Advances in Concentrating Solar Power Collectors

8/10/2019 Advances in Concentrating Solar Power Collectors

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Advances in Concentrating Solar PowerCollectors: Mirrors and Solar Selective

Coatings

C.E. Kennedy1National Renewable Energy Laboratory (NREL), 1617 Cole Boulevard, M/S 3321, Golden, CO

80401-3393, 303-384-6272, 303-384-6103 (fax), [email protected]

AIMCALScottsdale, AZ

October 10, 2007

NREL/PR-550-43695

Presented at the Association of Industrial Metallizers, Coaters and Laminators (AIMCAL) 2007 Fall Technical Conference,

21st International Vacuum Web Coating Conference held October 7-10, 2007 in Scottsdale

Arizona


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Outline

Solar Market Potential Solar Reflectors Solar Selective Coating

Conclusion


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Concentrating Solar Power TechnologiesPower TowerParabolic Trough Dish-Stirling

CPV Heliostat CPV Winston Collector

100kW LCPV Tracking

Solar concentrationallows tailored design

approachesCompact Linear

Fresnel Reflector

(CLFR)
http://www.jxcrystals.com/SolarPV.htmhttp://www.jxcrystals.com/SolarPV.htmhttp://www.jxcrystals.com/SolarPV.htmhttp://www.jxcrystals.com/SolarPV.htm


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DOE & WGA determined feasibility of1000MW in SW

Southwest Solar Resources


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Transmission Overlay


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Eliminate locations

< 6.75 kwh/m2/day



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Eliminate locations

< 6.75 kwh/m2/day


Exclude environmentally

sensitive lands, major

urban areas, and water

features


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Eliminate locations

< 6.75 kwh/m2/day


Exclude environmentally

sensitive lands, major

urban areas, and water

features

Remove land areas >

(3%) & 1% average

land slope

Remove land


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SW Solar Energy Potential

The table and map represent land that has no primary use today,

exclude land with slope > 1%,


10/69

Renewable Portfolio Standards

State RPS mandates successfully jump-starting desirable growth

LA

ID

UT

WY

AL

SC

TN

KY

INOH

NC

SD

KS

NE

AR

MS

OK

ND

MI

GA

AK

VAWV

DE: 20%by 2019

MD: 7.5% by 2019

VT: 10%by 2013*

NH: 16%

by 2025

MT: 15%

by 2015

CO: 20%by 2020

NV: 20%

by 2015

TX: 5,880 MWby 2015

NM: 20%

by 2020

AZ: 15%by 2025

CA:20%by 2010

33% by 2020

MN: 25% by 2025;

Xcel: 30% by 2020

IA:105 MW

WI: 10%

by 2015

IL: 25%by 2025

ME: 10%by 2017

NY: 24%by 2013

PA: 18%by 2020

WA: 15%by 2020

DC: 11%by 2022

NJ: 22.5%by 2021

CT: 23%by 2020

RI: 15%by 2020

MA: 4% new by 2009

FL

VA: 12%by 2022*

MO:11%by

2020*

HI: 20%by 2020

OR: 25%by 2025

NC: 12.5% by 2021

* Voluntary Goals


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Market for Solar in US SW

California: 500 MW by 2010 8,000 MW by 2020 peaking demand

354 MW SEGS trough plants in CA 2 PPAs for 1.75 GW Dish Stirling plants in Southern

CA 500 MW (option to expand to 850 MW) Mojave Desert 300 MW (two options to expand to 900 MW) Imperial

Valley 553 MW PPA signed PGE, CA 300 MW PGE, CA Pending contractual announcement 175 MW PGE/FPL CLFR (commitment) 200 MW FPL CLFR (commitment) 1000 MW PGE (commitment) probably in CA

Arizona: 2,000 MW 1 MW trough plant in AZ

Nevada: 1,500 MW 64 MW trough project in NV New Mexico: TBD

West Texas: 1,000 + MW Colorado:500 MW after 2010

Numerous RFPs in CO, TX, AZ,

Florida: 300 MW CLFR (FPL Commitment) 10 MW initial (w/ option to expand to 300 MW) 500 MW FPL (commitment) in CA, FL, & other states

