Plug-In Hybrid with Fuel Cell Battery Charger
G. J. Suppes
Department of Chemical Engineering, University of Missouri,
W2028 EBE, Columbia, MO 65211, U.S.A.
ABSTRACT
A new approach on vehicular fuel cell technology uses an on-board fuel cell stack as a battery charger and could be
one of the most viable methods to displace imported oil when incorporated into plug-in hybrid vehicles. A sensitivity
analysis evaluating vehicle specification and component performances suggests that small fuel cell stacks (e.g. 1
kW) would be commercially viable in plug-in vehicles at prices as high as $1800 per kWh. The combination of these
small fuel cell stacks and a battery pack would cost less than the use of either an appropriately sized battery pack or
fuel cell stack alone. Tribrid systems using fuel cell batter chargers, battery packs, and internal combustion engines
could be viable decades before fuel cell systems relying on a hydrogen refueling infrastructure. Furthermore, these
vehicles will not rely on infrastructure development for them to be successfully introduced to the market.
While fuel cells can be purchased today at about $2,500 per kW, the DOE estimates that mass-production using
today's technology would cost about $300 per kW. Based on these estimates, the use of fuel cells as battery
chargers in Battery Electric Vehicles and Plug-In Hybrid Electric Vehicles is commercially viable today and can
evolve to increasingly large percentages of the U.S. automotive market.
Key Words: Fuel Cell, Hydrogen, Recharge, Plug-In, Efficiency
INTRODUCTION
Important industrial issues on sustainability, balance of trade, and creation of quality domestic jobs culminate on
petroleum fuels and the U.S. importing of $150 billion in crude oil each year. For decades, efforts to displace
petroleum imports have fallen short due to the high costs of alternatives and the limited energy feed stock options
large enough to displace crude oil. Today, fuel cell technology is receiving much attention due to its potential to
change the rules in transportation sector. Plug-in approaches that use onboard electrolysis to produce hydrogen are
particularly attractive since they do not rely on a hydrogen refueling infrastructure and do not require the distribution
of new fuels1.
The Plug-In Fuel Cell Hybrid Electric Vehicle (PFCHEV) relies on any number of combinations of fuel cells, batteries,
capacitors, and engines to power the vehicle2, 3. The “Plug-In” aspect of this vehicle allows grid electricity to charge
batteries and produce electrolysis hydrogen/oxygen during the night for use by the vehicle during the first 20 or more
miles of travel during the day—during these initial miles the engine does not operate. About half the miles traveled
by automobiles each day in the U.S. are within the first twenty miles traveled by each vehicle in a day. Renault
introduced a commercial PHEV to the French market in 2003.4
In a timeline presented by Bob Graham5 of the Electrical Power Research Institute in December of 2002, battery
electric vehicles (BEV) and hybrid electric vehicles (HEV) were noted to have hit the market before 2003. The plug-in
HEV (PHEV) and PFCHEV were projected to hit the U.S. market in 2005 and 2008 respectively. Non-Plug-In
versions of fuel cell vehicles (FCHEV) were projected for 2015. Since the PFCHEV does not rely on a hydrogen
refueling infrastructure, it is commercially viable on a shorter timeline. Other advantages of the PFCHEV are not as
obvious but perhaps even more important.
Fuel cells and batteries (or capacitors) have a powerful synergy, the combination of the two can provide better
performance and lower cost than batteries alone or fuel cells alone. Batteries are good at high power output (e.g. 50
kW) but only provide storage capacity at high cost and weight penalties. Fuel cells provide affordable capacity
relative to batteries (in the form of stored hydrogen and oxygen) but have costs that are roughly proportional to power
output. In the PFCHEV a synergy is achieved by having a fuel cell (e.g. 2 kW) perform primarily as a battery charger
throughout the day while batteries provide the high power output (e.g. 50 kW).
For a typical day in a PFCHEV, overnight electrolysis and charging provide about 7.5 miles of range from the
batteries and about 30 miles of capacity form hydrogen/oxygen. During the 8-mile commute to work, the batteries
are used to power the vehicle with some assistance from the fuel cell. When parked at work, the fuel cell charges the
batteries. When the workday is complete, the battery is charged with 7.5 miles of capacity and about 20 miles of
hydrogen/oxygen are available to supplement the battery. Throughout the evening and day, the fuel cell operates as
long as the battery is less than fully charged. For many applications the internal combustion engine (ICE) would
never be started but is available if additional range is needed.
