
© 2013 SunPower Corporation
21
May 1, 2000
Fateful Decision:
Adapt SunPower high-efficiency concentrator cell to low cost, flat-plate PV
© 2013 SunPower Corporation
22
2003, Cypress Synergies
Highest efficiency solar cells:
The volume manufacturer:
• Strong technical expertise - 15 years of solar cell R&D expertise • Solar cells and opto-electronics • World leader in ultra-high efficiency solar cells
• Building cost effective products for 20 years • $1 bn revenue in 2004 • Leading edge, high volume wafer fabs • Broad portfolio of integrated circuits
23 © 2013 SunPower Corporation
23
Osaka 2003: Introduced the 20% A-300 Solar Cell
Back Side
© 2013 SunPower Corporation
Front Side
24
2004; SunPower goes to the Philippines
SunPower Confidential © 2013 SunPower Corporation
25 25
2005: SunPower goes public
© 2013 SunPower Corporation
26
Importance of Efficiency
© 2013 SunPower Corporation
27
Conventional Wafered Silicon Value Chain:
Polysilicon
Ingot
Wafer
Solar Cell
Solar Panel
System
Rough percentages for conventional c-Si: 12%
6% 9%
14%
25%
41%
34%
59%
Total Cost: $2.63/Wac
© 2013 SunPower Corporation
28
SunPower vs. Conventional c-Si Cell
Lightly doped front diffusion • Reduces recombination loss
Texture + ARC
Gridlines
Texture + ARC
N-Type diffused junction
. . .
FRONT
BACK Localized Contacts Passivating Backside Mirror SiO2 layer • Reduces contact • Reduces back light recombination loss • Reduces surface absorption & causes recombination loss light trapping Backside Gridlines • Eliminates shadowing • High-coverage metal reduces resistance loss
© 2013 SunPower Corporation
.
Silver Paste Pad
Aluminum paste
29
The Maxeon Solar Cell is the Core of the SunPower Technology Maxeon cells are back-contact silicon cells built on a solid copper foundation • up to 24.2% efficient. SunPower Maxeon Cell Efficiency Advantage 24%
SunPower holds the world-record large Silicon panel efficiency (21.4%). Green, M. A., et. al. “Solar Cell
22% 20%
Efficiency Tables (version 39),” Progress in Photovoltaics, 2013, vol. 21, p1-11.
18% 16%
14% 12% 10% Thin Films
Standard Silicon
© 2013 SunPower Corporation
Sanyo HIT
SunPower Maxeon Gen 2
SunPower Maxeon Gen 3
SunPower continues to out-innovate the competition
30
Overview: the New “X21” Solar Panel Best PV Panel on Every Dimension: Energy Production1, Reliability2, Efficiency3 And Aesthetics
335 Watts 21.2% average efficiency
345 Watts 21.5% average efficiency (limited availability)
World’s highest energy and power solar panel Delivers the maximum power possible from your roof3 More energy output in hot locations and summer months when sunlight is strongest1 1 Compared
Unique pure black uniform look Delivers the most energy even when located in small shadows like vent pipes, pole or wire shadows, or when partly covered with fallen leaves or dirt1 Average X21 panel efficiency of 21.5% beats the currently listed world record of 21.4%!3
© 2013 SunPower Corporation
2 Same
with E-Series.
copper foundation as E-Series.
3 20.5%
average efficiency beats the currentlylisted world record for a large Silicon panel in the internationally recognized source of efficiency records, updated every 6 months: Green, M. A., et. al. “Solar Cell Efficiency Tables (version 39),” Progress in Photovoltaics, 2013, vol. 21, p1-11. 31
University of California Davis Project
© 2013 SunPower Corporation
3232
UC Davis Project In partnership with Carmel Partners and University of California at Davis 663 student apartments, plus retail, restaurants and student amenities – built over 3 phases Designed to be 100% net zero energy Largest net zero energy project in the nation Total project is 50% more energy efficient than required by code (Title 24) (No gas, system is 100% electric)
© 2013 SunPower Corporation
33
PV Today
© 2013 SunPower Corporation
34
13% of Germany’s electricity generation is coming from wind and solar so far this year!
