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Sustainable transportation based on electric vehicle concepts:
a brief overview
Ulrich Eberle* and Rittmar von Helmolt
Energy Environ. Sci., 2010, 3, 689–699
DOI: 10.1039/c001674h
*Corresponding author
was published in the June 2010 issue of “Energy & Environmental Science”.
Received 26th January 2010, Accepted 26th March 2010, First published on the web 14th May 2010
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Sustainable transportation based on electric
vehicle concepts: a brief overview
Dr Ulrich Eberle*and Dr Rittmar von Helmolt
DOI: 10.1039/c001674h
The energy storage system is of decisive importance for all types of electric vehicles, in contrast
to the case of vehicles powered by a conventional fossil fuel or bio-fuel based internal
combustion engine. Two major alternatives exist and need to be discussed: on the one hand,
there is the possibility of electrical energy storage using batteries, whilst on the other hand
there is the storage of energy in chemical form as hydrogen and the application of a fuel cell as
energy converter. The advantages and limitations, and also the impact of both options are
described. To do so, existing GM concept vehicles and mass production vehicles are presented.
Eventually, an outlook is given that addresses cost targets and infrastructure opportunities as
well as requirements.
Introduction
The development of electric vehicle and
powertrain concepts has a very long
tradition at General Motors and Opel,
regardless of whether fuel cell electric
(FCEV), pure battery electric (BEV), or
hybrid-electric vehicles are concerned.
For example, the world’s first fuel cell
electric vehicle, the GM Electrovan of
1966, was developed and designed by
General Motors. Over the course of the
late 1990s, this technology was revived
and re-introduced within the framework
of a large-scale global development
program. These efforts have led to the
development of the current GM
HydroGen4 fuel cell car, a mid-sized
crossover vehicle based on the Chevrolet
Equinox.
Also during the 1990s, a large devel-
opment effort on pure battery electric
vehicles (BEVs) was initiated. These
automobiles were deployed to large-scale
demonstration projects. For example,
the Opel Impuls—equipped with
ZEBRA batteries with a nominal battery
pack density of 90 W h kg
1
and an
energy content of 26 kW h—was
demonstrated during the ‘‘European
Electric Vehicle Fleet Demonstration’’
project in the Aachen area.
1
EV ranges
of up to 120–150 km (between recharg-
ing the batteries) and a total fleet mileage
of more than 400 000 km were achieved.
Opel Impuls vehicles were also deployed
to the so-called ‘‘R€
ugen-Projekt’’ on the
German island of R€
ugen in the Baltic
Sea.
In the context of this publication the
latest vehicle projects like the GM
HydroGen4 and the Chevrolet Volt
(as well as the respective VOLTEC pow-
ertrain system) are introduced and
discussed.
2
Also, the effects on the fuel
infrastructure will be evaluated. The
development of zero-emission vehicles
has become more and more important
over the last few years since the depletion
of the fossil resources and the climatic
change caused by anthropogenic CO
2
emissions are considered very important
and urgent issues.
Therefore, a key element of the
advanced propulsion strategy of many
global car manufacturers is the electrifi-
cation of the automobile and the
displacement of gasoline by alternative
energy carriers. This would lead to
reduced fuel consumption, reduced emis-
sions and also to increased energy security
via geographic diversification of the
available energy sources. At General
Motors, this strategy has its roots with the
introduction of the first modern electric
vehicle, the 1996 GM EV1. The EV1 was
a pure battery electric vehicle (BEV),
developed as a mass production car for the
average driver. Unfortunately, the market
experience with the EV1 and its initial
lessees indicated that further significant
improvements in BEVs were needed.
Some EV1 drivers coined the term ‘‘range
anxiety’’, describing their omnipresent
concern, or even fear, of becoming
stranded with a discharged battery in
Hydrogen, Fuel Cell & Electric Propulsion
Research Strategy, GM Alternative Propulsion
Center Europe, Adam Opel GmbH, IPC MK-01,
65423 R€
usselsheim, Germany
Broader context
Approximately 900 million vehicles worldwide are on the roads today. About 96% of the fuel used for propulsion purposes is thereby
produced from fossil sources of energy. There are estimates for the year 2020 that the number mentioned above will increase to
approximately 1.1 billion vehicles worldwide, in particular due to the economic expansion and industrial development of India and
China. This will inevitably have consequences for global crude oil demand and also consequently for worldwide CO
2
emissions. Since
an increase in demand for oil and CO
2
production proportional to the projected number of vehicles is unsustainable for financial,
ecological and political reasons, every implementation strategy must aim at the replacement of fossil fuels as a source of energy for
automotive applications.