The PFCHEV can have a powerful impact on the oil imports. For many applications, especially as the second car in
a 2-car family, a 40 mile-per-day range can meet more than 90% of the travel needs. Approximately 78% of all miles
traveled are within the first 40 miles traveled in a day. Advantages of the PFCHEV include:
•
Zero point-source emissions
•
Near-zero noise pollution
•
Near-zero carbon dioxide emissions when using electricity from wind or nuclear sources
•
Imported oil is fully displaced with domestic energy sources (for this vehicle)
•
A variety of sources of electrical power are fully sustainable
•
Substantial elimination of time and inconvenience of refueling gasoline
A disadvantage of the PHEV and PFCHEV vehicles are their poor well-to-wheel efficiencies; however, efficiency has
historically only indirectly impacted commercial viability in the form of increased operating expenses3. As discussed
in this paper, the economics are good and poor efficiencies do not translate to commercialization barriers.
Table 1 summarizes the projected costs for the BEV, PFCHEV, and FCHEV to achieve 30 miles of engine-free
operation for a vehicle requiring 50 kW of power. The $500 / kW fuel cell costs should be attainable within the
decade. The data illustrates how the PFCHEV power system costs less than fuel cells or batteries alone for
providing the specified performance.
METHODS
The fuel cell stack of the PFCHEV systems of Table 1 are not designed to replace the engine of today's SUV, but
with a 30-mile plug-in capability the power system could find many useful applications. Having an engine backup, the
PFCHEV could compete with conventional automobiles because range can be extended by refueling with gasoline.
The summary of Table 1 illustrates how the PFCHEV will typically cost at least a factor of 6 less than the FCHEV
using oxygen and a factor of 12 less for a fuel cell stack using air. As the prices of fuel cells decrease, the PFCHEV
will cost less than the PHEV as is the case for the system specifications of Table 1. The data of Table 1 is based on
projected $500 / kW costs for PEM fuel cells for 2010. The summary of Table 1 and subsequent sensitivity analysis
in the paper summarize how the PFCHEV is likely to develop a powerful market niche and will likely become
commercially viable years, perhaps decades, before FCHEV vehicles.
While the summary of Table 1 is specific to the underlying assumptions of that projection, the uncertainty of the
implications of the PFCHEV is greatly reduced though a sensitivity analysis on key parameters. The impact of key
technologies and design specifications on the cost of the PFCHEV versus the FCHEV and PHEV was evaluated by
this sensitivity analysis, including the following factors:
•
Vehicle Plug-In range in miles.
•
Battery range in miles.
•
The fuel cell sizing factor that determines the FC size based on the ability of the fuel cell to consume the
tank of hydrogen in a specified number of hours. A sizing factor of 0.2 h-1 corresponds to consuming the
tank of hydrogen in 5 hours. A t0 kWh tank of hydrogen would thus be sized with a 2 kW (10 kWh X 0.2 h-1)
fuel cell.
•
Battery costs in $/kWh allow the energy needs to be converted to battery costs on a delivered energy basis.
•
Fuel economy in kWh/mile allows the range of the vehicle to be converted to the required kWh of energy
delivered to the electric drive train.
•
Specific energy in Wh/kg allows the mass of the battery pack to be calculated based on deliverable energy.
•
Hydrogen tank weights (kg/kWh) and costs ($/kWh) are estimated to be directly proportional to the
deliverable energy from the hydrogen in the tank.
•
Specific cost penalties in $/kg for weight are applied to the weight of batteries and tanks.
•
Battery efficiencies are applied when converting miles of hydrogen to kWh of hydrogen stored. These
efficiencies account for the fact that some of the energy is lost both in charging the batteries and then
subsequently discharging the batteries. For example, 10 miles of hydrogen at a fuel economy of 0.5
kWh/mile going through a 90% efficient battery requires 10 X 0.5 / 0.9 / 0.9 = 6.17 kWh of deliverable
energy from the fuel cell using the stored hydrogen. If the fuel cell is operating at 50% efficiency, this
translates to a lower heating value of stored hydrogen equal to 12.34 kWh.