From Prof. Eicke Weber’s Plenary Talk at PVSC-38 © 2013 SunPower Corporation
3
35
EU PV: 10+ GW in 2010…21GW in 2011 European 2011 New Installed and Retired Capacity (MW)
In 2011 Solar was the largest source of new capacity in the EU at 47% of additions
Source: EWEA, February 2012
© 2013 SunPower Corporation
36
Solar Already Competitive in Many Regions Globally with Rooftop Power Prices
Source: Citigroup, July 2012 37 © 2013 SunPower Corporation
37
PV Today • The subsidized grid-connected distributed market spurred incredible growth and cost reduction through scale and innovation • This module cost reduction opened up the large power plant market • And is now doing the same for remote markets in the developing world • In other words, all the originally conceived markets are now blossoming…just in different order than originally envisioned
© 2013 SunPower Corporation
38
Looking Forward
© 2013 SunPower Corporation
39
Zooming in on Recent Times Historical
2005
Projected iSupply
Module ASP ($2010/W)
PJC SunShot
3.00
Required by ITC end
2011
$1.12/W 2015 2020
$1.25/W $0.99/W $0.75/W
Cumulative Production (MW) 0.30 1,000
10,000 © 2013 SunPower Corporation
100,000
$0.50/W
1,000,000 40
Zooming in on Recent Times Historical
2005
Projected iSupply
Module ASP ($2010/W)
PJC SunShot
3.00
Required by ITC end
2011
$1.12/W 2015 2020
$1.25/W $0.99/W $0.75/W
Cumulative Production (MW) 0.30 1,000
10,000 © 2013 SunPower Corporation
100,000
$0.50/W
1,000,000 41
Looking Forward Historical
2005
Projected iSupply
Module ASP ($2010/W)
PJC SunShot
3.00
Required by ITC end
2011
$1.12/W 2015 2020 $0.82/W
$1.25/W $0.99/W
Probable price range going forward
$0.75/W
Cumulative Production (MW) 0.30 1,000
10,000 © 2013 SunPower Corporation
100,000
$0.50/W
1,000,000 42
5-Year Market Forecast – Solarbuzz Moving toward PV industry maturity 5-Year Forecast Regional Breakdown: Most Likely GW 60 Latin America & Caribbean
15% CAGR
Middle East & Africa
45
Other APAC & Central Asia 30 Major Asia-Pacific
Europe
15
N. America 0
2012
© 2013 SunPower Corporation
2013
2014
2015
2016
Source: NPD Solarbuzz
43
PV Tomorrow • Cost reductions continue unabated • Ever expanding cost-effective markets and applications emerge • Growth rates moderate into the 15% to 25% range • PV is becoming a mature industry poised to provide an increasing share of pollution-free renewable energy to the world
© 2013 SunPower Corporation
44
Tehnology
© 2013 SunPower Corporation
45
46 © 2013 SunPower Corporation
46
1970s Solar Cell Analysis Approach: Think of a solar cell as a big diode and solve the semiconductor device modeling equations Current = Drift + Diffusion Continuity: dJ/dx = Volume Generation - Volume Recombination Voltage = kT/q ln(nNA/ni2) - Resistance Loss Problem: Not Very Obvious How Cell Converts Light Energy Into Electric Energy • No explicit mention of total photo-generation • Lots of approximations are involved • Hard to grasp three dimensional effects © 2013 SunPower Corporation
47
© 2013 SunPower Corporation
48
Solar Cell Operation Light
Electron-Hole Production
e
Electron Collection
h Hole Collection
© 2013 SunPower Corporation
49
The Hydropower Analogy to PV Conversion
© 2013 SunPower Corporation
50
New Method: 1980s Current = Total Generation - Total Recombination Voltage = Difference in n and p Quasi-Fermi Level = kT/q ln(nnpp/ni2) - Base Resistance Loss
© 2013 SunPower Corporation
51
Solar Cell Operation Step 1: Create electron at higher energy Conduction Band
Bandgap
E ph
Valence Band
Thermalization loss
© 2013 SunPower Corporation
52
Solar Cell Operation Step 2: Transfer electron to wire at high energy (voltage/electrochemical potential/Fermi level) Collection loss
Vout
E ph
Thermalization loss
© 2013 SunPower Corporation
53
Step 3: Deliver Energy to the External Circuit
E ph
Vout
Eout qV E out ph 54 © 2013 SunPower Corporation
54
The goal in a solar cell is to: 1.
Generate as many electron hole pairs as possible from the incident sunlight
2.
Coax as many electrons and holes as possible to go to the correct lead
3.
