A national laboratory of the U.S. Department of Energy 

Office of Energy Efficiency & Renewable Energy 

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Conference Paper Energy Storage Fuel Cell NREL/CP-540-37567 Vehicle Analysis April 2005 

Preprint 

T. Markel, A. Pesaran, M. Zolot, and S. Sprik 

National Renewable Energy Laboratory 

H. Tataria 

General Motors Corp. 

T. Duong 

U.S. Department of Energy

To be presented at the 21st Electric Vehicle Symposium

Monte Carlo, Monaco

April 2–6, 2005 

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 Energy Storage Fuel Cell Vehicle Analysis 

Tony Markel, Ahmad Pesaran, Matthew Zolot, Sam Sprik, Harshad Tataria, Tien Duong 

Abstract 

Hybridizing fuel cell (FC) vehicles with energy storage (ES) could result in improved performance and 

fuel economy, and reduced cost. We analyzed ES needs for a light mid-size car with a hydrogen FC as the 

main power source. We used the ADVISORTM vehicle simulator with its ES and FC components for the 

analysis, and tested several different drive cycles, FC characteristics, and different ES to FC power ratios. 

We assumed that at idle, the fuel cell is not shut down and consumes enough hydrogen fuel to sustain 

itself without generating net power. Regen braking and vehicle deceleration were the major sources of 

charging for the ES for later use. The optimum fuel economy occurs when peak FC efficiency is around 

the average power demand for a particular drive cycle. There is positive benefit to downsizing the FC if 

the peak efficiency is shifted toward the typical power operating point. We proposed an ES system with 

25 kW discharge (12 seconds), 20 kW charge (5 seconds) with available energy of 250 Wh and a 56 kW 

FC for the light mid-size car. The fuel consumption of this hybridized case was about 30% less than fuel 

cell only case. 

Keywords: energy storage, fuel cell, simulation, HEV (hybrid electric vehicle), regenerative braking 

1 Introduction 

In recent years, hydrogen fuel cell (FC) vehicle technology has received considerable attention as a 

strategy to decrease oil consumption and reduce harmful emissions. However, the cost, transient 

response, and cold performance of FC systems may present significant challenges to widespread adoption 

of the technology for transportation in the next 15 years. Several previous studies have shown that 

hybridization of FC vehicles with electrochemical energy storage (ES) devices provides cost, 

performance, and operational improvements, as well as fuel economy benefits that are attractive and 

should be considered [1 - 4]. Among the current pre-production hybrid FC vehicles, the Toyota FCHV [5] 

has a nickel-metal hydride ES system similar to that of the Toyota Prius, and the Honda FCX-V4 uses an 

ultracapacitor ES system that provides regenerative braking and power assist capability [5 and 6]. The 

requirements of the ES for power assist and 42V hybrid vehicles are defined by the United States 

Advanced Battery Consortium (USABC) and FreedomCAR Program and can be found at 

www.uscar.com/consortia&teams/consortiahomepages/con-usabc.htm. 

The objectives of this effort were to perform ES modeling with FC vehicle simulations to quantify the 

benefits of hybridization and to identify a process for setting the requirements of ES for hydrogenpowered FC vehicles for U.S. Department of Energy’s Energy Storage Program. The analysis was in 

support of USABC and the FreedomCAR Electrochemical Energy Storage (EES) Technical 

Team, which are developing requirements for ES systems for FC vehicles for the FreedomCAR Program 

in the United States. 

It is important to note that the ES sizes recommended here strongly depended on our assumptions. Using 

different vehicle characteristics and requirements, fuel cell characteristics, and operating strategies would 

1�
--

--

--

--

32

2 

have resulted in a different set of energy storage requirements. However, the approach we used here 

could be applied to other scenarios. 

Major Assumptions 

For the vehicle, the EES Technical team suggested using an aerodynamic, lightweight, mid-size car. The 

vehicle was assumed to be similar to average mid-sized cars in the United States such as the Chevrolet 

Malibu or Chrysler Stratus. The weight of the glider (vehicle without powertrain) was assumed to be 

about 60% of today’s cars to account for future reductions in weight, such as using a structural aluminum 

body. The drag coefficient was assumed to be around 0.25, with a frontal area of 2 m2

 and rolling 

resistance of 0.007. The requirements for the car to meet were: minimum range of 500 km, maximum 

speed of 160 km/h, 0-100 km/h acceleration of 11 seconds, and ability to sustain grade of 5.5% at 88 

km/h. 

