Developments in Thermoelectric Power Generation. Gao Min School of Engineering, Cardiff University

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1 Developments in Thermoelectric Power Generation Gao Min School of Engineering, Cardiff University

2 1. Thermoelectric Effects 2. TE Power Generation 3. Typical Applications 4. Future Prospects

3 THERMOELECTRIC EFFECTS Seebeck effect Peltier effect TH conductor b 1 2 V 12 conductor a TC qh TH I TC qc V =α ( T T 12 ab H C Generation α the Seebeck coefficient ) q = π ab I Refrigeration π the Peltier coefficient

4 Power Output: POWER GENERATION Q & Conversion Efficiency: η P max = N 2 2 α ( TH TC ) N P N P 4R Power delivered = Heat absorbed at to the load ( P) the hot end ( Q& ) I R L T H T C η max T = H T T H Carnot efficiency C 1/2 (1+ ZT) 1 1/2 (1+ ZT) + TC T H Material properties ZT = 2 α T RK Thermoelectric Figure-of-merit

5 POWER GENERATION PERFORMANCE CONVERSTION EFFICIENCY POWER OUTPUT Conversion Efficiency (%) Present situation DT=1000 K DT=600 K DT=300 K DT=100 K Power Output (W) Copper contact Ceramic plate P-type thermoelement N-type thermoelement Dimensionless figure-of-merit, ZT Temperature Difference (K)

6 THERMOELECTRIC SYSTEMS Generation Refrigeration Heat Source Cold HEX Hot HEX Fans TE Module Heat Sink W Refrigerator cabinet TE Module Power Supply Advantages: Disadvantages: Q No harmful working fluids - environmentally friendly No moving parts reliable and no noise Wide power range totally scalable from µw to MW Relatively low efficiency

7 Radioisotope Thermoelectric Generator for Space Power Output: 280 W L: 1.1 m D: 0.4 m Half life: 87 years Pu-238 SiGe Pioneer (1972, 42W) Voyager (1976, 156W) Galileo (1989, 290W) Cassini (2002) New Horizon (2006, 280W) Bellona (~80W, 136 for Russian lighthouses, Sr - 29 years) GPHS-RTG No any other alternative

Tellurex, NASA-JPL, Iowa State United Technologies with Pratt & Whitney, Hi-Z, Pacific Northwest National Lab.

8 Thermoelectric Generation from Waste Heat US FreedomCar Program: 4 thermoelectric consortium: BSST with BMW, Visteon, Marlow, Virginia Tech, Purdue, UC-Santa Cruz GM with GE, U of Michigan, U of South Florida, ORNL, RTI Michigan State with Cummins, Tellurex, NASA-JPL, Iowa State United Technologies with Pratt & Whitney, Hi-Z, Pacific Northwest National Lab., and Caterpillar Japanese National Thermoelectric Project: IHI Komatsu Toshiba UBE Industries Yamaha Hot Water Generator (100W, 3.5%) Cardiff University

9 Heat Distribution in Vehicles Vehicle Operation Gasoline Diesel Gasoline 100% Combustion 38% Engine 5% Friction & Radiated 33% Mobility & Accessories 33% Exhaust Gas 24% Coolant An ambitious goal: Recover 10%? Fuel saving? CO 2 reduction

Control Seat (CCS ) Cooling laser Distributed

10 Thermoelectric Cooling Applications Competitive for small volume cooling Picnic coolbox Amerigon: Climate Control Seat (CCS ) Cooling laser Distributed Cooling/Heating: Eliminate R-134a refrigerant World market:us$ m/yr

TE Power Generation Using Flame Used in remote area where frequent maintenance is not impossible, such as: Oil or gas pipelines Well sites Offshore platforms Telecommunications sites Cathodic

11 TE Power Generation Using Flame Used in remote area where frequent maintenance is not impossible, such as: Oil or gas pipelines Well sites Offshore platforms Telecommunications sites Cathodic protection Well automation Monitoring equipment Navigational aids Communications systems 500 W TEG, natural gas pipeline, Peru [LeSage, Global Thermoelectric] Niche market for TE power generation (US$25-50M/yr) Natural gas: 48 m 3 /day Propane: 76 litre/day Ethylene: 30 m 3 /day Diesel:

Thermoelectric Regenerative Combustion Q h P Advantages: Improved conversion efficiency Lean-fuel combustion Heat and power co-generation Q c A lot of waste! Make use of it?

12 Thermoelectric Regenerative Combustion Q h P Advantages: Improved conversion efficiency Lean-fuel combustion Heat and power co-generation Q c A lot of waste! Make use of it? combustor hot fluid Conversion efficiency h Generator efficiency: η= System efficiency: η s = P Q S T h1 c 2 P Q G Th Tc = T h 2 Mc η( Th ) dth Th1 = = Mc( T T ) h T h2 h1 T h1 1+ ZT 1 1+ ZT + T / T electric power = fuel consumption T η( T ) dt h T c2 h c h fuel+air Preheat temperature difference, DT p (=T u -T 0 )

13 Philips Research Woodstove Stove with self-powered fan using thermoelectric generator Philips Research Eindhoven, The Netherlands (Paul van der Sluis) 400 million stoves world wide market Pilot of 1000 pieces in India TEG powers fan to regulate combustion and charge the ignition battery Benefits: Burn more efficiently Regulated combustion Reduce smoke and toxic emission

