Solar Thermoelectric Energy Conversion Gang Chen Massachusetts Institute of Technology Cambridge, MA 02139 Email: gchen2@mit.edu http://web.mit.edu/nanoengineering NSF Nanoscale Science and Engineering Grantees Conference December 5-7, 2011, Arlington, VA
Nano for Energy Increased surface area Interface and size effects Molecules Λ = 1 100 nm λ=1 nm Λ---Mean free path λ---wavelength Photons Λ > 10 nm λ=0.1-10 μm Electrons Λ=10-100 nm λ=10-50 nm Thermodynamics Kinetics Phonons Λ=10-100 nm λ=1 nm
Energy Technology Constraints Cost Efficiency Favorable Thermodynamics Favorable Transport Environmental Portability
Thermoelectric Energy Conversion COLD SIDE COLD SIDE - + HOT SIDE I N P HOT SIDE Nondimensional Figure of Merit Joule Heating Seebeck Coeff. Electron Cooling ZT = 2 σs T k Reverse Heat Leakage Through Heat Conduction
Device Efficiency Zebarjadi et al., Energy & Env. Sci., in press.
Nanoscale Effects for Thermoelectrics Interfaces that Scatter Phonons but not Electrons Electrons Λ=10-100 nm λ=10-50 nm Phonons Λ=10-100 nm λ=1 nm THERMAL CONDUCTIVITY (W/ mk) 10 3 10 2 10 1 K X,BULK (FOURIER LAW) K Z,BULK (FOURIER LAW) K Z,FILM, EXPERIMENTAL Si K X,FILM, EXPERIMENTAL 0.5 Ge 0.5 BULK ALLOY (300K) In-Plane P=0.6 P=0.5 Cross-Plane Lines--Fitting with CHen'sModel Superlattices 10 0 P=0.6 80 120 160 200 240 280 TEMPERATURE (K) Nanocomposites
Nanostructured Thermoelectric Materials Poudel et al. Science, v. 320, p. 634, 2008
Nanocomposite Synthesis Increase interfacial scattering by mixing nano-sized particles. Batch fabrication for large scale application. Graphite piston Graphite cylinder Sample powder A Current for heating Force for pressing Poudel et al. Science, v. 320, p. 634, 2008 Nano Bi 2 Te 3 Professor Z.F. Ren Boston College
Recent Progress in ZT Zebarjadi et al., Energy & Env. Sci., in press.
From Micro Watts to Giga Watts Vehicles Power Plants μw W kw MW GW Sensors Stove Furnace Solar Industrial Waste Heat
Solar Energy Utilization Solar Fuel Solar Electricity: PV http://www.phschool.com/science/biology_place/biocoach/photos ynth/overview.html Solar Heating homesolarpvpanels.com Solar Electricity: Thermal-Mechanical http://www.global-greenhouse-warming.com/solar-hot-water.html http://www.treehugger.com/solar-thermal-plant-photo.jpg
Solar Hot Water Systems http://www.freewebs.com/solarwyse/solar_tubesspecs.html http://www.made-in-china.com
Solar Thermal Installed Capacity, 2009 China in 2009, total of 134 Million m 2 Evacuated Tubes
Solar Thermoelectric Energy Conversion US Patent No. 389124: E. Weston in 1888 M. Telkes, JAP, 765, 1954 Efficiency: 0.63%
Heat Flux Consideration q = k ΔT L 1 W m K 100 K L q=1000 W/m 2 (1 Sun); L=100 mm q=100,000 W/m 2 (100 Sun); L=1 mm
Possible Configurations Solar Radiation Optical Concentrator Optical Concentration p n Selective Surface Area A s Enclosure
Solar Thermoelectric Power Conversion Kraemer et al., Nature Materials, 10, 532, 2011
GMZ/ goal 12 10 x current state 18 Efficiency (%) 8 6 4 2 0 Eye-Balled Data from 1 st Solar APS Presentation Series1 2000 2002 2004 2006 2008 2010 Year
Phonon Engineering Host Λ nano < Λ bulk Λ bulk Nanoparticles Thermal Conductivity k 1 1 = CωvωΛωdω = CvΛ 3 3 Specific Heat Speed of Sound Mean Free Path
First-Principles Computation of Phonon Thermal Conductivity
Phonon Mean Free Path Distribution Zebarjadi et al., Energy & Env. Sci, in press.
Optical Measurement of Phonon Mean Free Path D=55μm D=30μm D=15μm Thermal conductivity (W/mK) 10 3 10 2 10 1 10 2 Temperature (K) Literature TTR, D=55 μm TTR, D=30 μm TTR, D=15 μm Minnich et al., PRL, 107, 095901, 2011
Phonon MFP Distribution D q q Bω Dω ~ D Λω Minnich et al., PRL, 107, 095901, 2011
Pushing to Nanoscale Bulk TC of sapphire T = 300 K 400 nm
Modulation Doping Zebarjadi et al., Nano Letters, 11, 2225, 2011.
High Thermal Conductivity Polymers NSF Grant No. CBET-0755825 Shen et al, Nature Nanotechnology, 2010. Shen et al, Nature Nanotechnology, 2010. Henry and Chen, Physical Review Letters, 101, 235502, 2008.
Summary Significant progress made in materials ZT. New solar thermoelectric generators with excellent application potential. Understanding phonon and electron transport in bulk nanostructures is very important for further ZT improvements and thermoelectric technology. Sponsors: DOE EFRC S 3 TEC on solar thermoelectric NSF on polymers and phonon transport