For the rest of the assumptions, we used the 2010 FreedomCAR Program technical targets [7] for FC, ES, 

power electronics, traction motor, and hydrogen storage systems (Tables 3-7). The fuel was assumed to be 

hydrogen from compressed hydrogen cylinders. For the FC system, we assumed a system peak efficiency 

of 60% at 25% rated power and a system efficiency of 50% at full rated power (designated as 

FC_FC50_P25). We assumed that the FC system ramps up in power from 10% to 90% in 1 second while 

it takes 15 seconds to warm up the fuel cell from cold start to the rated power. The FC system’s specific 

power was assumed to be 500 W/kg. For the ES system, we assumed average specific power of 1200 

W/kg and total specific energy of 70 Wh/kg with 90% round trip efficiency. The following tables 

summarize the assumptions we used. 

Table 1: Vehicle characteristics Table 2: Vehicle performance requirements 

Assumption De scription Assumption De scription Units Value

all wheel dri ve mdriidVehicle Description size carsize car

Base Vehicle Glider Mass Base Vehicle Glider Mass

Cargo Mass

kg

kg

636

136

Aero. Drag Coef. Aero. Drag Coef. 0.25

Frontal Area m^2 2

Tire SizeTire Size P215/60R16

Rolling Resi stance ling Resistance 0.007

Vehicle Range km 500 

Table 3: 2010 fuel cell system assumptions Table 4: 2010 energy storage assumptions 

Assumption Description Units Value

Fuel TypeFuel Type --- hydrogenhydrogen

Fuel Cell Peak Efficiency % 60

Fuel Cell Efficiency at 25% Power % 60

Fuel CelFuel Cell Efficiency at Rated Power % 50

Fuel Cell System Specific Power W/kg 500

Fuel Cell System Power Density W/L 500

Fuel Cell System Cost $/kW 1032 5

Fuel Cell System 10-90% Power Fuel Cell System 10-90%Power

Transient Response Capability s 1

Time from Start to Full Power Output Time from Start to Full Power Output 

Capability (20C) s 15

Assumption Description Units Value 

Capacity Ah 12 

Charge Mode Efficiency % 95 

Discharge Mode Efficiency % 95 

Mass per cell kg 0.525 

Volume per cell L 0.245 

Packing factor -- 0.6 

Mass factor -- 0.85 

Energy Wh 42.7 

Power W 709 

Specific power W/kg 1200 

Energy Storage Cost $/kW 20 

2 
64

Table 5: 2010 hydrogen storage assumptions Table 6: 2010 power electronic assumptions 

Assumption Description Units Value

H2 Storage Energy Density kWh/L 1.2

H2 Storage Specific Energy kWh/kg 1.5

H2 Storage Cost $/kWh 4 

Assumption Description Units Value 

Efficiency % 95 

Specific Cost $/kW 5 

Table 7: 2010 motor/controller assumptions 

Assumption Description Units Value 

Specific Power (Motor and Controller) kW/kg 0.75 

Specific Cost (Motor and Controller) $/kW 11 

Power Density (Motor and Controller) kW/L 3.53 

It is important to note that we assumed that the “combined” FC and ES hybridized system must meet the 

performance target requirements of the vehicle (Table 2), which are acceleration, top cruising speed, and 

grade. To avoid a large ES system, we assumed that top cruising speed or grade sustainability was met 

with power from only the fuel cell. 

In addition, we made the following assumptions about the operation of the vehicle and FC, and the roles 

of ES: 

•� 700 W of constant accessory loads during idle or operation. But during vehicle driving, the 

accessory load requirement is supplied by the FC. 

•� FC is always “on” even at vehicle stops/idles (i.e. no start/stop operation like in internal 

combustion engines or hybrid electric vehicles). 

•� At idle (or vehicle stops) the hydrogen fuel consumption of the FC was 0.3% of rated power 

consumption. This means that although there is “gross” power from the FC, its auxiliary loads such 

as compressors and pumps consume all this “gross” power and the “net” power from the FC is 

zero. 

•� The ES is used for traction assist during acceleration. 

•� When the FC is downsized, the ES provides traction assist during high power transients to meet the 

drive cycle power requirements. 