This journal is ªThe Royal Society of Chemistry 2010 Energy Environ. Sci., 2010, 3, 689–699 | 689
OPINION www.rsc.org/ees | Energy & Environmental Science
a limited-range vehicle, away from the
electric infrastructure. Hence, improve-
ments in on-board energy storage are
needed (directly proportional to vehicle
range) and, in particular, charging time
were assessed to be essential for a more
widespread deployment of BEVs. Due to
these constraints, pure battery electric
vehicles have not reached the commercial
mass market until now. However, in the
meantime, most of the EV-enabling elec-
tric components and systems have found
utility by adapting them for usage in mild
and full hybrid electric vehicles (HEVs):
e.g., GM pioneered the 2-Mode system
for buses and eventually passenger cars.
1
Considering sales, the currently most
popular example of such a vehicle concept
is the Toyota Prius. Such hybrid electric
vehicles do not provide full power by
exclusively using the electric motor, and
therefore the power and energy level
requirements for the system components
are reduced in comparison to a conven-
tional BEV. Furthermore, although
conventional hybrid electric technologies
improve vehicle efficiency (thus reduce
gasoline consumption and, thereby, CO
2
emissions), all the energy the powertrain
consumes is generated exclusively from
a liquid hydrocarbon-based energy
carrier. The on-board electric motor and
the electric energy storage system are only
used to shift the operating point of the
internal combustion engine (ICE) to
a more favourable point on the efficiency
map and to enable recuperation. There-
fore, HEV technologies unfortunately do
not provide any additional pathways to
utilize CO
2
-neutral renewable energy
sources.
Zero-emission vehicles based on
hydrogen fuel cells (FCEV) or pure
battery-electric systems (BEV) that are
fully competitive to conventional vehicles
regarding performance and ease-of-use
represent the ultimate target of the GM
strategy. An important step into this
direction is the start of mass production
of the Chevrolet Volt (an extended-range
electric vehicle, E-REV) at the end of
2010, as well as the introduction of other
vehicles like the Opel Ampera which are
also based on the VOLTEC technology.
2
Fuel cell electric vehicles and
battery electric vehicles—two
completely distinct and
competing worlds?
These days, within the general public and
also within the automotive and energy
R&D community, very often the impres-
sion is created that a decision has to be
made between hydrogen fuel cell vehicles
(FCEV) and pure electric vehicles (BEV),
which is seen as a question of either/or.
However, this is definitely not the case
since both technologies address different
areas of the vehicle market. This is caused
by the extremely different energy densities
of the applied energy carriers (see Fig. 1).
To realize a vehicle with a range of
500 km using today’s diesel technology,
a tank system that weighs approx. 43 kg
and requires a volume of just less than
50 L is needed. To realize a corresponding
zero-emission vehicle on a hydrogen
basis, one has to install on a system
weighing about 125 kg (based on a 700
bar compressed gaseous hydrogen vessel).
The energy storage gets even heavier if
a future highly advanced Li-ion battery
system (usable system energy density:
120 W h kg
1
; current technology is closer
to 90 W h kg
1
) would be implemented
(see Fig. 1): the weight of the energy
storage system would be just below one
metric ton to provide a range of 500 km.
Furthermore, a hydrogen tank can be
refilled completely within 3 to 5 min, very
similar to a conventional diesel or gaso-
line tank. In contrast, re-charging
a battery can take—depending on the
available infrastructure and battery size—
from 30 minutes (50–80 kW DC charging
station) up to many hours or even a whole
day (conventional 230 V/16 A electrical
outlet).
Projections show that a hydrogen tank
system for a vehicle range of 500 km could
be manufactured for approx. US$ 3000 at
high-volume production; on the other
hand, a comparable 100 kW h battery
would cost approximately US$ 50 000.
Therefore, it makes sense to develop
and use a battery-electric vehicle for
a driving & duty cycle for which a smaller
battery and a lower range is sufficient and
viable. The impact of the energy storage
densities, drive cycles and duty cycles,
respectively, on an appropriate pro-
pulsion technology is shown in Fig. 2.
Dr Ulrich Eberle
Ulrich Eberle studied Physics at
Stuttgart University and
received his PhD for a thesis
conducted at the Max-Planck-
Institut f€
ur Metallforschung. In
2003, he joined GM, where he
has coordinated several projects
on hydrogen storage and infra-
structure. He co-authored the
strategy paper of the working
group ‘‘Hydrogen Storage’’ for
the German national innovation
program, and he is the GM
representative at ‘‘NewEnergy-
World’’ (an EU Joint Tech-
nology Initiative) and at ELAN2020 (an initiative by the German
association of utilities on the integration of electric vehicles into
a smart-grid). His work focuses on technology strategy develop-
ment on alternative powertrains and energy storage systems.
Dr Rittmar von Helmolt
Rittmar von Helmolt studied
Physics at Goettingen Univer-
sity and earned his PhD for
a thesis conducted at the
Siemens R&D Center. During
his time at Siemens, he discov-
ered the fundamental ‘‘colossal
magneto resistance’’ effect in
1993. Eventually, he joined the
fuel cell development team at
Siemens as project scientist and
manager for low-temperature
fuel cells. In 2000, he began to
work for General Motors as
manager of ‘‘Fuel Cell Develop-
ment & Manufacturing Concepts’’. He represents Opel on several
national and international bodies, and currently serves as the head
of the ‘‘Government Collaboration & Electric Propulsion Research
Strategy’’ department.
