Plug-in hybrid with fuel cell battery charger - all-craft
International Journal of Hydrogen Energy 30 (2005) 113–121 www.elsevier.com/locate/ijhydene
Plug-in hybrid with fuel cell battery charger
G.J. Suppes ∗
Department of Chemical Engineering, University of Missouri, W2028 EBE, Columbia, MO 65211, USA
Received 20 January 2004; received in revised form 24 March 2004; accepted 20 April 2004
Available online 17 June 2004
Abstract
A new approach on vehicular fuel cell technology uses an on-board regenerative fuel cell (RFC) stack as a battery charger.
The RFC’s electrolyser capability uses grid electricity to produce hydrogen and oxygen during an overnight charging process.
By using the RFC to recharge the vehicle’s battery pack during the day, the size of the battery pack can be reduced by ¿ 50%.
A sensitivity analysis evaluating vehicle speci9cation and component performances suggests that small RFC stacks (e.g.
1 kW) would be commercially viable in plug-in vehicles at prices as high as $1800/kW for the RFC stack. The combination of a
RFC stack and a battery pack would cost less than the either an appropriately sized battery pack or fuel cell stack alone. Vehicles using so-called tribrid power systems based on the combination of RFCs, battery packs, and internal combustion engines (ICE) could be viable decades before vehicles powered solely by fuel cells that rely on a hydrogen refueling infrastructure.
?
2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Keywords: Fuel cell; Hydrogen; Recharge; Plug-in; E?ciency
1. Introduction
Important industrial issues on sustainability, balance of trade, and creation of quality domestic jobs culminate on petroleum fuels and the US crude oil imports now exceeding $150 billion each year. For decades, eBorts 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 the transportation sector. In addition, closed-loop fuel cell systems that are recharged with grid electricity would emit zero tail-pipe emissions and lead to signi9cant reductions in municipal air pollution.
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 re-
quire the distribution of new fuels [
as an electrolyzer and fuel cell.
ative fuel cells (RFC) would be used; a RFC operates both
∗ Tel.: +1-573-884-0562; fax: +1-573-884-4940.
E-mail address: suppesg@missouri.edu
(G.J. Suppes).
The plug-in fuel cell hybrid electric vehicle (PFCHEV) relies on any number of combinations of fuel cells, batter-
ies, capacitors, and ICEs to power the vehicle [ 2 , 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 9rst 32 or more kilometers (20 miles) of travel during the day—during these initial kilometers the ICE does not operate. About half the distance traveled by automobiles each day in the US are within the 9rst 32 km traveled by each vehicle in a day
[ 4 ]. Renault introduced a commercial PHEV to the French market in 2003 [ 5 ].
In a timeline presented by Bob Graham [ 6 ] of the Elec-
trical 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 US market in 2005 and 2008 respectively. Non-plug-in versions of fuel cell vehicles (FCHEV) were projected for
2015. 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
0360-3199/$ 30.00
?
2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.ijhydene.2004.04.017
114 G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121
Fig. 1. Illustration of plug-in HEV where battery pack and RFC work in combination to provide both the needed range and power output. The dashed lines illustrate Pow of electrical power.
family with two cars, a 64 km-per-day range can meet more than 90% of the travel needs. On the average, approximately
78% of automobile mileage is traveled within the 9rst 64 km
(40 miles) of travel each day. Advantages of the PFCHEV include:
• Zero or near-zero tail-pipe emissions.
• Near-zero noise pollution.
• Near-zero carbon dioxide emissions and sustainability when using electricity from wind or nuclear sources.
• Imported oil is fully displaced with domestic energy sources (for this vehicle).
• Substantial elimination of time and inconvenience of refueling gasoline.
A disadvantage of the PHEV and PFCHEV vehicles are their poor well-to-wheel e?ciencies; however, e?ciency has historically only indirectly impacted commercial viability in
the form of increased operating expenses [ 3 ]. As discussed
in this paper, the economics are good and poor e?ciencies
do not translate to commercialization barriers. This paper presents a general investigation of the economic viability of
PFCHEV vehicles versus other fuel cell vehicle approaches.
