Technologies        
  Hauptmenu
 
    Introduction
    Database
    -  Technologies
  -  Projects
    Calendar
    Discussions
    Contact & Links
    Imprint & Disclaimer
    Sitemap
 
 


     
 
Content
 
back to list go back to technology list      previous previous technology  next technology  next

   PEM fuel cell  evaluated  
Fuel cells produce electric energy by a cold "combustion"; of hydrogen. Similar to batteries, they are conversion devices rather than genuine energy sources.
Technology field: Innovative traction concepts and energy sources
close main section General information
  close sub-section Description
   

Fuel cells directly convert chemical energy into electric energy. The conversion does not create any noise or vibrations. Whereas the efficiency of engines is limited by the Carnot process, the efficiency of a fuel cell is not.

Types of fuel cells

The following table gives an overview of different existing fuel cell types. Due to high power density, low process temperature and flexible use, the PEM type is seen as the most promising candidate for mobile applications. The following evaluation therefore refers to this type.

 

Type

Electric efficiency

fuel cell

Electric efficiency of the system

Operating temperature [°C]

Fuel

Power density

[kW/kg]

AFC

70%

62%

60-90

Hydrogen

?

PEMFC

50-68%

40-58%

60-80

hydrogen

0,15-0,30

DMFC

50-68%

30-40%

80-120

Hydrogen/ methanol

0,04-0,06

PAFC

55%

40%

160-200

natural gas/ carbon gas

0,04-0,06

MCFC

65%

50%

580-660

natural gas/ carbon gas

0,05-0,07

SOFC

60-65%

55%

800-1000

natural gas/ carbon gas

0,03-0,07

 

Source: Hörl et al. 2001

Principle of PEM fuel cell

A PEM fuel cell consists of two reaction chambers separated by an electrolyte. The two reaction chambers are fed with oxygen (or ambient air) and hydrogen (or hydrogen containing gas) respectively.

The electrolyte is realised by a polymer membrane plated with a thin platinum coating containing a catalyst. This membrane conducts only protons.

The power generating process is based on the following overall reaction:

2 H2 O2 ? 2 H20

This reaction can be split up into two sub-processes:

1. Hydrogen is ionised (split into electrons and protons) on the anode-side by a catalytic process according to the following scheme:

H2 ? 2 H 2 e-

2. The protons pass the membrane and react on the cathode-side with oxygen to form water:

½ O2 2 H 2 e- ? 2 H20

These reactions create an electron excess on one side and a corresponding lack on the other side thus causing a potential difference or voltage.

This process can be seen as a cold combustion of hydrogen with oxygen. This yields the following advantages over conventional combustion in an internal combustion engine:

  • efficiency not limited by Carnot process
  • no noise generated
  • no harmful emissions
  • process is easier to control

Voltage and power density

At its working point a single cell only produces a voltage of 0,7 V. In order to reach operating voltage desired for a given system, several cells have to be combined to form a fuel cell stack. The effective current of a cell is proportional to the membrane area. The power density is a function of current density and reaches a peak of 0,5 W/cm2 at 900mA/cm2.

Auxiliary devices

Apart from the fuel cell stack, a fuel cell system requires several auxiliary devices for fuel supply and heat removal.

The commercially available 230 kW fuel cell system P4/P5 (from XCellsis) includes the following components:

  • Fan/radiator module
  • Water/glycol cooling system system module
  • Engine inverter/Controller Module
  • Fuel Cell stack module
  • fuel cell air system module
  • fuel cell hydrogen regulating system and diffuser module
  • P4VA auxiliary drive & electric motor
  • P4T Auxiliary drive & electric motor including traction
  • major pipe interconnection system
  • major electric power interconnection system
  • interfaces to the vehicles
  • dynamic braking

Hydrogen supply

Fuel cell powered vehicles can be either supplied directly by hydrogen or by other fuels (especially methanol) to be reformed on-board before injection into fuel cell.

1) Hydrogen stored on-board: Hydrogen can be either stored in a pressurized or in a liquefied form to save volume.

2) Hydrogen can be generated from methanol or hadrocarbons by an on-board reformer. See below.

