energy storage requirements for hybrid fuel cell … duration (s) f u e l c o ns um pt i o n i m p r...

NREL, CENTER FOR TRANSPORTATION TECHNOLOGIES AND SYSTEMS

Energy Storage Requirements for Hybrid Fuel Cell Vehicles

Tony Markel, Matthew Zolot, Keith WipkeAhmad Pesaran

National Renewable Energy Laboratory

June 13, 20032003 Advanced Automotive Battery Conference

www.ctts.nrel.gov/BTM


Presentation Outline

• Objectives• Previous Studies• Current Approach• Results

- Technical Results- Cost Analysis

• Conclusions


Objectives

• Extend previous studies to determine how the fuel cell and battery sizing choices can impact not only efficiency but also cost, mass, and volume constraints.

• Analyze the fuel cell and energy storage system demands under drive cycle and performance tests for two vehicle platforms using ADVISORTM.

• Consider several sizing scenarios and energy storage technologies.

• Support the FreedomCAR technical teams in defining energy storage requirements for fuel cell vehicles.


Previous Studies

0 100 200 300 400 500 6000

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S tartup Duratio n (s )

Fuel

Con

sum

ptio

n Im

prov

emen

tH

ybrid

vs.

Non

-Hyb

rid (%

)

• Hybridization of a fuel cell vehicle with energy storage improves fuel economy and make it practical (UCD, VTech, NREL)– Smaller fuel cell - lower cost – Fuel cell or reformer warm up– Improving transient response– Capturing regenerative breaking

• Pre-production prototype fuel cell vehicles are hybrids– Toyota FCHV – (NiMH)– Honda FCX – (ultra-capacitors)


Optimization of Fuel Cell Vehicle Design Provides Insight into System Trade-offs

• Derivative-free optimization algorithms necessary for complex design space of HEVs

• Drive cycle influences optimal degree of hybridization and control parameters

– NEDC provides robust design

• Fuel cell transient response capability critical for “pure” fuel cell vehicle

• An optimized hybrid design can nullify the effects of fuel cell transient response

• Fuel economy impact of gasoline reformer warm-up may be substantial

• Relatively small energy storage system can overcome warm-up limitations of reformer

0.0

10.0

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50.0

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70.0

80.0

90.0

Minimum Power Maximum Power Charge Power Minimum Off TimeControl Parameter

Pow

er (k

W),

Tim

e (s

*10)

US06 VehicleComp. VehicleNEDC Vehicle1015 Vehicle


Approach for This Study

• Summarize Study Assumptions• Determine the Potential Roles of the Battery• Run Simulations to Quantify Requirements

Associated with Individual Roles• Compile the Battery Requirements• Compare Requirements to Existing Technology

EnergyPo

wer


Vehicle and Performance Assumptions

Vehicle CharacteristicsVehicle CharacteristicsAssumption Description Units mid-size SUV mid-size Car

Vehicle Description -- Rear wheel drive

mid-size SUVFront wheel drive

mid-size carBase Conventional Vehicle Mass kg 1865 1480Base Vehicle Glider Mass kg 1276 1074Cargo Mass kg 136 136Fuel Cell Vehicle Mass kg 1923 1553Aero. Drag Coef. -- 0.41 0.33Frontal Area m^2 2.6 2Rolling Resistance Coef. -- 0.012 0.009Wheel Radius (effective) m 0.343 0.314Vehicle Range mi (km) 300 (483) 300 (483)

PerformancePerformanceAssumption Description Units

mid-size SUV

mid-size Car

0-60 mph (0-97 kph) s <=11.2 <=1240-60 mph (64-97 kph) s <=4.4 <=5.30-85 mph (0-137 kph) s <=20.0 <=23.4Grade @ 65mph (105kph) for 20min. @ Curb Mass + 408kg % >=6.5 >=6.5Drive Cycle Tolerance mph (kph) <=2 (3.2) <=2 (3.2)SOC Balancing % <=0.5% <=0.5%