In this sensitivity analysis, rough estimates are used with the range of sensitivity analysis set to include likely parameter scenarios. More detailed studies will be needed as the industry takes shape.
alone. Batteries are good at high power output (e.g. 50 kW) but only provide storage capacity at high cost and signi9cant weight penalties. Fuel cells provide aBordable 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 12 km (7.5 miles) of range from the batteries and about 48 km of capacity form hydrogen/oxygen. During the 12-km 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 12 km (7.5 miles) of capacity and about 32 km
(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 ICE would never be started but is available if additional range is needed.
Fig.
illustrates one version of a PFCHEV. The plug-in option allows the battery and fuel cell system to be charged using grid electricity. The vehicle model assumes auxiliary equipment is powered by electricity rather than shaft work.
The PFCHEV can have a powerful impact on the oil imports.
For many applications, especially as the second car in a
2. Methods
Table
summarizes the projected costs for the BEV,
PFCHEV, and FCHEV to achieve 48 km of ICE-free operation for a vehicle requiring 50 kW of power. The $500/kW fuel cell costs should be attainable within the decade. The data illustrate how the PFCHEV power system costs less than fuel cells or batteries alone for providing the speci9ed performance.
The fuel cell stack of the PFCHEV systems of Table
are not designed to replace the ICE of today’s sports utility vehicle (SUV), but with a 48-km plug-in capability the power system could 9nd many useful applications. Having an ICE backup, the PFCHEV could compete with conventional automobiles because range can be extended by refueling with gasoline.
The summary of Table
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 speci9ed in Table
is based on projected $500/kW costs for PEM fuel cells for
2010. The summary of Table
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.
G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121 115
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 ICE and having a 145 km (90 mile) range would cost about $18,874. All energy and power units are in delivered energy.
For example, the hydrogen (H
2
) in kWh must be divided by the fuel cell e?ciency to estimate the amount of hydrogen in the tank
FCHEV
(oxygen)
FCHEV
(air)
PFCHEV
(1.95 kW FC)
PFCHEV
(1.3 kW FC)
PHEV
Total range (km)
Battery pack range (km)
Battery pack (kWh)
H
2 range (km)
H
2
(kWh)
Fuel cell power (kW)
ICE ($)
Battery cost ($)
Fuel cell cost ($)
Weight and tank costs ($)
Electrolyzer ($)
Total power system cost ($)
48
0
0
48
20.76
50.00
$0
$0
$25,000 a
$114
$0
$25,114
48
0
0
48
20.76
50.00
$0
$0
$50,000
$114
$0
$50,114 a
48
12
3.75
36.2
15.57
1.95
$1000
$1500
$973
$158
$973
$4604
48
24
7.5
24
10.38
1.30
$1000
$3000
$649
$201
$649
$5499
48
48
15
0
0.00
0.00
$1000
$6000
$0
$288
$0
$7288 a Much larger fuel cells are required when the fuel cell is sized based the capacity to power the vehicle as compared to the capacity to charge the battery pack. For FCHEV (oxygen) operation a 50 kW fuel cell costs $500/kW or $25,000. For FCHEV (air) operation a
50 kW fuel cell costs $1000/kW or $50,000.
While the summary of Table
is speci9c 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 speci9cations 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 kilometers.
• Battery range in kilometers.
• 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 speci9ed number of hours. A sizing factor of 0 : 2 h − 1 corresponds to consuming the tank of hydrogen in 5 h. At 10 kWh tank of hydrogen would thus be sized with a 2 kW (10 kWh × 0 : 2 h cell.
− 1 ) fuel
• Battery costs in $/kWh allow the energy needs to be converted to battery costs on a delivered energy basis.
• Fuel economy in kWh/km allows the range of the vehicle to be converted to the required kWh of energy delivered to the electric drive train.
• Speci9c energy in Wh/kg allows the mass of the battery pack to be calculated based on deliverable energy.
• Hydrogen tank weights (kg/kWh) and costs ($/kWh) are estimated to be directly proportional to the deliverable energy from the hydrogen in the tank.
