PV: The Path from Niche to Mainstream Source of Clean Energy Dick Swanson

Outline History of PV PV Market Dynamics PV Applications Satellites to Mainstream (almost) PV Market Dynamics Growing fast PV Applications Grid-connected distributed generation How Solar Cells Work It’s simple

Sun Day, May 5, 1978, SERI I can’t believe he said that. The 1970s oil crises sparked interest in PV as a terrestrial power source I can’t believe he said that. Don’t worry Mr. President, solar will be economical in 5 years! Sun Day, May 5, 1978, SERI

Situation in 1975 Wafered Silicon Process $300/kg 3 inches in diameter Polysilicon Wafer Solar Cell Solar Module Systems Ingot $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 Concentrators Remote Habitation Solar Farms

What Actually Happened Wafered Silicon Emerges as the Dominant Technology Breakthrough Needed DOE Wafered Silicon Program Thin Films Concentrators Residential/ Commercial Grid connected Remote Habitation Solar Farms

PV Market Growth 95% Wafered Silicon

Historical PV Landscape Era Main Players Characteristics 1975-1885 Small Start-ups Solar Technology International → ARCO Solar Power Corp. → Exxon Solarex → BP Tyco → Mobile Rapid Growth Development of technology paradigm 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 Sharp Sanyo Kyocera Emergence of residential roof market Improved manufacturing 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

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 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 1880 1860 500 1000 1500 1900 1920 1940 1960 1980 2000 2020 2040 2060 Surprise Geothermal Solar Biomass Wind Nuclear Hydro Gas Oil &NGL Coal Trad. Bio. Exajoules Source: Shell, The Evolution of the World’s Energy Systems, 1995 Renewable Energy Drivers: Climate Change Fossil Fuel Depletion Energy Security

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

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 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 PowerLight SunTileTM

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

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

The Hydropower Analogy to PV Conversion Energy as light H2O

Solar Cell Operation Light Electron Collection e Electron-Hole Production h Hole Collection

Step 1: Create electron at higher energy Solar Cell Operation Step 1: Create electron at higher energy Conduction Band Bandgap Valence Band Thermalization loss

Step 2: Transfer electron to wire at high energy Solar Cell Operation Step 2: Transfer electron to wire at high energy (voltage/electrochemical potential/Fermi level) Collection loss Thermalization loss

Step 3: Deliver Energy to the External Circuit

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

Bulk Recombination Loss A) Radiative recombination

Bulk Recombination Loss B) Defect mediated recombination (SRH recombination) Defect related mid-gap energy level

Surface and Contact Recombination Loss

Cell Current

Cell Voltage

Generic Solar Cell Loss Mechanisms Reflection Loss 1.8% I2R Loss 0.4% 0.4% 0.3% Recombination Losses 1.54% 3.8% 2.0% 1.4% Back Light Absorption 2.6% Limit Cell Efficiency 29.0% Total Losses -14.3% Generic Cell Efficiency 14.7%

SunPower’s Backside Contact Cell N-type Silicon – 270 um thick N-type FZ Silicon – 240 um thick reduces bulk recombination P+ N+ Texture Texture + Oxide Texture + SiO2 + ARC Backside Gridlines Eliminates shadowing Thick, high-coverage metal reduces resistance loss Lightly doped front diffusion Reduces recombination loss Localized Contacts Reduces contact recombination loss Backside Mirror Reduces back light absorption Causes light trapping Passivating SiO2 layer Reduces top and bottom recombination loss

SunPower Cell Loss Mechanisms Texture + Oxide 0.5% 0.8% Texture N-type Silicon – 270 um thick 1.0% 0.2% 0.2% 0.2% 0.3% 1.0% I2R Loss 0.1% Limit Cell Efficiency 29.0% Total Losses -4.4% Enabled Cell Efficiency 24.6%