Procurement of alternatively-powered rolling stock (hydrogen or battery)
Shifting passenger- and freight-transport activities to rail can reduce CO2 emissions given the low carbon intensity of rail operations. However, further CO2 emissions reductions are feasible by employing truly carbon-neutral rail technologies. Electrification has been highlighted as a potential way forward, but electrification itself can carry high front-end infrastructure costs. The CO2 reduction potential of electrified rail lines is also highly dependent on the energy mix of the territory it is operating in. Various analysts have suggested adopting rolling stock capable of using alternative energy sources as an option for balancing environmental benefits with economic, commercial and competitive constraints. However, the fundamental physics of rail traction requirements, especially for heavy freight trains, pose a challenge for alternatives.
Two main types of alternative rolling stock have been highlighted: hydrogen-based technologies and battery-based ones.
Hydrogen fuel cells can serve as a source of energy for train propulsion with clean direct emissions: a chemical process converts the energy in the hydrogen molecule to generate electricity, as well as heat and water. How clean this technology really is will depend on the initial way in which hydrogen is produced. Steam reforming through fossil fuels can still entail high emissions, even if lower than conventional diesel combustion. Using electricity from renewable or nuclear energies can yield a cleaner form of propulsion than conventional fuels (depending on the energy mix) but is, at present, a more expensive option than the use of fossil fuels as the source of hydrogen. The development of a hydrogen-based fuel system will entail the development and cost of a new and separate supply and logistics system. These must be included in any comparative economic evaluation.
Battery-related technologies involve the use of rechargeable batteries for powering rolling stock. Their main claimed advantage for decarbonisation purposes is linked to their lower comparative cost when compared to the investment needed for electrifying infrastructure. However, battery technologies do not yet possess the energy density to support the operation of conventional freight trains, even over relatively short distances. Freight trains are much heavier than the passenger trains in which battery applications have so far been trialled and demonstrated. The option to use batteries for “last mile” applications – i.e. to allow freight trains to operate directly in/out of terminals in urban areas without the need for a separate diesel shunting locomotive or an integral I/C power pack – may have the potential to service new markets which are wholly served by road at present. This model could yield significant decarbonisation and operational benefits.
Hybrid vehicles, which combine combustion fuels or hydrogen fuel cells with batteries, can also provide CO2 mitigation gains. In all cases, the weight and capacity of batteries can raise operational difficulties, such as not allowing for longer trips when battery capacity does not permit it. Battery technologies’ potential will also depend on the energy mix of the context of application.
Both hydrogen- and battery-based technologies are still being evaluated, as their mass uptake is only expected in the next 5 to 10 years, in a "best case" scenario. Further empirical evidence will be needed to contrast current estimated benefits obtained from pilots and modelling exercises with real-life and sustainable applications of these technologies.
The CO2 mitigation impact in this case depends on the chosen technology, as well as on the energy mix (and its carbon footprint) with which the rolling stock would be powered.
In the United Kingdom, simulations for a specific route showed that a hydrogen-powered train and hydrogen-hybrid train led to CO2 decreases of 59% and 77%, respectively, compared to diesel propulsion. An overall analysis in Europe set the potential for CO2 mitigation at around 40% when compared to a diesel-propelled train. In the United States, a recent analysis showed that hydrogen energy generated with renewable sources brings about 20 times more benefits than thermal electricity or natural-gas-generated hydrogen.
The CO2 mitigation potential of battery-powered trains has been set lower: the above-mentioned US study finds that the benefits brought about by batteries in terms of decarbonisation potential stand midway between hydrogen-based and diesel technologies.
In Montreal, a full electrification of a railway line brought about 98% of CO2 reductions, compared to a maximum of around 70% for renewable-energy-generated hydrogen; most of the electricity produced in Montreal comes from hydroelectric plants.
Electrification will generate new energy demand for utility companies. There will need to be adequate incremental capacity available to sustain the additional demand of train operations. This is especially the case as rail operators typically no longer provide their own power and rely on the adequacy of national or international pooled grid supplies for effective operation. Given the rail system represents a wholly new market for the power suppliers, potential collaboration between electricity providers, rail infrastructure managers and train operators will be useful when developing functioning business models.
Procurement of hydrogen and battery rolling stock could in some circumstances be less expensive than traditional electrification, due to the high initial infrastructure costs that electrification entails. However, this will come at the cost of train speed and train capacity (in terms of weight). For instance, in a study for Montreal, Canada, it was estimated that the electrification of a commuter line would have cost around CAD 1.3 billion, compared to only CAD 655 million for a hydrogen fuel cell system. The electrification option had lower operational costs, but higher total costs due to the higher initial infrastructure costs. But these estimates did not take into account the costs of storage, distribution and production infrastructure for hydrogen. The claimed cost-related comparative advantage of the hydrogen fuel can be further eroded if demand on a given electric line is high and makes infrastructure costs (per vehicle-kilometre) fall. Estimates indicate that in the United States, overhead line equipment electrification has lower annual costs than all other cleaner technologies. This is expected to remain the case to 2050 and likely beyond.
Estimations for years after 2020 put hydrogen fuel cells closer to diesel combustion in terms of costs. This was seen in recent analyses for the United States. Nonetheless, it will be necessary to add costs of the recharging stations for hydrogen, plus all related distribution and hydrogen production infrastructure. Batteries are less cost-competitive, as their cost is considerably higher and their performance is lower than that of hydrogen fuel cells. Nonetheless, this is expected to change as battery technologies evolve. In Norway, costs for full-battery rolling-stock systems are estimated to gradually close in and almost equal those for hydrogen-fuel-cell ones by 2050. By that year, it is projected that full-battery rolling-stock systems will cost around USD 16 million per year, compared to around USD 15 million per year for hydrogen-based systems (though this is a highly specific case with abundant hydropower availability).
Hydrogen- and hybrid-propelled trains can reduce energy consumption, thus potentially decreasing prices. Trials in the United Kingdom showed that the two technologies reduced energy consumption in return journeys by 34% and 55%, respectively, compared to diesel. At the same time, alternative technologies can have higher acceptance than other technologies: an analysis of potential adoption of alternative rolling-stock technologies in the United States showed that battery-based rolling stock has a higher public acceptance (based on noise reduction, aesthetics and safety) than other forms of technology, including electrification. Hybrid vehicles bring the added value of being able to take advantage of already-electrified lines and shift to tracks that are not electrified without high infrastructure investments. At the same time, one of the highest co-benefits of this measure is its reduced costs vis-à-vis electrification of rail lines with low demand and train frequencies.
Lowering the upfront cost of infrastructure electrification, speeding up the electrification process and extending the life of the fixed equipment (masts, power supply etc.) are options that could be readily pursued to secure decarbonisation and enhanced operational performance for railways.
One of the highest adverse effects of these alternative energy technologies is their much lower efficiency when compared with rail electrification. For example, in the United Kingdom, a trial-based test for a hydrogen-fuel-cell train showed a generally low energy efficiency: a duty-cycle peak of 14% and a steady-state peak of 17%. Longer-distance trips can also be harder, as the lifespans of batteries and hydrogen fuel cells are not yet adapted for them. These difficulties could be improved with the provision of charging stations and hybrid vehicles, as well as by future technological improvements.
ITF (2021) Transport Climate Action Directory – Procurement of alternatively-powered rolling stock (hydrogen or battery)
https://www.itf-oecd.org/policy/procurement-alternatively-powered-rollin...
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