Analysis of Fuel Cell Vehicle Hybri

Implications for Energy Storage 

4th Advanced Automotive Battery Conferenc

San Francisco, CA

June 2-4, 2004

Matthew Zolot

Tony Markel

Ahmad Pesaran

(ahmad_pesaran@nrel.gov) NREL/PR-540-41039
2 4th Advanced Automotive Battery Conference

Disclaimer and Government Lic

• This work has been authored by Midwest Research Institute (MRI) u

AC36-99GO10337 with the U.S. Department of Energy (the “DOE”Government (the “Government”) retains and the publisher, by acceppublication, acknowledges that the Government retains a non-excluworldwide license to publish or reproduce the published form of this 

do so, for Government purposes.

• Neither MRI, the DOE, the Government, nor any other agency there

employees, makes any warranty, express or implied, or assumes an

for the accuracy, completeness, or usefulness of any information, aprocess disclosed, or represents that its use would not infringe any 

Reference herein to any specific commercial product, process, or se

trademark, manufacturer, or otherwise does not constitute or imply recommendation, or favoring by the Government or any agency theopinions of the authors and/or presenters expressed herein do not n

those of MRI, the DOE, the Government, or any agency thereof. 
3 4th Advanced Automotive Battery Conference

Previous Studies

• Hybridization of a fuel cell vehicle with ene

storage improves fuel economy, performanand make it practical (UCD, VTech, ANL, NREL)

– Capturing regenerative breaking – Improving transient response– Smaller fuel cell - lower cost 

– Fuel cell or reformer warm up

• Some demonstration prototype fuel cell 

vehicles are hybrids

– Toyota FCHV, Ford Focus– (batteries)– Honda FCXV4 – (ultracapacitors)
4 4th Advanced Automotive Battery Conference

Content 

• Objectives

• Motivation for using energy storag

in fuel cell (FC) vehicles 

• Analyses

• Summary
5 4th Advanced Automotive Battery Conference

Objectives

• Investigate the degree of hybridiza

from:

(A) Fuel cell efficiency characteris

(B) Fuel cell downsizing(C) Displacing fuel cell tasks with 

functionality

(D) Energy recovery through rege

braking 
6 4th Advanced Automotive Battery Conference

Motivation for this St

• Previous studies have n

degree of hybridization 

(a) fuel cell efficiency c(b) fuel cell downsizing(c) displacing fuel cell t

ES functionality

(d) energy recovery thr

regenerative brakin

• Supporting FreedomCA

requirements of energy fuel cell vehicles

Energy 

Storage

Fuel 

Cell 
7 4th Advanced Automotive Battery Conference

Fuel Cell System Efficiency Variab

Affect FC-ES Hybridization Ou

Enchdesy
8 4th Advanced Automotive Battery Conference

Fuel Cell and Hydrogen Storag

Assumptions

• Fuel Cell

– Sized to provide at least grade performance.– 1 s or 3 s transient response time (10% to 90% p– Reaches maximum rated power in 0 s (ideal cas

15 s (2010 target), or 60 s (today’s) for cold star

– System efficiency of 60% at maximum &

50% at rated peak power (DOE Technical Targets) .

• Hydrogen Storage

– Pure compressed hydrogen.

0

10203040506070

0 20 

Percen

System Efficiency (%) 

Proposed theoretical FC efficiency curves are based on DOE Targets
9 4th Advanced Automotive Battery Conference

Objectives

• Investigate the degree of hybridiza

from:

(A) Fuel cell efficiency characte

(B) Fuel cell downsizing(C) Displacing fuel cell tasks with 

functionality

(D) Energy recovery through rege

braking 
10 4th Advanced Automotive Battery Conference

Fuel Economy is Affec

by the Position of FC Peak E

• 10% p

achievcity/hig

+12oveeffic+32oveeffic
11 4th Advanced Automotive Battery Conference

When Peak Efficiency ≅

 

Typical 

Results in the Best Fuel Ec

• 10% pe

the highbecausis bettepower r

05

10152025303540

05

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90+

Discharge Power (kW)

010203040506070

Fuel Cell System Efficiency (%) Highway Cycle FC 10% P_Peak FC 25% P_Peak FC 40% P_Peak

Average Power 12.25 kW

% of Operation, Highway Cycle
12 4th Advanced Automotive Battery Conference

When Peak Efficiency ≅

 

Typical 

Results in the Best Fuel Ec

• 10% pe

the highbecausis bettepower r

05

10152025303540

05

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90+

Discharge Power (kW)

