Department of

Electrical & Computer Engineering

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High Impact, Renewable Energy

R&D at UC Davis:

The Woodall Group

Jerry M. Woodall

National Medal of Technology Laureate

Distinguished Professor

Electrical and Computer Engineering Department

University of California, Davis, CA 95616

Current Research Areas

• Compound Semiconductor Photonics

– Materials focus (wide band gap GaInP, ZnSe-GaAs)

– Deposition tools (LPE, custom MBE for II-VI / III-V compounds)

– Devices (PV, LEDs, MS, MIS)

• Novel THz Transistors using Heterogeneous Integration

– High speed and high power using LT-GaAs on GaN

– High speed not just for HEMTs! We use HBTs!

• Full Spectrum Photo-thermal Solar Energy Converters

– Development of intrinsic silicon as a selective absorber

– Realize 50% efficiency using economical components

• Hydrogen Generation Using Earth-Abundant Aluminum

– Split water using Al-Ga alloys

– Energy density of Al far surpasses any current battery technology

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Our Group

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Leadership

Jerry Woodall

Distinguished

Professor

• Waves the baton

Students

Jackson Thomas

MS Student

• H2 Delivery Systems

• Fuel Cell Applications

Xin Zhao

PhD Student

• LPE of GaInP

• AlGaAs PN Solar Cells

Cristian Heredia

PhD Student

• Hybrid Solar Converters

• Optical Characterization

Vincent Lee

MS Student

• MBE

Camron Noorzad

MS Student

• LPE

Ranesh Kumar

MS Student

• Energy Storage

Zhaoquan “Joe” Zeng

Development Engineer

• MBE Expert

Vache Harotoonian

PhD Student – Student

Group Leader

• THz High-power HBTs

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National Medal of Technology

“For the invention and development of technologically and commercially

important compound semiconductor heterojunction materials, processes

and related devices, such as light emitting diodes, lasers, ultra fast

transistors, and solar cells” (launched a $30+billion/yr industry)

A Brief Bio:

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• 2 Energy Storage and Conversion Projects

• 2 Solar Cell Projects

• Photo-thermal Project

AGENDA

Department of

Electrical & Computer Engineering

Splitting Water Using Al-Ga Alloys

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• Energy Storage and Conversion: Part I

Energy Density Comparison

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Aluminum has the highest

volumetric energy density

and a higher specific energy

than ethanol, methanol or

bituminous coal!

Technology Sustainability & Large

Scale Use

• US annual energy consumption: ~100 Quads

• Current worldwide annual Al production: 32 billion kg from bauxite + 400 billion kg of scrap elemental Al available for recycling!

• Therefore, aluminum is abundant and recyclable by currently used, large scale aluminum smelters

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3rd Most Abundant Element on Earth

The Discovery

In 1968 we discovered that aluminum (Al)

dissolved in liquid gallium (Ga) just above

room temperature would split water into pure

hydrogen (H2) and aluminum hydroxide plus

heat.

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The Fundamental Process

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Aluminum Tri-Hydroxide

Powder on Top of Liquid Ga

1 2 3

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Add Water

25 gms Al in 1 kg liquid

Ga + 50 gms H2O

2.8 gm UHP H2 + 72 gms

UHP Al(OH)3 Ga is

99.9% recovered.

The 1968 Water Splitting Discovery

Model

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2Al + 6H20 3H2 + 2Al(0H)3 + Heat

The Reaction Cycle

Reaction generates (per kg-Al):

– 3.73 kWh of Hydrogen Energy (LHV)

– 2.89 kg of Aluminum Hydroxide (to recycle back to aluminum)

– 4.42 kWh of Heat Energy

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99%

) Ga

Big Ideas

• 10-20 kW EVs with fuel cells; 20 kg of Al will run a 10 kW EV for 4 hours

• Electric utility co-located with solar and wind farms. (Smelt alumina back to Al when the sun shines and the wind blows

• Power for large ocean liners

• Al-Ga-water kiosks to enable the hydrogen highway at random, off-grid locations

• Steam locomotive trains running on heat and hydrogen generated from Al-Ga and water in in-line storage cars

• Power and potable water at remote, off-road/off-grid locations

• Back up/reserve power packs

• Hydrogen for ICE powered utility vehicles

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HVAC Conditioning

H2

Storage WATER

Alumina

Storage

Phase Change

Heat Storage

Alumina

Processing

Fuel Cell

Reactor

10,000 PSI

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0 C

Fig. 1 Block diagram of an off-the-grid decentralized system to produce

UHP hydrogen, heat, and UHP alumina

FCV

H2

2Al+6H2O 3H2+2[Al(OH3)]

All water is recovered, i.e.2[Al(OH)3 + heat Al2O3+3H2O; 3H2+3/2O2 3H2O

REACTION

Electricity

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Economic Projections (per 10 kg of Al)

• Wholesale price of Al stock - $17

• Wholesale price net Ga* - $33

• Price of 20 kg D.I. water - $2

• Amortized equip and labor - $18 Total $70

*To dissolve 10 kg of Al at 3 wt% solubility we need 333 kg Ga. At a lose rate of Ga

of 0.1% per 10 kg of processed Al, net Ga = 0.33 kg. At $100/kg net Ga cost = $33

Input Costs:

Output Value:

• UHP hydrogen, 1.1 kg -$125

• UHP alumina, 19 kg @ $15/kg -$285 Total $400

The Bottom Line

• ALUMINUM!

