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3rd Annual IEEE Green Energy

Workshop, 2012 CSULB

Dr. Chaw-Long Chu

November, 19th, 2012

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1. Why Solar Power we need to know…Current Status

2. Source: Solar Spectrum

3. Solar Power Application:

3A Water Heater--- a device has been used for

more than 100 years.

3B Solar Cell--- In recent 40 years, systematic R/D

on solar power has generated sophisticated

devices to convert light to electricity

4. Discussion

Agenda

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1. Global warming and extra CO2 generation

2. Nuclear and coal plants are not favored, petroleum price is high,

natural gas is cheap, but still generate CO2. Hydraulic, geothermal

have geography limitation, wind power has advantage on lower

cost but not so dependable and suitable for residential area.

3. New emerging economic regions consume more energy (Asia,

Africa, middle East, and South America)

4. Multi Government sponsored incentive programs to encourage

Solar Electricity

5. Due to production improvement, significant price reduction on

Solar module; solar electricity is cheaper than new nuclear energy

plant and is approaching grid parity.

6. Global Installed Solar Module increased from 71.5 MW (1995) to

30 GW (2012)

7. It is a convenient and low cost emergency relief power.

Part 1. Why Solar Power and What is the status

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Halloween, 2012 will be a horrible night for so many northeast

residents…Storm, Flood, Fire, and Power Outage…….

Trick or Treat!

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Where is Electricity?!

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Hurricane Sandy Power Outage Map (11/1/2012)

Where is electricity?

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11/2/2012 Jersey City residents lined up for gas supply to operate

house generator, it took 3 hours to wait…. Where is electricity?

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New Yorkers were waiting for gas; day and night, no

electricity to operate oil pump and shut down most

gas stations. Where is electricity? (11/3/2012)

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CO2 reach

tipping point

Higher See

level

Higher See

water

temperature

Matched by

Cold storm

Hurricane

Sandy Moved

upward

Form a Perfect

Storm to attack

NE USA

Flood

Power

Plant

Explosion

Fire

Power

Outage

We need green

energy to reduce

CO2 emission to

save the earth

KYOTO PROTOCOL TO THE UNITED NATIONS FRAMEWORK

CONVENTION ON CLIMATE CHANGE

UNITED NATIONS 1998

How about nuclear energy? It

won’t generate CO2.

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San Onofre Nuclear Generating Station

(~ 50 miles from CSULB)

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Diablo Canyon Nuclear Power Plant (San Louis Obispo, CA)

1927, Lompco Earthquake (magnitude 7.1) was 2.5 miles

offshore from the NPP and Shoreline Fault is 1 mile from NPP

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Worldwide Solar PV Growth (GW)

30.0

On 2012, USA will install more than 2.5 GW (This is larger

than the summation from 2000 to 2010)

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Annual Value of Renewable Energy Installation

(2012 and after is estimation)

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USA Annual Installed Grid-Connected PV Capacity (2002-2011)

If 1 watt charges $2.5, $4.61 billion was spent in 2011 by USA.

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Why solar power knowledge is important

• Solar energy will be more popular in coming 20 years

• Solar energy and related business will hire more

employees (current employee number ~ 100,000 in USA)

• Solar power will be popular in emerging economic area

• More solar module will be fabricated in USA for domestic

supply (international?)

• Most solar heat is used for hot water generation, it

indirectly reduced the consumption of electricity and

natural gas

• Solar electricity is directly used to power daily life.

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Part 2, Solar Spectrum

Solar Power is characterized by its spectrum, the intensity is affected by the distance (solid angle) and the materials existing between the light source and the ‘detecting spot’;

Outside but close to the atmosphere of earth, AM0 (air mass zero) -

135.3 mW/cm2, on the surface of earth (sunny) AM1.5 – 100 mW/cm2 (average). Both intensity and spectrum are affected by atmosphere and water vapor.

Photon energy at specific wavelength (λi) = Σ niһc/λi (ni: number of photon, һ: Planck's constant = 6.626068 × 10-34 m2 kg /s, c: light velocity)

Direct industry application of solar energy: to warm up any media by absorbing the solar spectrum

In-Direct industry application of solar energy: to produce electron by absorbed photon (ideal case: one photon to generate one electron)

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135.3 mW/cm2

100.0 mW/cm2

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Solar Heater: Supply Hot Water

To save heating energy (electricity or gas)

• 9 million water heaters (~USD 450/unit) sold in USA, total revenue is about 4 billion/y.