•� The ES system provides traction assist during FC “warm” startup from idle. 

•� The ES provides power/energy to start the FC from cold starts. 

•� The ES was not used for sustained gradeability. 

•� All or a major portion of the available regenerative braking is captured by the ES for later traction 

use. We used two regen braking strategies. 

o	 ES is sized to limit regen power pulse to a “fixed” percentage (100%, 75%, or 50%) of the peak 

regen power observed during a drive cycle. Friction braking absorbs the remainder. 

o	 % of regen energy recaptured is based on a “deceleration-rate” strategy. 

� A fractional split between driveline and friction brakes defined as a function of 

deceleration rate is assumed. 

� We assumed that below 1g deceleration force (=9.8 m2

/s * mass), all braking is driveline 

(i.e., it is captured as regen braking), above 3g all braking is friction (i.e., no regen 

braking captured). 

� Between the 1g and 3g, the split between drivetrain and regen braking is proportioned 

linearly. 

� We found that, in this strategy, the driveline would recapture between 70% and 90% of 

the available braking energy depending on the drive cycle. 

3�
3 Approach 

We used the ADVISOR vehicle simulator for the analysis. We simulated a range of FC-ES configurations 

(cases) as shown in Table 8. In all cases, we assumed that top cruising speed or grade sustainability was 

met with power only from the FC. This dictated the minimum size of the FC for the power needed for this 

vehicle. The minimum power for the top cruising speed was found to be 47 kW, and the minimum power 

needed for grade sustainability was 34 kW. Therefore, the minimum FC size was selected to be 47 kW. 

As mentioned before, we assumed that the combined ES discharge power and FC power must meet the 

acceleration and drive cycle requirements. In the case of the fuel-cell-only with no ES and no regen 

capture (Case 5), the vehicle needed 75 kW of power. 

In Case 1, we picked the smallest FC that is sized for top speed and largest ES (discharge) that when 

combined with FC power can meet the required acceleration. The ES charge capability was sized for 

maximum regen capture. We used a DOE-target FC system that is at its maximum efficiency (60%) at 

25% rated power and is 50% efficient at full rated power (FC_FC50_P25). In Case 1, we used a 

deceleration-based strategy discussed in the Assumptions Section. Cases 1a through 1c have similar FC 

and ES power ratios, but with different regen capture capability. Case 1f is the same as Case 1a, but the 

maximum FC efficiency at 10% rated power (FC_FC50_P10). 

In Cases 2 through 4, FC size was increased incrementally while the ES was sized to satisfy acceleration 

constraints. Note that the total mass of the hybrid vehicle in Cases 1–3 is less than the FC only case, so 

the vehicle power requirement for acceleration is less than 75 kW as seen in Table 8. Case 5 is with a FC 

only, with maximum efficiency at 25% rated power (FC_FC50_P25). Case 5f is the same as Case 5 with 

a FC that is most efficient at 10% rated power (FC_FC50_P10). In Cases 5a through 5c, while the FC 

remains at 75 kW, ES is added to capture an increasing percentage of peak regen pulse power. Our 

strategy included maintaining the ES state of charge (or energy) and included regen recovery, kinetic 

energy accounting, and opportunity to charge and discharge the ES to make the system more efficient; 

i.e., ES charge/discharge was executed if it made the overall system efficiency better. 

4�
Table 8: Matrix of vehicle configurations evaluated 

Fuel Cell ESS 

Name Description (kW) Regen (kW) Discharge(KW) 