Fuel reforming to obtain hydrogen

The main advantage of an on-board reformer lies in the higher energy density of methanol and other "indirect" fuels. This leads to higher range compared to hydrogen storage.

A methanol reformer produces hydrogen and CO2 from methanol and water. In the process a number of by-products are produced some of which have a negative effect on the fuel cell catalyst. Therefore the reforming gas has to be cleaned before use inaside the fuel cell.

Types of fuel production and transport

Figure 1 gives an overview of the most important fuel supply chains for fuel cells.

h2-supply.gif

Figure 1: Fuel supply chains for PEM fuel cells

Source: IZT

Layout of a fuel cell driven rail vehicle

A study by DB AG examined the layout of a fuel cell driven MU (DMU of type VT 610). The results for the fuel cell system NEBUS (by XCellsis) are given in the following table: 

 

Power

500 kW

Mass (cells)

2800 kg

Mass (tank including insulation and fuel)

2610 kg

Volume (cells)

4,2 m3

Volume (tank)

8,3 m3

Number of modules

2

Fuel

hydrogen

New axle load

13,49 tons

 

Source: Hörl et al. 2001

Fields of application

Stationary: decentralised power generation

Mobile devices: energy supply for notebooks, camcorders etc.

Transportation: cars, busses, railways, vessels

Railway applications

The following areas of application for fuel cells in railways are conceivable:

  • traction
  • energy supply for auxiliaries and/or comfort functions
  • stationary applications

The evaluation focuses on an application for traction.

Manufacturers

Ballard Power Systems (Canada)

Siemens

close main section General criteria
  close sub-section Status of development: research & experiments
    Some railways and manufacturers have carried out feasibility studies on mobile fuel cell deployment (cf. for example Niehues, Edwards 2000).
  Time horizon for broad application: in > 10 years
    Introduction into railway markets could start in 10-15 years, if prices drop and efficiency is improved.
  Expected technological development: highly dynamic
    Cf. Application outside railway sector - Potential for further development
    Motivation:
    Replace diesel traction in view of future environmental legislation and limited world oil reserves.
  Benefits (other than environmental): medium
   

Weight reduction

Future fuel cell systems for rail vehicles could be a much lighter option than diesel-electric systems.

  Barriers: high
   

Costs

Investement costs are far too high.

Risk for developers

  • R&D in fuel cells is risky for industry (especially railway manufacturers) since development costs before mass production are particularly high.
  • Development potential uncertain: Some experts hold that hydrogen technology is over 60 years old and given such a long development period has not evolved sufficiently in order to justify expensive R&D efforts.

Technological shortcomings

  • Power density is far from sufficient for most railway traction applications.
  • liability to defect and lifetime: one reason for liability to defect lies in the high number of internal interconnections between fuel cells in the stack. Lifetime of present fuel cells is ~ 5000 hours.
  • Fuel supply and storage: hydrogen storage unsatisfactory, progress too slow in this area.
  • Efficiency: Total efficiency of fuel cell system must be improved in order to become a diesel alternative.

Range

Present technology could lead to range problems due to low fuel densities.

Environmental

If hydrogen from fossil sources is used and assuming present efficiencies of fuel cells, environmental balance of fuel cells is worse or at best equal as for diesel traction (cf. Environmental criteria – Other environmental impact).

Infrastructure transition

New infrastructure needed. Gaseous fuel requires more careful handling than diesel.

Interoperability

Problematic as long as fuel supply infrastructure is not fully deployed.

Safety

Explosiveness of hydrogen-oxygen mixtures. This problem can be considered as principally solved.

There are restrictions concerning fuel cell powered vehicles in tunnels and underground service.

Technological inertia

Scepticism rules in both railway and manufacturing companies to deviate from conventional and successfully technology.

    Success factors:
   
  • Research funding (national or European)
  • Strict emission regulations
  • Clear regulations (emissions, safety etc.) providing a good planning basis
  • Successful developments in automotive sector (both technological and market).

A co-operation and co-ordination of European railways could prepare a common view on fuel cells and set the basis for a later introduction.