10,000 MW of CSP by 2020


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International CSP ProjectDevelopments

1000MW CSP USA 30MW ISCCS Mexico

500MW CSP Spain

30MW ISCCS Morocco 30MW ISCCS Egypt 250MW SEGS Israel

400MW ISCCS Iraq 30MW ISCCS Algeria

100MW CSP South Africa

720 kW CPV Australia 154MW CPV Australia


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Parabolic Trough Plants

Source: KJC Operating Company


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Parabolic TroughCost Reduction Scenario

0.236

0.162

0.143

0.1200.110

0.1020.094

0.00

0.05

0.10

0.15

0.20

0.25

1 - 50 MW

Plant (NV)

1 - 100 MW

Plant (CA)

4 x 100MW

Solar Park

Advanced

Technology

@ 1000 MWe

Deployment

@ 2000 MWe

Deployment

@ 4000 MWe

Deployment

Nominal(LCO

E)

Location: Barstow, CA

Incentives: Current California

Deployment Assumes:

- 90% PR in Solar Field

- 95% PR in Power Plant

Competitive Range

CA MPR Range

Gas Price: $6 /MMBtu

Future

Good SolarResource Site

AdvancedTechnology

Learning &

Competition Increasing Plant

Size

AlternativeFinancing

Tax Neutrality forSolar Fuels

Tax Incentives


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Goals for Improved

Optical Materials

>90% Specular reflectanceinto a 4-mrad cone angle Unofficially 95%

10 - 30 year lifetime Unofficially 30 y

Manufacturing cost$10.76/m2 ($1/ft2)

1992 Cost Goal

Adjusted for inflation to$15.46/m2 ($1.44/ft2)

Structural (self-supporting)mirror to $27/m2 ($2.50/ft2)


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Technical Approach Samples supplied by:

Industry

Subcontracts Developed in-house

Optical Characterization: Perkin-Elmer (PE) Lambda 9 & 900 UV-VIS-NIR

spectrophotometers (250-2500 nm) w/ integratingspheres

PE IR 883 IR spectrophotometer (2.5-50 m)

Devices & Services (D&S) Field PortableSpecular Reflectometer (7, 15, & 25-mrad coneangle at 660 nm)

Outdoor (OET) &Accelerated ExposureTesting (AET):

Atlas Ci65 & Ci5000 WeatherOmeters (WOM) (1X& 2X Xenon Arc/60C/60%RH)

QPanel QUV (UVA 340@ 290- 340 nm/ 4 h UV at40 / 4 h dark at 100%RH)

1.0 & 1.4 kW Solar Simulators (SS) ( 5X Xenon300-500 nm. 1.0-kW SS 80C/ 80% RH,1.4 kW-SS-4 quadrants 2 RH &T, light /dark)

BlueM damp heat (85C/85%RH/dark)

3 meterologically monitored sites at Golden,Colorado (NREL), Miami, Florida (FLA), and

Phoenix, Arizona (APS)

3

2

1

3

2

1


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Reflective Layer (wet-silver)

Low-iron Glass (4- or 5-mm thick)

Acrylic (w/ high UV stability)

2nd coat Paint Layer (heavy Pb)

(1% Pb)

1st coat Paint Layer (heavy Pb)

(2.5% Pb)

Parabolic Trough Glass MirrorArchitecture

Back Layer (Cu)

Thick glass is slumped

Three-coat paint system designed for outdoor applicationsFlabeg mirrors still use Cu back protection

Mactac adhesiveCeramic ad


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Low-iron Glass (4- or 5-mm thick)

Acrylic (w/ high UV stability)

2nd coat Paint Layer (heavy Pb)

(1% Pb)

1st coat Paint Layer (heavy Pb)

(2.5% Pb)

Parabolic Trough Glass MirrorArchitecture

Back Layer (Cu)

Thick glass is slumped

Three-coat paint system designed for outdoor applicationsFlabeg mirrors still use Cu back protection

Mactac adhesiveCeramic pad


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Original Flabeg Mirror

85

90

95

100

0 10 20 30 40 50 60 70 80

Total UV Dose (100 x MJ/m2

)