• Speci9c cost penalties in $/kg for weight are applied to the weight of batteries and tanks.
• Battery e?ciencies are applied when converting kilometers of hydrogen to kWh of hydrogen stored. These e?-
Table 2
Projected performance of nickel metal hydride batteries
2003 a 2010 2020
Speci9c energy (Wh/kg)
Speci9c power (W/kg)
Charge/discharge cycles
Cost $/kWh
70
160
1000
550
78
180
1000
400
80
200
1100
300 a Estimates include numbers from survey with adjustments made based on other references.
ciencies account for the fact that some of the energy is lost both in charging the batteries and then subsequently
• The electrolyzer cost is calculated as a percentage of the fuel cell cost.
The range of parameters for the batteries are based on an
Argonne National Laboratory summary of projections on
nickel metal hydride batteries [ 7 ]. 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
summarizes projected performance characteristics for the
1 For example, 10 miles of hydrogen at a fuel economy of
0 : 5 kWh/mile going through a 90% e?cient battery requires 10 ×
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% e?ciency, this translates to a lower heating value of stored hydrogen equal to 12 : 34 kWh.
116 nickel metal hydride batteries based on this the Argonne report.
2.1. Plug-in range
Plug-in range [ 8 ] is the distance 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 64 km (40 miles) per day.
About 76% of the distance traveled in the US are within the
9rst 40 traveled by an automobile in a day and about 78% of the automobiles do not travel more than 64 km (40 miles) in a randomly selected day. Plug-in ranges of 32, 64, 97,
129 km (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.
2.2. Sizing factors
G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121
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 RFC used to its full potential would produce electrolysis hydrogen for 12 h and would produce electrical power on the vehicle for 12 h. 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 h, a sizing factor of 0.1/h would be multiplied by 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 to recharge the batteries three times in 12 h. At a constant sizing factor, larger fuel cells are required to utilize the capacity of larger hydrogen storage tanks. For comparison purposes, the ICE of the Toyota Prius, one of several HEVs on the market today, has a
57 kW ICE—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.
2.3. Battery costs
The costs of the batteries were evaluated at 300, 400, and 550 $/kWh. The batteries pack was sized based only on energy (kWh) needs and not power (kW). The kWh needs were calculated based on the speci9ed range in kilometers of the battery pack, and this range was set at 0%, 25%, 50%,
75%, and 100% of the plug-in range.
2.4. Fuel economy
The kWh of energy required per kilometer of travel is an important measure of vehicle energy e?ciency. A vehicle designed to operate at a sustainable 145 km/h (90 mph) at
50 kW power would have a fuel economy of 2 : 9 km/kWh.
A vehicle with a fuel economy of 2 : 3 km/kWh and a
50 kW power source could maintain 115 km/h (71.4 mph)
for extended periods of time. Vyas and Ng [ 7 ] assume a
fuel economy of 5 : 95 km/kWh (210 miles for 35 : 1 kWh of energy). Fuel economies of 0.889, 1.24, and 2 : 07 kWh/km
(1.43, 2, and 3.33 kWh/mile) were evaluated in this study.
The fuel economy of 2.07 kWh/km is more consistent with a 30 kW ICE than the 57 kW Toyota Prius ICE. These fuel economies provide a rough estimate and should be adjusted when extrapolating the results to vehicles with diBerent fuel economies.
2.5. Battery e8ciency
The batteries were characterized and sized based on delivered energy (kWh). However, battery e?ciencies were necessary to estimate the overall e?ciency when converting the energy of stored hydrogen to what is actually delivered after the RFC stack is used to charge the batteries. E?ciencies of 80%, 85%, and 90% were assumed. The amount of stored hydrogen and the fuel cell kW rating were increased to account for these e?ciencies. For example, 10 kWh of battery energy translates to 10/0.8/0.8 or 15.625 kWh of hydrogen when the battery has an e?ciency of 80%. Since the fuel cells are sized based on delivered power, their e?ciency
does not enter into equipment costs calculations when the impact on the size of the hydrogen tanks is neglected.