Do this at as high a voltage as possible
(as high a difference in electromotive force between the leads as possible)
© 2013 SunPower Corporation
55
Recombination Loss • Any outcome of the freed electron and hole other than collection at the proper lead is a loss called “recombination loss.” • This loss can occur in several ways
© 2013 SunPower Corporation
56
Bulk Recombination Loss A) Radiative recombination
© 2013 SunPower Corporation
57
Cracked Standard Efficiency Cells in the Field Conventional Panels Black areas = No Power
SunPower Panel
Likely damaged in installation or from repeated hot/cold temp cycles
Likely damaged from poor soldering process and hot/cold temp cycles.
Left side has broken copper ribbons between a pair of cells.
Even with a crack, all parts of the cell are running (no black).
Conventional panels commonly fail from hot/cold temperature cycles that crack solar cells, solder joints and copper ribbons over time. © 2013 SunPower Corporation
58
Bulk Recombination Loss B) Defect mediated recombination (SRH recombination)
Defect related mid-gap energy level
© 2013 SunPower Corporation
59
Surface and Contact Recombination Loss
© 2013 SunPower Corporation
60
Cell Current
J out J ph J rec © 2013 SunPower Corporation
61
SunPower’s Backside Contact Cell Lightly doped front diffusion • Reduces recombination loss
Backside Mirror • Reduces back light absorption • Causes light trapping P+
Texture + SiO Texture Oxide 2 + ARC
N-type FZ Silicon Silicon – 270 – 240 umum thick thick • reduces bulk recombination N+ P+ N+ P+
Localized Contacts • Reduces contact recombination loss
N+
Passivating SiO2 layer • Reduces top and bottom recombination loss
Backside Gridlines • Eliminates shadowing •Thick, high-coverage metal reduces resistance loss
62 © 2013 SunPower Corporation
62
SunPower Cell Loss Mechanisms 0.5%
0.8% Texture + Oxide
1.0% 0.2%
N-type Silicon – 2700.2% um thick 0.3%
0.2% 1.0%
I2R Loss 0.1%
Limit Cell Efficiency
29.0%
Total Losses
-4.4%
Enabled Cell Efficiency
24.6% 63
© 2013 SunPower Corporation
63
Thank You
© 2013 SunPower Corporation
64
Dick Swanson EE237, April 3, 2013
Outline • The Genesis and Growth of the PV Industry • History of SunPower • Importance of Efficiency • PV Today • Looking Forward • How Solar Cells Work
© 2013 SunPower Corporation
2
THE GENESIS AND GROWTH OF THE PV INDUSTRY
© 2013 SunPower Corporation
3
Commercial Solar Cell, ca 1960 Hoffman Electronics
~0.04 W ~8% Efficiency ~$400/W Cost © 2013 SunPower Corporation
44
The 1970s Oil Crises Sparked Interest in PV as a Terrestrial Power Source Don’t worry Mr. President, solar will be economical in 5 years!
I can’t believe he said that.
Sun Day, May 5, 1978, SERI 5
© 2013 SunPower Corporation
5
Situation in 1973; the beginnings of the terrestrial PV industry Wafered Silicon Process
Polysilicon
Ingot
Wafer
Solar Cell
Solar Module
Systems
$300/kg 3 inches in diameter Sawn one at a time 0.5 watts each $100/watt $200/watt © 2013 SunPower Corporation
6
1975 View Wafered Silicon Hopelessly Too Expensive
Breakthrough Needed
Thin Films
Remote Power
© 2013 SunPower Corporation
Concentrators
Solar Farms
7
What Actually Happened Wafered Silicon Emerges as the Dominant Technology
Breakthrough Needed
Thin Films
Remote Power
© 2013 SunPower Corporation
Concentrators
Solar Farms
DOE Wafered Silicon Program
Residential/ Commercial Grid connected
8
Historical PV Module Shipments
Japanese companies Japanese roof program
Entrepreneurial companies Early innovation Rapid growth German FIT
Oil companies
© 2013 SunPower Corporation
9
Historical Module Price Experience Curve
Module Price (2010 $/W)
60.00
81% Progress Ratio 1979 $33.69/W
Excess Capacity
6.00
Silicon Shortage
2012 $0.85/W
0.60 1
10
100
1000
10000
100000
Cumulative Production (MW) © 2013 SunPower Corporation
10
The Rollercoaster Ride
CSI
10000
Annual Shipments (MW)
Natural Gas Shortages PURPA
German FiT
1000
2nd Three Mile Island
oil crisis
Natural Gas Shortages
German FiT dead
100
Thin Films To take over
Natural Gas Glut Reagan
Thin Films don’t take over
Japan PV rooftop prog.