%

HemisphericalR

eflectance

APS - OLDFLA - OLD

NREL - OLD

Ci65 - OLD

Equivalent NREL Exposure Time (years)

3 6 12 15 180 24219


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Original vs. New Flabeg Mirror% Hemispherical Reflectance of Old Flabeg (w/Cu & Pb paint) vs New Flabeg (w/ Cu & low-Pb

paint) Mirrors as a function of accelerated exposure in Ci65 WOM (65C/65%RH/~3sun light

exposure) and BlueM (85C/85%RH/dark), and outdoors in Colorado

80

85

90

95

100

0 4 8 12 16 20 24

Exposure Time (Months)

%

HemisphericalReflect

ance

SWV - Old - BlueM

SWV - New - BlueM

SWV - Old - Ci65

SWV - New - Ci65

SWV - Old - NREL

SWV - New - NREL


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Low-iron Glass (3- or 4-mm thick flat)

2nd coat Paint Layer (lead-free


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Alternate Thick Glass Mirror

65

70

75

80

85

90

95

100

0.0 3.3 6.7 10.0 13.3 16.7 20.0 23.3 26.6 30.0 33.3 36.6 40.0 43.3 46.6 50.0 53.3

Total UV Dose (100 x MJ/m2)

%

HemisphericalReflectance

NREL - Pilkington

NREL - Spanish

Ci65 - Pilkington

Ci65 - Spanish

qu va en xposure me years

1 2 3 4 50 6 7 8 9 11 12 13 14 15 1610

Pilkington: 4-mm glasscopper-free mirrors

Spanish: CristaleriaEspanola S.A. (SaintGobain) 3-mm glass,copper-free, lead-freepaint mirrors


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Effect of Adhesive on Thick Glass Mirror

80

85

90

95

100

0.0 3.3 6.7 10.0 13.3 16.7

Total UV Dose (100 X MJ/m

2

)

%

HemisphericalR

eflectance

SPA/GE TSE 392-C ADH PIL/GE TSE392-C ADH

SPA/GE D1-SEA210B Pil/GE D1-SEA210B ADH

SPA/KRAFF SILKRAF ADH PIL//KRAFF SILKRAF ADH

SPA/DOW Q3-6093 ADH PIL/DOW Q3-6093 ADH

NREL Exposure Time (years)

1 2 3 4 50


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80

85

90

95

100

0.0 3.3 6.7 10.0 13.3 16.7 20.0 23.3 26.6 30.0 33.3 36.6 40.0 43.3 46.6

Total UV Dose (100 X MJ/m2

)

%

HemisphericalReflectance

SPA/GE TSE 392-C ADH PIL/GE TSE392-C ADH

SPA/GE D1-SEA210B ADH PILS/GE D1-SEA210B ADH

SPA/KRAFFT SILKRAF ADH PIL/KRAFFT SILKRAF ADH

SPA/DOW Q3-6093 ADH PIL/DOW Q3-6093 ADH


1 2 3 4 50 6 7 8 9 1110 12 13 14

Effect of Adhesive on Thick Glass Mirror


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Low-iron Glass (~1 mm- thick)

Substrate (SS, Al)

Adhesive (PS, spray)

Paint Layer (Pb)

(Pb-free)

Thin Glass Mirror Architecture

Back Layer (Cu)

(Cu-less)

Thin glass mirrors are designed for indoor applications.