690 | Energy Environ. Sci., 2010, 3, 689–699 This journal is ªThe Royal Society of Chemistry 2010
The pure battery vehicle is the tech-
nology of choice for small urban vehicles
with ranges up to 150 km. Besides GM
activities (e.g., such as the EN-V
two-wheeler concept for urban mobility)
other car manufacturers, mainly Mitsu-
bishi and the Renault-Nissan alliance,
are currently working on the develop-
ment and market introduction of large-
volume battery electric vehicles for such
an application. By contrast, a so-called
E-REV vehicle (extended-range EV),
such as the Chevrolet Volt or the Opel
Ampera, is perfectly suited for those
customers who sometimes—but not too
often—need longer ranges of up to
500 km; and especially for those willing
to accept a small internal combustion
engine in order to ensure the range
beyond the initial 60 km of pure
EV operation. Also, further car
manufacturers, such as Daimler and
Toyota, pursue similar or related tech-
nology paths for concept vehicles. On the
other hand, fuel cell electric vehicles
(FCEV) offer a different set of advan-
tages: they always operate as zero-emis-
sion vehicles, can be refueled within three
to five minutes, and offer ZEV ranges of
about 500 km at full performance for
family-sized cars.
Due to its comparatively high energy
density of 1600 W h per kilogram of tank
system weight, hydrogen is the ideal
energy carrier to serve as intermediate
store of fluctuating renewable energy such
as solar and wind power, and to
enable the usage of this green energy as
transportation fuel. Daimler, GM,
Honda, Hyundai, Kia, the Renault-
Nissan alliance, and Toyota share the
view that early commercialization of the
automotive fuel cell technology is ex-
pected to start in between 2015 to 2020.
To conclude this section, it may be
stated that depending on the required
vehicle range, a future electric powertrain
will either be combined with just a battery
(BEV), or the needed energy for longer
ranges will be provided by an ICE-gener-
ator set (E-REV) or by a high-performance
Fig. 1 Energy storage system weight and volumes for various energy carriers. The comparison is based on a vehicle range of 500 km.
Fig. 2 Application map for various electric vehicle technologies.
This journal is ªThe Royal Society of Chemistry 2010 Energy Environ. Sci., 2010, 3, 689–699 | 691
fuel cell (FCEV). Both latter concepts and
their technology status will be introduced
and discussed in detail in the following
sections.
Technology status of extended-
range electric vehicles
In 2007, on the occasion of the North
American International Auto Show, the
Chevrolet Volt (see Table 1) and the
VOLTEC propulsion system (see Fig. 3)
were presented to the public for the first
time.
2
The Volt is an electric vehicle
equipped with an additional gasoline
engine that is just used to extend the
vehicle range beyond the electric range
when required (E-REV). The main energy
storage is a lithium-ion battery with
a nominal energy content of 16 kW h
(depth-of-discharge is about 50%, i.e.
about 8 kW h are usable), enabling a pure
battery-electric range of up to 60 km
(depending on driving habits/conditions,
weather, and battery age). The T-shaped
battery consists of four modules contain-
ing more than 220 single cells in total. The
complete automotive battery pack weighs
approx. 180 kg. That energy storage
system was developed by General Motors
in cooperation with the Korean battery
cell manufacturer LG Chem.
The electric powertrain offers
a maximum power output of 111 kW and
a maximum torque of 370 N m at the
motor. This is sufficient to accelerate the
Volt from 0 to 100 km h
1
in less than 9 s
and the VOLTEC powertrain enables
a top speed of 160 km h
1
. The nominal
size of the battery of 16 kW h was derived
from the fact that a vehicle range of about
50 to 60 km is needed to cover at least 80%
of the daily driving profiles of regular
customers in many countries (as an
example: data for Germany is given in
Fig. 4). For these distances, the vehicle is
operated as a pure electric car and,
therefore, as a zero-emission vehicle (see
Fig. 5). This operating mode is, hence,
called ‘‘charge-depleting’’ mode or ‘‘EV
mode’’. By limiting the battery size, it is
possible to integrate such an extended-
range drivetrain concept into GM’s
global compact architecture (see Fig. 3).
In doing so, the total battery costs can
also be limited since these costs are more
or less proportional to the nominal energy
content.
