NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Thermal Science—Enabling Renewable Energy Innovation

8th World Conference: Experimental Heat Transfer, Fluid Mechanics and Thermodynamics

Lisbon, Portugal June 17, 2013 Dr. Dan E. Arvizu, Laboratory Director

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Global Dynamics in the Energy Landscape

Renewable industry rapid growth

Changing energy demand profile

Fiscal challenges dominate policy

Natural gas impacts energy landscape

Infrastructure investment required

Annual RE Capacity Growth Rate

Electricity Demand to Grow

Global GDP Fluctuation

Natural Gas Will Grow

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Renewable Energy Share of Global Final Energy Consumption

Source: REN21 Global Status Report 2012 http://www.map.ren21.net/GSR/GSR2012.pdf

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Global Assessments of Renewable Energy Potential

Technical potential for renewables is enormous.

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Innovation, Integration and Adoption

Reducing Investment Risk

• Enable basic and applied clean energy technology innovation

• Accelerate technology market introduction and adoption

• Integrate technology at scale

• Encourage collaboration in unique research and testing “partnering” facilities

Mobilizing Capital

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20x-100x 500x Cu(In,Ga)Se2 ~ 1-2 um c-Si ~ 180 um

Photovoltaics Technologies

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Wind Technologies • Modular large components – blades,

drivetrains, and tall towers • Advanced drivetrain power conversion

systems – superconducting direct drive generators

• Flexible, ultra-large rotors and systems • Active controls for structural load

reduction, improved wind plant performance, and grid-friendly operation

• Floating offshore wind turbines • Airborne wind power systems

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Biofuels New conversion technologies are being developed, offering the possibility of revolutionary, high volume methods for producing biofuel hydrocarbon fuels for our trucks, trains, ships, and aircraft

Biological Conversion

Chemical Catalytic Conversion

Pyrolysis/Bio-Oil Pathways

Heterotrophic Algae Conversion Hybrid Conversion Technologies

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Buildings Technologies

High Performance Buildings BIPV Products & PV-T Array Compressorless Cooling

Electrochromic Windows Polymer Solar Water Heaters Computerized optimization & simulation Tools

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Transportation

Degree of electrification (power electronics & energy storage )

8 speed transmissions

Improved aerodynamics

Start/stop

Diesel powered & or Alternative Fuels, H2

Electric powered steering

Regenerative braking

Turbocharging, direct fuel injection, advanced combustion

Variable cylinder mgmt

Light weighting Electric infrastructure

Low rolling resistance tires

Portfolio of technologies leading to 54.5 mpg

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Efficiency-Integration Buildings • Whole building systems

integration • Computerized building energy

optimization tools • Advanced HVAC (Heating

Ventilating and air conditioning)

Grid Interconnection Standards • IEEE Standards Development • Standards Testing and Validation RE Grid Integration • Power Electronics for Interconnection monitoring and control

Advanced Vehicles • Fuels utilization • Component technologies • Electric vehicle-to-grid interface

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Fundamental Science

Engineered Microbe Makes Ethylene from Sunlight, H2O, CO2

BIPV Products & PV-T Array High Purity Semiconducting Carbon Nanotubes

Ethylene-containing Bubbles Polymer Solar Water Heaters Carrier Diffusion in poly-CdTe

Energetic Barrier to Carrier Recombination in OPV Systems

Nanoscale p-n Junctions

laser

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DOE Energy Storage Goals HEV (2010) PHEV (2015) EV (2020) Equivalent Electric Range (miles) N/A 10–40 200–300

10-sec Discharge Pulse Power (kW) 25 38–50 80 Regen Pulse Power (10 seconds) (kW) 20 25–30 40

Recharge Rate (kW) N/A 1.4–2.8 5–10 Cold Cranking Power @ -30°C (2 seconds) (kW) 5 7 N/A

Available Energy (kWh) 0.3 3.5–11.6 30–40 Calendar Life (year) 15 10+ 10

Cycle Life (cycles) 3,000 3,000–5,000, deep discharge 750+, deep discharge

Maximum System Weight (kg) 40 60–120 300 Maximum System Volume (l) 32 40–80 133

Operating Temperature Range (ºC) -30 to +52 -30 to 52 -40 to 85 Selling Price of System (@100K units/year) $20/kW $300/kWh $150/kWh

Source: David Howell, 2011 DOE Vehicle Technologies Annual Merit Review USABC: United State Advanced Battery Consortium

DOE and USABC Battery Requirements for Electric Drive Vehicles

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DOE Battery R&D Activities

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DOE Battery Targets

Battery Technology Comparison

4X Cost Reduction

2X Size

Reduction

>2X Weight

Reduction

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Battery Thermal Management Needed for xEVs

