1 3 rd Annual IEEE Green Energy Workshop, 2012 CSULB Dr. Chaw-Long Chu November, 19 th , 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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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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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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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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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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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
• 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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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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Single axis trackers with roughly 20 degree tilt at
Nellis Air Force Base in Nevada, USA
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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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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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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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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?