•
The electrolyzer cost is calculated as a percentage of the fuel cell cost.
Table 2 summarizes the base case, high, and low values of the parameters used in the sensitivity analysis. The
range of parameters for the batteries are based on an Argonne National Laboratory summary of projections on nickel
metal hydride batteries.6 In this survey, nickel metal hydrides and nickel-cadmium batteries provided the most
competitive combination of light weight, reasonable number of charge/discharge cycles, and costs. Table 3
summarizes projected performance characteristics for the nickel metal hydride batteries based on this the Argonne
report.
Plug-In Range7 is the miles of travel possible in a day from plug-in electricity. The American Automobile Association
(AAA) uses 12,500 miles as a typical yearly mileage on a vehicle to determine operating costs. 12,000 divided by
300 days of travel in a year is 40 miles per day. About 76% of the miles traveled in the U.S. are within the first 40
traveled by an automobile in a day and about 78% of the automobiles do not travel more than 40 miles in a randomly
selected day. Plug-In ranges of 20, 40, 60, and 80 miles were studied. The total Plug-In range is split into the range
available from batteries and the range available from electrolysis hydrogen.
The fuel cell size is a function of the electrolysis hydrogen storage capacity. High, low, and base case sizing factors
used in this study were 0.25, 0.083, and 0.125 h-1. A fully reversible fuel cell8, 9 used to its full potential would
produce electrolysis hydrogen for 12 hours and would produce electrical power on the vehicle for 12 hours. The Fuel
Cell Sizing Factor uses the capacity of the hydrogen storage tank to size the fuel cell appropriately. For example if
30 kWh of stored hydrogen is consumed in 10 hours, a sizing factor of 0.1 h-1 would be multiplied times the 30 kWh
of stored hydrogen to estimate the fuel cell stack size at 3 kW. A car designed with 10 kWh of batteries and 30 kWh
of stored hydrogen could use a fuel cell with a sizing factor of 0.25 h-1 to recharge the batteries 3 times in 12 hours.
At a constant sizing factor, larger fuel cells are required to utilize the capacity of larger hydrogen storage tanks. For
comparison purposes, the engine of the Toyota Prius, one of several HEVs on the market today, has a 57 kW
engine—having a much higher power output than the fuel cell stacks of this study. The FCHEV systems evaluated
for comparison purposes in this study were sized with 50 kW fuel cell stacks.
The costs of the batteries were evaluated at 300, 400, and550 $ / kWh. The batteries pack was sized based only on
kWh needs and not kW. The kWh needs were calculated based on the specified range in miles of the battery pack,
and this range was set at 0%, 25%, 50%, 75%, and 100% of the plug-in range.
The kWh of energy required per mile of travel is an important measure of vehicle energy efficiency. A vehicle
designed to operate at a sustainable 90 mph at 50 kW power would have a fuel economy of 1.8 miles per kWh. A
vehicle with a fuel economy of 1.43 miles / kWh and a 50 kW power source could maintain 71.4 mph for extended
periods of time. Vyas and Ng6 assume a fuel economy of 3.7 miles / kWh (130.4 miles for 35.1 kWh of energy). Fuel
economies of 1.43, 2, and 3.33 kWh/mile were evaluated in this study. The fuel economy of 3.33 kWh/mile is more
consistent with a 30 kW engine than the 57 kW Toyota Prius engine.
The batteries were characterized and sized based on delivered kWh. However, battery efficiencies were necessary
to convert kWh of hydrogen to kWh of delivered energy via first charging batteries and then discharging the stored
energy. Efficiencies of 80, 85, and 90% were assumed. The amount of stored hydrogen and the fuel cell kW rating
were increased to account for these efficiencies. For example, 10 kWh of battery power translates to 10 / 0.8 / 0.8 or
15.625 kWh of hydrogen when the battery has an efficiency of 80%.