  Applicability for railway segments: high
    Type of traction:  diesel
    Type of transportation:  passenger - main lines, passenger - high speed, passenger - regional lines, passenger - suburban lines, freight
    At present the power classes (~ 250 kW) of available fuel cells are too low for most railway traction applications typically requiring power classes of 600 - 1000 kW. This will require long-term R&D still. Fuel cells could in mid-term be interesting for auxiliaries functions. Various big railway operators in Europe consider an application of fuel cell but scepticism is high in view of immense costs. Some believe that in long-term perspective fuel cells could even replace electric traction due to lower overall costs.
    Grade of diffusion into railway markets:
  Diffusion into relevant segment of fleet: 0 %
  Share of newly purchased stock: 0 %
    (no details available)
  Market potential (railways): highly uncertain
    (no details available)
    Example:
    (no details available)
close main section Environmental criteria
  close sub-section Impacts on energy efficiency:
  Energy efficiency potential for single vehicle: not applicable
  Energy efficiency potential throughout fleet: not applicable
   

Since fuel cells run on a different fuel, an assessment of the direct energy efficiency effects is difficult. There are however two quantities directly related to energy efficiency that may be used for a comparison between fuel cell and diesel-electric vehicles:

  • Efficiency of the conversion chain
  • Greenhouse gas emissions (in CO2 equivalents)

Efficiency of the conversion chain

Since fuel cells do not involve a combustion process, their efficiency is not limited by the Carnot process and may be well over 50 % (the manufacturer XCellsis even gives an efficiency rate as high as 80 %, a figure which is hardly reached in practice).

The efficiency of the fuel cell itself however does not tell much about the energy performance of the system. It is essential to look at the entire energy chain rather than the on-board conversion processes only.

A comparison between a fuel cell and a conventional diesel-electric vehicle performed by DB AG (Hauser, Kleinow, Ponholzer 1999) yielded the following results:

Whereas diesel-electric traction has an overall efficiency of 31,7 %, the efficiency of fuel cell traction lies between 6,1 % and 31,1 % depending on fuel supply chosen. Details are shown in Figure 2. Supply chain 1 refers to H2 production through electrolysis (power from public grid) and storage and transport in liquid state. Supply chain 2 refers to H2 production through natural gas reforming and storage and transport in gaseous state.

Figure 2: Comparison of overall efficiencies between diesel-electric and fuel cell traction (two supply chains)

fuel_cell_efficiency.gif

Source: IZT, data from Hauser, Kleinow, Ponholzer 1999.

Greenhouse gas emissions

Just like the overall efficiency, the GHG balance of the fuel cell vitally depends on the prechain. A study by the IFEU institute (Patyk 2000) gives a comparison between the GHG balance of different fuel cell solutions and conventional diesel engines (referring to road transport). The following table gives the results of this study:

 

Fuel chain

GHG emissions relative to diesel engine (=100%)

H2-Fuel Cell-PC, Compressed Gas. H2 from natural gas, centrally located reformer (big)

87 %

H2-Fuel Cell-PC, Compressed Gas. H2 from natural gas, non-centrally located reformer

100 %

H2-Fuel Cell-PC, Liquid H2 from natural gas, centrally located reformer (big)

140 %

H2-Fuel Cell-PC, Liquid H2 from regenerative electricity

1 %

Methanol-Fuel Cell-PC (PEMFC), MeOH from natural gas

113 %

DME-Fuel Cell-PC (PEMFC), DME from natural gas

114 %

Methanol-Fuel Cell-PC (PEMFC), Biomethanol

14 %

DME-Fuel Cell-PC (PEMFC), BioDME

14 %

Ethanol-Fuel Cell-PC (PEMFC), Bioethanol

29 %

 

Source: Patyk 2000, IZT calculations

These figures show that only the fuel chains starting out from renewable sources offer substantial advantages over diesel propulsion. The only fuel chain slightly better than conventional diesel chain is hydrogen production from natural gas in big centralised reforming plants.

Conclusion

If fossil fuels are used for hydrogen production, then the fuel cell only offers an advantage if the energy efficiency over the whole chain is as good as for modern diesel-electric chain. This is roughly the case for natural gas reforming.

If renewable energy is used for hydrogen production, then fuel cells operate with almost no (fossil) carbon dioxide emission. This however is true for the use of H2 not only in fuel cells but also in internal combustion engines. Therefore the overall efficiency will decide on the most environmentally favourable technology to be used.