Case 1 

FC sized for grade/top speed; decel regen 

strategy; FC_FC50_P25 47000 34000 25000 

Case 1a Case 1 + 100% regen 47000 34000 25000 

Case 1b Case 1 + 75% regen 47000 25500 25000 

Case 1c Case 1 + 50% regen 47000 17000 25000 

Case 1f Case 1a + FC_FC50_P10 47000 34000 25000 

Case 2 

Fuel cell - sized to 25% point; decel regen 

strategy; FC_FC50_P25 54250 34000 18000 

Case 2a Case 2 + 100% regen 54250 34000 18000 

Case 2b Case 2 + 75% regen 54250 25500 18000 

Case 2c Case 2 + 50% regen 54250 17000 18000 

Case 2f Case 2a + FC_FC50_P10 54250 34000 18000 

Case 3 

Fuel cell - sized to 50% point; decel regen 

strategy; FC_FC50_P25 61500 34000 12500 

Case 3a Case 3 + 100% regen 61500 34000 12500 

Case 3b Case 3 + 75% regen 61500 25500 12500 

Case 3c Case 3 + 50% regen 61500 17000 12500 

Case 3f Case 3a + FC_FC50_P10 61500 34000 12500 

Case 4 

Fuel cell - sized to 75% point; decel regen 

strategy; FC_FC50_P25 69000 34000 7500 

Case 4a Case 4 + 100% regen 69000 34000 7500 

Case 4b Case 4 + 75% regen 69000 25500 7500 

Case 4c Case 4 + 50% regen 69000 17000 7500 

Case 4f Case 4a + FC_FC50_P10 69000 34000 7500 

Case 5 Fuel cell only - no ess; FC_FC50_P25 75000 0 0 

Case 5a Fuel cell only plus 100% ess 75000 36000 36000 

Case 5b Fuel cell only plus 75% ess 75000 27000 27000 

Case 5c Fuel cell only plus 50% ess 75000 18000 18000 

Case 5f Case 5 + FC_FC50_P10 75000 0 0 

4 Results 

4.1 Energy Analysis 

As mentioned, the analysis showed that the power needed for sustained gradeability of 5.5% at 100 km/hr 

was 34 kW, and for a top speed of 160 km/h was 47 kW, which dictated the minimum size of the fuel 

cell. The power needed for acceleration of 0-100 km/h for the FC-only case was 76 kW. We used the 

ADVISORTM simulator to analyze the cases in Table 8 for U.S. City (UDDS), U.S. Highway, US06, and 

HYZEM drive cycles. The Delta ESS energy to fuel-use ratio was monitored for correcting fuel economy. 

We used multiple parameters to manage the strength of various elements of control. We performed 

Design of Experiments on each case to determine the best parameter settings. 

Figure 1 shows the results of the adjusted combined city and highway fuel consumption for each of the 25 

cases in Table 8. Here are the observations from Figure 1. 

•� Comparing Case 5 and 5f (FC only cases) with other cases, indicates that fuel consumption decreases 

as the vehicle is hybridized with ES. This is due to capturing and using regen energy for traction to 

support the drive cycle. 

•� Most of the time downsizing the FC creates a positive fuel consumption benefit. 

5 
•� Comparing FC only (Case 5) to the best case of the hybridized vehicle (Case 1b), the fuel 

consumption is reduced from 4.25 Lit/100 km to about 3 Lit/100 km or a roughly 30% reduction in 

fuel consumption. This is due to both downsizing and capturing and using regen. 

•� The lower fuel consumption (higher fuel economy) case occurs when the peak FC efficiency occurs at 

10% rated power (comparing cases 5 with 5f, 1a with 1f, 2a with 2f, 3a with 3f, and 4a with 4f). This 

is due to the fact that the average power demand for both city and highway drive cycles is 10%-15% 

of the rated power from the FC and thus the FC is more efficient at 10% rated power than 25% rated 

power [2]. 

•� The smaller FC and largest ES gives the lowest fuel consumption (Case 1). 

•� Adding ES, even to a full size FC (Cases 1a-1c), improves the fuel economy since the regen energy is 

captured and used later. 

4.5 

4 

3.5 

3 

2.5 

2 

) 

C o m pos ( adjust ed) 

Fuel Consumption (L/100km

it e

Figure 1: Fuel consumption of various hybridized FC cases shown in Table 8 

Figure 2 shows the impact of energy storage charge acceptance capability on the amount of energy that 

could be recaptured from regen braking. From this and other results, not shown due to limited space, we 

can observe the following: 

•� The reduction of fuel consumption from Case 5 to the cases with added energy storage (5a, 5b, 

and 5c) to capture regen is roughly 20% for US06 cycle. 

•� When limiting energy storage charge acceptance to 18 kW, 15% of regen braking could not be 

captured during the US06 cycles since some of the peak power pulses are more than 18 kW. For 

the city cycle this is only about 6% opportunity loss. 

•� Increasing the ES charge acceptance to 36 kW to capture almost 98% of available regen has only 

a small impact on reducing fuel consumption (2% for US06 and even lower for City and Highway 

cycles). 