The weights of batteries were estimated by the specific energy of the battery. Hinrichs and Kleinback10 report nickel
metal hydride batteries at 60 to 80 Wh/kg. Battery specific energy of 70, 78, and 80 Wh/kg were used in this study.
The weights of hydrogen/oxygen tanks were assumed to be a linear function of the kWh of gases stored. Values of
1, 2, and 3 kg/kWh were used. Assuming the average weight of an occupied automobile at 1500 kg, the cost of
propulsion per kilogram is about $2250 / 1500 kg or $1.5/kg. The costs of extra weight was 1, 1.5, and 2 $/kg for the
weights of the batteries and tanks. The costs of the tanks were calculated at $2, $4, and $6 per kWh of hydrogen
storage capacity.
The cost of the electrolysis capabilities was calculated as 0%, 100%, and 200% of the cost of the fuel cell stack. The
0% represents a fully reversible fuel cell that is reversible at no extra cost and the 200% represents an electrolysis
system that costs twice as much as the fuel cell system.
With the above specifications, a spreadsheet was prepared to calculate the cost of the entire power system based on
the input of the cost of a fuel cell stack per kW of power generation capabilities. At a constant Plug-In range, the
power system cost was a linear function of the fraction of the range provide by the battery pack—a line with negative
slope when the battery pack is less expensive than the fuel cell system to meet performance specifications. As the
price of the fuel cell stack decreases, the negative slope of the line becomes zero at a "threshold" price where all
combinations of battery packs and fuel cells stacks have the same price to meet the mileage range. The sensitivity
analysis was performed to identify these "threshold" fuel cell stack prices.
RESULTS
Table 5 summarizes the sensitivity analysis. the base case analysis projects that when fuel cell stacks are available
at less than $1,184 per kW, the combination of a fuel cell stack and batteries would be more cost effective in a plugin hybrid than the use of batteries alone. Other threshold fuel cell stack prices were calculated by adjusting the base
case to include high and low values for each of the parameters.
For a 40 mile Plug-In vehicle, the battery pack would likely provide between about 10 and 20 miles of range with the
remainder provided by stored hydrogen. At less than 10 miles of battery capacity, the vehicle would be too limited by
this 10-mile limit for travel over a short time period. At greater than 20 miles one-way to a destination, the engine
would have to operate during part of the roundtrip, and so, a battery range greater than 20 miles would have little
performance advantage over a battery range of 20 miles.
The base case solution is valid with fuel cells of 2.59 and 1.73 kW paired with battery packs having 10 and 20 mile
ranges respectively. These fuel cells stacks are quite small in comparison to the 50 kW that would be required to
provide full power demands from the fuel cells stack. In fact, the FCHEV power system costs over six times as much
as the PFCHEV.
In comparing the FCHEV to PFCHEV, an engine (cost at $1000) is used to provide backup power for the PFCHEV,
and the cost of the electrolyzer is included in the PFCHEV. For the FCHEV, no electrolysis capability is included and
the $1000 is assumed to be applied to auxiliary equipment such as a reformer system or high capacity hydrogen
storage.
As indicated by the sensitivity analysis of Table 5, the FCHEV is consistently about four to twelve times more costly
than the PFCHEV with a 40 mile plug-in range. The cost of the electrolyzer had the greatest impact on the threshold
fuel cell stack cost. The sizing factor had the second greatest impact, and the battery efficiency had the third
greatest impact. The fuel economy did not impact the threshold fuel cell cost, but did impact the cost of the PFCHEV
relative to the FCHEV. The latter was primarily due to an artifact of the calculation where a 50 kW fuel cell stack
supply was always assumed for the FCHEV when it may have been a more-even playing field if a 30 kW fuel cell
were matched up with the 3.33 fuel economy.
The electrolyzer cost is a most important research and development area that will allow PFCHEV systems to be more
cost competitive sooner.
In the best case, reversible fuel cells would produce both electrical power and
hydrogen/oxygen with zero incremental price above a conventional fuel cell.