2012 Nissan Leaf EV

Impact of Temperatures on Range

Air cooling Liquid cooling Conduction cooling

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Temperature Impacts Batteries in xEVs

• Lithium-ion battery (LIB) technology is the energy storage of choice for electric drive vehicles (xEVs) in the coming years

• Temperature has a significant impact on life, performance, safety, and thus cost of LIBs and xEVs

Dictates power capability through cold cranking

Also limits the electric driving range

Dictates the size depending on the power and energy

fade rate

Limiting power to reduced T increase and

degradation

Kandler Smith, NREL Milestone Report, 2008

Desired Operating

Temperature

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NREL–Electrochemical/Thermal Modeling for Battery Thermal Management

Prototype build for 24-cell module

CAD Geometry model

FLUENT simulations Inflow

Outflow

Chevy Volt plug-in hybrid

NREL has transferred its electrochemical-thermal model to GM & ANSYS to develop a battery design software tool

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Battery Thermal Characterization

• NREL has developed isothermal battery calorimeters for measuring waste heat from batteries under various loads and temperatures.

• NREL has partnered with NETZSCH Instruments to commercialize its isothermal battery calorimeter technology

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RMS Discharge Current (Amps)

Initial Temp = -15 C Initial Temp = 0 C Initial Temp = 30 C° ° °

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Transient Thermoreflectance (TTR) • Ultrafast laser utilized in a

technique for measuring o Thermal conductivity of very high-

performance materials o Thermal resistance between layers

in a multilayer packaging structure

• Significance o Helps quantify thermal resistance

of high-performance interfaces and materials

o Helps solidify NREL’s position as Lead Laboratory for Thermal Management of Power Electronics and Electric Motors

Pump Laser

Function Generator Lock-In Amplifier

Photodiode

Probe Laser

Multi-mode Optical Fiber Lens Tube

Sample Modulated pump laser

Reflecting mirrors

Collimating lenses

Modulated pump laser

Heat transfer

Probed temperature

variation

Probe laser Sample

Schematic of TTR technique

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Thermal-Electrochemical Modeling of Batteries

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Comparison of two 40 Ah flat cell designs

This cell is cycled more uniformly, can

therefore use less active material ($) and

has longer life.

2 min 5C discharge

working potential working potential

electrochemical current production

temperature temperature

soc soc

electrochemical current production

High temperature promotes faster electrochemical reaction Higher localized reaction causes more heat generation

Larger over-potential promotes faster discharge reaction Converging current causes higher potential drop along the collectors

SOC: State of Charge

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Thermal Management for Power Electronics: Reducing Cost, Improving Reliability

* Inverter: cold plate, drive boards, thermal interface material, bus bar, current sensors, housing, control board, etc.Motor: bearings, housing, sensors, wire varnish and insulation, potting materials, shaft, etc.

EM Active Material

Power Module

Capacitors

Misc. Material

Manufacturing

$19/kW

$8/kW

Reduce motor losses, eliminate use of rare earth PMs, improve thermal management

High-temperature solutions using WBG, improve power electronics performance, integrate functionality, improve efficiency , improve thermal management

Reduce capacitance req., increase capacitor performance

Reduce part count and material costs, increase efficiency

Reduce part count, simplify manufacturing0

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Cost

($/k

W)

Courtesy: Oak Ridge National Laboratory

Prototype inverter-scale heat exchanger

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R&D Agenda

Electric Motor Thermal Management • Higher-power duty cycles for electric-drive vehicles increase the thermal impact on electric

motors leading to increased motor size • Improvements in motor thermal management enable robust performance within cost, weight,

volume, and efficiency constraints

Interior Permanent Magnet (IPM) Motor Cross-Section

Passive Thermal Design

Cooling Technology Development

Transmission Oil Cooling

• Measure bulk thermal conductivity, specific heat, and thermal contact resistance of motor steel lamination materials

• Quantify thermal properties for slot windings • Complete parametric finite element thermal sensitivity

analysis of motor materials, interfaces, and cooling mechanisms

• Develop flexible test bench for measuring the heat transfer potential of electric motors cooled with automatic transmission fluid

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Integrated Power Module Single-Phase Liquid Cooling

• Improved heat dissipation enables increased power for robust operation within cost and size constraints

• Thermal management impacts power silicon, cooling, and housing costs

• Double power per die area with comparable or better power density relative to current state-of-art commercial systems

• Enable low cost, scalable, and low waste manufacturing methods

• Enable use of less aggressive convective cooling technologies

Credit: Gilbert Moreno, NREL

1. Synthesis Partners LLC. “Technology and Market Intelligence: Hybrid Vehicle Power Inverters and Cost Analysis.” July 2011.