Case 1 

Case 1a 

Case 1b 

Case 1c 

Case 1f 

Case 2 

Case 2a 

Case 2b 

Case 2c 

Case 2f 

Case 3 

Case 3a 

Case 3b 

Case 3c 

Case 3f 

Case 4 

Case 4a 

Case 4b

Case 4c 

Case 4f 

Case 5 

Case 5a 

Case 5b 

Case 5c

Case 5f 

6�
Braking Losses (% of fuel cell only case)

 Power (kW)

UDDS Braking Loss

US06 Braking Loss

Charge Power Limit

Largest EES 

to capture 

100% Regen

Small EES 

to capture 

Mid-size EES 50% Regen

to capture 

75% Regen

% Opportunity Energy Loss

(Energy Not Captured/ Total Braking Energy Available for Vehicle with FC Only ) 

US06 Fuel Consumption (Lit/100km) :

• Case 5 (75 kW FC only) = 4.22

• Case 5a (75 kW FC + 36 kW ES) = 3.38

• Case 5a (75 kW FC + 27 kW ES) = 3.41

• Case 5b (75 kW FC + 18 kW ES) = 3.45

Braking Losses (% of fuel cell only case)

 Power (kW)

UDDS Braking Loss

US06 Braking Loss

Charge Power Limit

Largest EES 

to capture 

100% Regen

Small EES 

to capture 

Mid-size EES 50% Regen

to capture 

75% Regen

% Opportunity Energy Loss

(Energy Not Captured/ Total Braking Energy Available for Vehicle with FC Only ) 

Braking Losses (% of fuel cell only case)

 Power (kW)

Best 

Cases

4000 

4500 

35 35

0 

25 

30 

40 

Case 5a Case 5b Case 5c 

0 

25 

30 

40 

0

25

30

40

Case 5a Case 5b Case 5c

0

25

30

40

0

25

30

40

Case 5a Case 5b Case 5c

UDDS Braking Loss 

US06 Braking Loss 

Charge Power Limit 

Largest EES 

to capture 

100% Regen 

Small EES 

to capture 

Mid-size EES 50% Regen

to capture 

75% Regen 

0

25

30

40

US06 Fuel Consumption (Lit/100km) : 

• Case 5 (75 kW FC only) = 4.22 

• Case 5a (75 kW FC + 36 kW ES) = 3.38 

• Case 5a (75 kW FC + 27 kW ES) = 3.41 

• Case 5b (75 kW FC + 18 kW ES) = 3.45 

% Opportunity Energy Loss 

(Energy Not Captured/ Total Braking Energy Available for Vehicle with FC Only ) 

Charge Power Limit (kW)

20 20

15 15

10 10

5 5

Figure 2: Breaking energy not captured because of ES charge acceptance limitations 

Since the projected cost of energy storage per unit power is lower than the projected cost of fuel cell per �

unit power, it would also make economical sense to replace some of the fuel cell functions with energy�

storage. We estimated the cost of the powertrain containing the fuel cell system, energy storage system,�

power electronics, motor and controller, and the hydrogen storage system. The size and cost of the �

hydrogen system was selected so that each vehicle case has a range of 500 km. Figure 3 shows the �

powertrain cost and a figure of merit (fuel economy divided by total powertrain cost) for each of the �

cases. Total cost decreased with decreasing FC size increase and decreasing ES size. Figure 3 indicates �

that Cases 1b or 1c are the best cases to consider since they have the highest fuel economy to powertrain �

cost. �

0 

1500 

2000 

2500 

3000 

3500 

Powertrain Cost ($) 

Energy Storage (20 $/kW) 

Power Electronics (5 $/kW) 

Traction Motor ($12/kW) 

Hydrogen Storage (4 $/kWh) 

Fuel Cell (32 $/kW) 

5000 0.025 Best 

Cases 

lower costlower cost 0.02

0.005

Lower fuelLower fuel

0

Higher 

fuel 

economy,economy,

Figure of Merit (mpgge/$) 0.015

0.01

economy,economy,

higher 

cost

e 1 

a 

1b

Case 1c

e 1f 

2 

2a 

2b

2c

 2f

e 3

a 

3

Case 3

b 

c 

3f

e 4 

a 

4b

e 4c 

4f 

5 

5a 

b

se 5c

 5f 

1 a b

 1c

 1f

 2

a

ase 2b

 2c

 3

se 3a

 3b

e 3c

 3f

 4

a b

 4c

 4f

 5

a

 5b

 5c

e 2f

e 5f

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4

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se

se

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 2

 4

 4

 5

se

se

se

se

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ase

ase

ase

ase

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as

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as

se

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se

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se

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as

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s

Cas

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as

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a

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Figure 3: Total hybrid powertrain cost (left) and fuel economy normalized by powertrain cost 

Now that the best case was identified, we needed to determine the energy and power requirements of the 

energy storage system based on the drive cycles. 

