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Fuel cell bus
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A fuel cell is essentially a battery using an external fuel supply, connected to an electric motor. Electrodes within the cell house a catalytic reaction where the fuel and oxidant are electrochemically transformed, producing DC power, water and heat. Hydrogen is the cleanest and most efficient fuel for a fuel cell-powered vehicle in the long term but several other fuels are being investigated as shorter-term hydrogen carriers.

Fuel cells represent a technology entirely different from that of the internal combustion engine. Many of the characteristics, expectations and problems regarding fuel cell buses are similar to those of electric buses. See ( 1 ) and ( 2 ) for concise introductions to fuel cell technology. A fuel cell system using hydrogen includes the following on-board components:

  • Hydrogen storage tanks
  • An air compressor
  • Fuel cell stacks
  • An electric motor
  • Additional balance-of-plant components.

Other fuels may be used, requiring an on-board fuel reformer.

In addition, hydrogen production and fueling infrastructure is required. If the hydrogen is produced on-site, this includes the following ( 3 ):

  • An electrolyzer or reformer, producing hydrogen by water electrolysis or natural gas steam reforming, respectively
  • A hydrogen processing module and hydrogen compressor
  • Hydrogen storage tanks
  • Fueling technology

Furthermore, where hydrogen is not produced on-site, a distribution network (pipelines and/or tanker trucks) is necessary for the transportation of the fuel.

Hydrogen is the cleanest and most efficient fuel for a fuel cell-powered vehicle in the long term but several other fuels are being investigated as shorter-term hydrogen carriers. Methanol powered fuel cells, for example, should reduce GHG emissions substantially, perhaps as much as 50 percent when fully optimized; if the methanol fuel is produced from cellulose, the reductions can be even greater.

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Since fuel cell buses only emit water vapor at the point of use, they can for all practical purposes be considered local zero emission vehicles (ZEVs). In addition, the system efficiency of fuel cell buses will be clearly higher than the efficiency of diesel buses, resulting in a lower fuel consumption. MAN for instance expects a tank-to-wheel efficiency of over 40% compared to about 30% or less in a diesel bus ( 4 ).

However, since the production, compression, cooling and transport of hydrogen require energy, the global impact of fuel cell usage depends very much on the methods and raw materials used. If fossil fuels are used as a hydrogen source, and in addition the energy required to generate hydrogen gas is also obtained from fossil fuels (e.g. natural gas), then carbon dioxide will be generated at the production site - in similar, or even greater, amounts than if the fossil fuel were used directly in the car (see the hydrogen fuel section).

If on the other hand renewable energy sources (e.g. hydropower, wind or solar energy) are used for hydrogen generation, handling and transport, then fuel cells save significant amounts of greenhouse gases in comparison to the combustion of fossil fuels.

In such a case a life cycle assessment will have to be carried out taking the specific local conditions into account, in order to determine the overall environmental effects of fuel cell usage compared to diesel fuel. It is expected by fuel cell manufacturers that fuel cell systems have a better overall ("well-to-wheel") energy balance compared to the direct use of hydrogen in an internal combustion engine of a car, as for example practiced by BMW. Life cycle assessments of various fuel cell systems are discussed in ( 5 ).

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Considering the very early stage of fuel cell development, the day-to-day working reliability of fuel cell buses cannot yet be adequately assessed. At present, the durability of fuel cell stacks is still limited in comparison to diesel engines, but since fuel cells have no moving parts, they may be expected to be more reliable and to require less maintenance than internal combustion engines once the technology has matured ( 2 ). Of course, diesel technology has been demonstrated to be very durable over many years.

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As with reliability, cost assessments are not very meaningful at this early stage of development. Since only prototypes of fuel cell buses exist so far, they are exceedingly expensive. According to however, fuel cell buses have the potential to become cost-competitive with diesel buses on a life cycle basis: "detailed comparisons of full life cycle costs show that hydrogen fuel cell buses, once they have achieved their series-production cost and durability targets, will be much cheaper than trolley-buses and within 30% of the cost of diesel buses". This success in lowering costs however will depend on a series of technical advances which are far from certain.