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Thin Glass Corrosion


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Thin Glass Mirror Matrix

LevelsFactors

MirrorType

BackProtection

Adhesive /Substrate

EdgeProtection

SubstrateCleaning

BackPriming

1 Naugatuck/Cu Epoxy 3M504FL/AL steel None SAIC 3M

2 Naugatuck/ No Cu Polyurethane 3M504FL/AL Exuded Adh. SES None

3 Glaverbel None 3M966/AL steel CPFilm4 3M966/AL

5 Mactac/AL steel

6 Mactac/AL

7 Epoxy/AL steel

8 Epoxy/AL

9 Urethane /AL steel

10 Urethane /AL

11 Contact /AL steel

12 Contact /AL

13 None

D-optimal fractional factorial algorithm using Design-Expert software

B: Back Protect


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ANOVA Analysis

Glaverbel - best overallmirror in Mirror matrix test Commercial vs. prototype

1- vs. 2-coat paint system

Difference in EU and US lead-free

regulations Epoxy-based adhesive

probably good choice

No additional back

protection - survive thelongest

Polyurethane poor choice BlueM - more accelerated

exposure chamber

B1 EpoxyB2 Polyurethane

B3 None

Actual Factors

A: Mirror = Glaverbel

D: Test method = Ci5000

B: Back Protect

C: Adh/SS

Reflectance(SolWt

)

3M504FL/Alsteel

3M504FL/Al

3M966/Alsteel

3M966/Al

Mactac/Alsteel

Mactac/Al

Epoxy/Alsteel

E

ox/Al

Urethane/Alsteel

Urethane/Al

Contact/Alsteel

Contact/Al

None

30

40

50

60

70

80

90

100

D H t lt i il b t 6X


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Damp-Heat results similar but ~6Xfaster than Ci5000

Discontinued in

Damp-Heat 5.9 MO

Discontinued in

Ci5000 18.9 MO


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Thin Glass MirrorSpectral Reflectance of Naugatuck copperless mirrors with 1 coat paint system after

accelerated exposure in Blue M (dark / 85oC / 85%RH) chamber

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%

Reflectance

0.0 MO

1.72 MO

2.70 MO

3.99 MO

5.24 MO

7.51 MO

1-coat paint system formulated for Cu freemirrors.


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Thin Glass Mirror

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%Refle

ctance

0.0 MOBlueM 3.52 MO

BlueM 7.21 MOCi65 3.16 MOCi65 6.15 MONREL 3.82 MONREL 9.57 MO

(Naug/Clearcoat/966


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Enhanced Al Reflective Layer

Protective Oxide Topcoat

Polished Aluminum Substrate

Protective Overcoat

Aluminized Reflector Architecture


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Aluminized Reflectors

80

85

90

95

100

0 333 666 999 1332 1665 1998 2331

Total UV Dose (MJ/m2)

%H

emisphericalR

eflectance

Original

Improved Miro2

Improved Miro2 Set#2

Miro/4270kk

xposure me y

1 2 3 4 50 6 7

Al i i d R fl t S l it


34/69

Aluminized Reflector Specularity

Alanod 4270/kk

FLA 11.8 m

APS 27.7 m

NREL 11 m

WOM 10.2 m0

20

40

60

80

100

0.0 3.3 6.7 10.0 13.3 16.7 20.0 23.3 26.6


7-mradianSpecularReflectanceat660nm

APS

FLA

NREL

Ci65


1 2 3 4 50 6 7 8

Al i i d R fl t


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Aluminized ReflectorSpectral Reflectance of Alanod MiroSun mirrors after outdoor exposure in Phoenix, AZ at APS

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%

Reflectance

0.0 MO

10.72 MO

Al i i d R fl t


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Spectral Reflectance of Alanod MiroSun mirrors after outdoor exposure in Miami, FL at FLA

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%

Reflectance

0.0 MO

12.0 MO

Aluminized Reflector

Al i i d R fl t


37/69

Aluminized ReflectorSpectral Reflectance of Alanod MiroSun mirrors after outdoor exposure in Golden, CO at

NREL

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%

Reflectance

0.0 MO

5.16 MO

11.37 MO

Al i i d R fl t


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Spectral Reflectance of Alanod MiroSun mirrors after accelerated exposure in Ci65 WOM

(1 sun / 60oC / 60%RH) chamber

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%R

eflectance

0.0 MO

3.51 MO

6.63 MO

11.54 MO




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Spectral Reflectance of Alanod MiroSun mirrors after accelerated exposure in Blue M (dark /

