Energy Storage in Advanced Vehicle Systems

Andrew BurkeInstitute of Transportation Studies

University of California-DavisDavis, California 95616

Presentation at theStanford UniversityGCEP Advanced Transportation WorkshopOctober 10,2005

Outline of the presentation

1. Introduction/scope

2. System characteristics

3. Electrical energy storage (batteries and ultracapacitors)

4. Mechanical and chemical energy storage

5. Vehicle applications using various technologies

6. Economic and life cycle considerations

7. Summary and conclusions

Applications

Passenger cars, vans, and SUVs

Light and medium duty trucks

Transit buses

Advanced Vehicle Systems

Electric vehicles (ZEVs)

Hybrid-electric vehicles•Charge sustaining (liquid fuel only)

•Charge depleting (grid-connected)

Fuel cell powered vehicles (hydrogen fueled)

Energy storage technologies

Electrical energy storage•Batteries•Ultracapacitors

Mechanical energy storage

• flywheels•Hydraulics•Compressed air

Chemical storage

•Liquid fuels•Hydrogen

Roles of energy storage on a vehicle

Primary energy storage (average power)

• liquid fuel•Batteries on an EV•Hydrogen on a FCV

Secondary energy storage (pulsed power)

•Batteries or ultracaps on a hybrid•Flywheel or hydraulics

Energy storage system characteristicsSystem designed for specified peak (pulse) power kW

and useable energy storage Wh or kWh

Either the peak power or energy stored can be the determining requirement that sizes (weight and volume) of the energy storage system

The peak power is the critical requirement for most vehicle designs

Trade-offs between power density W/kg and energy density Wh/kg become important for vehicle applications

Variation of power density with SOC and charge/discharge can be important

Very high cycle life is needed

Pulsed operation of the energy storageNear peak power for short periods 5-30 seconds

High power charge and discharge pulses

High efficiency at high power is needed for both charge and discharge pulses

Average power is much less than pulse power

Hundreds of thousands of pulses over the lifetime of the devices

Energy storage required (Wh) is use-cycle dependent

SOC variation must be controlled

Energy Density and Peak Power Density Projections for Various Energy Storage

Technologies

Ultracapacitors•High power and low resistance (2 kW/kg, 95%)

•Long cycle life (>100K cycles)

•Cycle life independent of the pattern of SOC

•Long shelf life (>10 years)

•Relatively low energy density (< 10 Wh/kg)

•Power characteristics independent of SOC

Batteries

•High energy density (30-150 Wh/kg)

•Moderate power (< .5 kW/kg at 95% effic.)

•Relatively short shelf life (1 year w/o recharge)

•Relatively short cycle life (1Kcycles, deep disch.)

•Cycle life can dependent on the pattern of SOC

•Variation of power characteristics with SOC

Power density examplesPrius battery Ni Mt. Hydride Panasonic EV Claimed peak power 1080 W/kg, V min =.7 EF= .9, 443 W/kg, EF=.95, 205 W/kg Saft Li-ion battery Claimed peak power 2000 W/kg, V min =2.7 EF= .9, W/kg=820, EF=.95, W/kg= 432 Panasonic Lead -acid battery Claimed peak power 360 W/kg, V min =1.48 EF=.9, 154 W/kg, EF= .95, W/kg=81

When does the use of Ultracapacitors make sense?

The battery can be sized by the energy storage or peak power requirement. If the battery weight to meet the power requirement is several times greater than that needed to meet the energy requirement or the battery design or its operation must be compromised to meet the power requirement, then it makes sense to consider the use of ultracapacitors either in place of the batteries or in combination with batteries.

A key issue in making this judgement is the peak pulse power density assumed for a particular battery. In some applications, the efficiency of the charge and discharge is a key issue. This is the case for hybrid vehicles. The power density of the battery and ultracapacitor should be compared at the same efficiency. The voltage drop due to the current pulse is the best measure of the efficiency (EF=Vp/Videal) of the discharge. The high power quoted for ultracapacitors is for 90-95 % efficiency and that for batteries is in most cases for 65-70% efficiency.

Commercially available devices Carbon/carbon (Large devices > 1000F)

• Panasonic Industrial (Japan)

• Maxwell/Montena (US and

Switzerland) • EPCOS (Germany)

• Ness (Korea)

• Nippon-Chemical (Japan)

Device V

rated C

(F) R

(mOhm) RC

(sec) Wh/kg

(1)

W/kg (95%)

(2)

W/kg Match. Imped.

Wgt. (kg)

Vol. lit.

