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

Sun Day, May 5, 1978, SERI

Don’t worry Mr. President, solar will be economical in 5 years!

I can’t believe he said that.

The 1970s oil crises sparked interest in PV as a terrestrial power source

Situation in 1975

$300/kg

3 inches in diameter

Sawn one at a time

0.5 watts each

$100/watt

$200/watt

Wafered Silicon Process

Polysilicon Wafer Solar Cell Solar Module SystemsIngot

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

Thin Films Concentrators

Remote Habitation Solar Farms

DOEWaferedSilicon

Program

Residential/Commercial

Grid connected

PV Market Growth

95% Wafered Silicon

1

10

100

1000

10000

1975 1980 1985 1990 1995 2000 2005 2010

Year

MW

/yr

Rapid Growth in Subsidized,Grid-Connected Market.41% CAGR

Early period of rapid innovationand growth

Historical PV LandscapeEra 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 LandscapeEra 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

0%

5%

10%

15%

20%

25%

30%

94 95 96 97 98 99 00 01 02 03 04 05 06

Ma

rke

t Sh

are

Sharp

BP

Kyocera

Shell /SolarWorld

RWE

Sanyo

Mitsubishi

Q-cells

SunTech

SunPower

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

-100

0

100

200

300

400

500

600

700

2004 2005 2006 2007 F

Mill

ion

$

RevenueNet Income

2007 forecast non-GAAP net income as presented in Q4 conference call

Distributed Generation Strategies are Shaping the Future

Residential Retrofit

New Production Homes Commercial & Public

Power Plants

PV Applications

Shell Sustained Growth Scenario

18801860

500

0

1000

1500

1900 1920 1940 1960 1980 2000 2020 2040 2060

Surprise

Geothermal

Solar

Biomass

Wind

Nuclear

Hydro

Gas

Oil &NGL

Coal

Trad. Bio.

Exa

jou

les

Source: Shell, The Evolution of the World’s Energy Systems, 1995

Renewable Energy Drivers:•Climate Change•Fossil Fuel Depletion•Energy Security

Polysilicon

Wafer Solar Cell Solar Panel SystemIngotPolysilicon

Value Chain Cost Distribution

20%30%

50%

2006 US Solar System Cost Allocation by Category

2006 2016

Downstream Savings (50%)

Panel Savings (50%)

Cell Savings (25%)

Silicon Savings (50%)

Conversion Efficiency (15%)

Downstream

Panel

Cell

Silicon

60% Drop in System Cost

50%+ cost reduction from CA system cost is achievable50%+ cost reduction from CA system cost is achievable

SAMPLE APPLICATIONS

Commercial Roofs New Production Homes

Commercial Ground Power Plants

Systems Business Segment

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

32

Factory Assembled Unitary Product Reduces CostTracking improves Energy Delivery

15 MW PlantNellis AFB

Television for 1st Time

Energy from the Desert, Kosuke Kurokawa, ed., James & James, London, 2003.

•Advanced Crystalline?•Thin film?•Concentrating PV?

The Terrawatt Future

35

How Solar Cells Work

36

H 2O

Energy as light

The Hydropower Analogy to PV Conversion

37

Solar Cell Operation

e

h

Electron-HoleProduction

Electron Collection

Hole Collection

Light

38

Solar Cell OperationStep 1: Create electron at higher energy

phE

Thermalization loss

Conduction Band

Valence Band

Bandgap

39

Solar Cell OperationStep 2: Transfer electron to wire at high energy(voltage/electrochemical potential/Fermi level)

phE outV

Thermalization loss

Collection loss

40

Step 3: Deliver Energy to the External Circuit

phE outV

phoutout EqVE

41

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

42

Bulk Recombination LossA) Radiative recombination

43

Bulk Recombination LossB) Defect mediated recombination

(SRH recombination)

Defect related mid-gap energy level

44

Surface and Contact Recombination Loss

45

Cell Current

recphout JJJ

46

Cell Voltage

outVn

p

npoutV

47

1.8%

0.4%

1.4%

1.54% 3.8%

2.6%

2.0%

0.4%

0.3%

I2R LossReflection Loss

Generic Solar Cell Loss Mechanisms

RecombinationLosses

Back LightAbsorption

Limit Cell Efficiency 29.0%

Total Losses -14.3%

Generic Cell Efficiency

14.7%

48

SunPower’s Backside Contact Cell

PassivatingSiO2 layer• Reduces top and bottom recombination loss

N-type Silicon – 270 um thickN-type FZ Silicon – 240 um thick• reduces bulk recombination

P+ P+ P+N+ N+ N+

TextureTexture + OxideTexture + SiO2 + ARC

Backside Gridlines• Eliminates shadowing•Thick, high-coveragemetal reduces resistance loss

Lightly doped front diffusion• Reduces recombinationloss

Localized Contacts• Reduces contact recombination loss

Backside Mirror• Reduces backlight absorption• Causes light trapping

49

SunPower Cell Loss Mechanisms

N-type Silicon – 270 um thick

TextureTexture + Oxide

0.5%

0.2%

0.8%

1.0%

1.0%

0.2%

0.3%0.2%

I2R Loss0.1%

Limit Cell Efficiency 29.0%

Total Losses -4.4%

Enabled Cell Efficiency 24.6%