Energy Storage System Assumptions

Assumption Description Units PbA NiMH Li-IonUltra-

capacitorEnergy Storage Energy Density Wh/L 75 100 190 5Energy Storage Specific Energy Wh/kg 35 55 100 4Energy Storage Energy Density W/L 1600 2000 2800 4500Energy Storage Specific Energy W/kg 550 1000 1300 3500Energy Storage Cost (power) $/kW $10.00 $40.00 $60.00 $15.00

DOE-OTT High-Power Vehicle Energy Storage Target UnitsEnergy Storage Cost (energy) $/kWh $1,666.67Energy Storage Cost (power) $/kW $20.00


Fuel Cell and Hydrogen Storage Assumptions

Fuel Cell SystemFuel Cell SystemAssumption Description Units 2005 2010Fuel Type -- hydrogen hydrogenFuel Cell Peak Efficiency % 62.9 62.9Fuel Cell Efficiency at 25% Power % 60 60Fuel Cell Efficiency at Rated Power % 53.6 53.6Fuel Cell System Specific Power W/kg 500 650Fuel Cell System Power Density W/L 500 650Fuel Cell System Cost $/kW 96 27Fuel Cell System 10-90% Power Transient Response Capability s 2 1

Hydrogen StorageHydrogen StorageAssumption Description Units 2005 2010H2 Storage Energy Density kWh/L 1.2 1.5H2 Storage Specific Energy kWh/kg 1.5 2H2 Storage Cost $/kWh 6 4


Roles of the Energy Storage System

• Traction power during fuel cell startup• Power-assist during drive cycles • Regenerative braking recapture• Gradeability performance• Acceleration capability• Electrical accessory loads• Fuel cell startup

and shutdown


Pictorial Description ofRoles of the Energy Storage System

Reduced FC Power Reduced FC Power During FC StartupDuring FC Startup

Lagging FC Power Lagging FC Power Due to FC Ramp RateDue to FC Ramp Rate

timetime

Acceleration, Grade, and Acceleration, Grade, and Peak Pulse Power Shaving Peak Pulse Power Shaving from FC Downsizingfrom FC Downsizing

Regen Regen CapabilityCapability

PowerPower


Drawing Power Envelope during a Drive Cycle

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-5

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Trac

tion

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Time (s )


Traction Power During Fuel Cell Startup

Energy Mid Car 2005Energy Mid Car 2005

Power Mid Car 2005Power Mid Car 2005

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Pow

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midCar_2005_2UDDSmidCar_2005_HWFETmidCar_2005_US 06

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Time (s )

Cum

mul

ativ

e E

nerg

y - N

o R

egen

(Wh)



Traction Power During Fuel Cell Startup

Energy Mid SUV 2005Energy Mid SUV 2005

Power Mid SUV 2005Power Mid SUV 2005

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Time (s )

Pow

er (k

W)

midS UV_2005_2UDDSmidS UV_2005_HWFETmidS UV_2005_US 06

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Time (s )

Cum

mul

ativ

e E

nerg

y - N

o R

egen

(Wh) midS UV_2005_2UDDS

midS UV_2005_HWFETmidS UV_2005_US 06


100kW Example - Energy Storage Traction Power/Energy During Fuel Cell Startup

EnergyEnergy

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Time (s )

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Fuel CellEnergy S torage

SUV requirements during SUV requirements during the US06 assuming limited the US06 assuming limited

fuel cell performance

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100

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Cum

ulat

ive

Ene

rgy

(Wh)

Time (s )

midS UV_2005_US 06 fuel cell performance

PowerPower


Traction Power Assist During US06 Drive Cycle

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Fue l Ce ll S iz e (kW)

Ene

rgy

Sto

rage

Pea

k P

ower

(kW

)

midCa r_2005_US 06midS UV_2005_US 06

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Fuel Ce ll S ize (kW)