2.6. Costs of tanks and weight
The weights of batteries were estimated by the speci9c
energy of the battery. Hinrichs and Kleinback [ 9 ] report
nickel metal hydride batteries at 60 to 80 Wh/kg. Battery speci9c 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 loaded automobile at 1500 kg, the cost of propulsion/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 which is roughly the cost of an
ICE/kg of vehicle. The costs of the tanks were calculated at
$2, $4, and $6/kWh of hydrogen storage capacity. The cost of compressed-gas storage is about $6/kWh ($200/kg) for
hydrogen as based on US Department of Energy goals [ 10 ].
2.7. Cost of electrolysis
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 RFC that is reversible at no extra cost and the 200% represents an electrolysis system that costs twice as much as the fuel cell system.
3. Results
Table the parameters used in the sensitivity analysis. Using these speci9cations, 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/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 speci9cations. 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 (see Table
Table
G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121 summarizes the base case, high, and low values of
summarizes the sensitivity analysis. The base case analysis projects that when fuel cell stacks are available at less than $1,184/kW, the combination of a fuel cell stack and batteries would be more cost eBective in a plug-in 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 64 km (40 mile) plug-in vehicle, the battery pack would likely provide between about 16 and 32 km (10–
20 miles) of range with the remainder provided by stored hydrogen. At less than 16 km of battery capacity, the vehicle would be too limited by this 16-km limit for travel over a short time period. At greater than 32 km one-way to a destination, the ICE would have to operate during part of the roundtrip, and so, a battery range greater than 32 km would have little performance advantage over a battery range of
32 km for this vehicle with a total 64 km plug-in range.
The base case solution is valid with fuel cells of 2.59 and
1 : 73 kW paired with battery packs having 16 and 32 km 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 ICE (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 $1000 is assumed to be applied to auxiliary equipment such as a reformer system or high capacity hydrogen storage.
As indicated by the sensitivity analysis in Table
FCHEV is consistently about four to twelve times more costly than the PFCHEV with a 64 km plug-in range. The cost of the electrolyzer had the greatest impact on the threshold fuel cell stack cost. The sizing factor had the second greatest impact, and the battery e?ciency had the third greatest impact. The fuel economy did not impact the threshold fuel cell cost, but did impact the cost of the PFCHEV relative to the FCHEV. The latter was primarily due to an artifact of the calculation where a 50 kW fuel cell stack supply was always assumed for the FCHEV when it may have been a more-even playing 9eld if a 30 kW fuel cell were matched up with the 3.33 fuel economy.
4. Discussion
4.1. Sensitivity of RFC system costs
117
The electrolyzer cost is a most important research and development area that will allow PFCHEV systems to be more cost competitive sooner. In the best case, RFCs would produce both electrical power and hydrogen/oxygen with zero incremental price above a conventional fuel cell.
The sizing factor is a design degree of freedom. Sizing factors that provide the fuel cell with more time to consume the stored hydrogen (e.g. smaller sizing factors like 0.125/h
Table 3
Values of parameters used in sensitivity analysis. Most operating costs and e?ciencies are not included since the sensitivity analysis only includes capital costs. Battery e?ciencies de9ne the extent to which the fuel cell must be oversized. Electrolysis is performed at the pressure of hydrogen storage, and so, no compression equipment is required
Plug-in range (miles)
Sizing factors (h − 1 )
Battery costs ($/kWh)
Fuel economies (km/kWh)
Battery speci9c energy (Wh/kg)
Hydrogen tank weights (kg/kWh)
Hydrogen tank cost ($/kWh hydrogen)
Cost of weight ($/kg)
Battery e?ciency
Cost of electrolysis ($, factor times fuel cell cost)
Low
2
1
70
1
20
0.083
300
0.889
0.80
0
Base case
78
2
4
1.5
40
0.125
400
1.24
0.85
1
High
6
2
80
3
60 (80)
0.25
550
2.07
0.90
2
118 G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121 that allow 8 h to fully charge the hydrogen tank) lead to less costly power systems; however, these systems would have greater limitations on performance which translates to the
ICE being needed more frequently to provide power when the fuel cell stack has not had su?cient 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 entry-level systems for this market. For the
PFCHEV system of Table
1 , the cost of the power sys-
tem could be further reduced by use of a sizing factor less than 0.125/h.