7 

500 

1000 

C

C 1
Average 

Pulse 

Power

Peak 

Pulse 

Power

4.2 Power Profile Analysis 

The major question is: “How can we determine ESS requirements for meeting instantaneous power 

demands for a particular cycle?” From the analysis, one must come up with the required discharge power 

for a specified duration, required charge power for a specified duration, and amount of available energy 

needed to support the power profile from a drive cycle. We analyzed all the drive cycles previously 

indicated and separated the power demands of the FC and the ES. For the ES power profile, we overlaid 

all pulse power events of a driving profile on the same figure with start times set to zero. The ranges of 

the profile shapes were varied, some with sharp tall peaks and some broad with multiple small peaks in 

the middle. To simplify the analysis to be able to extract information, we assigned the duration of the 

events for the broad peaks and an associated average pulse power for that peak. For the sharp peak 

portion of each segment, we assigned a short duration for the pulse peak power and magnitude of the 

pulse peak power. Figure 4 depicts this representation. 

Duration at 

Peak Power 

Duration of Event 

Duration at

Peak Power

Duration of Event

Average 

Pulse 

Power 

Peak 

Pulse 

Power 

Figure 4: Analysis of energy storage power profile (example is for Case 1 with US06) 

The energy captured or needed in each peak was calculated based on the average pulse power times 

during the duration of the event and is called usable or available energy. We then plotted the average 

pulse power versus the available energy for various cases. Figure 5 shows such a plot for various cases. 

We also looked at the distribution of the energy storage system operating points for all the cycles to 

estimate mean, median, and standard deviation for the peak pulse power. Peak pulse power and average 

pulse power were plotted versus the duration of associated event. We included the required power for 

acceleration. Figure 6 shows peak pulse and average pulse power as a function of duration for various 

drive cycles and acceleration. It can be seen that peak power events typically only last for short durations 

of less than 1 second. From Figures 5 and 6, we believe that we need an ES system with 25 kW discharge 

capability for 12 seconds and charge capability of 20 kW for 5 seconds for all the categories in Case 1. 

Either NiMH or Li-ion batteries could deliver such power and energy capabilities. Of course other 

requirements such as cost, cycle life, calendar life, operating temperature range, and self-discharge rate 

will dictate the final selection. Acceleration performance sets discharge requirements and the US06 cycle 

sets charge requirements. 

We should note that for FC startups (not traction), some FC systems may need up to 10 kW of power for 

15 seconds. The energy requirements would be 42 Wh. So the energy and power requirements for cold 

startup will be within the capability of the recommended energy storage. The startup of the FC vehicles 

8�
100% regen cases

75% regen cases

50% regen cases

5 

from very cold temperatures (below -10°C) with batteries may be challenging since the batteries have 

limited performance capabilities at low temperatures. Ultracapacitors have better performance 

capabilities than batteries at cold temperatures, so it is possible that we may select ultracapacitors over 

batteries for this reason, even though it may not be the most desirable approach. 

60

Rated Power (kW)

50�

40�

30�

20�

10�

0

50 100 150 200 250 300

100% regen cases 

75% regen cases 

50% regen cases 

100% regen cases

75% regen cases

50% regen cases

Usable Energy Range (Wh)

Figure 5: Power and associated energy needs for various cases studied. 

Figure 6. Peak pulse power (left) and average pulse power (right) versus duration for multiple cycles 

Concluding Remarks 

We analyzed ES roles in a FC vehicle. Hybridizing a FC vehicle with an ES system improves the fuel 

economy and reduces cost based on the 2010 DOE/FreedomCAR targets for components of a hybrid FC 

vehicle. The ES will also improve vehicle response by supplementing the FC’s limited transient response. 