010203040506070

Fuel Cell System Efficiency (%) Highway Cycle FC 10% P_Peak FC 25% P_Peak FC 40% P_Peak

Average Power 12.25 kW

% of Operation, Highway Cycle

05

101520253035404550

05

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90+

Discharge Power (kW)

% of Operation, City Cycle

010203040506070

City CycleFC 10% P_PeakFC 25% P_PeakFC 40% P_Peak

Average Power 6.96 kW

Fuel Cell System Efficiency(%)
13

4th Advanced Automotive Battery Conference

When Peak Efficiency 

≅

 

Typical 

Results in the Best Fuel Ec

• 10% pe

the highbecausis bettepower r

05

10152025303540

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Dischar

ge Power (kW)

010203040506070

Fuel Cell System Efficiency (%) Highway Cycle FC 10% P_Peak FC 25% P_Peak FC 40% P_Peak

Average Power 12.25 kW

% of Operation, Highway Cycle

05

101520253035404550

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Dischar

ge Power (kW)

% of Operation, City Cycle

010203040506070

City CycleFC 10% P_PeakFC 25% P_PeakFC 40% P_Peak

Average Power 6.96 kW

Fuel Cell System Efficiency (%)

02468

101214161820

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Dischar

ge Power (kW)

% of Operation, US06 Cycle

010203040506070

US06 CycleFC 10% P_PeakFC 25% P_PeakFC 40% P_Peak

Average Power 22.46 kW

Fuel Cell System Efficiency (%)

• Little 

differcycle- wide

- sim
14 4th Advanced Automotive Battery Conference

Objectives

• Investigate the degree of hybridiza

from:

(A) Fuel cell efficiency characteris

(B) Fuel cell downsizing(C) Displacing fuel cell tasks with 

functionality

(D) Energy recovery through rege

braking 
15 4th Advanced Automotive Battery Conference

4045505560657075

63 74 85 96

Fuel Cell Net Power Output (kW)

Fuel Economy (mpgge)

10% Peak, Cty/Hwy Combo 25%Peak, Cty/Hwy Combo 40% Peak, Cty/Hwy Combo

The Benefit of Downsizing the Fu

as a function of Peak Efficienc

• Downsiz

efficiencleast poimprove

≤

1.0% 

city/h

• Downsiz

efficiencmoderatpotentiaimprove

≤

15.0

city/h
16 4th Advanced Automotive Battery Conference

4045505560657075

63 74 85 96

Fuel Cell Net Power Output (kW)

Fuel Economy (mpgge)

10% Peak, Cty/Hwy Combo 25%Peak, Cty/Hwy Combo 40% Peak, Cty/Hwy Combo

The Benefit of Downsizing the Fu

as a function of Peak Efficienc

• Downsiz

efficiencleast poimprove

≤

1.0% 

city/h

• Downsiz

efficiencmoderatpotentiaimprove

≤

15.0

city/h

05

101520253035404550

05

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90+

Discharge Power (kW)

% of Operation, City Cycle

010203040506070

City CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW

Average Power 6.96 kW

Fuel Cell System Efficiency(%)
17

4th Advanced Automotive Battery Conference

4045505560657075

63 74 85 96

Fuel Cell Net Power Output (kW)

Fuel Economy (mpgge)

10% Peak, Cty/Hwy Combo 25%Peak, Cty/Hwy Combo 40% Peak, Cty/Hwy Combo

The Benefit of Downsizing the Fu

as a function of Peak Efficienc

• Downsiz

efficiencleast poimprove

≤

1.0% 

city/h

• Downsiz

efficiencmoderatpotentiaimprove

≤

15.0

city/h

05

101520253035404550

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Discharge Power (kW)

% of Operation, City Cycle

010203040506070

City CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW

Average Power 6.96 kW

Fuel Cell System Efficiency (%)

05

101520253035404550

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Dischar

ge Power (kW)

% of Operation, City Cycle

010203040506070

City CycleFC 40% 96kWFC 40% 85kWFC 40% 74kWFC 40% 63kW

Avera

ge Power 6.96 kW

Fuel Cell System Efficiency (%)
18 4th Advanced Automotive Battery Conference

Downsizing the Fuel Cell Can Hav

Affect on the US06 Cycle Fuel 

• Downsi

peak ef

in up to2 mpg 

• Downsi

efficienfairly e

40424446485052

63 74 85 96

Fuel Cell Net Power Output (kW)

Fuel Economy (mpgge)

10%Peak, US06 25%Peak, US06 40% Peak, US06
19 4th Advanced Automotive Battery Conference