The sizing factor is a design degree of freedom. Sizing factors that provide the fuel cell with more time to consume
the stored hydrogen lead to less costly power systems; however, these systems would have greater limitations on
performance which translates to the engine being needed more frequently to provide power when the fuel cell stack
has not had sufficient time to recharge the batteries. In principal, this predominantly translates to more frequent
gasoline refueling stops. Low sizing factors and relatively small fuel cells (e.g. 1.72 kW) would make excellent entrylevel systems for this market. For the PFCHEV system of Table 1, the cost of the power system could be further
reduced by use of a sizing factor less than 0.125 h-1
The PFCHEV would benefit from highly efficient batteries and batteries with large charge/discharge lives. This
suggests that-high capacity capacitors, flywheels, and other efficient and robust storage means could be used to
advantages on the PFCHEV. Regenerative braking is also more important in the PFCHEV than in conventional HEV
vehicles due to the premium paid for plug-in capabilities. Batteries with higher power outputs would also be needed
since the specific power outputs listed in Table 2 would be insufficient.
Other parameters such as battery costs, costs for tanks, and cost penalties for weight had relatively minor impacts
within the range of parameters. The estimated costs for the PFCHEV power systems at the threshold fuel cell cost
solutions ranged from $6000 to $12000.
Table 6 summarizes a series of analysis on the impact of Plug-In range on threshold fuel cell costs. The range had
no impact on the threshold fuel cell costs, but it did impact the size of the fuel cell needed to meet power
requirements. As the size of the fuel cell stack became larger to achieve greater ranges, the advantage over the
FCHEV diminished to a factor of 3.4 at a range of 80 miles per day.
DISCUSSION
The sensitivity analysis indicates that a vehicle similar to that specified in Table 1 would be an entry-level vehicle
having a threshold fuel cell price of $1,792/kW and system price of $4,773 (Table 7 summarizes entry level pricing).
This would be an efficient, light-weight vehicle with up to 30 miles per day in plug-in range. The HEV version of this
vehicle would include about 6.6 miles in battery capacity at a cost of about $830 plus the engine ($1000). A premium
of about $2,957 is paid for the "Plug-In" option with a 30 mile capacity. At $1,792/kW, a 50 kW power system would
cost about $90,000.
For a hybrid car, the extra cost for the battery pack and electronics is partially recoverable in the form of reduced fuel
consumption. Plug-In vehicles would have considerably less gasoline consumption, but per-mile energy costs would
be about the same as with the HEV. The fuel costs3 are about $0.025 and $0.032 per mile1 for gasoline ($1.00 per
gallon, no highway tax) ICE and hydrogen produced by grid (off-peak, $0.056 per kW-hr11). Entry level vehicles will
not pay for themselves based on saved fuel cost in the U.S.—in countries where fuel prices are more than $4.00
gallon it is possible for the PHEV and PFCHEV to pay for themselves based on savings in fuel costs if they are able
to tap into cheap off-peak grid electricity.
Two potential U.S. niche markets for the Plug-In approach are the alternative fuel markets created by Environmental
Policy Act (EPACT) regulation and consumers who are willing to pay additional money for an automobile that
displaces imported petroleum with electrical power produced for indigenous feed stocks. The markets would not be
huge, but they would create additional momentum in the fuel cell industry to further reduce costs.
At a fuel cell cost of $500 / kW and a 50% premium for reversible performance (possible by 2010), a power system
with the same economy and fuel cell sizing factor as that of Table 7 would cost about $2750. This vehicle would
replace about 300 gallons per year of imported petroleum with electrical power. From a societal perspective, the
benefits would warrant the additional cost. If the engine and gasoline tank were removed from this engine and it
were used for limited local transit, the price of the power system could be further reduced to about $1500 and the
vehicle itself would realize reduced costs due to weight reductions. Such a vehicle would be particularly appropriate
as a second vehicle in a 2-car family or as a short trip vehicle for a college student. Vehicles with and without the
backup engine could realize substantial markets.
