Analysis of Fuel Cell Vehicle Hybridization and Implications for Energy Storage Devices
4th
Advanced Automotive Battery ConferenceSan Francisco, CA
June 2-4, 2004
Matthew ZolotTony Markel
Ahmad Pesaran([email protected])NREL/PR-540-41039
2 4th Advanced Automotive Battery Conference
Disclaimer and Government License•
This work has been authored by Midwest Research Institute (MRI) under Contract No. DE-
AC36-99GO10337 with the U.S. Department of Energy (the “DOE”). The United States Government (the “Government”) retains and the publisher, by accepting the work for publication, acknowledges that the Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for Government purposes.
•
Neither MRI, the DOE, the Government, nor any other agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe
any privately owned rights. Reference herein to any specific commercial product, process, or
service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the Government or any agency thereof. The views and opinions of the authors and/or presenters expressed herein do not necessarily state or reflect 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 energy storage improves fuel economy, performance and 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)
Fuel Cell
EnergyStorage
4 4th Advanced Automotive Battery Conference
Content
•
Objectives•
Motivation for using energy storage (ES)
in fuel cell (FC) vehicles •
Analyses
•
Summary
5 4th Advanced Automotive Battery Conference
Objectives
•
Investigate the degree of hybridization benefit from:
(A) Fuel cell efficiency characteristics (B) Fuel cell downsizing
(C) Displacing fuel cell tasks with the ES functionality
(D) Energy recovery through regenerative braking
6 4th Advanced Automotive Battery Conference
Motivation for this Study•
Previous studies have not separated the degree of hybridization benefits from:
(a) fuel cell efficiency characteristics,
(b) fuel cell downsizing, (c) displacing fuel cell tasks with the
ES functionality(d) energy recovery through
regenerative braking
•
Supporting FreedomCAR in identifying requirements of energy storage for hybrid fuel cell vehicles
Energy Storage
Fuel Cell
7 4th Advanced Automotive Battery Conference
Fuel Cell System Efficiency Variability Could Affect FC-ES Hybridization Outcome
Energy storage system characteristics will depend on the fuel cell system characteristics
8 4th Advanced Automotive Battery Conference
Fuel Cell and Hydrogen Storage System Assumptions
•
Fuel Cell–
Sized to provide at least grade performance.–
1 s or 3 s transient response time (10% to 90% power).–
Reaches maximum rated power in 0 s (ideal case),
15 s (2010 target), or 60 s (today’s) for cold start from 20°C.
–
System efficiency of 60% at maximum &
50% at rated peak power (DOE Technical Targets) .
•
Hydrogen Storage–
Pure compressed hydrogen.
0
10
20
30
40
50
60
70
0 20 40 60 80 100Percentage of Peak Power (%)
Syst
em E
ffici
ency
(%)
Curve 1 - Peak Efficiency@ 10% Full Power
Curve 2 - Peak Efficiency@ 25% Full Power
Curve 3 - Peak Efficiency@ 40% Full Power
Proposed theoretical FC efficiency curves are based on DOE Targets
These fuel cells have the SAME net power
9 4th Advanced Automotive Battery Conference
Objectives
•
Investigate the degree of hybridization benefit from:
(A) Fuel cell efficiency characteristics (B) Fuel cell downsizing
(C) Displacing fuel cell tasks with the ES functionality
(D) Energy recovery through regenerative braking
10 4th Advanced Automotive Battery Conference
Fuel Economy is Affected by the Position of FC Peak Efficiency
•
10% peak efficiency FC achieved the best city/highway fuel economy
+12% improvement over the 25% peak efficiency configuration
+32% improvement over the 40% peak efficiency configuration
11 4th Advanced Automotive Battery Conference
When Peak Efficiency ≅
Typical Power Point, Results in the Best Fuel Economy
•
10% peak efficiency FC has the highest fuel economy because its peak efficiency is better aligned with the power requirements.
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +Discharge Power (kW)
0
10
20
30
40
50
60
70
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
Highway Cycle
FC 10% P_Peak
FC 25% P_Peak
FC 40% P_Peak
Average Power 12.25 kW
% o
f Ope
ratio
n, H
ighw
ay C
ycle
12 4th Advanced Automotive Battery Conference
When Peak Efficiency ≅
Typical Power Point, Results in the Best Fuel Economy
•
10% peak efficiency FC has the highest fuel economy because its peak efficiency is better aligned with the power requirements.