• A global-scale, earth-abundant, high energy

density storage material for splitting any kind

of water to make on-demand hydrogen, heat,

alumina, and potable water.

• Once you buy it, it is yours forever. Unlike

fossil fuels, it stays in the energy system.

• Think of Aluminum as Coal without Carbon.

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• Energy Storage and Conversion: Part II

Enabling Solar and Wind Power Technologies

via Intermittent Power Capture, Conversion to

Heat Energy, Storage and Conversion to a 24/7

Thermal Power Supply

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Whither Global Solar Cell Grid Technology

• Installed solar cell systems are still too costly – fossil fuel

installed at $1.5/cont. Watt; solar @ >$2/installed peak W

• Inventory only works 25% of the time. Without storage

fossil fuel has to be used to give 24/7 electric power to the

grid

• Second problem could be solved with intermittent

solar or wind power capture, conversion to heat energy,

storage and its delivery as thermal power on a 24/7 basis

. . . . . .We are trying to do that. . . . .

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Power Transfer and Energy Storage System for Converting

Intermittent Input Power into a 24/7 Power Output Embodiment

Fig. 1

solar power

absorber

w selective

absorber

layer on top

insulation

heat engine

Pin/4 at 24/7

(TBD)

Ga filled

pipe heat

exchanger

Al-Si phase

change material

for isothermal

energy storage

Pin at 6 hrs/7days

high temp

pump

high temp

pump

cover glass

heat mirror

shut of valve during

intermittent power down

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• Solar Cell Projects Part I

What’s Past is Prologue

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Woodall-Hovel: AlGaAs/GaAs

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• Solar Cell Projects Part II

A Ga0.8Al0.2As, 1.72 eV Band Gap Cell as the Top

Cell for a Two Junction CPV Stack with a Si PV as the

Bottom Cell. (Now go back and look at X. Zhao’s poster!)

solar photons

energy >1.72 eV

absorbed by

GaAlAs cell

GaAlAs cell

Si cell

solar photons not absorbed

by the GaAlAs cell pass through

to Si cell, i.e. > 1.12 eV, <1.72 eV

Concept: high energy photons

produce higher voltage when

absorbed by high band gap cell;

add current by absorbing pass

through photons with lower

band gap cell

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AlGaAs cell on top of Si cell, Iphoto = const

100x eff. >40%

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• Photo-thermal Project

Develop a robust selector absorber material that has a high

absorptivity for a large fraction of the solar irradiance spectrum and

a low emissivity for mid-temperature irradiance spectra

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Ph.D Research Question: Can Intrinsic Si Do the Job, and why would

it be expected to work?

First, what is the “job”?

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(thermal x carnot)

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Why should intrinsic Si have optical properties like this

for T = 400-800 C?

0

0

1

4000 nm

e

Eg

It has a band gap, 1.12 eV, so . . .

Many workers have measured optical properties of Si that enable

calculations of IR emissivity vs. T, but we seem to be the first to measure

its total emissivity, i.e. combined spectral and hemispherical emissivity.

What did we find?: for T between 400 and 800C, e = 0.22 ± 0.02

total

emissivity

for solar photons with hn > Eg, a = e = 1,

for thermal photons with hn < Eg, a = e ≅ 0

l

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Dendritic Tungsten Absorber

• Invented by IBM (1975, Cuomo and Woodall)

• Light trapping – without any fancy nano-patterning!

• High absorptivity in visible, low emissivity in IR

• Performance beats a standard blackbody

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Deposited on

Metal Foil

If the Si does not work in a system we have as a backup:

Department of

Electrical & Computer Engineering

Thank You. Q&A Time

jwoodall@ucdavis.edu,

Kemper 2001, cell phone 530-902-6428

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Q&A Stack

Stefan–Boltzmann Law power radiated from a

black body in terms of its temperature

P = AesT 4

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e =Pin

As (TS4 -T0

4 )

e =mc(DT / Dt)

As (T0

4 -TS4 )

Temp. oC

Time - sec

Typical Data

Q&A Stack

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erel _Si = 0.24 ± 0.03

0

0.2

0.4

0.6

0.8

1

350 450 550 650

eSi = 0.20 ± 0.01Total emissivity

by themal decay

Temperature oC

Total emissivity

by steady-state

Q&A Stack

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Topic Area 1: Small Innovative Projects in Solar (SIPS)

This topic area intends to fund small, focused projects in novel and/or

emerging areas of photovoltaics research which inherently involve

significant risk but have the potential to produce dramatic progress

towards a solar LCOE of $0.02-0.03/kWh by 2030. Applications of

interest will contain targeted, well-defined projects that, if successful,

will open up new avenues for continued study. Along with topics of

interest motivated by the Background Section (Section I.A), examples of

emerging areas that would merit focused study include rapid growth

techniques not previously demonstrated for PV materials, alternate

wafering routes, and improved understanding of PV module recycling

technology, as well as seeding other particularly high risk novel areas of

PV research. This topic area will have an accelerated review schedule

and will use an abbreviated application format. Separate “Concept

Papers” are not required for this topic and SIPS applications must be

submitted by the SIPS deadline stated in the FOA. Awards will be made

several months sooner than for Topics 2 and 3.

Q&A Stack

DOE