• Natural Gas is cheap in USA, Canada, Russia. But, it is very expensive in Japan, most Asia area, and Europe. Solar water heater system could also warm up house.

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Advertisement of Solar Water Heater (1902)

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Flat Plate Solar Water Heater for

Industrial or Commercial Areas

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Solar Heater for Residential Area

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Tube Shape Solar Water Heater

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Minimum Design Criteria of solar hot water system

1. The temperature and quantity of hot water

required from the system.

2. Changes in ambient temperature and solar

radiation between summer/winter and day/night.

3. The possibility of the potable water or collector

fluid overheating or freezing.

4. Potential application: house warming

5. Other requirements have to be satisfied:

1. Building code… it may vary from city to city,

2. Geographic limitation

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Classification of solar hot water systems

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Classification of solar hot water systems

• Direct system: Use solar heat to warm the water, no

protection design

• Indirect system: Use Heat Transfer fluid to transfer

the solar heat to water, overheat and anti-freezing

protection is provided (cost higher)

• Passive system: Use the heat as convection driven

force to circulate the water and heating fluid (for both

Direct or Indirect system)

• Active system: Use pump to circulate the water and

heating fluid (higher cost, but highest efficiency)

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1. Heating efficiency is wavelength dependent and it varies from liquid to liquid

2. The solar power could be properly shared by Solar cell and water heater.

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Engineering/Business Concerns of

Solar hot water system Design

1. Reliability of components

2. Water source criteria (hard or soft water)

3. Heating rate and solar spectrum

4. Average water temperature: >500C.

5. Criteria for heat transfer fluid selection

6. Weight limitation for roof top installation

7. Performance survey and user expectation

8. How many major vendors to provide the heater, globally and domestically

9. How to design a house warming system using this design

10. Discussion

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Global Installation of Solar hot water system

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Break Time

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Solar Spectrum Definition

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135.3 mW/cm2

100.0 mW/cm2

GaP

Si ZnS

Ge

ZnO

GaAs

CdSe

CdTe

InP

GaSb

InAs(3.44x10-6)

InSb(7.29x10-6)

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Band Gap and Lattice Constant

of II-VI, III-V, and IV-IV Compounds

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Point Focus Parabolic Dish

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Concentrated Photovoltaic Panel (CPV)

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Single axis trackers with roughly 20 degree tilt at

Nellis Air Force Base in Nevada, USA

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What is solar cell?

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• A device to convert light to electricity

– Any material or material combination to convert light

or EM-wave to energized electrons (engineering part)

and used for operation of motor or equivalent

machines (business part)

– Material selection, purification, processing

(solid, liquid, gas, vacuum….)

– Low resistivity conducting system to efficiently carry

the electrons

– Quantitatively defined operation

Suggestive definition of solar cell

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Classification of Solar Cell

• Crystalline Solar Cell: Si, Triple Junction (GaInP/GaAs/Ge,

GaInP/GaAs/InGaAs)

• Thin Film Solar Cell: Amorphous Si, CIGS, CdTe

• Dye Solar Cell, Organic Solar Cell (R&D only)

• Concentrator Solar Cell: 500 x ~ 1000x (GaInP/GaAs/Ge)

• Vacuum?

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Criteria to start PV Business

• Pre-Selection Criteria (Finance, Marketing, and Technology):

– Richness of material resource and cost of purification

– Fabrication cost, market demand, and competition

– Potential of solar cell/solar module quality improvement

– Investment and Incentive opportunities

– Patent Issues

( money, marketing, engineering, equipment, labor, law)

• PV Industry includes – Solar cell (materials, fabrication and test equipment, package)

– Solar module (materials, fabrication and test equipment, package)

– Solar cell/module environment evaluation

– Solar module installation, maintenance, and recycle

– Operation Insurance

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Solar Cell/Module Design Principle

