PV: The Path from Niche to Mainstream
Source of Clean Energy
Dick Swanson
Outline
• History of PV
– Satellites to Mainstream (almost)
• PV Market Dynamics
– Growing fast
• PV Applications
– Grid-connected distributed generation
• How Solar Cells Work
– It’s simple
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
Situation in 1975
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
1975 View
Wafered Silicon Hopelessly Too Expensive
Breakthrough Needed
Thin Films
Remote Habitation
Concentrators
Solar Farms
What Actually Happened
Wafered Silicon Emerges as the Dominant Technology
Breakthrough Needed
Thin Films
Remote Habitation
Concentrators
Solar Farms
DOE
Wafered
Silicon
Program
Residential/
Commercial
Grid connected
PV Market Growth
10000
Rapid Growth in Subsidized,
Grid-Connected Market.
41% CAGR
MW/yr
1000
95% Wafered Silicon
100
10
Early period of rapid innovation
and growth
1
1975
1980
1985
1990
1995
Year
2000
2005
2010
Historical PV Landscape
Era
Main Players
Characteristics
1975-1885
Small Start-ups
•Rapid Growth
•Development of
technology
paradigm
•Solar Technology
International → ARCO
•Solar Power Corp. → Exxon
•Solarex → BP
•Tyco → Mobile
1985-1995
Oil Companies
•ARCO
•Exxon
•BP
•Mobile
•Shell
•Moderate growth
•Search for market
•Massive losses
•Few start-ups
Historical PV Landscape
Era
Main Players
Characteristics
1995 - 2005
Japanese Companies
•Emergence of
residential roof
market
•Improved
manufacturing
•Sharp
•Sanyo
•Kyocera
2000 -
Entrepreneurial Co’s
•Q-Cells (Germany)
•Scanwafer (Norway)
•Solar World (Germany)
•Evergreen (US)
•SunPower (US)
•Suntech (China)
•MiaSole (US)
•Explosive growth
•Profitability
•Technology
evolution
Market Share Trends
30%
Sharp
BP
25%
Market Share
Kyocera
20%
Shell /
SolarWorld
RWE
15%
Sanyo
Mitsubishi
10%
Q-cells
5%
SunTech
SunPower
0%
94
95
96
97
98
99
00
01
02
03
04
05
06
Recent Industry Milestones
• 1999
1 GW accumulated module production
• 2001
More square inches of silicon used than
in entire microelectronics industry
• 2004
1 GW production during year
• 2006
More tons of silicon used than in
microelectronics
History of SunPower
• Founded in 1985-9 to
commercialize technology
developed at Stanford
• Utility-scale solar dish application
• High performance required
• All-back-contact cell developed
• NASA & Honda early customers
• Great technology, high cost
• Merged with Cypress
Semiconductor in 2001
• Went public in 2005
SunPower Growth
700
600
Revenue
Net Income
Million $
500
400
300
200
100
0
-100
2004
2005
2006
2007 F
2007 forecast non-GAAP net income as presented in Q4 conference call
Distributed Generation Strategies
are Shaping the Future
PV Applications
Residential Retrofit
Power Plants
New Production Homes
Commercial & Public
Shell Sustained
Growth Scenario
1500
Surprise
Exajoules
1000
Geothermal
Renewable Energy Drivers:
•Climate Change
•Fossil Fuel Depletion
•Energy Security
Solar
Biomass
Wind
Nuclear
Hydro
500
Gas
Oil &NGL
Coal
Trad. Bio.
0
1860
1880
1900
1920
1940
1960
1980
Source: Shell, The Evolution of the World’s Energy Systems, 1995
2000
2020
2040
2060
Value Chain Cost Distribution
Polysilicon
Polysilicon
Ingot
Wafer
Solar Cell
Solar Panel
System
2006 US Solar System Cost Allocation by Category
50%
30%
20%
50%+ cost reduction from CA system cost is achievable
60% Drop in System Cost
Downstream Savings (50%)
Panel Savings (50%)
Cell Savings (25%)
Silicon Savings (50%)
Conversion Efficiency (15%)
Downstream
Panel
Cell
Silicon
2006
2016
SAMPLE APPLICATIONS
Systems Business Segment
Commercial Roofs
New Production Homes
Commercial Ground
Power Plants
Santa Barbara, California – 12.6 kW
Walldürn, Germany – 8.0 kW
Osaka, Japan – 5 kW
Walnut Creek, CA
New York City – 27
kW
Los Altos Hills, California – 35 kW
Market Opportunity for PV Roof Tiles
PowerLight SunTileTM
• Product enables
homeowner to integrate
PV into the roof of the
building:
– Lower profile than traditional
modules means better
aesthetics
– Potential cost savings over
traditional PV system
– Traditionally targeted at new
home construction
New York City – 27 kW
Microsoft Silicon Valley Campus
Arnstein, Germany – 12 MW
Factory Assembled Unitary Product Reduces Cost
Tracking improves Energy Delivery
15 MW Plant
Nellis AFB
32
Television for 1st Time
The Terrawatt Future
•Advanced Crystalline?
•Thin film?
•Concentrating PV?
Energy from the Desert, Kosuke Kurokawa, ed., James & James, London, 2003.
How Solar Cells Work
35
The Hydropower Analogy to PV Conversion
36
Solar Cell Operation
Light
Electron-Hole
Production
e
Electron Collection
h
Hole Collection
37
Solar Cell Operation
Step 1: Create electron at higher energy
Conduction Band
Bandgap
E ph
Valence Band
Thermalization loss
38
Solar Cell Operation
Step 2: Transfer electron to wire at high energy
(voltage/electrochemical potential/Fermi level)
Collection loss
Vout
E ph
Thermalization loss
39
Step 3: Deliver Energy to the External Circuit
E ph
Vout
Eout  qVout  E ph 40
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
41
Bulk Recombination Loss
A) Radiative recombination
42
Bulk Recombination Loss
B) Defect mediated recombination
(SRH recombination)
Defect related mid-gap energy level
43
Surface and Contact Recombination Loss
44
Cell Current
J out  J ph  J rec
45
Cell Voltage
n
p
Vout
Vout   p  n
46
Generic Solar Cell Loss
Mechanisms
Reflection Loss
I2R Loss
1.8%
0.4%
0.4%
0.3%
1.54%
3.8%
Recombination
Losses
2.0%
1.4% Back Light
Absorption
Limit Cell Efficiency
2.6%
29.0%
Total Losses
-14.3%
Generic Cell
Efficiency
14.7%
47
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
48
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%
49