Chernobyl
10
German FiT Silicon GlutNot Dead
Financial Crisis
Silicon Shorage Natural Gas Glut, Fracing
1
© 2013 SunPower Corporation
11
Why Wafered Silicon Still Dominates
We never envisioned: • The dramatic cost reduction potential of wafered silicon • The early dominance of residential and commercial grid connected markets
© 2013 SunPower Corporation
12
HISTORY OF SUNPOWER FROM STANFORD UNIVERSITY TO GLOBAL LEADER
© 2013 SunPower Corporation
13
1985, Stanford University, Point Contact Cell 27% Efficiency at 100X
• Low Recombination • • • •
Minimal diffused regions Oxide/Alneal passivated surfaces Point arrangement of pn-junctions High injection operation
• High Generation • Zero grid obscuration • High-res, high-tau wafers • Good internal optics
• Low Parasitics • Rear electrodes • Double level metallization
• High-tau FZ wafers • Multiple High-tau Tube Diffusions • Photolithographic Features
Photo from M.A. Green, CLEAN ELECTRICITY FROM PHOTOVOLTAICS, eds Mary D Archer & Robert Hill (Imperial College Press, 2001)
© 2013 SunPower Corporation
14
1980, My Stanford solar research group visits PG&E
© 2013 SunPower Corporation
15
1990: SunPower begins operations
© 2013 SunPower Corporation
16
Concentrator Cells for Solar Systems, Pty.
© 2013 SunPower Corporation
17
1993, Honda Dream
© 2013 SunPower Corporation
18
Winning 1993 World Solar Challenge
© 2013 SunPower Corporation
19
1996, NASA/AeroVironment Helios
100,000 feet Record Altitude for an airplane © 2013 SunPower Corporation
20
1999, Project Mercury: Develop a low-cost back-junction cell
© 2013 SunPower Corporation
21
May 1, 2000
Fateful Decision:
Adapt SunPower high-efficiency concentrator cell to low cost, flat-plate PV
© 2013 SunPower Corporation
22
2003, Cypress Synergies
Highest efficiency solar cells:
The volume manufacturer:
• Strong technical expertise - 15 years of solar cell R&D expertise • Solar cells and opto-electronics • World leader in ultra-high efficiency solar cells
• Building cost effective products for 20 years • $1 bn revenue in 2004 • Leading edge, high volume wafer fabs • Broad portfolio of integrated circuits
23 © 2013 SunPower Corporation
23
Osaka 2003: Introduced the 20% A-300 Solar Cell
Back Side
© 2013 SunPower Corporation
Front Side
24
2004; SunPower goes to the Philippines
SunPower Confidential © 2013 SunPower Corporation
25 25
2005: SunPower goes public
© 2013 SunPower Corporation
26
Importance of Efficiency
© 2013 SunPower Corporation
27
Conventional Wafered Silicon Value Chain:
Polysilicon
Ingot
Wafer
Solar Cell
Solar Panel
System
Rough percentages for conventional c-Si: 12%
6% 9%
14%
25%
41%
34%
59%
Total Cost: $2.63/Wac
© 2013 SunPower Corporation
28
SunPower vs. Conventional c-Si Cell
Lightly doped front diffusion • Reduces recombination loss
Texture + ARC
Gridlines
Texture + ARC
N-Type diffused junction
. . .
FRONT
BACK Localized Contacts Passivating Backside Mirror SiO2 layer • Reduces contact • Reduces back light recombination loss • Reduces surface absorption & causes recombination loss light trapping Backside Gridlines • Eliminates shadowing • High-coverage metal reduces resistance loss
© 2013 SunPower Corporation
.
Silver Paste Pad
Aluminum paste
29
The Maxeon Solar Cell is the Core of the SunPower Technology Maxeon cells are back-contact silicon cells built on a solid copper foundation • up to 24.2% efficient. SunPower Maxeon Cell Efficiency Advantage 24%
SunPower holds the world-record large Silicon panel efficiency (21.4%). Green, M. A., et. al. “Solar Cell
22% 20%
Efficiency Tables (version 39),” Progress in Photovoltaics, 2013, vol. 21, p1-11.