Downsizing the Fuel Cell Can Hav

Affect on the US06 Cycle Fuel 

• Downsi

peak ef

in up to2 mpg 

• Downsi

efficienfairly e

40424446485052

63 74 85 96

Fuel Cell Net Power Output (kW)

Fuel Economy (mpgge)

10%Peak, US06 25%Peak, US06 40% Peak, US06

02468

101214161820

05

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90+

Discharge Power (kW)

% of Operation, US06 Cycle

010203040506070

US06 CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW

Average Power 22.46 kW

Fuel Cell System Efficiency(%)
20

4th Advanced Automotive Battery Conference

Downsizing the Fuel Cell Can Hav

Affect on the US06 Cycle Fuel 

• Downsi

peak ef

in up to2 mpg 

• Downsi

efficienfairly e

40424446485052

63 74 85 96

Fuel Cell Net Power Output (kW)

Fuel Economy (mpgge)

10%Peak, US06 25%Peak, US06 40% Peak, US06

02468

101214161820

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Discharge Power (kW)

% of Operation, US06 Cycle

010203040506070

US06 CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW

Average Power 22.46 kW

Fuel Cell System Efficiency (%)

02468

101214161820

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

+

Dischar

ge Power (kW)

% of Operation, US06 Cycle

010203040506070

US06 CycleFC 40% 96kWFC 40% 85kWFC 40% 74kWFC 40% 63kW

Average Power 22.46 kW

Fuel Cell System Efficiency (%)
21 4th Advanced Automotive Battery Conference

Objectives

• Investigate the degree of hybridiza

from:

(A) Fuel cell efficiency characteris

(B) Fuel cell downsizing(C) Displacing fuel cell tasks wi

functionality

(D) Energy recovery through reg

braking
22 4th Advanced Automotive Battery Conference

Energy Storage Requirem

Supplementing a Full-Size FC’s 

96 kW Fuel Cell Warm-Up Ramp Rate P req'd E req'd P regen E regen

Time (s) 10-90% (s) (kW) (kWh) (kW) (kWh)

Today's Perfomance 60 3 61.80 0.2206 -46.49 -0.7332

60 1 61.80 0.2206 -48.05 -0.733215 3 55.90 0.0580 -46.49 -0.8237

2010 Target 15 1 55.90 0.0580 -48.05 -0.8237

0 3 48.86 0.0067 -46.49 -0.8265

"Ideal" 96 kW Case 0 1 0.00 0.0000 -48.05 -0.8265

• S

Hr

• W

rr

• 2010 Target performance needs fairly similar 

power, but much less assist energy.
23 4th Advanced Automotive Battery Conference

Energy Storage Requirem

Supplementing a Full-Size FC’s 

96 kW Fuel Cell Warm-Up Ramp Rate P req'd E req'd P regen E regen

Time (s) 10-90% (s) (kW) (kWh) (kW) (kWh)

Today's Perfomance 60 3 61.80 0.2206 -46.49 -0.7332

60 1 61.80 0.2206 -48.05 -0.733215 3 55.90 0.0580 -46.49 -0.8237

2010 Target 15 1 55.90 0.0580 -48.05 -0.8237

0 3 48.86 0.0067 -46.49 -0.8265

"Ideal" 96 kW Case 0 1 0.00 0.0000 -48.05 -0.8265

• S

Hr

• 

• W

rr
24 4th Advanced Automotive Battery Conference

Energy Storage Requirem

Supplementing a Full-Size FC’s 

96 kW Fuel Cell Warm-Up Ramp Rate P req'd E req'd P regen E regen

Time (s) 10-90% (s) (kW) (kWh) (kW) (kWh)

Today's Perfomance 60 3 61.80 0.2206 -46.49 -0.7332

60 1 61.80 0.2206 -48.05 -0.733215 3 55.90 0.0580 -46.49 -0.8237

2010 Target 15 1 55.90 0.0580 -48.05 -0.8237

0 3 48.86 0.0067 -46.49 -0.8265

"Ideal" 96 kW Case 0 1 0.00 0.0000 -48.05 -0.8265

• S

Hr

• W

rr
25 4th Advanced Automotive Battery Conference

63 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 63 60 3 61.80 0.2206

63 60 1 61.80 0.220663 15 3 59.90 0.0889

2010 Target 63 15 1 55.90 0.0766

63 0 3 59.90 0.0889

"Ideal" 63 kW Case 63 0 1 50.70 0.0766

74 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 74 60 3 61.80 0.2206

74 60 1 61.80 0.220674 15 3 56.20 0.0611

2010 Target 74 15 1 55.90 0.0580

74 0 3 56.20 0.0611

"Ideal" 74 kW Case 74 0 1 39.67 0.0499

85 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 85 60 3 61.80 0.2206

85 60 1 61.80 0.220685 15 3 55.90 0.0580

2010 Target 85 15 1 55.90 0.0580

85 0 3 52.53 0.0333

"Ideal" 85 kW Case 85 0 1 28.67 0.0243

Energy Storage Requireme

Supplementing a Downsized FC’