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +Discharge Power (kW)
0
10
20
30
40
50
60
70
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
Highway Cycle
FC 10% P_Peak
FC 25% P_Peak
FC 40% P_Peak
Average Power 12.25 kW
% o
f Ope
ratio
n, H
ighw
ay C
ycle
05
101520253035404550
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, C
ity C
ycle
0
10
20
30
40
50
60
70
City CycleFC 10% P_PeakFC 25% P_PeakFC 40% P_Peak
Average Power 6.96 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
13 4th Advanced Automotive Battery Conference
When Peak Efficiency ≅
Typical Power Point, Results in the Best Fuel Economy
•
10% peak efficiency FC has the highest fuel economy because its peak efficiency is better aligned with the power requirements.
0
5
10
15
20
25
30
35
40
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +Discharge Power (kW)
0
10
20
30
40
50
60
70
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
Highway Cycle
FC 10% P_Peak
FC 25% P_Peak
FC 40% P_Peak
Average Power 12.25 kW
% o
f Ope
ratio
n, H
ighw
ay C
ycle
05
101520253035404550
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, C
ity C
ycle
0
10
20
30
40
50
60
70
City CycleFC 10% P_PeakFC 25% P_PeakFC 40% P_Peak
Average Power 6.96 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
02468
101214161820
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, U
S06
Cyc
le
0
10
20
30
40
50
60
70
US06 CycleFC 10% P_PeakFC 25% P_PeakFC 40% P_Peak
Average Power 22.46 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
•
Little fuel economy difference over US06
cycle. -
wider power distribution
-
similar efficiency at Pavg
14 4th Advanced Automotive Battery Conference
Objectives
•
Investigate the degree of hybridization benefit from:
(A) Fuel cell efficiency characteristics (B) Fuel cell downsizing
(C) Displacing fuel cell tasks with the ES functionality
(D) Energy recovery through regenerative braking
15 4th Advanced Automotive Battery Conference
40
45
50
55
60
65
70
75
96857463Fuel Cell Net Power Output (kW)
Fuel
Eco
nom
y (m
pgge
)
10% Peak, Cty/Hwy Combo 25%Peak, Cty/Hwy Combo40% Peak, Cty/Hwy Combo
The Benefit of Downsizing the Fuel Cell varies as a function of Peak Efficiency Position
•
Downsizing the 10% peak efficiency FC results in the least potential fuel economy improvement
≤
1.0% (combined
city/highway) improvement
•
Downsizing the 40% peak efficiency FC results in a moderate to significant potential fuel economy improvement
≤
15.0% (combined
city/highway) improvement
16 4th Advanced Automotive Battery Conference
40
45
50
55
60
65
70
75
96857463Fuel Cell Net Power Output (kW)
Fuel
Eco
nom
y (m
pgge
)
10% Peak, Cty/Hwy Combo 25%Peak, Cty/Hwy Combo40% Peak, Cty/Hwy Combo
The Benefit of Downsizing the Fuel Cell varies as a function of Peak Efficiency Position
•
Downsizing the 10% peak efficiency FC results in the least potential fuel economy improvement
≤
1.0% (combined
city/highway) improvement
•
Downsizing the 40% peak efficiency FC results in a moderate to significant potential fuel economy improvement
≤
15.0% (combined
city/highway) improvement
05
101520253035404550
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, C
ity C
ycle
0
10
20
30
40
50
60
70
City CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW
Average Power 6.96 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
17 4th Advanced Automotive Battery Conference
40
45
50
55
60
65
70
75
96857463Fuel Cell Net Power Output (kW)
Fuel
Eco
nom
y (m
pgge
)
10% Peak, Cty/Hwy Combo 25%Peak, Cty/Hwy Combo40% Peak, Cty/Hwy Combo
The Benefit of Downsizing the Fuel Cell varies as a function of Peak Efficiency Position
•
Downsizing the 10% peak efficiency FC results in the least potential fuel economy improvement
≤
1.0% (combined
city/highway) improvement
•
Downsizing the 40% peak efficiency FC results in a moderate to significant potential fuel economy improvement
≤
15.0% (combined
city/highway) improvement
05
101520253035404550
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, C
ity C
ycle
0
10
20
30
40
50
60
70
City CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW
Average Power 6.96 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
05
101520253035404550
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, C
ity C
ycle
0
10
20
30
40
50
60
70
City CycleFC 40% 96kWFC 40% 85kWFC 40% 74kWFC 40% 63kW
Average Power 6.96 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
18 4th Advanced Automotive Battery Conference
Downsizing the Fuel Cell Can Have a Negative Affect on the US06 Cycle Fuel Economy
•
Downsizing the 10% & 25% peak efficiency FCs
results
in up to…
2 mpg less fuel economy
•