Maxwell** 2.5 2700 .32 .86 2.55 784 6975 .70 .62 Ness 2.7 10 25.0 .25 2.5 3040 27000 .0025 .0015 Ness (3) 2.3 120 21.0 2.5 3.8 282 3700 .017 .010 Ness 2.7 1800 .55 1.00 3.6 975 8674 .38 .277 Ness 2.7 3640 .30 1.10 4.2 928 8010 .65 .514 Ness 2.7 5085 .24 1.22 4.3 958 8532 .89 .712 Asahi Glass (propylene carbonate)

2.7 1375 2.5 3.4 4.9 390 3471 .210 (estimated)

.151

Panasonic (propylene carbonate)

2.5 1200 1.0 1.2 2.3 514 4596 .34 .245

Panasonic 2.5 1791 .30 .54 3.44 1890 16800 .310 .245 Panasonic 2.5 2500 .43 1.1 3.70 1035 9200 .395 .328 EPCOS 2.5 220 3.0 .66 2.76 1126 10000

.052 .042

EPCOS 2.5 2790 .15 .42 3.46 2055 18275 .57 .377 Montena 2.5 1800 .50 .90 2.49 879 7812 .40 .30 Montena 2.5 2800 .39 1.1 3.33 858 7632 .525 .393 Okamura Power Sys.

2.7

1350

1.5

2.0

4.9

650

5785

.21

.151

ESMA 1.3 10000 .275 2.75 1.1 156 1400

1.1 .547

(1) Energy density at 400 W/kg constant power, Vrated - 1/2 Vrated (2) Power based on P=9/16*(1-EF)*V2/R, EF=efficiency of discharge

** Except where noted, all the devices use acetonitrile as the electrolyte (3) Psuedo-caps from Ness using carbon/metal oxide electrodes

Summary of the characteristics of carbon/carbon devices

Two EPCOS 2800F, 2.5V Devices

Maxwell/Montena 700F, 2.5V capacitor

Ness Capacitor 5000F, 2.7V

Ness 45V Module

18 Ness 3500F cells

19.1 kg, 26.1 liters

Balancing circuits between cells

PSFUDS Power Vs Time

-7

-6

-5

-4

-3

-2

-1

0

1

2

0 50 100 150 200 250 300 350 400 450 500

Time (sec)

Pow

er (k

W) Maximum power step

W/kg =500 based on weight of cells alone

Roundtrip Efficiencies for the Ness 45V Module on the PSFUDS cycle

Cycle*

Energy in Wh

Energy out Wh

Efficiency %

1 102.84 97.94 95.2 2 101.92 97.94 96.1 3 101.67 97.94 96.3

*PSFUDS power profile based on maximum power of 500 W/kg and the weight of the cells alone

Roundtrip Efficiencies for 48V Module on PSFUDS Cycle

Without Circuit With Circuit

Max Efficiency Max EfficiencyPower % Power %500W/kg 500W/kg

1 95 1 93.22 95.8 2 94.63 96.2 3 95

1000W/kg 1000W/kg1 92.4 1 912 92.4 2 91.7

3 92.41500W/kg 1500W/kg

1 89.1 1 88.52 90.7 2 89.93 90.8 3 88.7

Roundtrip efficiencies on Modified PSFUDS cycles

Flywheel Motor-Generator

Litz Wire Stator

Dipole Halbach Array Carbon Fiber Rotor

Magnetic Bearings

Parameter

Ness capacitors (3500 F)*

AFST NGT flywheel (design targets)

M3 DC FPS (existing unit)

Hydraulics/ Motor/ Generator (Present technology)

Hydraulics/ Motor/ Generator (future technology)

Usable energy kWh

.622

1.0

.42

.26

.26

Max. Power kW

260

200

200

300

300

System weight kg

267

182

500

230

80

System volume Liters

370

256

866

160

90

System voltage V

600-300

450-800

-----

200-800V self-regul. Self limit.

200-800V self-regul. Self-limit.

System efficiency (%) Roundtrip

94

90

90

70-75

80-85

Wh/kg 2.33 5.5 .84 1.13 3.25 Wh/liter 1.7 3.9 .49 1.6 2.25 W/kg – 90% 970 1100 400 1875 * 3330*

• Ness unit characteristic based on an existing 45V, 200F unit • * maximum power at maximum efficiency listed for the hydraulic

unit

Comparison of flywheel and ultracapacitor systems

Storage technology Wh/kg Wh/L Compressed air

carbon tanks

Isothermal-4500 psi

137 48

Polytropic n=1.3 59 21

Hydrogen-carbon tanks

5000 psi 2000 700 10000 psi 1666 1165

Hydrogen -

hydrides

100 deg C 535 2000 300 deg C 1880 1600

Batteries

Lead-acid 30 70 Nimthydride 70 180 Lithium-ion 120 250

Composite

flywheels syst.