An additional advantage of a battery of
such dimensions is that the usable 8 kW h
of electrical energy could be recharged in
just a few hours not only in Europe, but
also in the US (US standard wall outlet
120V/16A: about 8 h; European standard
wall outlet 230V/16A: about 3 h). On the
vehicle side, both Volt and Ampera are
equipped with a socket according to SAE
J1772. The required cord-set (SAE J1772
Table 1 Technical specifications of the Chevrolet Volt (based on the VOLTEC propulsion system)
Vehicle type Electric vehicle; front-wheel drive;
range extender; charging via
electrical grid using a standard
wall outlet
Dimensions
Length 4404 mm
Width 1798 mm
Height 1430 mm
Wheelbase 2685 mm
Battery system
Type Li-Ion battery
Cells >220
Weight 180 kg
Length 1.8 m, T-shaped
Power Provides full performance
Energy content 16 kW h (ca. 8 kW h usable)
Electric propulsion system
Type 3-Phase induction motor
Max. power 111 kW
Max. torque 370 N m
Range extender
Type Gasoline, naturally aspirated, 1,4
liter displacement, family 0-
derivative
Power 53 kW
Vehicle performance
Max. speed 160 km h
1
Acceleration (0–100 km h
1
)9s
Range EV range (EPA city cycle) up to
60 km; ca. 500 km extended
range on a full tank of gasoline
Fig. 3 a) Opel Ampera based on the VOLTEC propulsion system, b) T-shaped VOLTEC battery.
692 | Energy Environ. Sci., 2010, 3, 689–699 This journal is ªThe Royal Society of Chemistry 2010
plug /country-specific home plug) is
carried in the vehicle. In contrast, due to
their bigger batteries, pure battery EVs
would be dependent on off-board wall
box installations (or even 50–80 kW DC
fast-charging stations) applying higher
voltage and current levels in order to
achieve such acceptable recharging times.
A prominent advocate for off-board
charging (power level: about 50 kW) is the
Japanese utility TEPCO. This company is
one of the key members of the CHA-
deMO consortium that wants to
commercialize DC fast charging technol-
ogies globally. But these DC stations are
only available at the comparatively high
cost of about US$ 30 000 (without
installation).
By contrast, considering again the
VOLTEC E-REV system, a naturally
aspirated Family-0 gasoline engine with
a displacement of 1.4 L generates 53 kW
of power that can be utilized when the
state of charge drops below a certain
value: this operation mode is called
‘‘charge-sustaining’’ or ‘‘extended-range’’
mode. By adding the ranges of both the
charge-depleting and the charge-
sustaining modes, a total vehicle range of
more than 500 km can be achieved
(e.g. required for inter-urban journeys;
see Fig. 6 for a map of the 100 largest US
metropolitan areas and the interconnect-
ing corridors). For the normal daily
driving profiles, it is nevertheless ensured
that the VOLTEC vehicles are driven
without any fossil fuel consumption and
the related emission issues. For an annual
electric driving distance of 13 000 km, the
Chevrolet Volt or an Opel Ampera would
require only 1730 kW h of electrical
energy. This value corresponds to a level
of just about 40% of the annual energy
consumption of an average four-person
household in Germany of 4500 kW h.
3
Considering the new European driving
cycle (NEDC; according to ECE R101
and the respective appendices concerning
electric propulsion technologies), less
than 40 g CO
2
per km would be emitted by
an Opel Ampera.
As mentioned before, the Chevrolet
Volt and the VOLTEC propulsion tech-
nology have been presented for the first
time in January 2007. In the same year,
the decision was made to initiate the
product engineering and to introduce the
Volt as a volume production vehicle. The
first battery packs were already assembled
in late 2007, and the first components-in
vehicle tests were also started. In 2008, the
first packs were mounted on mule vehicles
for early tests of the production-intent
propulsion system. In addition, the first
vehicle crash tests were successfully per-
formed (see Fig. 7). Until early summer
2009, about 80 Volt pre-production cars
were built. The series production of the
Chevy Volt will start at the end of 2010;
the battery packs will be manufactured at
a GM facility in Brownstown Township,
Michigan, and the vehicle assembly will
take place at GM’s plant in Hamtramck,
Michigan. About one year later the
volume production of the Opel Ampera
with the same VOLTEC powertrain
technology is set to begin.
Fig. 4 Daily driving distances in Germany.
Fig. 5 E-REV operating concept; approximately 50% of the nominal battery energy content is used.
This journal is ªThe Royal Society of Chemistry 2010 Energy Environ. Sci., 2010, 3, 689–699 | 693
Technology status of fuel cell
electric vehicles
There is a long history of innovation
within the field of automotive hydrogen
technology: for instance, the world’s first
fuel cell car, the GM Electrovan was
developed and presented to the public in
1966. This vehicle was equipped with an
alkaline fuel cell and two cryogenic tank
vessels for liquid hydrogen and liquid
oxygen.
4
The fuel cell stack represents the core
component of the complete fuel cell
power system. There is a wide range of
fuel cell types available, including mid-
and high-temperature fuel cells. However,
only low-temperature fuel cells working
with a proton-conducting polymer
membrane (proton exchange membrane,
PEM) are viable for automotive applica-
tions. PEM fuel cells combine a compar-
atively low operating temperature,
typically between 60 and 80 C, with
a high power density, the option of
conventional air operation, and with the
potential of being manufactured at low
cost (based on projected large-volume
manufacturing processes). The fuel cell
stack is built up from hundreds of single
cells (Fig. 8a) and—like a battery—it
directly converts chemical energy into
electrical energy.
