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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
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
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
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
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
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
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
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
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
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
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