18% 16%
14% 12% 10% Thin Films
Standard Silicon
© 2013 SunPower Corporation
Sanyo HIT
SunPower Maxeon Gen 2
SunPower Maxeon Gen 3
SunPower continues to out-innovate the competition
30
Overview: the New “X21” Solar Panel Best PV Panel on Every Dimension: Energy Production1, Reliability2, Efficiency3 And Aesthetics
335 Watts 21.2% average efficiency
345 Watts 21.5% average efficiency (limited availability)
World’s highest energy and power solar panel Delivers the maximum power possible from your roof3 More energy output in hot locations and summer months when sunlight is strongest1 1 Compared
Unique pure black uniform look Delivers the most energy even when located in small shadows like vent pipes, pole or wire shadows, or when partly covered with fallen leaves or dirt1 Average X21 panel efficiency of 21.5% beats the currently listed world record of 21.4%!3
© 2013 SunPower Corporation
2 Same
with E-Series.
copper foundation as E-Series.
3 20.5%
average efficiency beats the currentlylisted world record for a large Silicon panel in the internationally recognized source of efficiency records, updated every 6 months: Green, M. A., et. al. “Solar Cell Efficiency Tables (version 39),” Progress in Photovoltaics, 2013, vol. 21, p1-11. 31
University of California Davis Project
© 2013 SunPower Corporation
3232
UC Davis Project In partnership with Carmel Partners and University of California at Davis 663 student apartments, plus retail, restaurants and student amenities – built over 3 phases Designed to be 100% net zero energy Largest net zero energy project in the nation Total project is 50% more energy efficient than required by code (Title 24) (No gas, system is 100% electric)
© 2013 SunPower Corporation
33
PV Today
© 2013 SunPower Corporation
34
13% of Germany’s electricity generation is coming from wind and solar so far this year!
From Prof. Eicke Weber’s Plenary Talk at PVSC-38 © 2013 SunPower Corporation
3
35
EU PV: 10+ GW in 2010…21GW in 2011 European 2011 New Installed and Retired Capacity (MW)
In 2011 Solar was the largest source of new capacity in the EU at 47% of additions
Source: EWEA, February 2012
© 2013 SunPower Corporation
36
Solar Already Competitive in Many Regions Globally with Rooftop Power Prices
Source: Citigroup, July 2012 37 © 2013 SunPower Corporation
37
PV Today • The subsidized grid-connected distributed market spurred incredible growth and cost reduction through scale and innovation • This module cost reduction opened up the large power plant market • And is now doing the same for remote markets in the developing world • In other words, all the originally conceived markets are now blossoming…just in different order than originally envisioned
© 2013 SunPower Corporation
38
Looking Forward
© 2013 SunPower Corporation
39
Zooming in on Recent Times Historical
2005
Projected iSupply
Module ASP ($2010/W)
PJC SunShot
3.00
Required by ITC end
2011
$1.12/W 2015 2020
$1.25/W $0.99/W $0.75/W
Cumulative Production (MW) 0.30 1,000
10,000 © 2013 SunPower Corporation
100,000
$0.50/W
1,000,000 40
Zooming in on Recent Times Historical
2005
Projected iSupply
Module ASP ($2010/W)
PJC SunShot
3.00
Required by ITC end
2011
$1.12/W 2015 2020
$1.25/W $0.99/W $0.75/W
Cumulative Production (MW) 0.30 1,000
10,000 © 2013 SunPower Corporation
100,000
$0.50/W
1,000,000 41
Looking Forward Historical
2005
Projected iSupply
Module ASP ($2010/W)
PJC SunShot
3.00
Required by ITC end
2011
$1.12/W 2015 2020 $0.82/W
$1.25/W $0.99/W
Probable price range going forward
$0.75/W
Cumulative Production (MW) 0.30 1,000
10,000 © 2013 SunPower Corporation
100,000
$0.50/W
1,000,000 42
5-Year Market Forecast – Solarbuzz Moving toward PV industry maturity 5-Year Forecast Regional Breakdown: Most Likely GW 60 Latin America & Caribbean
15% CAGR
Middle East & Africa
45
Other APAC & Central Asia 30 Major Asia-Pacific
Europe
15
N. America 0
2012
© 2013 SunPower Corporation
2013
2014
2015
2016
Source: NPD Solarbuzz
43
