CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Concentrated Solar Thermoelectric Power Principal Investigator: Prof. Gang Chen Massachusetts Institute of Technology
Cambridge, MA 02139 [email protected]
http://web.mit.edu/nanoengineering/
Subcontractor: Prof. Zhifeng Ren University of Houston
DOE EERE CSP Program: Funding Category: Seed Concept
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Solar to Electricity Conversion
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Solar Electricity: PV
http://www.treehugger.com/Solar-Thermal-Plant-photo.jpg
Solar Electricity: Thermal-Mechanical
http://www.homesolarpvpanels.com
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Thermoelectric Devices and Effects
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COLD SIDE
HOT SIDE
Nondimensional Figure of Merit
kTSZT
2σ=
Reverse Heat Leakage Through Heat Conduction
Joule Heating
Seebeck Coefficient Electron Cooling
-
I
+
N P
COLD SIDE
HOT SIDE
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Solar Thermoelectric Energy Conversion
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• US Patent No. 389124: E. Weston in 1888 • M. Telkes, JAP, 765, 1954
Efficiency: 0.63%
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Heat Flux Considerations
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LLTkq K 100
KmW1∗
≈∆
=
q=1000 W/m2 (1 Sun); L=100 mm q=100,000 W/m2 (100 Sun); L=1 mm
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Optical vs. Thermal Concentration
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Optical Concentration
Optical Concentrator
p n
Selective Surface Area As
Enclosure
Solar Radiation
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Flat Panel Solar Thermoelectric Generators (STEGs)
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Kraemer et al., Nature Materials, May, 2011
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Two-Stage Concentrated STEGs
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p n
p n
Skutterudite stage
Bi2Te3 stage
Selective surface
Heat sink
I1
I2
concentrator
sunlight
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Program Goals
• Demonstrate 10% solar-to-electric energy conversion by using optical concentration and a multi-stage TEG
• Limit required optical concentration to less than 10X, ideally less than 4X
• Demonstrate the potential for 24-hour operation by incorporating phase change materials into design
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CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Core Team
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Professor Gang Chen, Principal investigator
Professor Zhifeng Ren Co-Principal Investigator
Ken McEnaney Device Engineer
Daniel Kraemer System Engineer
Dr. Sveta Boriskina Optical Engineer
Dr. Weishu Liu Materials Scientist
Dr. Feng Cao Materials Scientist
Dr. Qing Jie Materials Scientist
Lee Weinstein System Engineer
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Major Tasks and Challenges • Devices
– Electrodes – Device joining
• Emittance – Selective surfaces – Optical design
• Systems – Modeling – Integration – Testing
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Effect of electrodes and contacts: • Parasitic losses have a linear negative effect on
system performance Effect of absorptance/emittance:
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
TEG Optimization: Critical Parameters
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Th
Tc
• Geometry must be optimized to • Reduce parasitic effects of electrode and
contact resistance • Reduce effect of radiative losses from
sidewalls
• For each thermoelectric leg: p-type skutterudite
p-type Bi2Te3
n-type skutterudite
n-type Bi2Te3
n hot electrode
n mid electrode
n cold electrode
p hot electrode
p mid electrode
p cold electrode
Ideal leg efficiency
Decreasing leg area
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Electrodes: Material Properties • Bi2Te3 electrodes: <1% of system resistance • New p-type skutterudite electrode alloy:
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Electrical resistivity reduced by a factor of 3+
Thermal conductivity increased 50% – 200%
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Electrodes: Contact Resistance • Bi2Te3/copper contact resistance < 1 μΩ•cm2
• Skutterudite/electrode contact resistance:
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n-type: <1 μΩ•cm2
p-type: 6 μΩ•cm2
electrode skutter.
electrode skutter.
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
TEG Device Testing • Currently testing single-stage devices; 9% efficiency
recorded. • Multi-stage devices should boost efficiency to ~13%
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CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Selective Surfaces • Optimized for operating temperature (500 – 600 °C) • Manufactured via sputtering • Surfaces with copper substrates not stable at high T
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400 500 600 700 800 900 1000 11000
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40
60
80
100
Refle
ctan
ce (%
)
Wavelength (nm)
Cu SS Cu_500_7d_in vacuum SS_500_7d_in vacuum Cu_550_7d_in vacuum SS_550_7d_in vacuum Cu_500_7d_in air
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Emittance Testing • Direct measurement of total hemispherical emittance at
high T:
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Sample surface
Heater
Thermocouple
Leads
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Receiver Cavity • Receiver cavity can reduce heat loss from black surface
or selective surface
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With blackbody absorber: With 20% selective surface:
Selective Surface Only
SS + Cavity
Black Surface + Cavity
CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Additional Leverage
• Experience: – Materials – Devices – Heat Transfer – Multiple Start-ups
• Other Programs: – EFRC S3TEC: thermoelectric materials – ARPA-E HEATS: Storage
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CONCENTRATING SOLAR POWER PROGRAM REVIEW 2013
Transformative Potential
• Third way: sunlight into electricity • Low cost due to:
– Solid state power block – Low optical concentration – Small amount of materials – Thermal storage
• Large market – Rooftops – Small communities – Power plants
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