Downsizing the 40% peak efficiency FC results in…
fairly even fuel economy
40
42
44
46
48
50
52
96857463Fuel Cell Net Power Output (kW)
Fuel
Eco
nom
y (m
pgge
)
10%Peak, US06 25%Peak, US06 40% Peak, US06
19 4th Advanced Automotive Battery Conference
Downsizing the Fuel Cell Can Have a Negative Affect on the US06 Cycle Fuel Economy
•
Downsizing the 10% & 25% peak efficiency FCs
results
in up to…
2 mpg less fuel economy
•
Downsizing the 40% peak efficiency FC results in…
fairly even fuel economy
40
42
44
46
48
50
52
96857463Fuel Cell Net Power Output (kW)
Fuel
Eco
nom
y (m
pgge
)
10%Peak, US06 25%Peak, US06 40% Peak, US0602468
101214161820
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, U
S06
Cyc
le
0
10
20
30
40
50
60
70
US06 CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW
Average Power 22.46 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
20 4th Advanced Automotive Battery Conference
Downsizing the Fuel Cell Can Have a Negative Affect on the US06 Cycle Fuel Economy
•
Downsizing the 10% & 25% peak efficiency FCs
results
in up to…
2 mpg less fuel economy
•
Downsizing the 40% peak efficiency FC results in…
fairly even fuel economy
40
42
44
46
48
50
52
96857463Fuel Cell Net Power Output (kW)
Fuel
Eco
nom
y (m
pgge
)
10%Peak, US06 25%Peak, US06 40% Peak, US0602468
101214161820
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, U
S06
Cyc
le
0
10
20
30
40
50
60
70
US06 CycleFC 10% 96kWFC 10% 85kWFC 10% 74kWFC 10% 63kW
Average Power 22.46 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
02468
101214161820
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 +
Discharge Power (kW)
% o
f Ope
ratio
n, U
S06
Cyc
le
0
10
20
30
40
50
60
70
US06 CycleFC 40% 96kWFC 40% 85kWFC 40% 74kWFC 40% 63kW
Average Power 22.46 kW
Fuel
Cel
l Sys
tem
Effi
cien
cy (%
)
21 4th Advanced Automotive Battery Conference
Objectives
•
Investigate the degree of hybridization benefit from:
(A) Fuel cell efficiency characteristics (B) Fuel cell downsizing
(C) Displacing fuel cell tasks with the ES functionality
(D) Energy recovery through regenerative braking
22 4th Advanced Automotive Battery Conference
Energy Storage Requirements for Supplementing a Full-Size FC’s Limitations
96 kW Fuel Cell Warm-Up Ramp Rate P req'd E req'd P regen E regenTime (s) 10-90% (s) (kW) (kWh) (kW) (kWh)
Today's Perfomance 60 3 61.80 0.2206 -46.49 -0.733260 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 -0.82370 3 48.86 0.0067 -46.49 -0.8265
"Ideal" 96 kW Case 0 1 0.00 0.0000 -48.05 -0.8265
•
Similar to stated Honda FCX4 ESS roles.
•
Warm-up and ramp rate ESS roles require relatively little energy.•
2010 Target performance needs fairly similar power, but much less assist energy.
23 4th Advanced Automotive Battery Conference
Energy Storage Requirements for Supplementing a Full-Size FC’s Limitations
96 kW Fuel Cell Warm-Up Ramp Rate P req'd E req'd P regen E regenTime (s) 10-90% (s) (kW) (kWh) (kW) (kWh)
Today's Perfomance 60 3 61.80 0.2206 -46.49 -0.733260 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 -0.82370 3 48.86 0.0067 -46.49 -0.8265
"Ideal" 96 kW Case 0 1 0.00 0.0000 -48.05 -0.8265
•
Similar to stated Honda FCX4 ESS roles.
•
Big Potential for more active ESS contributions.
•
Warm-up and ramp rate ESS roles require relatively little energy.
24 4th Advanced Automotive Battery Conference
Energy Storage Requirements for Supplementing a Full-Size FC’s Limitations
96 kW Fuel Cell Warm-Up Ramp Rate P req'd E req'd P regen E regenTime (s) 10-90% (s) (kW) (kWh) (kW) (kWh)
Today's Perfomance 60 3 61.80 0.2206 -46.49 -0.733260 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 -0.82370 3 48.86 0.0067 -46.49 -0.8265
"Ideal" 96 kW Case 0 1 0.00 0.0000 -48.05 -0.8265
•
Similar to stated Honda FCX4 ESS roles.
•
Warm-up and ramp rate ESS roles require relatively little energy.
25 4th Advanced Automotive Battery Conference
63 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 63 60 3 61.80 0.220663 60 1 61.80 0.220663 15 3 59.90 0.0889
2010 Target 63 15 1 55.90 0.076663 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'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 74 60 3 61.80 0.220674 60 1 61.80 0.220674 15 3 56.20 0.0611
2010 Target 74 15 1 55.90 0.058074 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'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 85 60 3 61.80 0.220685 60 1 61.80 0.220685 15 3 55.90 0.0580
2010 Target 85 15 1 55.90 0.058085 0 3 52.53 0.0333
"Ideal" 85 kW Case 85 0 1 28.67 0.0243
Energy Storage Requirements for Supplementing a Downsized FC’s Limitations
•
With FC downsized, ESS must also assist during max acceleration event.