85oC / 85%RH) chamber

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%R

eflectance

0.0 MO

4.47 MO

6.66 MO

9.41 MO

13.84 MO

16.95 MO




40/69

Aluminized ReflectorSpecular Reflectance at 7- and 25-mradians at 660 nm of Alanod MiroSun mirrors after

accelerated exposure in Blue M (dark / 85oC / 85%RH), WOM (1 sun / 60

oC / 60%RH)

chambers, and outdoor exposure at NREL, APS, FLA, and Sandia

30

40

50

60

70

80

90

100

0 3 6 9 12 15 18 21 24

EXposure Time (Months)

%

SpecularReflectance

NREL - 25 mr

NREL - 7 mr

NREL - SWV

APS - 25 mr

APS - 7 mr

APS - SWV

FLA - 25 mr

FLA - 7 mr

FLA - SWVWOM - 25 mr

WOM - 7 mr

WOM - SWV

Blue M - 25 mr

BlueM - 7 mr

BlueM - SWV

Sandia -25mr

R fl T h Sil d P l


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ReflecTech - Silvered PolymerReflector Architecture

UV-Screening Superstrate

Base Reflector

Bonding Layer

Flexible Polymer Substrate

R fl T h P


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ReflecTech Prototypes

70

75

80

85

90

95

100

0 3.3 6.6 9.9 13.2 16.5 19.8 23.1 26.4


%H

emisphericalRe

flectance

UV-Screen/SS95-NRELReflecTech A-NRELReflecTech B-NRELUV-Screen/SS95-WOMReflecTech A-WOMReflecTech B-WOM


0 1 2 3 4 5 6 7 8

R fl T h III NREL


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ReflecTech III -NRELSpectral Reflectance of ReflecTech pilot-run#3 (06-48) silver polymer mirrors after outdoor

exposure in Golden, CO at NREL

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%

Reflectan

ce

0.0 MO

3.82 MO

ReflecTech 06-48

R fl T h III NREL


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Spectral Reflectance of ReflecTech pilot-run#3 (06-60) silver polymer mirrors after outdoor

exposure in Golden, CO at NREL

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%Reflectan

ce

0.0 MO3.82 MO

ReflecTech (06-60)

ReflecTech III -NREL

R fl T h III Ci65 WOM


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ReflecTech III Ci65 WOMSpectral Reflectance of ReflecTech pilot-run#3 (06-48) silver polymer mirrors after

accelerated exposure in Ci65 (1 sun / 60oC / 60%RH) chamber

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%Reflectan

ce

0.0 MO

3.16 MO

6.15 MOReflecTech (06-48)

R fl T h III Ci65 WOM


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Spectral Reflectance of of ReflecTech pilot-run#3 (06-60) silver polymer mirrors after

accelerated exposure in Ci65 (1 sun / 60oC / 60%RH) chamber

0

20

40

60

80

100

250 500 750 1000 1250 1500 1750 2000 2250 2500

Wavelength (nm)

%

Reflectance

0.0 MO

3.16 MO

6.15 MO

ReflecTech (06-

ReflecTech III Ci65 WOM

Front Surface Solar Reflector


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Top Protective Layer (1-4m Al2O3)

Front Surface Solar ReflectorArchitecture

IBAD Al2O

3



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Reflective Layer (100 nm Ag)


Substrate (PET)




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Reflective Layer (100 nm Ag)


Substrate (PET) (Chrome Plated Steel,

Leveled Stainless Steel,

or Aluminum)

Anti-soiling Layer (100 nm TiO2)

Adhesion Promoting Layer (APL) (1-10 nm)


Metal Back Layer (30 nm Cu optional)

Outdoor exposure at NREL of


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80

85

90

95

100

0.0 3.3 6.7 10.0 13.3 16.7 20.0Total UV Dose (100 x MJ/m

2)

%He

misphericalReflectance

2um Al2O3/Ag/Cu 13AUG02-3 20nm/s

3.5um Al2O3/Ag/Cu 2AUG02 20nm/s1.5um Al2O3/PL/Ag/Cu 13AUG02-1 20nm/s

4.5um Al2O3/PL/Ag/Cu 15AUG02-1 20nm/s

Al2O3/Ag/Ti 27AUG02 20nm/s

Batch 1 nm/s

NREL Exposure Time (y)