R&D Focus Developed integrated heat spreader and heat exchanger design compatible with aluminum extrusion processes that meets performance metrics.

Optimized Heat Spreader

Refined Fin Geometry to Meet Targets

Built Hardware Prototype

Quantified System Impact

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Surface (Wolverine)

Metallized substrate

Base plate

Plastic Manifold

Device

Bonded interfaces/materials

Wire/ribbon bonds

WEG jets

Enhancedsurface

MicroCool Surface (Wolverine)

Single-Phase Liquid Jet Impingement

Perc

enta

ge in

crea

se

over

bas

elin

e

Experimental and Numerical Modeling Results

Approach

Jets on plain surface

Jets on enhanced surface

Enhanced Surfaces Copper

Microporous (3M) Copper

Nanowire (CU)

Spray Pyrolysis (NREL)

Microfinned Surface

(Wolverine)

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Heat Flux (W/cm2)

Refrigerant: HFO-1234yf

Two-Phase Cooling of Power Electronics Enhanced Surface Coatings

• Passive means to increase heat transfer coefficients by as much as 350%

• Simple means to increase power density of electronic devices

Microporous coating

Non-coated

Pool boiling heat transfer coefficients for microporous coated and non-coated surfaces

• Passive, two-phase cooling with microporous coating reduced thermal resistance by over 50% as compared with state-of-the-art automotive cooling system

• Increased performance translates to increased power density

• Better performance with no pump required

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Two-Phase Cooling

Conventional automotive cooling

Lower thermal resistance, increased power density

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High Temperature Air-Cooled Power Electronics Meet DOE’s 2015 technical targets using direct air cooling of the traction drive inverter

Everything on a vehicle is ultimately air-cooled

• Directly cooling with air can eliminate intermediate liquid cooling systems reducing cost, weight, volume, and complexity

• Project is on track to meet power density and specific power goals

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Thermomechanical Reliability of Power Electronics Components

1. Sample Synthesis

2. Accelerated Testing 3. Nondestructive Imaging

4. Electrical

5. Thermal 6. Physical

7. Thermomechanical Modeling

• Improve reliability of new technologies

• Develop predictive failure models which can be used for design Time

s1<s2<s3 s3 s2 s1

t(s3) t(s2) t(s1)

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Thermal management is a

key component of a balanced science

portfolio.

The value of basic research to meet broader energy goals….

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Visit us online at www.nrel.gov

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BACKUP

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Radiant Ceilings

Thermal Mass Walls

Operable Windows

Underfloor Ventilation

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Research Support Facility

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NREL High Performance Computing Data Center

• Showcase Facility – 10MW, 10,000 s.f. – Leverage favorable climate – Use evaporative rather

mechanical cooling. – Waste heat captured and

used to heat labs & offices. – World’s most energy efficient

data center, PUE 1.06! – Lower CapEx and OpEx.

• High Performance Computing – Petascale+ HPC Capability in 2013 – 20 year planning horizon

• 5 to 6 HPC generations. – Insight Center

• Scientific data visualization • Collaboration and interaction.

National Renewable Energy Laboratory Steve Hammond

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Data Center Design Points Warm water cooling • Water much better working fluid than air • Cooling supply at 75F (24C) • Eliminate inefficient chillers • Utilize evaporative cooling

Capture waste heat • Return water at 95F (35C) or warmer • Use heat for offices & labs

Component-level Liquid Cooling • Highest efficiency realized when heat exchange

occurs close to where heat is generated (at the chip)

• This permits higher temp. cooling supply and enables hotter return, more opportunities for waste heat use

• Heavily monitored so we can manage to efficiency targets

National Renewable Energy Laboratory Steve Hammond

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Example of NSF Funded Research in Thermal Transport

SEP Collaborative: Pathways to Scalable, Efficient and Sustainable Soil Borehole Thermal Energy Storage Systems, University of Colorado at Boulder and Colorado School of Mines

BIPV Products & PV-T Array

Polymer Solar Water Heaters NSF/DOE Thermoelectrics Partnership: Inorganice-Organic Hybrid Thermoelectrics, Texas A&M University Engineering Experiment Station

Development of Enhanced Performance Energy Storage Materials Using Tailorable Percolation Networks of Nanofibers, Villanova University

Transport-Enhanced Thermogalvanic Energy Conversion, Arizona State University

Catalothermionic Sold State Electric Generator with Nonadiabatic Functionality, University of Illinois at Chicago