Ene

rgy

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rgy

(Wh)

midCar_2005_US 06midS UV_2005_US 06

EnergyEnergy Battery provides peak Battery provides peak shaving capability during the shaving capability during the US06 drive cycleUS06 drive cycle

PowerPower


Traction Power/Energy Requirements Due to 2s Fuel Cell Power Response Capability

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Req

uire

d E

nerg

y S

tora

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ssis

t Pow

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FC P owe r (kW)


PowerPower

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Req

uire

d E

nerg

y S

tora

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FC P owe r (kW)


EnergyEnergy Battery provides ramp rates Battery provides ramp rates greater than fuel cell’s ramp greater than fuel cell’s ramp capabilitycapability


Total Available Regenerative Braking Energy possible for Recapture

CarCar

SUVSUV

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ilabl

e R

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Ene

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Regenerative Braking Event Analysis

CarCar

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Power (kW)Duration (s )

Ene

rgy

(Wh)

midCar_2005_2UDDSmidCar_2005_2UDDSmidCar_2005_HWFETmidCar_2005_HWFETmidCar_2005_US 06midCar_2005_US 06

SUVSUV

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Power (kW)Duratio n (s )

Ene

rgy

(Wh)

midS UV_2005_2UDDSmidS UV_2005_2UDDSmidS UV_2005_HWFETmidS UV_2005_HWFETmidS UV_2005_US 06midS UV_2005_US 06


Acceleration Performance – Power Demanding

PowerPower

EnergyEnergyDuring 0During 0--60 (060 (0--97kph) 97kph) mph maximum mph maximum accelerationacceleration


Gradeability Performance – Energy Demanding

EnergyEnergy

PowerPower

6.5% Grade @ 65 mph 6.5% Grade @ 65 mph (105kph) for 20 minutes(105kph) for 20 minutesAt curb mass + 408kg At curb mass + 408kg


Accessory Loads

• FTP– 750 W for 2738 s

• 570 Wh• HWFET

– 750 W for 765 s• 159 Wh

• US06– 1500 W for 600 s

• 250 Wh• SC03

– 3000 W for 600 s• 500 Wh

0100200300400500600

Ener

gy (W

h)

Battery for Accessory Loads

FTP HWFETUS06 SCO3


Summary of Energy Storage Requirements for SUV (for 100kW Fuel Cell Case)

Event Description

Peak Power (kW)

Duration (s)

Cumulative Energy (kWh)

Comments

A Startup Traction Loads

46.4 <11 0.15 50% rated power,120s warm-up over 2UDDS, HWFET, & US06

B Power-assist (response)

70.0 <3 0.08 2 second 10%-90% FC response (ramp) rate (during 2UDDS, HWFET, & US06)

C Power-assist (downsize)

43.3 <3 0.05 During 2UDDS, HWFET, & US06. US06 is limiting case

D Gradeability (see Table 2)

0.0 1200 0.00 81.4 kW sustained load for 1200s

E Acceleration 40.0 20 0.22 140 kW sustained load for 20sF Accessory

Loads1.5 600-2800 0.10 US06 peak power, energy is for

US06 4 min, or FTP 8 minG Fuel Cell

ShutdownN/A N/A N/A -

H Regenerative Braking

70.0 <30 1.50 Pmax is during US06, energy is FTP cycle max

•• Power Requirement = max(A,B,C,D,E) + aux. load if applicablePower Requirement = max(A,B,C,D,E) + aux. load if applicable•• Energy Requirement = greatest of four casesEnergy Requirement = greatest of four casesCase(1)Case(1) The energy required to sustain the continuous grade power, plusThe energy required to sustain the continuous grade power, plus a a

750W accessory power for 20 minutes;750W accessory power for 20 minutes;Case(2)Case(2) The energy required to sustain the energy storage power requireThe energy required to sustain the energy storage power requirement ment

over six consecutive acceleration tests;over six consecutive acceleration tests;Case(3)Case(3) The energy required to sustain the Highway or FTP accessory loaThe energy required to sustain the Highway or FTP accessory load for d for

eight minutes, or the US06 accessory load for 4 minutes;eight minutes, or the US06 accessory load for 4 minutes;Case(4)Case(4) The summation of the energies in A, B, and C. Minus overlap inThe summation of the energies in A, B, and C. Minus overlap in cases cases

A and C,cases A and B are additive (neglecting slight overlap).A and C,cases A and B are additive (neglecting slight overlap).