1 2 3 40 5 6

Outdoor exposure at NREL ofRoll-Coated IBAD Al2O3 Samples

Both adhesion-promoting interlayer andTi backlayer were among most durable samples but:

Adhesion layer may slightly improve durability Ti backlayer may slightly degrade durability

Need more

exposure time todetermine lifetime

Cost Analysis


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Cost Analysis

0

10

20

30

40

50

0 50 100 150 200 250 300

Al2O3Deposition Rate (nm/s)

Tot

alProductionC

osts($/m

2)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ann

ualProduction

(1x10

6m

2)

1 zone

2 zones3 zones1992 Cost GoalCost Goal in 2004$1 zone Ann. Prod.2 zones Ann. Prod3 zones Ann. Prod. PET substrate

1-m Al2O3 Modified ASRM $200/h machine

burden 1200-mm web

High-purityHigh-volume(i.e.,$200/kg)

Al2O3

30% yield Coating 79%

time 10 to 200 nm/s

rate Machine cost:$2M-$4.1M

Loan%/length:12% for 5 yrs

1 vs. 2 vs. 3zones in 1

machine

Field Requirements for


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Field Requirements forAdvanced Receivers

Receivers: 4 m (13.1 ft) long 70 mm (2.25 in) diameter

New 64 MWe Nevada plant 820 collectors and each

collector has 24 (96 m)receivers 19,680 receivers 82 km of receivers (50 mi)

Existing SEGS plants have5x this many receivers

New 553 MW plant willneed 8.5x this manyreceivers

3-4%/yr Failure Rate

~$1000/tube

Advanced Selective Coating Goals


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200C (0.31 kW/m2)

300C (0.80 kW/m

2

)

400C (1.78 kW/m2)

500C (3.56 kW/m2)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100 1000 10000 100000

Wavelength (nm)

BlackbodyIrradiance(W/m2-nm)

0

20

40

60

80

100

%Reflect

ance()

Direct AM 1.5 (0.77 kW/m2)

Ideal Solar Selective



54/69

Advanced Selective Coating Goals To develop receiver

coatings that have:

Good optical andthermal performance:absorptance () 96%,

& emittance () 7%>400C

High temperaturestability in air attemperatures 550C

Manufacturingprocesses withimproved quality control

Lower cost

200C (0.31 kW/m2)

300C (0.80 kW/m2)

400C (1.78 kW/m2)

500C (3.56 kW/m2)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

100 1000 10000 100000

Wavelength (nm)

BlackbodyIrradiance(W/m

2-nm)

0

20

40

60

80

100

%

Reflectance()

Direct AM 1.5 (0.77 kW/m2)

Ideal Solar Selective

High Temperature Solar


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0.10

0.11

0.12

0.13

0.14

0.15

0.80 0.82 0.84 0.86 0.88 0.90 0.92

Energy Absorbed by Receiver

eveze

osto

nergy

= 0.05

= 0.15

= 0.25

Black Chrome

Mo-Cermet

UVAC (t)

UVAC (s)

New

Cermet (s)

Goal

High Temperature SolarSelective Coating Development

Selective coatingproperties impactcollector opticalperformance andthermal losses.

Improvements inthe receiver canenhance collectorefficiency & lowercost.

The internationalcommunity

currently leads thisarea and thereexists minimal USresearch & no USmanufacturer ofhigh-temperatureselective coatings.

Reduced

Thermal

Losses

(lower )

Increased Optical Properties

(higher )

