Photo-Thermal Engineering for Clean Energy and Water Applications

Ravi PrasherAssociate Lab Director

Energy Technology AreaLawrence Berkeley National Lab

Adjunct ProfessorDepartment of Mechanical Engineering

University of California, Berkeley

Sean Lubner & Sumanjeet KaurScientist, Lawrence Berkeley National Lab 1

AgendaThermal Problems and Opportunities in

1) Selective absorbers/emitters

2) Volumetric solar heating using nanofluids

2

Acknowledgement

• Vehicles Technology Office (DOE)

• Solar Energy Technologies Office (DOE)

• LDRD (LBNL)

3

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

Solar

Cheap Distributed High-T Storage

Higher T higher energy density ~ 1 MWht/m3

Cheaper than batteries, more versatile than pumped hydro etc.

Electricity prices

High-TIndustrial Application

Heat

Cheap, high T material

Heat to 2000+ °CmcΔT storage

High-Toptical coatings

(Electrically conducting; can be Joule heated) Electricity

(W MW)

TPV

5

Thermo Photovoltaics (TPV)

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3-Pronged Approach: Theory, Nano, Macro

ε2, κ2

ε1, κ1

Oxidation

Inter-Diffusion

High-T-Stable Optical

Coatings

Theoretical Modeling

Solve Maxwell’s Equations

T >> 0t >> 0

Degradation

In-Situ TEM (Up to 1200 °C)

TEM image of gold particle at 800 oC from NCEM

Nano-Scale Characterizations

Fiber coupling

Optical Spectrometer

insulation

Macro-Scale High-T Optical Spectroscopy (2000 oC)

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Ideal Solar Absorber

• Spectral selectivity: High solar absorptance & low IR emittance• High temperature stability: Avoid oxidation, interfacial diffusion,

mechanical failure

Challenges for solar thermal absorbers:

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Previous Work for Selective Absorbers

Metamaterials & Nanostructures

Wang et al., Solar Energy Mater. & Solar Cells 137, 235-242 (2015)

Cermet Based Structures

Wäckelgård et al., Solar Energy Mater. & Solar Cells 133, 180-193 (2015)

Metal-dielectric Stacks

Wang et al., submitted to Solar Energy Mater. & Solar Cells (2017)

Semiconductor-Metal Stacks

Craighead et al., Appl. Phys. Lett. 37, 653-655 (1980).

Significant Degradation at High Temperatures due to Oxidation of Metals and Semiconductors

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

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Structure SchematicHemispherical R at Normal Incidence

Can We Use Oxide Based Materials to Solve Oxidation Problem?

Drude ModelDrude Model

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Dr. Hao Wang Iwan Haechler

O

Si

In & Sn

Black absorber Substrate

Incorporation of oxygen into ITO

RBS for Sample Before & After Annealing

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Temperature Soak at 800oC

High Temperature Soak and Cycling Test

• Kept at high temperature for 5 hrs with ramp rate of 20 oC/min• Naturally cooled down to room temperature• Minimal degradation observed

Temperature Soak at 900oCTotal soak time: 60 hrs Total soak time: 60 hrs

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Comparison to Black Chrome

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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

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• 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

Volumetric Absorption Using Nanoparticles

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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

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Simulated Geometry

Freedman et al., 2018

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Dr. Justin Freedman

Theoretical Modeling

( ) ( )( ) ( )

( )

, , ,

1,

1

, ,, , , ,

, , ( )2

bb e

s

J x yJ T x y J x y

y

J x y d

λα λ λ λ λ

µλλµ

µµ σ µ σ µ

σµ ξ µ µ µ

=

=−

∂= −

∂

′ ′ ′+ →∫

To obtain radiative intensity qr: RTEGoverning Equation:

Boundary Conditions:

( )( , )

0 yT x y Lk x

y∂ =

=∂

Inlet temperature

Adiabatic in termsof conduction and convection

Adiabatic in termsof conduction and

( , )of conduction and convectionof conduction and

Conduction Absorptionof radiation

Change of energyChange of energy Conduction Absorption

Re-emission Extinction

Scattering

Boundary Conditions:

( )

0 ,

0 ,

1

01

( , 0, ) (1 ( )) ( )(1 ( )) ( )

2 ( ) , 0,

bb sun

bb amb

J x y A J TA J T

J x y d

λ λ

λ

µ

λµ

µ ρ µ

ρ µ

ρ µ µ µ µ=

=−

= + = − +

+ − +

′ ′ ′ ′+ − = −∫

( ),

1

1

( , , ) 2 ( ( , ))

2 ( ) , ,

y L bb y

L y

J x y L J T x y L

J x y L d

λ λ

µ

λµ

µ ε

ρ µ µ µ µ=

=−

= − = =

′ ′ ′ ′+ + = −∫

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Solar-to-thermal Efficiency

Solar Thermal Efficiency Surface Spectral Radiative Flux

Existence of an optimal efficiency w.r.t particle volume fraction20

Comparison With Surface Based Absorption

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