The ‘‘fuel’’, however, is not contained in
the electrode, but supplied to the elec-
trode from a separate sub-system. As long
as fuel and oxidant are supplied to the fuel
cell at sufficient quantities, the generation
of electrical energy is ensured. The chal-
lenge consists in evenly supplying all
single cells of the stack with fuel and also
in removing the reaction products prop-
erly. In the case of a hydrogen PEM fuel
cell, the waste product is just pure water.
During the 1990s, triggered by an
increasing environmental debate, but also
by the PEM fuel cell development at
Daimler–Benz AG (now Daimler AG),
several car companies started to seriously
work on PEM fuel cells for automotive
applications.
After the technology transition away
from alkaline fuel cells, the various
generations of GM HydroGen1 to
HydroGen4 were developed. The inte-
gration of the fuel cell system into vehicles
can be done similarly to the integration of
internal combustion engines (ICE). It has
been demonstrated that sufficiently
powerful and compact drivetrains could
be realized. The fuel cell system and the
electric traction system of the GM
HydroGen3 were packaged in a way so
that they fitted into the same volume as an
ICE propulsion module; even the same
mounts could be used. Such an integrated
fuel cell module (propulsion dress-up
module, PDU) allows a simple and cost
efficient vehicle assembly in existing
facilities. Thus, PDUs are a likely tech-
nology scenario for the introduction of
volume production on the basis of exist-
ing platforms. There is, however, no
technical restriction that would rule out
Fig. 6 100 largest US metropolitan areas and interconnecting corridors.
Fig. 7 Integration of single cells into complete battery packs and the Chevrolet Volt vehicle platform; first crash test (T-shaped VOLTEC battery /
orange structure).
694 | Energy Environ. Sci., 2010, 3, 689–699 This journal is ªThe Royal Society of Chemistry 2010
a completely different configuration of
the fuel cell powertrain components on
board of the vehicle.
The scalability of fuel cell systems also
facilitates the adaptation to different
vehicle sizes. One example is the fuel cell
system that was originally developed for
the GM HydroGen3 van, and later was
adapted to a small vehicle, the Suzuki MR
Wagon FCV, using a shorter fuel cell
stack with reduced cell count. Eventually,
it was adapted to a GMT800 truck by
doubling the stack and some other
components.
2
700 bar CGH2 compressed gaseous
hydrogen storage systems are state of the
art since the public presentation of the
HydroGen3. As shown in Fig. 1, 1600
Whkg
1
can be achieved for such
a single-vessel tank system. Typically, 4–
7 kg of hydrogen have to be stored on-
board. Furthermore, cylindrical vessels
are required for CGH2 fuel storage.
Considering conventional vehicle archi-
tectures without modifications, there is
not enough space for hydrogen storage
devices that could provide a range
comparable to conventional vehicles.
Hence, rear body modifications are
necessary to integrate the hydrogen
storage vessel(s). In an extreme case, one
could imagine concepts where the car is
built around the hydrogen storage. As
mentioned above, vehicle designers at
GM have developed the Chevrolet Sequel
concept car (see Fig. 9) providing enough
space for three large 700 bar CGH2
vessels (total fuel capacity: 8 kg of
hydrogen). By doing so, for the very first
time, an FCEV operating range of
significantly more than 300 miles could be
achieved and demonstrated on public
roads between suburban Rochester and
New York City in May 2007. In the
meantime, the Toyota FCHV-adv (a fuel
cell SUV based on the Toyota High-
lander) has also reached operating ranges
greater than 500 km on public roads
without re-filling hydrogen. The fuel cell
system of the Sequel has been packaged
into the vehicle underbody as well,
offering flexibility for the interior design.
Although the Sequel is only a concept
vehicle with no production intent at this
time, one may imagine that vehicles one
day will be developed and optimized for
the specific characteristics and opportu-
nities that fuel cells and H
2
can offer. Also
Honda pursues the concept of a purpose-
built and optimized fuel cell vehicle and
presented the "FCX Clarity" sedan as
a production car to the public in 2008.
Since autumn 2007, within the frame-
work of ‘‘Project Driveway‘‘,more than 100
cars of the current generation HydroGen4
were deployed to demonstration projects
all over the world (e.g. in the US and in
Germany). These vehicles offer an
improved everyday-capability and a higher
performance than their predecessors
(see Table 2). For instance, the cars can be
both operated and started at very low
temperatures of down to 25 C (Fig. 9).