As fuel cells become less expensive, increased plug-in ranges would become viable and the engine would be used
less. As the engine is used less, less expensive, lighter, and possibly air-cooled engines could be used to reduce the
1
Costs are based on a vehicle getting 30 mpg and fuel at $1.00 per gallon (not including highway taxes). An energy
content of $114,500 Btu/gal for gasoline translates to 3817 Btu gasoline / mile. This translates to 687 Btu of wheel
energy per mile applied to all fueling options.
premium prices paid for these vehicles—this would reduce the premium paid for the plug-in option. When fuel cell
prices are low enough and the premium paid for the "reversible" aspect of the fuel cell is low enough, the reduced
engine cost will allow the cost PFCHEV power system to become less, eventually being equal to the cost for HEV
power systems. The ability of the PFCHEV to evolve into a platform that is both less expensive than ICE options and
will be powered by indigenous fuels is its greatest attribute.
Today, PEM fuel cell costs are about $2,500 / kW when used with pure oxygen and about $5,000 / kW when used
with air. The costs are projected12 to be $650-$1150 by 2010. The large automobile market could readily reduce the
prices to less than $500 by 2010 due to both mass production and increased competition.
The entry level $4,773 vehicle of Table 7 could be attained by about 2007 based on trends in current fuel cell prices.
Increased demands for fuel cells could expedite the reductions in fuel cell prices to the point where the $500 / kW
fuel cells with a 50% premium for reversible performance could be attainable by 2010. The evolution from 2010
would PFCHEV vehicles with increase plug-in ranges both with and without backup engines. When considering that
current fuel cell prices are not based on mass production, the 2007 and 2010 timeframes are rather conservative.
The DOE estimates that through mass production, fuel cells could be produced today at $300 per kW13—this
suggests that the technology could be commercialized to great advantage in today's market.
One to 5 kW fuel cells operated from electrolysis oxygen and hydrogen are considerably less complex than internal
combustion engines. Also, electronics and electric motors have the potential to be produced for lower costs and
lighter weights than current mechanical drive trains and transmissions. Fuel cell technology makes entry of new
companies into the automobile market easier than has been possible with engines and mechanical drive trains. This
is especially true for light-weight vehicles. Competition could increase resulting in lower prices for vehicles—lowmaintenance and dependable vehicles could become available at a fraction of today's automobile prices (possible by
2012). Table 8 summarizes the typical operating costs of a vehicle. Substantial reductions in the cost of owning and
operating a vehicle can be achieved by reducing the vehicle cost and those expenses like financing, insurance, and
taxes that are related to the cost of the vehicle.
The PFCHEV will push the limits of battery technology due to the high power output and the large number of
charge/recharge cycles. It is likely that large strides can be made in power output as the power output currently does
not drive the price of batteries—prices correlate with the energy content (kWh) of the batteries. A PFCHEV would put
a large number of cycles on the batteries, up to one cycle for every 10 miles.
A 1,000-cycle battery life (see Table 2) translates to 10,000 miles before the battery pack would need to be changed.
Fortunately, EPRI14 reports that products like the Saft nickel metal hydride batteries are achieving greater than 2800
cycles. In addition, through the use of capacitors, directing fuel cell power directly to the engines, and accounting for
backup engine operation, a vehicle designed for 10 miles range from the battery pack could average near 20 miles
per cycle. This translates to 56,000 miles before replacing the batteries. A single replacement of the battery pack
during the life of the vehicle is an attainable short-term goal.
CONCLUSIONS
The PFCHEV approach using the fuel cell battery charger provides for market entry vehicles that would cost ten
times less than FCHEV counterparts using pure hydrogen and oxygen. If air were used with FCHEV fuel cells, the
PFCHEV power systems would cost a factor of twenty less. The PFCHEV also does not rely on a hydrogen refueling
infrastructure and provides a commercially viable entry point for vehicles benefiting from fuel cells which is likely at
least a decade earlier than FCHEV vehicles. Table 9 qualitatively compares the cost of the FCHEV using hydrogen
refueling with the PFCHEV.
The PFCHEV vehicles would use the versatility of the electrical power grid to tap into domestic energy sources.
When wind and nuclear are used, petroleum imports are displaced with technology having near-zero carbon dioxide
emissions and near-zero point source emissions in the cities. Other than the modified vehicle design, no additional
infrastructure would be required for the PFCHEV to enter the market. Increased electrical power infrastructure would
occur through private investment in well-established supply-demand economics in providing electrical power. The
versatility to use off-peak electricity for recharging PFCHEV will allow baseline power generation to increase, and this
can be used to great advantage to improve the electrical power grid infrastructure so that it is more efficient and
reliable.