The PFCHEV would bene9t from highly e?cient batteries and batteries with large charge/discharge lives. This suggests that high-capacity capacitors, Pywheels, and other e?cient and robust storage means could be used to advantage 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 speci9c power outputs listed in Table
would be insu?cient.
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 $12,000. Electricity costs were not considered because electricity is an operating cost. The
operating costs are discussed elsewhere [ 2 ].
Table
summarizes a series of analyses 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 129 km per day.
4.2. Market entry products
The sensitivity analysis indicates that a vehicle similar to that speci9ed in Table
would be an entry-level vehicle having a threshold fuel cell price of $1792/kW and system price of $4773 (Table
summarizes entry level pricing).
This would be an e?cient, light-weight vehicle with up to
48 km per day in plug-in range. The HEV version of this vehicle would include about 10 : 6 km in battery capacity at a cost of about $830 plus the ICE ($1000). A premium of about $2957 is paid for the “plug-in” option with a 48 km capacity. At $1792/kW, a 50 kW power system would cost about $90,000.
For a hybrid car, the extra cost for the battery pack and electronics is partially recoverable in the form of reduced fuel consumption. Plug-in vehicles would have considerably less gasoline consumption, but per-km energy costs would be about the same as with the HEV. The fuel costs 3
G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121 119
Table 5
Fuel cell costs ($/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 64 km (40 miles) of plug-in range for a PFCHEV. The fuel cell kW ratings are based on 16-km range from the batteries and 48-km range from the fuel cell stack. All energy and power units are in delivered energy. For example the hydrogen (H
2
) in kWh must be divided by the fuel cell e?ciency to estimate the amount of hydrogen in the tank
FC
(kW)
Sizing factor
(1/h)
Economy Spec.
(kWh/km) energy
(Wh/kg)
EB.
Cost bat Cost tank bat (%) ($/kWh) ($/kWh)
Cost
(% FC)
Cost wt FC/PFC Total electrol.
($/kg) ($/$) ($)
Cost FC
($/kW)
2.60
1.72
5.19
0.125
0.083
0.25
0.311
0.186
0.435
78
70
80
0.85
0.8
0.9
400
550
300
4
2
6
100%
0
2
1.5
1
2
7.1
6.5
6.1
6.4
6.3
12.7
4.2
6.4
6.4
4.7
6.3
6.3
5.6
6.3
9.5
3.2
9.8
$9385
$9385
$9385
$6031
$1184
$1782
$592
$1184
$12,738 $1184
$9429 $1190
$1182 $9375
$9385
$9385
$1051
$1336
$12,385 $1617
$7385
$9385
$9385
$9385
$9385
$9256
$9513
$895
$1198
$1182
$2379
$793
$1173
$1206
Table 6
Impact of vehicle plug-in range on threshold fuel cell prices and fuel cell power rating
Total (km) Battery (km) FC (kW) FC/PFC ($/$)
32
48
64
64
97
129
8
12
16
32
24
32
1.30
1.95
2.60
1.73
3.89
5.19
11.5
8.2
6.4
6.4
4.4
3.4
Total ($)
5192
7288
9385
9385
13,577
17,769
Cost FC ($/kW)
1190
1190
1190
1190
1190
1190
Table 7
Example entry level PFCHEV speci9cations and costs
Total kilometers
Battery pack (km)
Battery pack (kWh)
H
H
2
2
(km)
(kWh)
Fuel cell (kW)
ICE ($)
Battery cost ($)
Fuel cell cost ($)
Electrolyzer ($)
Total ($)
FC ($/kW)
Spec.
48
16
3
32
8.30
0.69
1000
1200
1235
1235
4773
1792 are about $0.0155 and 0.0199/km ($0.025 and $0.032 per
for a gasoline ($0.25/l, no highway tax) ICE and
hydrogen produced by grid (oB-peak, $0.056/kWh [ 11 ]).