•
ESS is the same as a full-sized FC requires for “Today’s”
fuel cell
performance.
26 4th Advanced Automotive Battery Conference
63 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 63 60 3 61.80 0.220663 60 1 61.80 0.220663 15 3 59.90 0.0889
2010 Target 63 15 1 55.90 0.076663 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'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 74 60 3 61.80 0.220674 60 1 61.80 0.220674 15 3 56.20 0.0611
2010 Target 74 15 1 55.90 0.058074 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'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 85 60 3 61.80 0.220685 60 1 61.80 0.220685 15 3 55.90 0.0580
2010 Target 85 15 1 55.90 0.058085 0 3 52.53 0.0333
"Ideal" 85 kW Case 85 0 1 28.67 0.0243
Energy Storage Requirements for Supplementing a Downsized FC’s Limitations
•
With FC downsized, ESS must also assist during max acceleration event.
•
ESS is the same as a full-sized FC requires for “Today’s”
fuel cell
performance.
27 4th Advanced Automotive Battery Conference
63 kW Fuel Cell Peak Shaving Warm-Up Ramp Rate P req'd E req'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 63 60 3 61.80 0.220663 60 1 61.80 0.220663 15 3 59.90 0.0889
2010 Target 63 15 1 55.90 0.076663 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'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 74 60 3 61.80 0.220674 60 1 61.80 0.220674 15 3 56.20 0.0611
2010 Target 74 15 1 55.90 0.058074 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'dFC Power (kW) Time (s) 10-90% (s) (kW) (kWh)
Today's Perfomance 85 60 3 61.80 0.220685 60 1 61.80 0.220685 15 3 55.90 0.0580
2010 Target 85 15 1 55.90 0.058085 0 3 52.53 0.0333
"Ideal" 85 kW Case 85 0 1 28.67 0.0243
Energy Storage Requirements for Supplementing a Downsized FC’s Limitations
•
With FC downsized, ESS must also assist during max acceleration event.
•
ESS is the same as a full-sized FC requires for “Today’s”
fuel cell
performance.
•
Therefore, downsizing provides improvement in fuel economy, fuel cell costs, and [in minimal control case] has little to no affect on ESS sizing.
•
ESS is nearly the same as a full-sized FC requires for “2010 Target”
fuel cell
performance.
28 4th Advanced Automotive Battery Conference
Current Work -
Potential Active Roles for Supplementing Fuel Cell Operation
Curve 2 - Peak Efficiency @ 25% Full Power
0
10
20
30
40
50
60
70
0 20 40 60 80 100Percentage of Peak Power (%)
Syst
em E
ffici
ency
(%)
Opportunity DischargeSOC is high and fuel cell
efficiency could increase if load request is decreased.
Opportunity ChargeSOC is low and fuel cell
efficiency could increase if load request is increased.
29 4th Advanced Automotive Battery Conference
Current Work -
Multi-region “Spring” SOC Maintenance Algorithm
High SOCLow SOC Target SOC
•
Opportunity region•
only take action if it makes the prime power plant more efficient
•
Could assume different charging rates in each region
•
Number of parameters makes it harder to optimize and understand impacts -Charge Power
+Charge Power
0
Fc_pwr_r
= dl_pwr_r
+ charge_pwr
Mus
t Cha
rge
Cha
rge
Req
uire
d
Opp
ortu
nity
Cha
rge
Mus
t Dis
char
ge
Dis
char
ge R
equi
red
Opp
ortu
nity
Dis
char
ge
Med-low SOC Med-high SOC
30 4th Advanced Automotive Battery Conference
Summary
•
The best fuel economy occurs when peak FC efficiency ≅
typical power operating point (cycle
dependant).•
There is positive benefit of downsizing the FC if the peak efficiency is shifted toward the
typical power
operating point (cycle dependant).•
ES requirements for supplementing FC limitations are suitable for Ultracapacitors or High Power Batteries.
•
Downsizing a FC (toward the gradeability
limit) with today’s or 2010 projected characteristics, Does NOT significantly affect ES requirements (with minimal ES control case).
•
There is significant potential for more actively using the ES to manage the FC operation points because of un-used regenerative energy capture.
31 4th Advanced Automotive Battery Conference
Acknowledgements
•
ADVISORTM
is used to simulate the fuel cell
and energy storage system demands under drive cycle and performance tests.
•
This work supports the FreedomCAR Energy Storage technical team in defining energy storage requirements for fuel cell vehicles.