• What is customer’s expectation

– Dependability, economy, maintenance availability

• Design for successful field operation

– Reliability

– Minimum environment contamination

– Operation flexibility for both regular operation and emergency

relief

– Functional enhancement

– User friendly

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Designs of Solar Cell and Solar Panel

• Solar Cell Structure: p/n junction, p- and n- contacts, AR-Coating

• Solar Module Structure: Solar Cell, Rear Side Supporting, Front Side

protection, Adhesive, Interconnection

• Design Guidance: Efficiency, Cost, Weight, Reliability (20 years field

operation)

• Fabrication Concerns: Yield, Operation Cost (including contamination

control)

• Tooling Used for Cell Design (light intensity dependent)

– Cell parameters: Voc, Isc, FF, Eff

• Voc determined by solar cell material (band gap), junction

preparation, cell process determined passivation effect, metal

contact resistance and series resistance

• Isc determined by Solar Cell Material (minority carrier life time),

junction preparation process, front and rear contact, passivation,

AR-coating

• FF (the squareness of diode IV curve), determined by solar cell

material (direct or indirect band gap), p/n junction preparation,

contact resistance and series resistance

• Eff (efficiency) = (Voc * Isc * FF)/(Cell Area * Light Intensity)

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– Software used for Solar Cell Design • PC-1D, essential solar cell parameters estimation (Voc, Isc,

Eff)

• AR-Coating layer thickness optimization (Isc)

• No software available to calculate FF

– Equipment used for Solar Cell Testing • Minority Carrier Lifetime – Hall Effect, EBIC (SEM)

• Band Gap Measurement – Photoluminescence

• Sheet Resistance Measurement (Bulk material) – 4-point probe, spreading resistance

• Doping Profile -- Back Scattering Effect, SIMS, Auger, ECV

• Ohm Meter – Resistance Measurement

• Solar Simulator – Voc, Isc, FF, and EFF

• Quantum Efficiency (or spectral response) – Isc Estimation

• Solar Radiometer – Solar Simulator Spectrum Calibration

• X-Ray Diffractometer – Lattice size determination of Epi-layer

Designs of Solar Cell and Solar Panel

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Single Junction Solar Cell and Future

• Ge solar cell to begin with: low bandgap, low efficiency, high cost material (failed)

• Si solar cell is a successful example: wider bandgap (1.1 eV), higher efficiency (AM1.5, ~24.7%, 1989), low cost material, most popular global installation solar module (>85%). It will be the main stream product in PV industry.

– Concerns on weight, efficiency, and application for special environments, R&D on multi-junction solar cell started.

– To reduce the cost of solar cell/module; thin film, dye, organic solar cells started

• As solar module popular; retired module recycle and environment contamination and other supporting factors, such as house insurance, mortgage, tax will be required

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Essential Solar Cell Parameters

• Independent Parameters: – Voc = kt/q*ln(IL/I0 + 1) (open circuit voltage)

• K: Boltzmann’s constant

• t: absolute temperature (0K)

• q: electronic charge

• IL: light generated current (Isc)

• I0: diode saturation current (determined by material and related process)

– Isc = Σ QE(λ)*ni(λ)*Δλ = QE(λ)*ni(λ)*dλ

• Derivative parameters: – Curve Factor (FF) = (Vmax*Imax)/(Voc*Isc)

– Cell Efficiency (η) = (Vmax *Imax)/(Power Intensity * Cell area)

• Dominating factors to Voc, Isc, FF – Material characteristics (Band Gap, Indirect/Direct, crystal

defects, impurities)

– Solar Cell design

– Materials and procedures used for process

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Silicon Solar Cell (single Junction) Spectral Response

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Spectral Response of GaInP/GaAs/Ge

Triple Junction Solar Cell

0.0

0.2

0.4

0.6

0.8

1.0

1.2

300 600 900 1200 1500 1800

Wavelength (nm)

Sp

ec

tra

l R

es

po

ns

e (

A/W

-cm

2)

Top Junction (15.88 mA/cm2)

Middle Junction (16.19 mA/cm2)

Bottom Junction (27.67 mA/cm2)

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How to Test Solar Cell

• Light Source Calibration (multi-artificial light

sources used to simulate the sun light)