Entry level vehicles will not pay for themselves at current
RFC prices based on saved fuel cost in the US—in countries where fuel prices are more than $1.00/l 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 oB-peak grid electricity.
2 Costs are based on a vehicle getting 12 : 75 km/l (30 mpg) and fuel at $0.25/l (not including highway taxes). An energy content of 411 ; 426 kJ/l (114,500 Btu/gal) for gasoline translates to
2500 kJ/km of gasoline (3817 Btu gasoline/mile). This translates to 450 kJ/km (687 Btu) of wheel energy per mile applied to all fueling options.
120 G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121
Two potential US 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
would cost about $2750. This vehicle would replace about 75 l per year of imported petroleum with electrical power. From a societal perspective, the bene9ts would warrant the additional cost. If the ICE and gasoline tank were removed from this ICE and it were used for limited local transit, the price of the power system could be further reduced to about $1500 and the vehicle itself would realize reduced costs due to weight reductions. Such a vehicle would be particularly appropriate as a second vehicle in a
2-car family or as a short trip vehicle for a college student.
Vehicles with and without the backup ICE could realize substantial markets.
4.3. Evolution of fuel cell-battery-ICE tribrids
Table 8
Typical operating costs for vehicle. Ranges include low end cost
of mid-sized car and upper end costs for luxury car and SUV [ 15 ]
Vehicle operating cost range ($/mi)
Average cost (%)
Depreciation
Insurance
Financing
Fuel
Maintenance, oil, tires
License & registration
22.5–31.8
6.9–10.5
4.8–8.3
4.5–6.9
4.7–5.3
1.4–3.2
49.2
14.3
12.3
10.9
9.1
4.2
Table 9
Qualitative comparison of PFCHEV approach to FCHEV relying on hydrogen refueling
Hydrogen refueling
Plug-in & reformer
Fuel cell cost breakthroughs
Improved fuel cell durability
Improved hydrogen production
Hydrogen storage breakthroughs
Hydrogen refueling breakthroughs
Hydrogen infrastructure cost
H
2
Refueling time/anxiety/risk
$$$
$$
$$
$$$
$$
$$$$$
$$$
$$
$
$
N/A
N/A
N/A
N/A
As fuel cells become less expensive, increased plug-in ranges would become viable and the ICE would be used less.
As the ICE is used less, less expensive, lighter, and possibly air-cooled ICEs could be used to reduce the 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 ICE cost will allow the cost PFCHEV power system to become less, eventually being equal to the cost for HEV power systems. The greatest attributes of the PFCHEV are its abilities to evolve into a platform that is less expensive than ICE options and that will be powered by indigenous fuels.
Today, PEM fuel cell costs are about $1100/kW when
used with pure oxygen and about $2200/kW [ 12 ] when used
with air. The costs are projected to be $650–$1150 by 2010
[ 13 ]. 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 $4773 vehicle of Table
could be attained by about 2007 based on projected 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 include PFCHEV vehicles with increased plug-in ranges both with and without backup ICEs.
Fuel cells operated from electrolysis oxygen and hydrogen are considerably less complex than ICEs. 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 ICEs and mechanical drive trains. This is especially true for light-weight vehicles. Competition could increase resulting in lower prices for vehicles
—low-maintenance and dependable vehicles could become available at a fraction of today’s automobile prices (possible by 2012). Table
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 9nancing, insurance, and taxes that are related to the cost of the vehicle.
Table
qualitatively compares the cost of the FCHEV using hydrogen refueling with the PFCHEV. No major cost or technological barriers exist for the PFCHEV, while items like the cost of a hydrogen refueling infrastructure will make it di?cult to make the transition from ICEs directly to FCHEVs.
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 16 km.
A 1000-cycle battery life (see Table
10,000 miles before the battery pack would need to be changed. Fortunately, EPRI reports that products like the
Saft nickel metal hydride batteries are achieving greater
than 2800 cycles [ 14 ]. In addition, through the use of ca-
pacitors, directing fuel cell power directly to the ICEs, and accounting for backup ICE operation, a vehicle designed for 16 km range from the battery pack could average near
32 km (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.
