Photo-Thermal Engineering for Clean Energy and Water Applications

Transcription

1 Photo-Thermal Engineering for Clean Energy and Water Applications Ravi Prasher Associate Lab Director Energy Technology Area Lawrence Berkeley National Lab Adjunct Professor Department of Mechanical Engineering University of California, Berkeley Sean Lubner & Sumanjeet Kaur Scientist, Lawrence Berkeley National Lab 1

2 Agenda Thermal Problems and Opportunities in 1) Selective absorbers/emitters 2) Volumetric solar heating using nanofluids 2

3 Acknowledgement Vehicles Technology Office (DOE) Solar Energy Technologies Office (DOE) LDRD (LBNL) 3

4 Solar Exceeds 50% in CA but Price drops Below Zero Solar

5 Cheap Distributed High-T Storage Electricity prices Cheap, high T material Heat to C mcδt storage Heat High-T Industrial Application (W MW) High-T optical coatings (Electrically conducting; can be Joule heated) Electricity TPV Higher T higher energy density ~ 1 MWh t /m 3 Cheaper than batteries, more versatile than pumped hydro etc. 5

6 Thermo Photovoltaics (TPV) 6

7 3-Pronged Approach: Theory, Nano, Macro ε 1, κ 1 ε 2, κ 2 Solve Maxwell s Equations Macro-Scale High-T Optical Spectroscopy (2000 o C) Optical Spectrometer Fiber coupling Theoretical Modeling T >> 0 t >> 0 Degradation insulation High-T- Stable Optical Coatings Oxidation I nter-diffusion Nano-Scale Characterizations In-Situ TEM (Up to 1200 C) TEM image of gold particle at 800 o C from NCEM 7

8 Ideal Solar Absorber Challenges for solar thermal absorbers: Spectral selectivity: High solar absorptance & low IR emittance High temperature stability: Avoid oxidation, interfacial diffusion, mechanical failure 8

9 Previous Work for Selective Absorbers Semiconductor-Metal Stacks Metamaterials & Nanostructures Craighead et al., Appl. Phys. Lett. 37, (1980). Cermet Based Structures Wang et al., Solar Energy Mater. & Solar Cells 137, (2015) Metal-dielectric Stacks Wäckelgård et al., Solar Energy Mater. & Solar Cells 133, (2015) Wang et al., submitted to Solar Energy Mater. & Solar Cells (2017) Significant Degradation at High Temperatures due to Oxidation of Metals and Semiconductors 9

10 Lack of high temperature selective absorber under ambient conditions: Significant oxidation at high temperatures 10

11 Can We Use Oxide Based Materials to Solve Oxidation Problem? Structure Schematic Hemispherical R at Normal Incidence Dr. Hao Wang Iwan Haechler Drude Model 11

12 RBS for Sample Before & After Annealing O S i In & Sn Incorporation of oxygen into ITO Black absorber Substrate 12

13 High Temperature Soak and Cycling Test Temperature Soak at 800 o C Total soak time: 60 hrs Temperature Soak at 900 o C Total soak time: 60 hrs Kept at high temperature for 5 hrs with ramp rate of 20 o C/min Naturally cooled down to room temperature Minimal degradation observed 13

14 Comparison to Black Chrome 14

15 Use Temperature Radiative Properties Measurement Overall IR Specular Reflectance Reflectance at 15 µm Most measurement in literature done at room temperature Reflectance follows the electrical conductivity trend 15

16 Volumetric Absorption Using Nanoparticles Parabolic Trough is the most commonly used concentrated solar power plant technology Fluid is heated using convection (surface heating) from the absorber Can we heat the fluid volumetrically? Use of nanoparticles in fluid to absorb radiation 16

17 Literature on Volumetric Heating Using Nanofluids Low temperature applications: Ignored emission Gupta et al., 2015 Otanicar et a., 2010 Tyagi et al., 2009 High temperature applications Stagnant liquid: Lenert and Wang, 2012 Laminar flow in flow film: (Kumar and Tien, 1990) Parabolic trough: Flow is turbulent, the liquid is therminol 17

18 Simulated Geometry Freedman et al., 2018 Dr. Justin Freedman 18

19 Theoretical Modeling Governing Equation: To obtain radiative intensity q r : RTE Change of energy Conduction Absorption of radiation Re-emission Extinction Jλ ( xy,, µ ) µ = σ αλ, Jbb, λ T xyµ σ, λjλ xyµ y Scattering σ µ = 1 s, λ + J ( xy,, ) ( ) d 2 µ 1 λ µ ξ µ µ µ = ( (,, )) e (,, ) Boundary Conditions: ( ) 0 = k x Txy (, = L y ) y Inlet temperature Adiabatic in terms of conduction and convection Boundary Conditions: J( xy, = 0, + µ ) = A(1 ρ ( + µ )) J ( T ) λ + A(1 ρ ( + µ )) J ( T ) µ = 1 µ = 1 0 bb, λ 0 amb 0 bb, λ ( ) + 2 ρ ( µ ) J xy, = 0, µ µ dµ µ = 1 µ = 1 λ J( xy, = L, µ ) = 2 ε J ( Txy (, = L)) λ y L bb, λ y ( y ) + 2 ρ ( + µ ) J xy, = L, µ µ dµ L λ sun 19

20 Solar-to-thermal Efficiency Solar Thermal Efficiency Surface Spectral Radiative Flux Existence of an optimal efficiency w.r.t particle volume fraction 20

21 Comparison With Surface Based Absorption 21