14 POWER GENERATION PERFORMANCE CONVERSTION EFFICIENCY POWER OUTPUT Conversion Efficiency (%) Present situation DT=1000 K DT=600 K DT=300 K DT=100 K Power Output (W) Copper contact Ceramic plate P-type thermoelement N-type thermoelement Dimensionless figure-of-merit, ZT Temperature Difference (K) ZT = α 2 T RK Thermoelectric figure-of-merit

15 Materials with Large ZT ZT Bi 0.97 Sb 0.03 Bi Bi 0.5 Sb 1.5 Te 2.91 Se Te 3/Sb2 Te3 superlattice PbTe(3N) ZnSb 4 Fe 4 CoSb 12 8Ga16Ge30 NaCo 2 O 4 Si 0.8 Ge 0.2 -GaP Temperature (K) Is it worth of the efforts? Ba Last 10 years ~ $50M/year Over 40 years $, $, $, $, $, $

16 Past, Present and Future Future ZT ~ 0.6 ZT ~ 1.0 ZT ~ 1.5 ZT > 4? The birth of useful TE devices with limited military and space applications. The launch of TE industries with a steady growth and a niche market. Steady growth of TE markets. Resurging of interests in TE research. Breakthrough will lead to a revolution in the renewable energy field.

17 Two Exciting Predictions in 1950s Discovery of Semiconductors Well-known Less well-known Vacuum Valves replaced by solid-state transistors Invention of silicon based integrated circuits ZT > 4 Turbine engines or compressors to be replaced by thermoelectric converters Information technology revolution Reality! Energy technology revolution Save the planet Dream?

18 Thank You

Module Design for Waste Heat Recovery Cost-per-kilowatt-hour (0.01 /kw.h) 60 50 40 30 20 10 Power-per-unit-area (kw/m 2 ) 15.0 14.0 13.0 11.0 8.0 5.0 C C = + p T M C F 2.0p/kWh 1.

19 Module Design for Waste Heat Recovery Cost-per-kilowatt-hour (0.01 /kw.h) Power-per-unit-area (kw/m 2 ) C C = + p T M C F 2.0p/kWh 1.0p/kWh Fuel cost at 0.5p/kWh Fuel cost is essentially free φ Conversion efficiency The power output can be increased by reducing the length of thermoelements. Waste heat recovery 1.5 Power output (W) Suitable for waste heat recovery Increasing the power output will lead to reduce the cost of power per module Theory optimised Best commercially available module Temperature difference (K)

20 THERMOELECTRIC APPLICATIONS Environmentally friendly Advantages: No moving parts reliable and no noise Wide power range From µw to kw Disadvantages: Relatively low efficiency Generations: Refrigeration: Space power long period,unattended power source Industrial waste heat Geothermal Waste heat recovery: Vehicle exhaust Body heat Electronic components: Low-temperature cabinet: Infra-red detectors Laser diodes Computer chips Photomultipler Mobile picnic box Dehummiditifier Constant T bath Dew point dectector

21 Engineering v.s. Science Conversion Efficiency Improvement during : ~30% Improvement during : ~400% Ulysses Galileo Voyager 1&2 Pioneer 10 Apollo 12 Viking 2 Transit-4A Apollo Launch date (year) Specific Power (W/kg)

22 Thermoelectric Energy Conversion A Great Concept!

23 Symbiotic Applications: Central Heating System W Q Making Q useful by heating the water! Ref: Gao Min and D.M. Rowe, Energy Conversion and Management, 43 (2002)

24 Ring-Structured Thermoelectric Module Hot Fluid Cold Fluid P N P N PN Copper Insulator N-type thermoelement Insulator P-type thermoelement Hot-pressing Copper Insulator

25 Thermoelectric Figure-of-Merit, ZT Seebeck coefficient Electrical conductivity α α 2 σ σ ZT = α 2 σ λ T Insulator Semiconductor Metals λ λ e Thermal conductivity λ l Carrier concentration The Seebeck effect was discovered in However, practical thermoelectric materials were only developed more than 100 years after its discovery.

26 Thermoelectric Power Generation using Body Heat Cardiac Pacemaker Seiko (45mW), Citizen (14mW) Miniature RTG battery Power output: ~ 30 µw Life-time: > 20 years

US DoE FreedomCar Thermoelectric/Vehicle Programs Thermoelectric Generator Teams BSST with BMW, Visteon, Marlow,

Cummins, Tellurex, NASA-JPL, Iowa State United Technologies with Pratt & Whitney, Hi-Z, Pacific Northwest National Lab.

Acceptance of change Competition Honda / Rankine (+3.

27 US DoE FreedomCar Thermoelectric/Vehicle Programs Thermoelectric Generator Teams BSST with BMW, Visteon, Marlow, Virginia Tech, Purdue, UC-Santa Cruz GM with GE, U of Michigan, U of South Florida, ORNL, RTI Michigan State with Cummins, Tellurex, NASA-JPL, Iowa State United Technologies with Pratt & Whitney, Hi-Z, Pacific Northwest National Lab., and Caterpillar Nano/high ZT materials not yet available Barriers to entry Cost Heat transfer to/from TEG Weight Acceptance of change Competition Honda / Rankine (+3.8%) BMW / Turbosteamer (15%) 160 mm 500 Watt BiTe TEG [BSST] 1 kw TEG on a Kenworth Truck [Hi- BMW 530i Concept with TE Generator (yellow) [BMW] The most promising TE greentech application: vehicle waste heat

Thermoelectric Energy Harvesting

Energy Harvesting 2011 IET London, Savoy Place 07 February 2011 Thermoelectric Energy Harvesting Gao Min (min@cardiff.ac.uk) Cardiff Thermoelectric Laboratory School of Engineering, Cardiff University