We described a process for determining ES requirements. We found that the peak power events for most 

drive cycles are very brief and less than 1 second. In general, 25%-30% improvement in fuel consumption 

can be achieved with hybridization. As long as the majority of regen is captured, regen strategy is not 

critical. The most fuel-efficient scenario was also the least expensive scenario (smallest fuel cell with 

moderate ESS). Intelligent energy management strategies to utilize captured regen energy in FC hybrid 

vehicles are critical. Fuel consumption is lower with a FC with peak efficiency of around 10% rated 

9�
power. For the lightweight, aerodynamic, midsize car, we proposed an energy storage system with 25 kW 

discharge (12 seconds), 20 kW charge (5 seconds), and available energy of 250 Wh and a 56 kW FC. 

We will continue working with the FreedomCAR Technical Teams to further refine the assumptions and 

the analysis to recommend final requirements for ES for FC hybrids. Of interest is the quantification of 

the energy and power available from a fuel cell system to charge the energy storage during long idles or 

ramping down of the fuel cell from high to lower power. 

Acknowledgments 

The U.S. Department of Energy (DOE), Office of the FreedomCAR and Vehicle Technology supported 

this effort. We appreciate the technical guidance provided by the United States Advanced Battery 

Consortium and FreedomCAR Electrochemical Energy Storage Technical Team, particularly Ted Miller 

from Ford and Cyrus Ashtiani from DaimlerChrysler. 

References 

[1] Markel, et, al. “Fuel Cell Energy Storage Analysis,” Proceedings of Advanced Automotive Battery Conference, 

San Francisco, CA, June 4-6, 2004. 

[2] Zolot, et.al “Energy Storage Requirements for Hybrid Fuel Cell Vehicles,” Proceedings of Advanced Automotive 

Battery Conference, Nice, France, June 14-16, 2003. 

[3] Wipke, K.; Markel, T.; Nelson, D. “Optimizing Energy Management Strategy and Degree of Hybridization for a 

Hydrogen Fuel Cell SUV.” Proceedings of 18th Electric Vehicle Symposium. Berlin, Germany. October 2001. 

[4] Markel, T.; Wipke, K. “Optimization Techniques for Hybrid Electric Vehicle Analysis Using ADVISOR.” 

Proceedings of the ASME International Mechanical Engineering Congress and Exposition. New York, New York. 

November 11-16, 2001. 

[5] Yamaguchi, J. “Leading the Way: Fuel Cell Vehicles from Toyota and Honda Are Hitting the Streets for 

Customer Use in Both Japan and U.S.” Automotive Engineering International. March 2003. pp. 54-58. 

[6] Tamernori, K, Oki, N, Kato, S., and Yamamoto, K. “Application Studies of Electric Double Layer Capacitor 

System, for Fuel Cell Vehicles.” Third International Advanced Automotive Battery Conference, Nice, France, June 

10-13-, 2003. 

[7] DOE- FreedomCAR and Vehicle Technologies and Hydrogen, Fuel Cells & Infrastructure Technologies 

Programs. “Multi-Year Research, Development and Demonstration Plan”, 

http://www.eere.energy.gov/hydrogenandfuelcells/mypp/ and 

http://www.eere.energy.gov/vehiclesandfuels/resources/fcvt_mypp.shtml 

Authors 

Tony Markel, Senior Engineer, National Renewable Energy Laboratory, 1617 Cole Blvd, MS 1633, 

Golden, CO, 80401, 303-275-4478, 303-275-4415, tony_markel@nrel.gov 

As part of the vehicle systems analysis team, Mr. Markel applies computer modeling and 

simulation to the evaluation of advanced automotive systems. He has been instrumental in the 

development of the ADVISORTM software tool. His technology focus areas include advanced 

numerical and architectural methods for vehicle systems analysis and fuel cell systems research and 

development. Before joining NREL in 1996, Mr. Markel worked at Argonne National Laboratory on various 

transportation-related projects. He has a B.S.E. in mechanical engineering, with an emphasis in fluid and thermal 

sciences and is currently attending the University of Colorado to pursue a M.S. in mechanical engineering. 