At fuel cell costs less than about $1700 / kW, the combination of fuel cells, batteries, and capacitors would be less
costly than batteries used in PHEV or BEV power systems. Consumers that currently use BEV and EPACTqualifying alternative fuel vehicle in today's market using mass production techniques to produce reversible fuel cells.
The fuel cells should reduce PFCEV prices sufficiently to cause substantial growth in the traditional BEV market. The
FCHEV vehicles will tend to evolve toward use of larger fuel cell stacks and smaller battery packs, eventually
reaching fuel cell stack sizes that merge into the FCHEV classification with backup internal combustion engines no
longer being necessary—a speculative timeframe for this is about 2020.
Table 1. Comparison of PHEV, PFCHEV and FCHEV power system options for projected 2010 fuel cell
stack costs of $500 / kW. A BEV power system without an engine and having a 90 mile range would cost
about $18,874. All energy and power units are in delivered energy. For example, the hydrogen (H2) in kW-h
must be divided by the fuel cell efficiency to estimate the amount of hydrogen in the tank.
FCHEV
FCHEV
PFCHEV
PFCHEV
PHEV
(oxygen)
(air)
Total Range (Miles)
30
30
30
30
30
Battery Pack Range (Miles)
0
0
7.5
15
30
Battery Pack (kW-h)
0
0
3.75
7.5
15
H2 Range (Miles)
30
30
22.5
15
0
H2 (kW-h)
20.76
20.76
15.57
10.38
0.00
Fuel Cell Power (kW)
50.00
50.00
1.95
1.30
0.00
Engine ($)
$0
$0
$1,000
$1,000
$1,000
Battery Cost ($)
$0
$0
$1,500
$3,000
$6,000
Fuel Cell Cost ($)
$25,000
$50,000
$973
$649
$0
Weight and Tank Costs ($)
$114
$114
$158
$201
$288
Electrolyzer ($)
$0
$0
$973
$649
$0
Total Power System Cost
$25,114
$50,114
$4,604
$5,499
$7,288
Table 2. Values of parameters used in sensitivity analysis.
Low
Base
High
Case
Plug-In Range
20
40
60 (80)
Sizing Factors (h-1)
0.083
0.125
0.25
Battery Costs ($/kWh)
300
400
550
Fuel Economies (mile/kWh)
3.33
2
1.43
Battery Specific Energy (Wh/kg)
70
78
80
Hydrogen Tank Weights (kg/kWh)
1
2
3
Hydrogen Tank Cost ($/kWh hydrogen)
2
4
6
Cost of Weight ($/kg)
1
1.5
2
Battery Efficiency
0.80
0.85
0.90
1
2
Cost of Electrolysis ($ as % of Fuel Cell Cost) 0
Table 3. Projected performance of nickel metal hydride batteries.
2003*
2010
2020
Specific Energy (Wh/kg)
70
78
80
Specific Power (W/kg)
160
180
200
Charge/Discharge Cycles
1000
1000
1100
Cost $/kWh
550
400
300
* Estimates include numbers from survey with adjustments made based on other references.
Table 4. Example cost estimation at a threshold fuel cell price ($/kWh) where the cost of combinations of batteries and stored hydrogen with a fuel cell stack yield
the same cost for the energy system—at least 25% of the range must come from batteries to meet performance needs. When no batteries are needed, the fuel
cell stack is sized to meet all power requirements.