3

2 Hydraulics syst. 2 2 Carbon/carbon ultracapacitors

5

6.5

gasoline 11660 8750

Summary of the energy density characteristics of various energy storage technologies

Trade-offs between energy density and power density for batteries

Application/ battery type

Energy density Wh/kg

Energy density Wh/L

Pulse power density W/kg (90%)

Energy stored kWh

Fraction of energy useable

Electric vehicle Nimthydride 65 170 200 40-50 80% Lithium-ion 130 275 450 40-50 80%

Grid-connect

hybrid

Nimthydride 50 135 250 9-12 80% Lithium-ion 100 220 650 9-12 80%

Charge

sustaining hybrid

Nimthydride 40 110 450 2-3 10-15% Lithium-ion 70 150 1200 2-3 10-15%

Carbon/carbon ultracapacitors

5

6.5

2500

.3-.5

75%

Applications of energy storage in electric and hybrid vehicles

Commercial products are available primarily from Honda and Toyota

Examples shown will be based on Advisor simulations

Simulation results in agreement with test data from vehicles

Present status of energy storage for vehicles

Nimthydride batteries used in most electric and hybrid-electric vehicles available to the public

Lithium-ion batteries have the best performance of the available batteries, but are not yet ready for use in vehicles for the public

Carbon/carbon ultracapacitors are available for testing in proto-type vehicles, but not yet in planned commercial products

Battery electric vehicles

Electric Vehicles using Lithium-ion Batteries Vehicle

type Test

Weight kg

Max. power

kW

Battery weight

kg

Max. power density W/kg

Battery energy kWh

Energy density Wh/kg

Compact car

1133 50 178 280 25 140

Mid-size

SUV 1604 77 285 268 40 140

Vehicle type

Max power

kW

Energy use

Wh/mi

Range miles

0-60 mph sec

Battery weight

kg

Energy storage kWh

Compact car

12

178

25

FUDS 29 175 152 Highway 24 166 146

Mid-size

SUV

12

285

40 FUDS 44 274 155

Highway 36 263 145

Performance of electric vehicles with lithium-ion batteries

Plug-in (grid-connected) hybrid vehicles

Example of a compact car like a Honda Civic

Distance traveled miles -

FUDS

Fuel economy mpg

kWh electricity

Gallons gasoline

22.4 ZEV 4.05 0 37.3 230 6.15 .16 52.2 105 6.3 .50 67.1 78 6.3 .86 74.5 71 6.3 1.05 90 63 6.3 1.43

Compact car, test weight 3025 lbs, 9 kWh energy storage, 98 kg lithium-ion batteries, 55 kW engine, 50 kW electric motor 0-60 mph acceleration 11 sec

Fuel economy of a plug-in hybrid

Conventional ICE compact car 29 mpg FUDS, 43 mpg Federal highway cycle 0-60 mph 10 sec

Advisor output for a plug-in hybrid on the FUDS

Distance traveled miles – HW cycle

Fuel economy mpg

kWh electricity

Gallons gasoline

20.5 242 2.7 .085 31 149 3.6 .21 41 113 4.05 .36 51 97 4.275 .525 71 83 4.725 .85 92 76 5.175 1.21 123 70 5.85 1.76 154 67 6.3 2.30 205 62 6.3 3.31 512 56 6.3 9.14

Fuel economy of a plug-in hybrid on the Highway cycle

Advisor output for a plug-in hybrid on the highway cycle

Plug-in (Grid-connected) hybrid performance and economic characteristics for various all-electric ranges (0-60 miles)

Parameter ICE CV HEV0 HEV20 HEV60 Engine kW 127 67 61 70 Motor kW 0 44 51 55

Battery kWh 0 2 9 20 Bat $/kWh 410 320 270

Battery cycle life for 15

years

----

5200

2600

Engine/trans

cost $

6800

4100

3000

4280 Motor cost $ 0 2084 2313 2500 Battery cost $ 0 1230 2880 5400 Bat charger $ 0 0 700 900 Total driveline

cost $

6800

7414

8893

13080 Differential

cost $

0

614

2093

6280

Miles/yr 15000 15000 15000 15000 Miles/yr electric

0

0

5000

10000

Fuel economy mpg

28.9

41.9

75.6

120

Gallons gas/yr. 519 358 198 125 kWh elec./yr 0 0 1400 2800

Electricity cost/yr @ 8

ct/kwh

0

0

112

224

Breakeven gasoline price

$/gal. for 4 years driving.