5. Conclusions
G.J. Suppes / International Journal of Hydrogen Energy 30 (2005) 113–121
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. Neither does the PFCHEV rely on a hydrogen refueling infrastructure creating a commercially viable entry point for vehicles bene9ting from fuel cells which is likely at least a decade earlier than FCHEV vehicles.
The PFCHEV vehicles would use the versatility of the electrical power grid to tap into domestic energy sources.
When wind, other renewable energy, or nuclear sources are used, petroleum imports are displaced with technology having near-zero carbon dioxide emissions and near-zero tail-pipe emissions in the cities. Other than the modi9ed 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 oB-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 e?cient 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 EPACT-qualifying alternative fuel vehicles should also be receptive to PFCHEV vehicles that should become commercially competitive starting in about 2007. It will likely be about 2010 before fuel cells are inexpensive enough to cause growth in the traditional BEV market that will be replaced with limited range
FCHEV vehicles. 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 classi9cation with backup ICEs no longer being necessary—a speculative timeframe for this is about
2020.
References
121
[1] Keith DW, Farrell AE. Rethinking hydrogen cars. Science
2003;301.
[2] Suppes GJ, Lopes S, Chiu CW. Plug-in fuel cell hybrids as transition technology to hydrogen infrastructure. Int J
Hydrogen Energy 2004;29:369–74.
[3] Plug-In Hybrids: The Cars We Need for the Next Ten Years,
California Cars Initiative, an activity of the International
Humanities Center, 2003 (see http://calcars.org
).
[4] Renyl J, Schuurmans PJ. Policy implications of hybrid electric vehicles-9nal report to NREL, National Renewable
Energy Laboratory, Golden, CO, Report ACB-5-15337-01
(see www.ott.doe.gov/pdfs/nevcor.pdf
), April 22,
1996.
[5] Mullen R. Proposed car of near-future: plug-in hybrid. New
Technology Week. Washington, DC: King Communications
Group, Inc; October 20, 2003.
[6] Graham, Bob. Plug-In Hybrid Electric Vehicles Signi9cant
Market Potential. see http://www.arb.ca.gov/msprog/zevprog/
2003rule/1202wkshp/graham.pdf
, 2002.
[7] Vyas AD, Ng HK. Batteries for electric drive vehicles: Evaluation of future characteristics and costs through a Delphi survey.
1997.
http://www.transportation.anl.gov/pdfs/TA/103.pdf
[8] Your Driving Costs 1998, American Automobile Association, based on data from Runzheimer International, see http://www.vtpi.org/tdm/tdm66.htm Toc18284947 , 2002.
[9] Hinrichs RA, Kleinbach M. Energy Its use and the environment, 3rd ed. London: Thomas Learning Inc;
2002.
[10] Doe Solicitation Number DE-PS36-03GO93013, Grand challenge for basic and applied research in hydrogen storage,
US Department of Energy, Golden Field O?ce, 1617 Cole
Boulevard, Golden, CO 80401-3393, 2003.
[11] http://www.dcec.com/billing rate.html
, 2003.
[12] Based on price of 7 kW hydrogen power generator. See http://www.fuelcellstore.com
, Item #540118. Price estimates include 50% cost reduction for pure oxygen fuel cell stack versus air fuel cell stack.
[13] Energy Technology Fact Sheet. Published by United Nations
Environment Program, Division of Technology, Industry, and Economics (see http://www.uneptie.org/energy/ ). See http://www.etachase.com/Alt%20Energy%20papers/
UNEP fuelcell.pdf
2003.
[14] Duvall M. Advanced batteries for electric-drive vehicles.
Preprint Report, published by EPRI, Palo Alto, CA, Version
16, 2003 (see http://www.epri.com/corporate/discover epri/ news/downloads/EPRI AdvBatEV.pdf
).
[15] Anonymous, Your Driving Costs, American Automobile
Association, based on data from Runzheimer International
(see http://www.vtpi.org/tdm/tdm82.htm
), 1998.