The electrical propulsion system
provides a maximum torque of 320 N m at
the motor and accelerates the HydroGen4
in less than 12 s from 0 to 100 km h
1
. The
continuous power output of the electric
motor of 73 kW is sufficient for
a maximum speed of 160 km h
1
; the
maximum performance is 93 kW. Three
carbon-fiber tanks on board the vehicle
store 4.2 kg of hydrogen and enable
a range of 320 km. The empty hydrogen
storage system can be completely re-filled
again within 3 min (according to SAE
J2601 and SAE J2799). To further
improve the agility of the vehicle and to
increase the efficiency by enabling recu-
peration, a nickel metal-hydride battery
with an energy content of 1.8 kW h is
installed on board the vehicle.
Worldwide, more than 10 000
customers drove the 119 HydroGen4
vehicles used in four countries (10 of these
are operated within the ’’Clean Energy
Partnership‘‘ in Berlin) and more than 80
mainstream drivers have used vehicles for
extended periods of 2 to 3 months. The
vehicles went through a total road
performance of over 1 900 000 km (status
of March 2010). A fuel cell system
Fig. 8 a) Setup of PEM fuel cell; b) chemical reactions at the electrodes.
This journal is ªThe Royal Society of Chemistry 2010 Energy Environ. Sci., 2010, 3, 689–699 | 695
durability of about 30 000 miles has been
demonstrated within Project Driveway,
and an updated HydroGen4 system is
projected to reach 80 000 miles. Further
improvements will be achieved for the
2015–2020 early commercialization time-
frame.
The vehicles proved to be more effi-
cient than the comparable conventional
Chevrolet Equinox vehicle with gaso-
line engine by a factor of 2 (EPA
composite cycle 4.6 L/100 km of gaso-
line equivalent in comparison with
9.6 L/100 km of gasoline, see Fig. 10).
Particularly, passenger vehicles are
mostly operated at loads significantly
below their rated power. For such
operating conditions, the gain in effi-
ciency offered by fuel cells is maximal.
However, at very low power output,
even the fuel cell system efficiency
sharply drops, whilst the fuel
consumption increases. This is attrib-
uted to many balance-of-plant compo-
nents, such as the air compressor, as
these have to be operated even at idle
power. At full load, similar to internal
combustion engines, the fuel consump-
tion is significantly higher, but the
relative drop in efficiency (see Fig. 10)
is stronger than for IC engines.
For a detailed discussion of the fuel cell
vehicle efficiency and the corresponding
values for key components, the authors
recommend ref. [2b]. Many aspects of
hydrogen storage technology (including
Fig. 9 a) GM Sequel and the skateboard chassis; b) GM HydroGen4 vehicle.
696 | Energy Environ. Sci., 2010, 3, 689–699 This journal is ªThe Royal Society of Chemistry 2010
alternative storage options) are summa-
rized in ref. [2c] and [2d]. The planned
next-generation fuel-cell propulsion
system for 2015 is half the size, 220
pounds lighter and uses about a third of
the platinum of the system in the Chev-
rolet Equinox fuel cell electric vehicles.
Build-up of infrastructure and
related issues
To set up a sufficiently dense (and suffi-
ciently consumer-friendly) hydrogen
filling station infrastructure, for example
in the United States, approx. 12 000 gas
stations need to be built. The underlying
model
5
assumes that in the 100 biggest
metropolitan areas of the USA
(comprising about 70% of total pop-
ulation) the maximum distance between
two filling stations would not exceed two
miles, resulting in 6500 intra-urban
stations.
On the freeways connecting these large
conurbations, a filling station would have
to be installed every 25 miles.
5
This
highway network would correspond to
a number of 5500 additional stations.
Such a comprehensive filling station
network (see Fig. 6) could serve about one
million hydrogen vehicles and would cost
approx. US$ 10 to 15 billion over a time
period of 10 years. Considering Germany,
for example, a network of 1000 to 2000
hydrogen filling stations would be
required to provide a very convenient
network.
Similar to today’s gasoline infrastruc-
ture, a hydrogen gas station would be able
to serve hundreds of vehicles per day,
since just three to five minutes are needed
to re-fill a hydrogen car. This is not the
case for pure battery electric vehicles. For
battery technology and electric grid
stability reasons, charging times of at
least one to several hours or even longer
periods are required; a standard public
charging point becomes blocked for hours
by just one customer. Hence, such
a station could only serve a few vehicles
per day. For EVs, there exists a strong
inter-dependency between two normally
distinct activities, namely ‘‘parking’’ and
‘‘refueling’’. Furthermore, the typical
customer does not want to wait near the
vehicle for extended time periods until it is
recharged. On the other hand, the
charging points are comparatively cheap
even at low volumes (US$ 5000 to 10 000
including installation and excavation)
leading to low initial costs for early fleet
demonstrations. This is in particular valid
when the conventional 230 V/16 A tech-
nology (e.g. chargers, connectors and wall
outlets) could be used.
Although a single charging point is
considerably less expensive than an H
2
fueling station, considering an ultimate
scenario with an increasing penetration
of the vehicle fleet with electric vehicles
(i.e. >1 million zero-emission vehicles
in Germany). The cost for the im-
plementation of a local battery re-charging
infrastructure under these assumptions
approaches the initially much higher cost of
a more centralized hydrogen infrastructure.