  Other environmental impacts: ambivalent
   

Local emissions

The local emissions of a fuel cell powered traction are close to negligible.

Global emissions

A study by the IFEU institute (Patyk 2000) examined the pollutant emission along the whole chain for different fuel chains for fuel cells. This included the two impact categories

  • Acidification (with the balancing parameters SO2, NOX, NH3 and HCl)
  • Eutrophication (with the balancing parameters NOX and NH3)

 

Fuel chain

Acidification relative to diesel engine (=100%)

Eutrophication relative to diesel engine (=100%)

H2-Fuel Cell-PC, Compressed Gas. H2 from natural gas, centrally located reformer (big)

56 %

53 %

H2-Fuel Cell-PC, Compressed Gas. H2 from natural gas, non-centrally located reformer

56 %

54 %

H2-Fuel Cell-PC, Liquid H2 from natural gas, centrally located reformer (big)

71 %

70 %

H2-Fuel Cell-PC, Liquid H2 from regenerative electricity

77 %

72 %

Methanol-Fuel Cell-PC (PEMFC), MeOH from natural gas

120 %

100 %

DME-Fuel Cell-PC (PEMFC), DME from natural gas

38 %

44 %

Methanol-Fuel Cell-PC (PEMFC), Biomethanol

71 %

66 %

DME-Fuel Cell-PC (PEMFC), BioDME

217 %

240 %

Ethanol-Fuel Cell-PC (PEMFC), Bioethanol

262 %

240 %

 

Source: Patyk 2000, IZT calculations

These data show that as far as emission control is concerned, most fuel cell options offer advantages over diesel propulsion. However, fuel cells with biofuels have an emission performance considerably worse than diesel.

close main section Economic criteria
  close sub-section Vehicle - fix costs: high
    According to an article by DaimlerChrysler and Adtranz (Niehues, Edwards 2000), the current price of the complete 230 kW fuel cell system including the components but excluding a traction system and hydrogen tanks amounts to about 1,6 million euros per P4/P5 system. Vehicles need one or more (up to 8 in Intercity trains) of these systems. This corresponds to about 7000 Euro per kW. In order to be competitive, cost would have to drop below 10 % of present level. The manufacturer Ballard Power Systems aims at a long term target price for automotive applications of about 50 Euro per kW and has developed to reach this price level.
  Vehicle - running costs: strongly dependent on specific application
   
  • Fuel costs: uncertain. Depends on primary fuel used. In the case of hydrogen, price will strongly depend on demand. Considerable scale effects seem likely in case of dynamic demand development.
  • Niehues, Edwards expect maintenance costs to fall by a factor of four between 2000 and 2007.
  Infrastructure - fix costs: high
    Depending on primary fuel used, additional investment for additional supply infrastructure is required.
  Infrastructure - running costs: strongly dependent on specific application
    Depending on primary fuel used. Gaseous fuel has to be handled with more care than diesel.
  Scale effects: (no data)
   

Key factors for price development

Price effects will mainly come from three areas:

  • Manufacturing processes (cf. Application outside railway sector - Potential for further development)
  • A supply industry for individual components does not yet exist and has to be systematically developed in the future.
  • Production numbers have to increase substantially.

Expected price development

In a publication from 2000 (Niehues, Edwards 2000), DaimlerChrysler and Adtranz expected the following relative price development for the complete 230 kW FC system including the components but excluding a traction system and hydrogen tanks:

1999: 16.

2002: 4.

2004: 3.

2007: 1

Thus expected price in 2007: 100.000 Euro.

Niehues, Edwards specify the conditions for such a devlopment:

"By the year 2004 the production of 100.000 fuel cell stacks (ca. 50 kW) for the automobile sector has to be achieved and a dedicated fleet of fuel cell busses of about 1000 vehicles has to be in place by 2007. In case serial production has not reached 100.000 items per year by 2004, the costs for the stacks will stay at their current high level."

In 2002, it is already clear that a production of 100000 items in 2004 will not be reached. The above scale effects are therefore too optimistic as well and have to be postponed by at least 3 years.

Fuel prices

Scale effects are to be expected for fuel prices as well.