Weight
Battery
Battery
Total
Pack
Pack kW-
Miles
Miles
h
H2 Miles kW-h
kW
($)
(kg)
40
0
0
40
27.7
50
$0
40
10
5
30
20.7
2.59
40
20
10
20
13.8
40
30
15
10
40
40
20
0
H2
Fuel Cell Engine Battery
Weight
Weight
Weight
Battery
Fuel Cell Tank Cost Electrolyzer
Tank (kg) Battery ($) Tank ($)
Cost ($)
Cost ($)
($)
($)
Total
0.0
27.7
$0
$42
$0
$59,479
$111
$0
$59,631
$1,000
64.1
20.7
$96
$31
$2,000
$3,087
$83
$3,087
$9,385
1.73
$1,000
128.2
13.8
$192
$21
$4,000
$2,058
$55
$2,058
$9,385
6.92
0.86
$1,000
192.3
6.9
$288
$10
$6,000
$1,029
$28
$1,029
$9,385
0
0
$1,000
256.4
0
$385
$0
$8,000
$0
$0
$0
$9,385
Table 5. Fuel cell costs ($/kW) below which the combination of a fuel cell charger and battery pack is less expensive than use of the battery pack alone to meet
energy demands. Calculations are based on 40 miles of plug-in range for a PFCHEV. The fuel cell kW ratings are based on 10 miles range from the batteries
and 30 miles range from the fuel cell stack. All energy and power units are in delivered energy. For example the hydrogen (H2) in kW-h must be divided by the
fuel cell efficiency to estimate the amount of hydrogen in the tank.
Sizing
Spec.
Cost
FC
Factor
Economy Energy Eff. Bat Cost Bat Cost Tank Electrol. Cost Wt
FC /PFC
Total
Cost FC
kW
1/hr
kWh/m
Wh/kg
%
$/kWh
$/kWh
% FC
$/kg
$/$
$
$/kW
2.60
0.125
0.5
78
0.85
400
4
100%
1.5
6.3
$9,385
$1,184
1.72
0.083
9.5
$9,385
$1,782
5.19
0.25
3.2
$9,385
$592
0.3
9.8
$6,031
$1,184
0.7
4.7
$12,738
$1,184
70
6.3
$9,429
$1,190
80
6.3
$9,375
$1,182
0.8
5.6
$9,385
$1,051
0.9
7.1
$9,385
$1,336
550
6.5
$12,385
$1,617
300
6.1
$7,385
$895
2
6.4
$9,385
$1,198
6
6.3
$9,385
$1,182
0
12.7
$9,385
$2,379
2
4.2
$9,385
$793
1
6.4
$9,256
$1,173
2
6.4
$9,513
$1,206
Table 6. Impact of vehicle Plug-In range on threshold fuel cell prices and fuel cell power rating.
Total
Battery
FC
FC /PFC
Total
Cost FC
Miles
miles
kW
$/$
$
$/kW
20
5
1.30
11.5
$5,192
$1,190
30
7.5
1.95
8.2
$7,288
$1,190
40
10
2.60
6.4
$9,385
$1,190
40
20
1.73
6.4
$9,385
$1,190
60
15
3.89
4.4
$13,577
$1,190
80
20
5.19
3.4
$17,769
$1,190
Table 7. Example entry level PFCHEV
specifications and costs.
Total Miles
30
Battery Pack Miles
10
Battery Pack (kW-h)
3
H2 (Miles)
20
H2 (kW-h)
8.30
Fuel Cell (kW)
0.69
Engine ($)
$1,000
Battery Cost ($)
$1,200
Fuel Cell Cost ($)
$1,235
Electrolyzer ($)
$1,235
Total
$4,773
FC ($/kW)
$1,792
Table8. Typical operating costs for vehicle. Ranges include low end cost of mid-sized
car and upper end costs for luxury car and SUV15.
Vehicle Operating Cost Average Cost
Range ($/mile)
Depreciation
22.5-31.8
49.2%
Insurance
6.9-10.5
14.3%
Financing
4.8-8.3
12.3%
Fuel
4.5-6.9
10.9%
Maintenance, Oil, Tires
4.7-5.3
9.1%
License & registration
1.4-3.2
4.2%
Table 9. Qualitative comparison of PFCHEV approach to FCHEV
relying on hydrogen refueling.
Hydrogen
Plug-In
Refueling
Reformer
Fuel Cell Cost Breakthroughs
$$$
$$
Improved Fuel Cell Durability
$$
$
Improved Hydrogen Production
$$
$
Hydrogen Storage Breakthroughs
$$$
N/A
Hydrogen Refueling Breakthroughs
$$
N/A
Hydrogen Infrastructure Cost
$$$$$
N/A
H2 Refueling Time/Anxiety/Risk
$$$
N/A
&
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