This is caused by the high number of
required chargingpole installations. In fact,
the ratio of public charging points to vehi-
cles needs to be close to 1 or even higher.
However, for small to mid-sized fleets
of zero-emission vehicles, the infrastruc-
ture for pure battery or extended-range
electric vehicles can be set up more simply
due to the better scalability and the lower
initial cost for a sufficiently dense
network. But hydrogen offers a different
and very important advantage: due to its
high energy density, hydrogen as an
energy carrier is the ideal partner for the
intermediate storage of fluctuating,
renewable energies. In doing so, excess
amounts of sustainable energy sources
such as solar and wind power can be made
available not only for stationary but also
for automotive applications. Let us
consider, for example, the North German
electric power grid, the so-called ‘‘E.ON
Regelzone Nord’’ (in the meantime
acquired by the Dutch company TenneT).
In October 2008, the power fed into the
grid by wind mills fluctuated—sometimes
within a few hours, sometimes within
days—between a maximum of approx.
8000 MW and virtually zero (see Fig. 11).
An excess amount of available wind
power, for example, caused at several
points in time in late 2009 and early 2010
dramatic effects on the energy markets,
such as significantly negative prices for
electric energy at the European Energy
Table 2 Technical specifications of the GM HydroGen4
Vehicle Type 5-door, cross over vehicle, front-
wheel drive, based on the
Chevrolet Equinox
Dimensions
Length 4796 mm
Width 1814 mm
Height 1760 mm
Wheelbase 2858 mm
Trunk space 906 L
Weight 2010 kg
Payload 340 kg
Hydrogen storage system
Type 3 Type IV CGH2 vessels
Operating pressure 700 bar
Capacity 4.2 kg
Fuel cell system
Type Proton exchange membrane (PEM)
Cells 440
Power 93 kW
Battery system
Type Nickel-metal hydride (NiMH)
Power 35 kW
Energy content 1.8 kW h
Electric propulsion system
Type 3-Phase, synchronous motor
Continuous power 73 kW
Maximal power 94 kW
Maximal torque 320 N m
Vehicle performance
Top speed 160 km h
1
Acceleration (0–100 km h
1
) <12 s
Range 320 km
Operating temperature 25 C to +45 C; vehicle can be
parked at outside temperatures
lower than 0 C (without external
heating)
This journal is ªThe Royal Society of Chemistry 2010 Energy Environ. Sci., 2010, 3, 689–699 | 697
VLJQLILFDQWO\
ZHFRQVLGHUQRZDPDWXUH
WKH
Exchange (EEX). To solve similar chal-
lenges will become even more important
and urgent when gradually the already
approved or planned off-shore wind
farms (e.g., in the North Sea) will come
online later this decade. Hence it is self-
evident that it would be extremely helpful
to ‘‘buffer’’ excess energy in intermediate
stores to handle these fluctuations, i.e. to
absorb energy during a certain time
period from the grid or, vice versa,to
provide energy back to the grid in case of
a high market demand.
Today, this ‘‘buffer’’ is realized as pum-
ped hydro stores (the largest facility in
Germany, Goldisthal, offers a maximum
storage capacity of 8000 MWh, see ref. [6]
and Fig. 11) or in compressed air
reservoirs (typical salt cavern, volume two
million m
3
of volume, max. storage
capacity 4000 MWh). If hydrogen is used
as a medium instead of compressed air, up
to 600 000 MW h energy could be stored
in an identical salt cavern. Unlike
conventional technology, hydrogen
therefore offers not only a buffer store for
short time periods ranging from a few
minutes to hours, but also such a
large-scale hydrogen store could absorb
the excess wind energy of several days
(see Fig. 11). The stored gas eventually
could be either converted back into elec-
trical energy or could simply be used as
a fuel for hydrogen vehicles. By contrast,
even large fleets of pure battery EVs are
not able to provide a competitive energy
storage dimension: if 5 kW h of the usable
energy content of an EV battery
(for operating lifetime and customer ease-
of-use considerations, 10% of the total
nominal energy content should not be
exceeded) could be subscribed to and
utilized by the electric utility, just to
replace the pumped hydro store of Gold-
isthal, 1.6 million EVs would be needed.
Considering a smaller battery pack
typical for urban vehicle applications, the
required fleet size even needs to be
significantly larger: if only a value of 2 kW
h could be used, that number would
increase to about 4 million EVs (see also
ref. [6] and Fig. 11).
Also, other large-scale stationary
battery systems (based on Na–S or even
Li-ion technology) are not able by far to
provide energy storage dimensions
comparable to a hydrogen-based system.
