Energy Storage System Consid

Grid-Charged Hybrid Electric 

presented at

IEEE Vehicular Power and Propulsion Co

by

Tony Markel and Andrew Simpson

September 8, 2005

NREL/PR-540-40236
Disclaimer and Government License

This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-AC36Department of Energy (the “DOE”). The United States Government (the “Government”) retains athe work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrepublish or reproduce the published form of this work, or allow others to do so, for Government puNeither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employeeor implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulnesproduct, or process disclosed, or represents that its use would not infringe any privately owned ri

specific commercial product, process, or service by trade name, trademark, manufacturer, or othimply its endorsement, recommendation, or favoring by the Government or any agency thereof. authors and/or presenters expressed herein do not necessarily state or reflect those of MRI, the agency thereof. 
Overview

• Study objectives• Case study: plug-in HEV energy sto

requirements and options for a mid-

• Battery/engine sizing tradeoffs• Conclusion
Motivation for this Stu

• Traditional ZEV-range concept for plug-in 

ESS capable of high energy storage AND = bigger, more-expensive battery(high power, high energy, low annualized cost* 

Î 

(high power, high energy, low volume 

Î pick any 

• Other HEV control strategy concepts (e.g

can still provide net-discharge, but with repower requirements.Î This might facilitate the use of cheape

smaller batteries

* Annualized cost = battery replacement cost / life
Purpose of this Stud

1. Calculate ESS power and energy re

for plug-in HEV’s with different cont

2. Consider implications for rest of sys

particular, engine efficiency and fue
Some Definitions

Degree of Hybridization (DOH):Power-to-Energy Ratio (P2E):- relates suitability of energy storage to power events wit

(

)

battery ( ) kWmotor engine generator ( 

kW

battery kWmotor DOH

 /

/

 /

+

=

( ) ( ) ( )

(

)

( )

kg

Wh

kg

W

h

ene

po

specific energy

specific power

energy kWh

kWpower

2EP * * 

1 =

=

=
Case Study – Vehicle Speci

Mid-size car from EPRI study:• C

DA = 0.71m

2

• CRR = 0.008

• Pacc = 500W• Test mass 

≈ 1700kg

Peak motive power 

≈ 115kW

Continuous power requirement 

≈ 45kW

• Top speed @ 90mph• 7.2% gradeability @ 50mphElectric energy consumption 

≈ 300Wh/mile
Case Study – Battery Specif

No ICE help With IC

Power

(kW)

Energy

(kWh)

P2E

(1/h)

Power

(kW)

HEV10 115 3 38.3 70 HEV20 115 6 19.2 70 HEV60 115 18 6.4 70 
plugHEVs in this ra

ESS Technology Comparison - P/E Ratios

SAFT VLP 7

Avestor SE 48S63

SAF

SAFT VLP 20

SAFT VLP 30

Cyclon D

Cyclon E

Varta Li 60Ah

Varta Li 6Ah

Prius PEVE SAFT VLE modu

SAFT VL41M module

SAFT VL30P module

Cobasys 1000

Cobasys 4500

Cobasys 9500

2005001000 100 50 20

SAPHION U1-12FN40

SAPHION U24-12FN100

SAPHION U27-FN130

Optima D51

Optima D34

Optima D35

PEVE 7.5Ah

SAFT NiMH 12

SAFT VHF 10S

SAFT VHF 20S

SAFT VHF 30S

SAFT STM 5-100 MR

SAFT STM 5-140 MR

Sprinter Varta

Varta Ni HP

Varta Ni UHP

Prius+ SAPHION

Sprinter SAFT

0

200400600800

100012001400160018002000

0 30 60 90 

Available specific energy (Wh/kg)

Specific power (W/kg)
Battery Products for Comp

Battery Wh/kg Wh/L W/kg W/L Us

S

High Energy (for EVs)SAFT VLE 45 cell 149 313 664 1392 ~ 

Mid Range (for plugHEVs?)SAFT VLM 27 cell 124 252 987 2000 ~ 

Cobasys 4500 module 45 87 605 1180 ~ High Power (for HEVs)Cobasys 9500 module 60 155 250 650 ~ 

SAFT VLP 20 cell 89 187 1413 2973 < Cobasys 1000 module 43 83 1100 2200 < 
Battery/Engine Sizing Tra

45kW is only a lower constraint, engine can be larger than Î This allows a smaller battery to be used...HEV20 exam

Battery Total

Power

(kW)

BatteryEnergy

(kWh)

Battery

Mass

(kg)

Battery

Volume

(L)

Lithium-IonSAFT VLM 27 cell 115 6.0

6.06.06.0

61 30 

SAFT VLE 45 cell 115 50 24 Nickel-Metal-HydrideCobasys 4500 module 115 167 86 

Cobasys 9500 module 115 125 49 
Component Sizing and Control O

Battery power sufficient to provide EV-only operation

60 
Component Sizing and Control O

Only a few EV miles but many more blended miles
Component Sizing and Control O

Battery <half the original and fuel economy drop less than 10%
Component Sizing and Control O

Below 20kW battery, lost regen impacts consumption
Component Sizing and Control O

Cylinder deactivation in large engine could be used to regain efficiency
Battery/Engine Sizing Tra

So what’s the catch? 1) Lower engine efficiency!

η

All-electric Engine efficiency curve

Reduced DOH widens this envelope
Battery/Engine Sizing Tra

2) Sacrificed all-electric operation and regenerative braking

-100 -50 0 50 

0

0.020.040.060.08

0.1

US06

Probability

Power (kW)

-100 -50 0 50 

0

0.10.20.30.4

UDDS

Probability

-100 -50 0 50 

0

0.10.20.3

HWFET

Probability

-30kW 30kW
Conclusions

• P2E ratios for existing high-energy 

range battery products match with requirements for plug-in HEVs

– However, mid-range batteries may be 

expensive due to simultaneous power 

requirements

– Note that high-value V2G services (i.e

events) have high P/E ratios – does threquirements?

– Do dual-source ultracaps & EV batteri

alternative to mid-range batteries?
Conclusions (cont.)

• Engine size (power) can be increas

the use of smaller batteries with low(i.e. EV types)

– However, this incurs the cost of:

• Reduced engine efficiency• Sacrificed all-electric capability and maybe 

regenerative braking

• Potential reduction in vehicle fuel econom

charge-depleting and –sustaining operatio

– Reduced mass/volume of ESS & moto

traded against increased mass/volume 

– These issues should be explored furth

simulation (including consideration of 

practicalities)