Electricity is the primary product for all fuel
cell types, whereas the use of the output heat depends on the
amount of heat, its temperature and the intended application.
Combined heat and power (CHP) applications have been proposed
for PEM, solid oxide, and molten carbonate fuel cell technologies.
The solid oxide and molten carbonate systems operate at higher
temperatures than the PEM systems, and therefore are more likely
to be applicable to a wider range of CHP applications.
Transportation
For the transportation sector, the number of technologies
being developed for use with hydrogen fuel are much more diverse.
They include technologies for hydrogen production, storage,
transportation, refuelling and use. At this time, the developmental
stage for each of these technology categories ranges from basic
research to having been commercially available for a number
of years; additional details are presented in the sections that
follow.
1. Hydrogen Production – Hydrogen
production can occur through a wide variety of methods, although
only those at or near commercialization have been investigated
for this study. Hydrogen production from natural gas, electricity
and methanol are relatively well-established processes. Further
development is required, however, to allow these technologies
to supply a vehicle fuelling infrastructure. In particular,
the ability to supply hydrogen to a distributed network of fuelling
stations and the high purity requirements for PEM fuel cells
are issues currently being addressed with new product developments.
Fuelling station reformers (both centralized and
decentralized) fuelled by natural gas or methanol have been
demonstrated in field trials on a limited basis. In contrast,
decentralized electrolysis units are commercially available,
although currently at a relatively high cost due to low production
volumes. Methanol and gasoline reformers on-board the vehicle
have been demonstrated in a few vehicles at this time, although
there is still uncertainty as to whether they will reach prescribed
cost and performance targets set out by the United States Department
of Energy (DOE). According to the United States DOE, “on
board fuel processing presents serious technical and economic
challenges of its own that may not be overcome in the required
‘transition’ time frame. Consequently, DOE is deciding
whether to continue onboard fuel processing research and development
beyond 2004”. 5
2. Hydrogen Storage – While hydrogen
storage is a well-established industrial technology, to be suitable
for transportation applications higher energy and volumetric
densities and relatively low costs are needed. At present, there
are a number of different storage types that may be suitable
for this application; compressed and liquefied hydrogen are
the two most common methods currently used. Liquefied hydrogen
is fairly well established within current areas of use and focus
is on trying to achieve higher pressures for storing gaseous
hydrogen. Three hundred and fifty bar storage is currently being
demonstrated in various applications, whereas 700 bar storage
is a target for many developers. Advancements in gaseous hydrogen
storage include the development of high-pressure hydrogen compressors,
valves, seals and storage tanks. Another alternative to hydrogen
storage is to store liquid hydrocarbons such as methanol or
gasoline and then reform them to hydrogen at a point further
downstream, as described in the Hydrogen Production section
above.
Each storage medium has different advantages and
disadvantages, and it is still uncertain as to which ones will
reach commercial application. The majority of vehicle and refuelling
demonstrations up to this point have used 350 bar compressed
hydrogen, but this results in relatively limited range with
the current demonstration vehicles, and many believe that 700
bar compressed hydrogen is required to achieve comparable ranges
to gasoline vehicles.
3. Hydrogen Transportation – Hydrogen
transportation is again a well-established industrial process
and can occur by truck or pipeline. The primary issue with transporting
hydrogen is the relatively high initial costs during periods
when hydrogen demand at fuelling stations is relatively low.
Until demand increases, transporting relatively small amounts
of hydrogen will be very expensive. In the meantime, there is
a need to combine information related to transporting other
fuels by truck and pipeline with knowledge related to hydrogen
storage and pipelining to decrease the cost of transporting
this fuel. Currently, the amount of hydrogen consumed in North
America is approximately 2% of the total oil consumed on an
energy basis.6
4. Hydrogen Refuelling – Hydrogen
dispensers for refuelling vehicles are a relatively new technology
and have been demonstrated at several refuelling stations around
the world. Standardization for the interface between the nozzle
and the vehicle, one of the more critical features of hydrogen
dispensers, is currently being worked on. Developments in this
area are required before commercialization can take place.
5. Hydrogen Use – Two different types
of engines for hydrogen vehicles have seen the most development
over the past few years: fuel cell and internal combustion.
Fuel cell vehicles have been demonstrated by most of the large
automobile manufacturers (light-duty vehicles primarily) and
some urban transit companies. The California Fuel Cell Partnership
is the largest of these demonstration projects with eight automotive
manufacturers engaged with many other technology, fuel and government
organizations. Beyond demonstration, both Toyota and Honda have
leased fuel cell vehicles to government agencies, although only
in limited quantities and at a very high price. The number of
fuel cell bus demonstration vehicles produced since 1993 is
65, with 30 of those buses scheduled to be delivered in 2003/04
to two European Commission projects: Clean Urban Transport for
Europe (CUTE) and the Ecological City Transport System (ECTOS).
Hydrogen internal combustion engine (ICE) vehicles
have been demonstrated mostly through aftermarket conversions,
although Ford demonstrated an original hydrogen ICE light-duty
vehicle. The technology to convert ICE engines to run on hydrogen
is currently commercially available from a handful of aftermarket
conversion companies, and is anticipated by some to be an early
market application of hydrogen vehicles.
The above discussion describes the range of applications
(portable, stationary and transportation) for hydrogen technologies
as well as the many stages of hydrogen development that currently
exist. In the section that follows, we put these applications
into the context of other energy pathways and identify several
key hydrogen pathways for further consideration and modelling.