• Wit

musmax 

• ESS 

full-“Todperf
26 4th Advanced Automotive Battery Conference

63 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 63 60 3 61.80 0.2206

63 60 1 61.80 0.220663 15 3 59.90 0.0889

2010 Target 63 15 1 55.90 0.0766

63 0 3 59.90 0.0889

"Ideal" 63 kW Case 63 0 1 50.70 0.0766

74 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 74 60 3 61.80 0.2206

74 60 1 61.80 0.220674 15 3 56.20 0.0611

2010 Target 74 15 1 55.90 0.0580

74 0 3 56.20 0.0611

"Ideal" 74 kW Case 74 0 1 39.67 0.0499

85 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 85 60 3 61.80 0.2206

85 60 1 61.80 0.220685 15 3 55.90 0.0580

2010 Target 85 15 1 55.90 0.0580

85 0 3 52.53 0.0333

"Ideal" 85 kW Case 85 0 1 28.67 0.0243

Energy Storage Requireme

Supplementing a Downsized FC’

• Wit

musmax 

• ESS 

full-“Todperf
27 4th Advanced Automotive Battery Conference

63 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 63 60 3 61.80 0.2206

63 60 1 61.80 0.220663 15 3 59.90 0.0889

2010 Target 63 15 1 55.90 0.0766

63 0 3 59.90 0.0889

"Ideal" 63 kW Case 63 0 1 50.70 0.0766

74 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 74 60 3 61.80 0.2206

74 60 1 61.80 0.220674 15 3 56.20 0.0611

2010 Target 74 15 1 55.90 0.0580

74 0 3 56.20 0.0611

"Ideal" 74 kW Case 74 0 1 39.67 0.0499

85 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'd

FC Power (kW) Time (s) 10-90% (s) (kW) (kWh)

Today's Perfomance 85 60 3 61.80 0.2206

85 60 1 61.80 0.220685 15 3 55.90 0.0580

2010 Target 85 15 1 55.90 0.0580

85 0 3 52.53 0.0333

"Ideal" 85 kW Case 85 0 1 28.67 0.0243

Energy Storage Requireme

Supplementing a Downsized FC’

• Wit

musmax 

• ESS 

full-“Todperf

• Therefore, downsizing provides improvement 

fuel cell costs, and [in minimal control case] haffect on ESS sizing.

• ESS 

as a requTar

perf
28 4th Advanced Automotive Battery Conference

Current Work - Potential Act

for Supplementing Fuel Cell 

Curve 2 - Peak Efficiency @ 25% Full Powe

0

10203040506070

0 20 40 60 

Percentage of Peak Power (%)

System Efficiency (%) Opportu

SOC is h

efficiency 

load requ

Opportunity Charge

SOC is low and fuel cell 

efficiency could increase if 

load request is increased.
29 4th Advanced Automotive Battery Conference

Current Work - Multi-region 

SOC Maintenance Algor

Low SOC Target SOC High SOC

-Charge Power

+Charge Power

0

Fc_pwr_r = 

Must Charge

Charge Required

Opportunity

Charge

Must Discharge

Discharge Required

Opportunity

Discharge

Med-low SOC Med-high SOC
30 4th Advanced Automotive Battery Conference

Summary

• The best fuel economy occurs when pe

efficiency ≅ typical power operating poin

dependant).

• There is positive benefit of downsizing t

peak efficiency is shifted toward the typ

operating point (cycle dependant).

• ES requirements for supplementing FC 

suitable for Ultracapacitors or High Pow

• Downsizing a FC (toward the gradeabili

today’s or 2010 projected characteristicsignificantly affect ES requirements (witcontrol case).

• There is significant potential for more ac

the ES to manage the FC operation poiun-used regenerative energy capture.
31 4th Advanced Automotive Battery Conference

Acknowledgements

• ADVISORTM is used to simulate th

and energy storage system demadrive cycle and performance tests

• This work supports the FreedomC

Storage technical team in defining storage requirements for fuel cell