Types of Selective Coatings


56/69

Types of Selective Coatings

Intrinsic selective

material

SubstrateIntrinsic absorber

Dielectric

Metal

Dielectric

Metal

Substrate

Multilayer absorbers ARAR

AR

AR

LMVF cermet

HMVF cermet

LMVF cermet

HMVF cermet

Metal

Substrate

Multiple cermet

Double cermet

AR

LMVF cermet

HMVF cermetMetal

Substrate

Graded cermet

Graded metal

dielectric composite

Metal

Substrate

Surface texturing

Metal

Substrate

Literature Review of Candidate


57/69

High-temperature (> 400C) SolarSelective Materials

Graded Mo,W, ZrB, Pt- Al2O3 cermets

Si tandem absorber

Black Co, Mo,W

Double cermets- SS-AlN, AlN/Mo, or AlN/W

4-layer V-Al2O3, W-Al2O3, Cr-Al2O3, Co-SiO2, Cr-SiO2,Ni-SiO2

Double AR

Multilayers; Al-AlNx-AlN

Au/TiO2 cermet ZrCxNy/Ag

Ti1-xAlxN

Quasicrystals multilayers & cermets

Surface Texturing

Desirable Properties for Stable


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pCoating in Air > 400

C High thermal & structural stabilities for combined & individual layers

Elevated melting points Large negative free energies of formation

Materials that form a multicomponent oxide scale

Single-compound formation

Lack of phase transformations at elevated temperature

Suitable texture to drive nucleation, subsequent growth of layers with suitablemorphology Stable nanocrystalline or amorphous materials

Excellent adhesion between the substrate and the adjacent layers Enhanced resistance to thermal and mechanical stresses

Acceptable thermal and electrical conductivities Higher-conductivity materials have improved thermal shock resistance

Some ductility at room temperature reduces thermal-stress failures

Good continuity and conformability over the tube Compatibility with fabrication techniques

NREL Modeled Selective Coating


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NREL Modeled Selective Coating

Commercial (as tested) Modeled

Black Cr Mo-Cermet

UVAC # 6A # 6B

Solar

Absorptance 0.916 0.938 0.954 0.959 0.950Thermal Emittance@

25C 0.047 0.061 0.052 0.013 0.027

100C 0.079 0.077 0.067 0.017 0.033

200C 0.117 0.095 0.085 0.028 0.040

300C 0.156 0.118 0.107 0.047 0.048

400C 0.216 0.146 0.134 0.074 0.061

500C 0.239 0.179 0.165 0.110 0.073

Comparison of theoretical optical properties for NRELs modeled prototype solar selective

coating with actual optical properties of existing materials.

Modeled NREL Selective Coating


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Modeled NREL Selective Coating

0.00

0.20

0.40

0.60

0.80

1.00

0 1 10 100

Wavelength, um

Reflectance&

E

(norm.)

400C Black Body

ASTM G173-03

AM 1.5

Direct Normal

UVAC A

Ideal

Selective

Coating

Advanced

NREL #6A

Modeling Key Results


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Modeling Key Results

Solar Selective Coating Development Modeled solar-selective coatings with =0.959 and

=0.061 that meet CSP goals

Emittance excellent & absorptance of modeled

coatings is very good but further improvements are

expected. However, trade-off exists between

emittance and absorptance.

Deposition Capabilities


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epos t o Capab t es

Load-Lock Chamber

Pulsed DC Sputtering Chamber 3 - linear arrays of 5 - 1.5 Mini-mak

guns 2 - 12 planar cathodes

Electron-Beam/IBAD Chamber

6 multi-pocket e-beam source Co-deposition bottom plate IBAD w/ 12 Linear Ion Gun

System

12x12 ambient or heated substrate 4 Reactive Gases

Turbo molecular drag pumps 2x10-8 torr

Monitoring RGA Quartz Crystal Monitor Pressure/Gas

Computer

Three-Chamber In-line System

Prototyping Key Results


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Prototyping Key Results Key issue is making deposited coating

XPS showed evaporation from compounds producedlayered stoichiometry Despite depositing layers with over- and under-thickness and

compound layered structure, the optical performance of theprototype NREL#6A was quite encouraging.

Need to codeposit materials Required significant upgrade to equipment

Installed codeposition guns & sweeps

Pneumatic shutters

Second quartz crystal sensor Upgrade computer & RGA software

+ associated air, water, & electrical

Automating control

Prototyping Key Results


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Prototyping Key Results Codeposit individual layers and modeled coating

Codeposition development

Deposited individual layers Deposited modeled structure Characterize properties

Optical performance lower than modeled Typically optical coating need error 5% because of manual control

Install optical monitor Provide positive feedback between quartz crystal and optical

monitor Automate control remove human error and provide steering

and cutting at sensitive turning points allowing mid-coursecorrections to be made