.95

1.97

4.70

Based on the EPRI study for a mid-size passenger car gasoline engine, AC electric motor and electronics, nickel metal hydride batteries

Simulation results for non-plug-in hybrids(charge sustaining)

Similar to the Honda Civic and Accord hybrids

mpgVehicle

description Engine

kW Electric Motor

kW

Type of storage

Energy storage

kg

FDHW

FUDS

ES06

ICE 5-speed

120

34.5

22.6

25.3

ICE CVT

120

32.5

21.7

23.8

Single-shaft

hybrid CVT or 5-speed

carbon/ carbon

capacitors

120 25 12 38.4 36.6 30.4 120 25 7 36.1 29.4 120 15 24 37 30.3 120 15 12 38.6 36.8 29.7 120 15 7 36.1 29.0

120 10 24 35.5 29.0 120 10 12 35.1 28.6 120 10 7 37.8 34.2 28.4 120 8 24 34.5 28.8 120 8 12 34.0 28.5 120 8 7 37.7 33 28.2

Single-shaft

hybrid CVT

NiMtHd batteries 45 Wh/kg 300 W/kg

95%eff.

120 15 18 34.7 30.6 24.3 Li-ion

60 Wh/kg 730 W/kg

95%eff.

120 15 18 36.7 32.6 24.7

Gasoline PFI engine and AC induction motor used in all drivelines .

Advisor simulations for conventional and hybrid mid-size passenger cars

7 kg capacitors (35 Wh) , 10 kW, 120V electric drive

Driving cycle mpg % improvement FUDS 34.2 54

ES06 28.4 19

HW 37.8 15

Fuel economy improvements in a hybrid mid-size car

Energy storage cost and cycle life are the critical factors in marketing hybrid vehicles

Cost considerations for electrochemical energy storage

Cost parameters $/Wh, $/kW, $/kg

Material costs•Electrodes

•Current collectors

•Electrolyte

•Packaging

Comparisons of the performance and cost of batteries and ultracapacitors for use in mild hybrid-electric

vehicles

Type

Density gm/cm3

Wh/ kg

W/kg 90% effic.

Wh

Wgt. kg (1)

Cost $

$/kg

$/kWh

$/kW

Batteries Lead-acid Standard 2.8 25 160 1875 75 187 2.5 100 9.35 Thin-film 3.0 20 900 1000 50 200 4.0 200 10.0 NiMtHyd. 1.75 45 500 1800 40 900 22.5 500 45.0 Lithium-ion 2.2 65 1100 1170 18 820 45 700 41.0 Ultracapacitors (3)

Carbon/carbon 1.2 5 3500 100 20 357 18 3570 (2)

18

Carbon/PbO2

2.5 12 2000 120 10 72 6.0 600 3.6

(1) Storage unit to provide 20 kW power and store at least 1 kWh in the case of a

battery and 100 Wh in the case of an ultracapacitor for a mid-size car. (2) Carbon/carbon ultracapacitors priced at .25 cents/Farad and rated voltage of

2.6V/cell (3) Ultracapacitors can be deep discharged to one-half rated voltage (at least

75% of rated energy stored) and still have long cycle life of at least 100K cycles. The batteries operate over a narrow voltage range resulting in the use at most 10% of the stored energy in normal operation of the vehicle in order to get cycle life comparable to that of ultracapacitors.

Material costs for a 2.7V, 3500F ultracapacitor for various carbon and other component material unit costs

Carbon

Electrolyte

ACN

Device Cost

Unit

Costs

F/gm gmC/dev. $/kg $/L $/kg salt

Total mat. $

$/kg $/Wh $/kW Ct./F

75 187 50 10 125 15.9 24 6 24 .45 120 117 100 10 125 15.9 24 6 24 .45 75 187 5 2 50 3.2 6.0 1.2 4 .091

120 117 10 2 50 2.6 4.9 1.0 3.3 .075

Cycle life considerations

Batteries•Cycle life limited for deep discharge cycles (likely less than several thousand cycles)

•Cycle life for very shallow cycles (less than 5%) is very long for the nimthydride and lithium-ion batteries (hundreds of thousands of cycles)

•Calendar life (>10 years) is uncertain and depends on temperature during storage and operation .

Ultracapacitors•Cycle life for deep discharge of carbon/carbon capacitors is very long ( hundreds of thousands of cycles)

Summary and conclusionsEnergy storage is a critical technology for the

development of high efficiency vehicle systems

Electrical energy storage is the preferred technology for vehicle applications

Nimthydride batteries are currently the most used technology, but expectations are that lithium-ion will be used in the future

There is presently renewed interest in the use of carbon/carbon ultracapacitors in vehicle applications with cost being the primary consideration

Cost and life, not performance, is the primary concern for batteries in hybrid vehicles

For most vehicle applications, the power capability of the energy storage technology is of prime importance

Summary (cont.)

There is a renewed interest in plug-in hybrids primarily outside the auto industry as a means of diversifying energy sources for vehicles

The fuel economy of hybrid-electric vehicles can be 40-50% or more higher than that of conventional ICE vehicles using batteries or ultracapacitors as energy storage especially in urban driving