10�
Ahmad Pesaran, Principal Engineer, National Renewable Energy Laboratory, 1617 Cole Blvd, MS 

1633, Golden, CO, 80401, 303-275-4441, 303-275-4415, ahmad_pesaran@nrel.gov 

Dr. Pesaran joined NREL in 1983 and has been working on various energy systems such as solar 

cooling, ocean thermal energy conversion, air conditioning, desiccant dehumidification/cooling for 

buildings and buses, and most recently hybrid electric vehicles. Since 1995, he has been working on 

hybrid electric vehicle projects. He is currently the project manager for various activities related to 

battery thermal characterization, battery thermal analysis, and battery modeling and simulations. Dr. Pesaran holds a 

B.S. in chemical engineering from Shiraz University, as well as an M.S. in engineering and a Ph.D. in mechanical 

engineering from UCLA. He is a member of the FreedomCAR Electrochemical Energy Storage Technical Team. 

Matthew Zolot, Research Engineer, National Renewable Energy Laboratory, 1617 Cole Blvd, MS 

1633, Golden, CO, 80401, 303-275-4640, 303-275-4415, matthew_zolot@nrel.gov 

Matthew Zolot is a research engineer in the Center for Transportation Technologies and Systems 

(CTTS) at the National Renewable Energy Laboratory. He is in CTTS' Advanced Vehicle Systems 

Group, supporting the energy storage and advanced power electronics teams. Mr. Zolot received a 

B.S. in electrical engineering from Georgia Institute of Technology, and is currently working 

toward an M.S. at the Colorado School of Mines. During his engineering career, he has been employed at Agilent 

Technologies in the test and measurement division, and Lucent Technologies in the optical network division. He has 

worked on hybrid vehicle mobile data acquisition; simulation, testing, and analyses of hybrid vehicles and 

components, and contributes to the development of NREL's ADVISORTM vehicle simulator. 

Sam Sprik, Engineer, National Renewable Energy Laboratory, 1617 Cole Blvd, MS 1633, Golden, 

CO, 80401, 303-275-4431, 303-275-4415, sam_sprik@nrel.gov 

Mr. Sprik works on vehicle systems analysis and the graphic user interface development of 

ADVISORTM software, NREL's advanced vehicle simulator software. He is educated and interested 

in control theory, virtual reality, and manufacturing quality. While a research assistant at the 

University of Michigan, he measured and analyzed measurement processes at Chrysler on vehicle 

body parts. He is well versed in MATLAB/Simulink programming and in Virtual Reality Modeling Language, along 

with some geometric modeling programs. Mr. Sprik holds a B.S. in mechanical engineering from Calvin College 

and an M.S.M.E. from the University of Michigan. 

Harshad S. Tataria, USABC Technical Advisory Committee & FreedomCAR Program Manager, 

General Motors Corporation, 30001 Van Dyke Avenue MC 480-210-427, Warren, MI 48092 USA, 

586-575-3472, 586-492-6645, harshad.s.tataria@gm.com 

Mr. Harshad Tataria is a member of both the United States Advanced Battery Consortium (USABC) 

Technical Advisory Committee and the FreedomCAR Electrochemical Energy Storage Technical 

Team. He is a Staff Project Engineer at General Motors Corp, where he is responsible for the 

development of energy storage systems for HEVs. Mr. Tataria has over 30 years of experience in battery 

development. His experience includes Lead-Acid, NiMH, Li metal primary and secondary, and Li-Ion batteries. He 

has obtained many patents and published many papers in various scientific journals. 

Tien Q. Duong, Office of FreedomCAR and Vehicle Technologies, U.S. Department of Energy, 1000 

Independence Avenue, SW, Washington, DC 20585, USA 202-586-2210, 202-586-1600 (fax), 

Tien.Duong@ee.doe.gov 

Mr. Duong is Vehicles Technologies Team Lead at the Department of Energy’s FreedomCAR and 

Vehicle Technologies Program Office. Mr. Duong received his M.S. degree in Civil Environmental 

Engineering, and his B.S. degree in Electrical Engineering from Virginia Polytechnic Institute and 

State University in Blacksburg, Virginia. He is a member of USABC Managing Committee. 

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Energy Storage Fuel Cell Vehicle Analysis: Preprint 

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 In recent years, hydrogen fuel cell (FC) vehicle technology has received considerable attention as a strategy to 

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hybrid; energy storage; fuel cell; simulation; HEV; regenerative braking 

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