Required: Power = 71.5kW, Energy = 1.33kWh

(from Case 2 below)


Summary of Energy Storage Requirements for SUV (for varying Fuel Cell Size)

• Energy storage power (P), energy (E), and P/E ratio are compiled for many fuel cell sizes.

• Plot illustrates how P,E, and P/E change while the fuel cell is downsized.

Energy Storage Requirements vs Fuel Cell Peak Power Size

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50 60 70 80 90 100 110 120 130 140 150Fuel Cell Peak Power (kW)

Req

uire

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ergy

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rage

Peak

Pow

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W),

P/E

Rat

io

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uire

d En

ergy

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rage

Ener

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Peak Power (kW) P/E ratio Energy (kWh)

To 555 at 140 kW


Fuel Cell Cost and Volume - 2010

CostCost

VolumeVolume

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Cos

t ($)

Fue l Ce ll Po w e r (kW)

H2 S tora ge - 2010Fue l C e ll - 2010S ys te m - 2010

70 80 90 100 110 120 130 140100

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ume

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H2 S tora ge - 2010Fue l C e ll - 2010S ys te m - 2010


Chemistry Dependent Energy Storage System Cost and Volume

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$1,500

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$4,500

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Cos

t of R

equi

red

Bat

tery

Pac

k ($

)

PbA NiMH Li-Ion Ultra-capacitor

CostCost

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ergy

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rs)

PbA NiMH Li-Ion Ultra-capacitor

VolumeVolume


Powertrain System Cost and Volume - 2005

CostCost

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Ene rgy S torage S ys te mFue l Ce ll S ys te m - 2005Tota l S ys te m - 2005

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Ene rgy S torage S ys te mFue l Ce ll S ys te m - 2005Tota l S ys te m - 2005

VolumeVolume


Powertrain System Cost and Volume - 2010

CostCost

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Ene rgy S to rage S ys te m Cos tFue l Ce ll S ys te m - 2010Tota l S ys te m - 2010

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Ene rgy S to rage S ys te mFue l Ce ll S ys te m - 2010Tota l S ys te m - 2010

VolumeVolume


Conclusions• A methodology has been developed for determining the

requirements of an energy storage system to be included in a fuel cell hybrid vehicle.

• Requirements depends on the energy storage system’s expected roles.

• This study’s energy storage system requirements for a mid-size SUV ranged from 40-85 kW and 0.05-7 kWh depending on fuel cell system size and the role of the energy storage system.

• The best choice for energy storage chemistry may be different depending on the level of fuel cell downsizing.

• Downsizing fuel cell beyond the power level required for continuous gradeability led to dramatically increased energy requirements (and thus predicted cost) for the energy storage system.

• Short term costs drive design toward smaller fuel cell and larger battery while cost is less influential in long-term design scenarios


Future Work

• Refine vehicle and components assumptions to support identifying energy storage requirements for fuel cell vehicles

• Perform more detailed startup and shutdown load data for present/future fuel cell systems.

• Investigate use of ultracapacitors for hybrid fuel cell vehicles.• Define the bounds for future optimization problems in which

cost, volume, and mass constraints can all be evaluated simultaneously while maximizing fuel economy.


Acknowledgements

• This study was sponsored by U.S. Department of Energy’s Office of FreedomCAR and Vehicle Technologies.

• We appreciate the technical discussions we had with several FreedomCAR Technical Teams during the course of this study.

www.ctts.nrel.gov/BTM

energy storage requirements for hybrid fuel cell … duration (s) f u e l c o ns um pt i o n i m p r...

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