– Uniformity of illuminated area

– Single solar cell test

– Solar module test (LAPSS-pulse light source)

• Standard Cell Preparation

– Balloon flight (120000 ft, AM0)

– Jet flight (60000 ft, <AM0)

– Spectral response or Quantum efficiency measurement

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Schematic Drawing of Solar Cell Test Set Up

Concerns of Test:

Light Uniformity and Measurement Accuracy

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1. Steady Light Simulator

2. Large Area Pulse Solar Simulator

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• GaInP/GaAs/InGaAs (MOCVD)

Block Diagram of Major Solar Cell Process

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Equipment Used for Solar Cell Fabrication

• Si solar cell

– Si ingot grower, Wire Dicing machine (Wire saw and Disc Saw),

Junction Diffusion Machine, Si3N4 CVD, Screen Printing Machine,

Annealing Tube, AM 1.5 Simulator/Testing Setup, Microscope

• Thin Film Cell

– Substrate Preparation (Glass, Metal Sheet, or Kapton Sheet),

Sputtering or Co-Evaporation Machine, Transparent Conducting

Contact Sputtering Machine, Collector-Grid Screen Printer, Cell

Interconnector, AM 1.5 Simulator/Testing Setup

• GaInP/GaAs/Ge

– Ge Ingot Grower, Wire Dicing machine (Wire saw and Disc Saw),

Junction Generation Machine (MOCVD), Front and Rear Metal Grid

Evaporator, AR-Coating Evaporator, Annealing Chamber, Cell Dicing

Saw, Solar Simulator/Testing Setup, Microscope

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GE Flexible CIGS Module

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Triple Junction Solar Cell (4cm x 8cm) Includes

Monolithic Bypass Diode

Emitter: N - GaInP2

Window: N - AlInP2

Base: P - GaInP2

TC BSF

P++ -TD

N++-TD

MC Window

Emitter: N - GaAs

Base: P- GaAs

Nucleation / Buffer/MCBSF

Base/Substrate: P -Ge

P-Contact

N++ -TD

P++ - TD

Emitter: N - Ge

Top Cell

Middle Cell

Bottom Cell

Top Tunnel Diode

Bottom Tunnel Diode

P- Diode

N- Diode

Ju

mp

er

N-Diode Contact

P- Cell

Contact

Integral Bypass Diode

Diode/cell Contact

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Module Cell (Lab)

Dye-sensitized Solar Cells 3 – 5% (INAP) 11%

Single Crystalline Silicon 22.7% (UNSW) 24.7% (UNSW, PERL)

Amorphous Silicon

(Multijunction)

10.4% 13.2%

Polycrystalline Silicon 14 -18% 20.3% (FhG-ISE)

HIT Cell (α-Si/c-Si) 18.4% (Sanyo) 21% (Sanyo)

Cadmium Telluride (CdTe) 8 – 10% (First

Solar)

16.5% (NREL)

Copper Indium Gallium

Selenium (CIGS)

13.0% (TSMC) 20.3% (Miasolé)

InP N/A 21.9% (Spire)

AlInGaP/InGaAs/InGaAs (IMM) N/A 33.9% (Emcore)

GaInP/GaAs/Ge (~250X) N/A 40.7% (Boeing)

GaInP/GaAs/Ge (~450X) N/A 41.6% (Boeing)

Solar Cell and PV Module Efficiency (AM 1.5)

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Effort on PV Industry

• Reduce the fabrication cost

– Silicon material reduction (cost effective?)

– Enhance the production scale or business merge (STP, the

world largest company is facing financial problem, Schott Solar

stopped the cell fabrication in USA)

• More aggressive government incentive programs

required

• Multi-functional Solar module Development and Existing

Module Flexibility Improvement

• Encourage BIPV design (Many German Designs could

be considered)

• What is your contribution? How to approach?

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20 Micron Thick Si Cell

Proton radiation to lift off a thin layer Si

for solar cell process (existing Si cell is

500 um thick).

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What is your contribution? How to approach?

• To be an engineer as you, what will be

your contribution to this promising

industry?

• New design? New Material? New business

plan?

• In addition the solar car, could school and

industry support some student activities on

solar product design?

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