Compositional errors because stoichiometry not optimized

Composition with highest reflectance Phase formation from Pretorius effective heat of formation

model & TGA Optimize morphology with ion assist

Selective Coating Performance


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Selective Coating Performance can be measured at higher temperatures but is typically reported based on

calculations from reflectance measurements fitted to the black body curve

Actual performance of the absorber at high temperatures commonly doesnot correspond to the calculated Small errors in lead to large errors in

is a surface property & depends on surface condition of material and substrate

Surface roughness Surface film

Oxide layers Selective coatings can degrade at high T due to

Thermal load (oxidation) High humidity or water condensation on the absorber surface (hydratization and

hydrolysis) Atmospheric corrosion (pollution)

Diffusion processes (inter-layer substitution) Chemical reactions Poor interlayer adhesion

Therefore it is important that is measured accurately and to measure ofthe selective coating at operating temperatures & conditions before usingcalculated

Round Robin &

Purchase Perkin Elmer 883 IR spectrophotometer

Thermal Stability


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y Thermal stability is sometimes given based on the thermal

properties of the individual materials or the processingtemperature parameters

Actual durability data is uncommon for high temperatureabsorber coatings Durability or thermal stability is typically tested by heating the

selective coating, typically in a vacuum oven but sometimesin air, for a relatively short duration (100s of hours)compared with the desired lifetime (5-30 years)

IEA Task X performance criterion (PC) developed for flat platecollector absorber testing (i.e., non-concentrating, 1-2X sunlightintensity)

No analogous criterion known for testing high-temperature selectivecoatings for CSP applications

Building capability for long term testing of thermal stability

Purchased & installed high-temperature

(600C) inert gas oven

Conclusion


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Conclusion DOE, the WGA, state RPS mandates, and feed-in tariffs

have successfully jump-started growth in CSP technologies

that would require 7 to 10 million square meters of reflectorand more than 600,000 HCEs over the next 5 years.

Commercial glass mirrors, Alanod, and ReflecTech maymeet the 10-yr lifetime goals based on accelerated

exposure testing. Predicting an outdoor lifetime based onaccelerated exposure testing is risky because AET failuremechanisms must replicate those observed by OET.

Experimental IBAD Al2O3 front surface mirror has highpotential to meet need; but needs development by roll-coating company

None of the solar reflectors available have been in test longenough to demonstrate the 10-year or more aggressive 30-

year lifetime goal, outdoors in real-time

Conclusion


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Conclusion Modeled solar-selective coatings with =0.959 and

=0.061 that meet CSP goals

Emittance excellent & absorptance of modeled coatingsis very good but further improvements are expected.However, trade-off exists between emittance andabsorptance.

Key issue then becomes trying to make the coating Prototype development underway. Individual and

modeled structure deposited by e-beam compound andelemental codepostion & characterized. Need toeliminate thickness errors by upgrading monitor andcontrol and determine optimum stoichiometry.

Purchased & installed PE 883 IR Spectrophotometer(2.5- 50) and high-temperature inert gas oven. Round-robin data being analyzed and commercial & prototypedcoating samples being put into test

Patent being pursued

Acknowledgments


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AcknowledgmentsAlanod, Glaverbel, Naugatuck, ReflecTech, SAIC, and SES for providing

solar reflective samples.

Schott and Solel for providing solar selective samples.AZ Technology and Surface Optics Corporation for high-temperature optical

measurements .

Armstrong World Industries: Dr. J. S. Ross

Northeastern University: Dr. Jackie Isaacs

Penn State University: Prof. Singh, Tom Medill, and Dale DonnerSAIC: Dr. Russell Smilgys and Steve Wallace

Stat-Ease: Wayne F. Adams

Swisher and Associates: Dick Swisher

NREL:

Lynn Gedvilas, Gary Jorgensen, Mark Mehos, Judy Netter, CraigPerkins, Hank Price, Kent Terwilliger, and Student interns: MicahDavidson, Anthony Nelson, Michael Milbourne, and Christopher, andAndrea Warrick.

DOE supported this work under Contract No DE AC36 99GO10337

Documents

Advances in Concentrating Solar Power Collectors