Chemistry Reference
In-Depth Information
has major safety issues and problems with storage
both on board the vehicle and within the distribu-
tion system. The early demonstration vehicles have
tended to use pure hydrogen. Over the long term the
use of methanol within a direct methanol fuel cell
would be a particularly attractive option. As a liquid
it would be easy to distribute via the existing fuel
infrastructure and easy to store on board the vehicle.
It could be reformed easily to give hydrogen or used
directly within a direct methanol fuel cell. The major
criteria used to determine the suitability of a fuel cell
for a transport application are those of size, weight,
cost and performance. Rapid start-up, high power
density and a good dynamic response are desired,
and hence the SPFC is preferred.
Demonstration vehicles have been manufactured
and tested by various automobile companies.
Daimler Benz introduced the NECAR 1 in 1994,
which was powered by twelve Ballard SPFC stacks
and used hydrogen fuel to deliver 50 kW of power.
The fuel cell unit was large and required a Mercedes
Benz 190 van to contain it. In 1996, the NECAR 2
was developed with a much smaller SPFC unit and
it could be housed within a Mercedes Benz V-class
vehicle. A methanol-fuelled NECAR 3 was intro-
duced in 1997 based on a Mercedes Benz A-class
vehicle. The methanol capacity was 40 l, giving a
range of 400 km that is comparable with equivalent
petrol vehicles. The NECAR 4 is the latest demon-
stration vehicle and is also hydrogen fuelled. Daimler
Benz and Ballard have operated a fleet of fuel-
cell-powered buses (NEBUS) in the Chicago and
Vancouver regions since 1997.
Toyota has developed a demonstration fuel
vehicle, the RAV4, that uses methanol fuel and on-
board hydrogen generation. The RAV4 has a maxi-
mum speed of 120 km h
-1
and a range of 480 km,
although it also uses some battery power.
Ford introduced a P2000 vehicle in 1999, which
uses a 50-kW SPFC from International Fuel Cells Inc.
and hydrogen fuel. A THiNK FC5 prototype fuel cell
vehicle was unveiled during 2000.
Seimens has operated an SPFC-powered fork-lift
truck in Neunburg since 1997 and a consortium
of Seimens/MAN/Linde/Ludwig-Bolkow Foundation
have developed a bus.
Such activity illustrates the high level of interest
in using fuel cells to power vehicles of the future.
A photograph of a fuel cell bus is shown in Fig.
20.9.
Fig. 20.9
Photograph of a fuel-cell-powered bus. (Courtesy of
International Fuel Cells Inc.)
4.3 Stationary power generation applications
To use fuel cells for stationary power generation has
many advantages over conventional thermal gen-
erators. The technology of thermal generators such
as gas turbines has been developed to increase effi-
ciency and has tended to mean increasingly larger
units. These large power stations deliver their power
to customers through extensive distribution grids.
The World Bank has estimated that 300 billion kWh
of power is lost globally during transmission and dis-
tribution. Such losses could be reduced significantly
by using smaller local power plants. Unlike a thermal
power unit, the efficiency of a fuel cell is much less
dependent on capacity. The small physical size and
low level of emissions also would ensure low local
environmental impact. A variety of fuels could be
used, such as natural gas and methanol, including
locally generated gases from landfill sites and sewer-
age plants. A local fuel cell system would be partic-
ularly attractive to remote sites for which connection
to a grid distribution network would be prohibitively
expensive. Such locations have been used as testing
grounds for fuel cell systems. Another main advan-
tage for local fuel cell systems is that they would
have the ability to produce heat together with
power. Combined heat and power (CHP) units are
capable of producing low-grade heat at approxi-
mately 353 K for local space heating and hot water.
Alternatively, high-grade heat could be produced at
greater than 773 K for steam raising or gas turbine
operation, to increase further the efficiency of the
system and reduce the unit cost of power. The high-