Conclusions
The long-term advanced propulsion
strategy of virtually all car manufacturers
consists in displacing gasoline and diesels
as energy sources for automotive appli-
cations. This will be achieved by
a continuously increasing electrification
of the powertrain. However, the energy
density of current and future automotive
batteries unfortunately provides limita-
tions for the development of pure battery
electrical vehicles as soon as vehicle
ranges significantly longer than 100 miles
are required. Therefore, GM and Opel
pursue the concept of the extended-range
electric vehicle (E-REV) and the
hydrogen fuel cell vehicle (fuel cell electric
vehicle, FCEV) for this application field.
Ranges of 500 km can be achieved with
hydrogen fuel cell vehicles and 700 bar
CGH2 tanks; moreover, hydrogen can be
produced on a large scale at competitive
Fig. 10 a) Fuel consumption over vehicle speed for the GM HydroGen4 (green line, hydrogen
consumption converted into gasoline equivalent values) and the conventional ICE version of the
Chevrolet Equinox (blue line). b) Efficiency over vehicle speed.
698 | Energy Environ. Sci., 2010, 3, 689–699 This journal is ªThe Royal Society of Chemistry 2010
E\IDUQRWDEOH
DQGGLHVHO
prices. In the area of longer-range
sustainable mobility, the future of auto-
motive propulsion thus belongs to a smart
combination of E-REV and FCEV vehi-
cles and, for some urban applications,
also to small-sized BEVs. During the early
commercialization phases, all of these
vehicles will be more expensive than
comparable conventional vehicles; there-
fore, the support and cooperation of all
involved stakeholders are indispensable
during this initial phase. The most
important players here are primarily car
manufacturers, energy companies and the
governments. But also the end customer
has to be willing to accept and purchase
these innovative vehicles despite the re-
maining incremental cost and initial
technology limitations compared to
conventional vehicles.
Acknowledgements
The authors are very grateful to
D. Hasenauer, S. Berger and L.P. Thiesen
for interesting discussions on sustain-
able energy and transportation tech-
nologies.
References
1(a) R. Bady, J. W. Biermann, B. Kaufmann
and H. Hacker, SAE paper 1999-01-1156,
‘‘European Electric Vehicle Fleet
Demonstration with ZEBRA Batteries’’; (b)
T. M. Grewe, B. M. Conlon and
A. G. Holmes, SAE paper 2007-01-0273,
‘‘Defining the General Motors 2-Mode
Hybrid Transmission’’; (c) K. Tanoue,
H. Yanagihara and H. Kusumi, Hybrid is
a Key Technology for Future Automobiles,
in Hydrogen Technology, ed. A. Leon,
Springer, Heidelberg, 2008, pp. 235–272,
DOI: 10.1007/978-3-540-69925-5_8.
2(a) T. Johnen, R. von Helmolt and U. Eberle,
conference proceedings of the ‘‘Technischer
Kongress 2009’’ of the German automo-
tive industry association VDA,
‘‘Brennstoffzellenfahrzeuge und elektrische
Antriebssysteme bei General Motors
und Opel’’, 2009; (b) R. von Helmolt
and U. Eberle, Fuel Cell Vehicles:
Fundamentals, System Efficiencies,
Technology Development, and
Demonstration Projects, in Hydrogen
Technology, ed. A. Leon, Springer,
Heidelberg, 2008, pp. 273–290, DOI:
10.1007/978-3-540-69925-5_9; (c)
M. Felderhoff, C. Weidenthaler, R. von
Helmolt and U. Eberle, Hydrogen storage:
the remaining scientific and technological
challenges, Phys. Chem. Chem. Phys., 2007,
9, 2643–2653; (d) U. Eberle, M. Felderhoff
and F. Sch€
uth, Chemical and Physical
Solutions for Hydrogen Storage, Angew.
Chem., Int. Ed., 2009, 48, 6608–6630.
3 Statistisches Bundesamt (German Federal
Statistical Office), 2006.
4 C. Marks, E. A. Rishavy and
F. A. Wyczalek, SAE paper 670176,
‘‘Electrovan – a fuel cell powered vehicle’’.
5(a) B. K. Gross, I. J. Sutherland and
H. Mooiweer, GM/Shell study 2007,
‘‘Hydrogen fueling infrastructure assessment’’,
http://www.h2andyou.org/pdf/10Things.pdf;
(b)R.Wurster,M.Zerta,C.StillerandJ.Wolf
‘‘Energy Infrastructure 21: Role of Hydrogen in
Addressing the Challenges in the new Global
Energy System’’, retrieved in March 2010;
http://www.h2euro.org/wp-content/uploads/
2009/02/EHA_EI21_2010_EN_final.pdf.
6 Pumped hydro store Goldisthal, technical
specifications, retrieved in September 2009;
http://www.vattenfall.de/www/vf/vf_de/Geme
insame_Inhalte/DOCUMENT/154192vatt/
Bergbau_und_Kraftwerke/P02115223.pdf.
Fig. 11 Electric grid operated by the German utility E.ON, fluctuating wind power feed-in, October 2008; biggest German pumped hydro storage
Goldisthal.
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