The International Energy Agency (IEA) ( 7 ) provides the following comparison of current costs:

Category Bus Cost (thousands of US$) Other Costs
New diesel bus produced in developing countries by international bus companies that meets Euro II 30-150 Some retraining costs and possibly higher spare parts costs
Standard OECD Euro II diesel bus* 180-350
Diesel with advanced emissions controls 5-10 more than comparable diesel bus If low sulfur diesel, up to 10 cents per litre higher fuel cost (for small imported batches)
Fuel-cell buses (on a limited production basis) 1,000 (1 million US$) more than comparable diesel buses, even in LDCs at this time With up to US$ 5 million per city for refueling infrastructure and other support system costs **
Source: IEA data* Note that this range of prices includes transit buses in both Europe and North America. Buses in Europe are generally less expensive than in North America, with the prices in Europe for non-articulated buses generally below US$ 275 000.

** Author's note: the cost difference between diesel fuel and hydrogen fuel should also be considered in this context.

Cost estimates for the infrastructure installed at SunLine Transit Agency in California (see below) can be found in ( 3 ), but since this facility is a first of its kind, the estimates should be considered preliminary. The cost of adding infrastructure to another transit agency could be different depending on their approach, the specific equipment, the number of buses serviced, and other factors ( 3 ).

Germany's Federal Environmental Agency (Umweltbundesamt) has carried out an (arguably rather critical) cost-benefit analysis of fuel cell technology (FEA). For a summary, visit the relevant UBA-website.

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While the US space program has used fuel cells to power spacecraft for decades, fuel cells capable of powering automobiles and buses are still in the development phase. So far, several prototype fuel cell buses have been demonstrated in the US and Canada in the past few years and are expected to be available commercially on a limited basis by 2003 ( 3 ) ( 8 ) ( 2 ) (see below).

In conjunction with CARB and other members of the California Fuel Cell Partnership, a prototype fuel cell bus has been demonstrated at SunLine Transit Agency in Thousand Palms, California ( 3 ). Fuel cell engine manufacturer XCELLSiS/Ballard partnered with SunLine to demonstrate the bus in real-world service. Data gathered from this demonstration will be used to validate the technology and to develop a commercial product.

Nine European cities [Madrid and Barcelona (Spain), Porto (Portugal), Luxembourg, London (UK), Amsterdam (the Netherlands), Hamburg and Stuttgart (Germany) and Stockholm (Sweden)] will jointly test the new fuel cell technology in transport applications. The project is named Clean Urban Transport for Europe (CUTE) and its goal is to demonstrate and assess the feasibility of an alternative, emission free, energy efficient, low-noise and sustainable urban transportation system. This is the first major fuel cell demonstration project in Europe ( w1 ).

Some results are now available from the XCELLSiS/Ballard Phase 3 Fuel Cell Bus Demonstration Program in Chicago, US and Vancouver, Canada ( 8 ). Within the Info Pool section on Programs and Experiences, there is information on anticipated fuel cell bus projects worldwide. For product information on existing fuel cell buses, see ( w1 ).

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There is currently much research being done on fuel cells, and a number of challenges still have to be met in order for them to become competitive:

  • The costs of producing the fuel cell stacks need to be reduced ( 1 )
  • Breakthroughs in storage technology would have a large impact in accelerating the acceptance and commercialization of fuel cell vehicles ( 1 ).
  • The size and weight of all components of the fuel cell power system have to be reduced in order to improve overall fuel efficiency ( 1 )
  • Fuel cells need to be able to start faster and respond better to rapid changes in power requirements ( 1 )
  • Durability and reliability in extreme operating conditions must be increased ( 1 )
  • The processing systems that convert hydrocarbon fuels (such as gasoline) into hydrogen for the fuel cell need to be improved ( 1 )
  • Experience needs to be gained of operating, fuelling, maintaining and repairing a sufficient fleet of buses operated over a long-enough period of time for thorough de-bugging of the drive-line technology and for setting standards and guidelines for updating its design
  • Hydrogen-specific regulations must be introduced addressing safety ( 3 )
  • Hydrogen infrastructure needs to be established.

Finally, the main advantages of the fuel cell bus will have to be carefully assessed in comparison to the alternatives: other systems, too, show significant improvements over conventional systems with regard to emission reductions. Renewable hydrogen can also be used in internal combustion engines. Furthermore, it must be determined when, to what extent, and at which costs regenerative hydrogen can be made available for use in fuel cell buses.

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