  Amortisation: (no data)
   

In view of the present uncertainties concerning the price of both fuel cells and fuel, no general payback characteristics can be given.

The study by DB AG yielded the following economic feasibility (assuming two different investment costs 2000 and 50 EURO/kW):

 

Energy supply for traction

Annual operation costs

Costs for 20 year operation

2000 EURO/kW

50 EURO/kW

Diesel engine

1

1

1

fuel cell with hydrogen

2,54

6,67

2,75

fuel cell with methanol

0,95

5,13

1,02

 

Source: Hörl et al. 2001

This table shows that economic feasibility could be reached for investment costs of 50 EURO/kW and methanol operation.

close main section Application outside railway sector
  close sub-section Status of development outside railway sector: in use
   

A number of very advanced prototypes exist.

230 kW fuel cell system “P4/P5” (XCellsis) is commercially available.

Several vehicles by DaimlerChrysler and propulsion systems with fuel cells:

  • NECAR I, NECAR II:
  • NEBUS: modified city bus O 405 N equipped with PEMFC

Fuel cell-driven NECAR 5 (New Electric Car) from DaimlerChrysler and the Premacy FC-EV (Fuel Cell Electric Vehicle) from Mazda obtained a road permit from the Japanese Ministry for Infrastructure and Transport in Feb. 01. The fuel used in the system is methanol.

DMFCs are still in the stage of laboratory applications.

  Time horizon for broad application outside railway sector: in 5 - 10 years
    (no details available)
  Expected technological development outside railway sector: highly dynamic
   

Main overall development targets for future fuel cells are:

  • reduce size and weight (and thus increase power density)
  • increase reliability and life-time

R&D is done in the following fields:

  • New types of fuel cells
  • Improvement of methanol reformers and the related cleaning processes
  • Hydrogen generation by reforming commonly available hydrocarbons (gasoline, diesel or renewables hydrocarbons like biomass). An efficient and economic reforming of hydrocarbons could open new market segments for fuel cell technology especially in the ground transportation segment.
  • DMFC (Direct Methanol Fuel Cell): New developments also permit the direct conversion of liquid methanol inside the fuel cell itself (as opposed to a separate reformer). Depending on future research progress, a compact system could become available to be refuelled directly with liquid fuel.
  • Improvements for the complete fuel cell system. The dimensions and power consumption of the compressor could be reduced by lowering the pressure on the cathode side of the fuel cell. The decreased efficiency of the fuel cell itself at reduced operating pressure could be more than compensated by significant savings of compressor energy. Thus, such a measure would raise overall system efficiency.

Manufacturing processes:

At present there are still several components of a fuel cell which can only be produced manually. Despite intensive R&D efforts, convenient technology for mass production is not available yet. This is one of the key cost drivers.

  Market potential outside railway sector: highly uncertain
    Key markets for fuel cell technology are automotive and decentralised power generation. Both markets are highly uncertain mainly due to high price per kW.
close main section Overall rating
  close sub-section Overall potential: interesting
  Time horizon: long-term
    Fuel cells are an interesting long-term option for replacing diesel traction. A big advantage is seen in its independence from a particular primary energy source. However, technological, economic and environmental barriers will have to be resolved before a diffusion into railways becomes an option. Technological progress is undoubted but comes at a much slower pace than expected some years ago. Economic feasibility is low as long as small production numbers impede any substantial scale effects. The environmental performance is almost entirely dependent on the fuel chain. The introduction of fuel cells only brings the expected ecological quantum leap if hydrogen is produced using energy from renewables. As long as this option remains unrealistic, fossil sources have to be considered. The only option which may be as good as or even slightly better than diesel-electric propulsion is hydrogen production from natural gas reforming. Despite many limitations and uncertainties, fuel cells remain a very interesting option worthy of further R&D efforts. However, these will come mainly from companies producing for mass markets.
References / Links:
Attachments:
Related projects:  Energy chains of alternative fuels;  Fuel Cell
Contact persons:
 date created: 2002-10-09
 
 
© UIC - International Union of Railways 2003
 
Aktionmenu
 
 Your contribution
   add technology
 Views of this page
   show overview
   show evaluation
   show details
 Print options
   print data sheet
   print screen
 Help
   Evaluation briefing
   Technology list
    French - German