Transport and sustainability
Transport and sustainability

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Transport and sustainability

FCVs in practice

Interest in fuel cells for road transport developed with the rise in environmental concerns around transport in the 1980s and 1990s. Most of the major vehicle manufacturers have produced prototype FCVs; in addition, new companies have emerged that specialize in the manufacture of fuel cell systems. One such company is Ballard Power Systems, which in the 1990s collaborated with DaimlerChrysler and Ford to make the world's first fuel cell bus and the demonstration NECAR (New Electric Car).

A large number of prototypes and demonstration cars have been developed in the last 20 years. Recent examples of near-production vehicles include the Honda FCX Clarity, the Toyota FCHV-adv and the Mercedes-Benz F-Cell. Altogether, these various demonstration FCVs have driven around 3 million kilometres in trials.

Several car manufacturers have announced plans to introduce a production model of a fuel cell car from 2015, but there have been previous announcements of a similar kind, with launch dates being subsequently postponed. Policy assumptions are that FCVs will not be widely available until around 2025–2030. There remain several issues to address, including the following:

  • Costs – like all low-carbon vehicles, there is a price premium for FCVs. A 2015 launch price of US$50 000 is being mentioned for the Honda Clarity, although this will include a company subsidy.
  • On-board storage – although hydrogen contains three times more energy per weight than petrol, it contains only a third of the energy per volume, making on-vehicle storage bulky. Hence the large tank shown in the diagram of the Honda Clarity (Figure A.17) and the need for very space-efficient designs.
  • Hydrogen losses in on-board storage – some gas is vented and lost in storage on the vehicle.
  • Fuel cell stack durability – this is currently about half of what is needed for commercialization. Durability has increased substantially over the past few years, to 120 000 km, but needs to be closer to a 250 000 km lifetime.
  • Refuelling infrastructure – this is an even bigger issue than for BEVs (which only need limited public charging points, as electricity is readily available in homes and workplaces). Hydrogen refuelling will require a whole new system, with only a handful of refuelling points currently available globally. It is estimated that it would cost at least a billion euros to create a hydrogen refuelling network for Germany alone.
  • Source of hydrogen – producing hydrogen from non-fossil sources (biomass, wind, nuclear) has a limited potential and is expensive. The 2007 Concawe report suggested that the more efficient use of renewables would be through direct use as electricity rather than to manufacture hydrogen.

The last point is crucial and raises doubts as to whether hydrogen fuel cell cars are a viable route to low-carbon transport. For example, if you started with a renewable source of energy such as biogas, this could be compressed and directly used in a CNG or CNG/electric hybrid car. To be used in an FCV, the gas would have to be processed (reformed or used to power electrolysis) into hydrogen, compressed and pumped into a tank for fuelling a car. There are energy losses at each stage and in storage. Thus although the energy efficiency in use in an FCV is better than in an ICE or hybrid car, the overall energy loss is greater.

Activity 10 (exploratory)

Work out the energy losses for the following fuel supply chains from renewable fuel to powering an engine.

  • a.Renewable electricity → hydrogen by electrolysis → fuel cell → electric power to drivetrain
  • b.Biogas → electricity → hydrogen by electrolysis → fuel cell → electric power to drivetrain
  • c.Biogas → ICE vehicle → power to drivetrain
  • d.Biogas → ICE hybrid vehicle → power to drivetrain

Take a starting index of 1.0 and assume the following:

  • generating electricity from biogas is at 60% efficiency
  • electrolysis is at 65% efficiency
  • compression and distribution losses for hydrogen are 10% (i.e. 90% efficiency)
  • fuel cells operate at 45% efficiency
  • a CNG ICE vehicle operates at 30% efficiency
  • a CNG ICE hybrid vehicle operates at 35% efficiency.

Discussion

The energy efficiency chains are as follows.

  • a.Renewable electricity (1.0) → hydrogen by electrolysis (1.0 × 65% = 0.65) → hydrogen to car (0.65 × 90% = 0.59) → fuel cell (0.59 × 45% = 0.26) → electric power to drivetrain (0.26)

    Energy loss: 74%

  • b.Biogas (1.0) → electricity (1.0 × 60% = 0.60) → hydrogen by electrolysis (0.60 × 65% = 0.39) → hydrogen to car (0.39 × 90% = 0.35) → fuel cell (0.35 × 45% = 0.16) → electric power to drivetrain (0.16)

    Energy loss: 84%

  • c.Biogas (1.0) → ICE vehicle (1.0 × 30% = 0.30) → power to drivetrain (0.30)

    Energy loss: 70%

  • d.Biogas (1.0) → ICE hybrid vehicle (1.0 × 35% = 0.35) → power to drivetrain (0.35)

    Energy loss: 65%

The long fuel conversion chains result in serious energy losses, with 70–85% of the energy being lost. This supports the case for renewable fuels to be used as directly as possible.

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