PV Tomorrow • Cost reductions continue unabated • Ever expanding cost-effective markets and applications emerge • Growth rates moderate into the 15% to 25% range • PV is becoming a mature industry poised to provide an increasing share of pollution-free renewable energy to the world
© 2013 SunPower Corporation
44
Tehnology
© 2013 SunPower Corporation
45
46 © 2013 SunPower Corporation
46
1970s Solar Cell Analysis Approach: Think of a solar cell as a big diode and solve the semiconductor device modeling equations Current = Drift + Diffusion Continuity: dJ/dx = Volume Generation - Volume Recombination Voltage = kT/q ln(nNA/ni2) - Resistance Loss Problem: Not Very Obvious How Cell Converts Light Energy Into Electric Energy • No explicit mention of total photo-generation • Lots of approximations are involved • Hard to grasp three dimensional effects © 2013 SunPower Corporation
47
© 2013 SunPower Corporation
48
Solar Cell Operation Light
Electron-Hole Production
e
Electron Collection
h Hole Collection
© 2013 SunPower Corporation
49
The Hydropower Analogy to PV Conversion
© 2013 SunPower Corporation
50
New Method: 1980s Current = Total Generation - Total Recombination Voltage = Difference in n and p Quasi-Fermi Level = kT/q ln(nnpp/ni2) - Base Resistance Loss
© 2013 SunPower Corporation
51
Solar Cell Operation Step 1: Create electron at higher energy Conduction Band
Bandgap
E ph
Valence Band
Thermalization loss
© 2013 SunPower Corporation
52
Solar Cell Operation Step 2: Transfer electron to wire at high energy (voltage/electrochemical potential/Fermi level) Collection loss
Vout
E ph
Thermalization loss
© 2013 SunPower Corporation
53
Step 3: Deliver Energy to the External Circuit
E ph
Vout
Eout qV E out ph 54 © 2013 SunPower Corporation
54
The goal in a solar cell is to: 1.
Generate as many electron hole pairs as possible from the incident sunlight
2.
Coax as many electrons and holes as possible to go to the correct lead
3.
Do this at as high a voltage as possible
(as high a difference in electromotive force between the leads as possible)
© 2013 SunPower Corporation
55
Recombination Loss • Any outcome of the freed electron and hole other than collection at the proper lead is a loss called “recombination loss.” • This loss can occur in several ways
© 2013 SunPower Corporation
56
Bulk Recombination Loss A) Radiative recombination
© 2013 SunPower Corporation
57
Cracked Standard Efficiency Cells in the Field Conventional Panels Black areas = No Power
SunPower Panel
Likely damaged in installation or from repeated hot/cold temp cycles
Likely damaged from poor soldering process and hot/cold temp cycles.
Left side has broken copper ribbons between a pair of cells.
Even with a crack, all parts of the cell are running (no black).
Conventional panels commonly fail from hot/cold temperature cycles that crack solar cells, solder joints and copper ribbons over time. © 2013 SunPower Corporation
58
Bulk Recombination Loss B) Defect mediated recombination (SRH recombination)
Defect related mid-gap energy level
© 2013 SunPower Corporation
59
Surface and Contact Recombination Loss
© 2013 SunPower Corporation
60
Cell Current
J out J ph J rec © 2013 SunPower Corporation
61
SunPower’s Backside Contact Cell Lightly doped front diffusion • Reduces recombination loss
Backside Mirror • Reduces back light absorption • Causes light trapping P+
Texture + SiO Texture Oxide 2 + ARC
N-type FZ Silicon Silicon – 270 – 240 umum thick thick • reduces bulk recombination N+ P+ N+ P+
Localized Contacts • Reduces contact recombination loss
N+
Passivating SiO2 layer • Reduces top and bottom recombination loss
Backside Gridlines • Eliminates shadowing •Thick, high-coverage metal reduces resistance loss
62 © 2013 SunPower Corporation
62
SunPower Cell Loss Mechanisms 0.5%
0.8% Texture + Oxide
1.0% 0.2%
N-type Silicon – 2700.2% um thick 0.3%
0.2% 1.0%
I2R Loss 0.1%
Limit Cell Efficiency
29.0%
Total Losses
-4.4%
Enabled Cell Efficiency
24.6% 63
© 2013 SunPower Corporation
63
Thank You
© 2013 SunPower Corporation
64
