Zero-emission trains: energy transition or green-washing?

Recent developments in railways rolling stock have shown numerous applications of so-called “zero-emission trains” relying on innovative technologies. So far limited to buses and urban rail, this trend turning into conventional rail is a promising way to serve sustainable growth. But is it that simple to convert regional or intercity services to green? What is the price to pay? And are these trains really zero-emission?

Which innovations for zero-emission trains?

Beside electric trains, which operation is already zero-emission by the way, many technologies have been explored for passenger services applications as an alternative to diesel trains: other fuels, batteries, hydrogen, or even solar power, and combinations of them as “hybrid” trains.

  • Solar power can quickly be excluded from stand-alone solutions as the solar radiation on the Earth surface is too limited to power a train for regular passenger service, and eventually operate by night.
  • Alternative fuels like natural gas generally do not prove relevant for avoiding Green House Gas (GHG) emissions. Only BioGas, when relying on agricultural waste, is an interesting option: its combustion still emits other particles than GHG and large-scale application are a challenge but turning methane into less-prejudicial carbon dioxide even makes it a GHG-consumer with a negative balance!
  • Batteries-trains are the closest evolution of classic electric trains: onboard energy storage allows them to run where there is no catenary whilst relying on the same efficient principles rail traction engineers have been optimizing for decades, from wheel-rail contact to energy recovery. Autonomy and lifecycle (manufacturing, dismantling) of batteries are currently the two main concerns to focus on.
Battery train
  • Hydrogen-trains rely on the so-called “fuel cell” to generate electricity from hydrogen. As these devices run on stable duty cycles, extra batteries are needed to manage the power peaks the vehicle needs. Hydrogen-trains are battery-trains too, but autonomy is not a concern with a dense pressurized hydrogen tank onboard. With hydrogen not directly available in the environment, operating a Hydrogen-train is all about producing it – with costs, energy and GHG balance at stake: even more than Batteries-trains, Hydrogen-trains reflect the local electricity mix!
Similar propulsion principles, different power supply solutions: Hydrogen train

How to choose the best option?

All these technologies show pros and cons, so can we figure out what the best option is?

  • When the local electricity mix makes technical solutions similar in terms of GHG performance, rail operation parameters help select the best option: “How long is the interstation?”, “How fast shall the trains be refilled?”, “How demanding is the route?” are essential questions for a fast assessment of the potential solutions.
  • The capacity to rely on existing fleets or facilities and tune them up to “Zero-emission” shall also be considered, to adapt combustion engines to biogas or fit batteries into hybrid trains
  • Considering investments, there is obviously a scale factor to be considered. Selecting between available solutions is a matter of splitting costs between Infrastructure, Rolling Stock and Energy expenses: the relative network span, fleet size or facilities needed are service-related parameters with limited correlation.
A diesel train in the South the France, where SYSTRA assessed the regional council in finding relevant zero-emission alternatives © CAF

This variety of solutions is a global opportunity. It makes the industry capable of offering emission-reducing solutions adapted to the local context. Emerging countries forced to scale the development of their energy industry and limit the span of sources locally available are not bound to diesel: they can find the Zero-emission trains fitting their energy pattern, thus proving that economic development does not contradict environmental sustainability – should global decisions be the right ones!

Which evolutions can be expected?

Generally, it can be foreseen that authorities will regulate energy transition by law. This is already the case for buses in some countries like France: SYSTRA takes part in many of these e-mobility projects and supports local authorities anticipating similar changes for rail.

  • Regarding batteries, there is room for a quick improvement over the next years. The power of the automotive industry is likely to come up with increased capacity and lifetime while decreasing costs, thus benefitting the rail industry too… Looking at some oil & gas giants buying smaller batteries suppliers gives us a clue on the potential of this trend.

  • Biogas solution is often overlooked for cultural and historical reasons, with a probably limited scalability. But its adequacy for some particular needs may let local initiatives emerge for rail lines with little traffic and looking for easy-to-implement solutions to reduce their carbon footprint.

  • Hydrogen is a topic in itself. Seen from the sole mobility point-of-view, hydrogen solutions never prove the best option in current conditions. But more than just a fuel for transportation, hydrogen should rather be seen as a storage means for carbon-free electricity. In other words, should electricity producers, gas supplier and rail industry cooperate, developing hydrogen trains could be the flagship to introduce zero-emission transportation in countries with carbon-full electricity mix…

Hydrogen train: the flagship to introduce zero-emission transportation in countries with carbon-full electricity mix? © Alstom

Relying on a versatile portfolio is the solution

Where traffic is too small to justify electrification, the rolling stock industry proves reactive in offering relevant alternatives to reduce the environmental footprint whilst controlling costs. But no stand-alone solution exists yet to compete with a catenary.

As the very effective batteries show intrinsic constraints on the operation over their whole lifecycle, it is up to the technology to make progress for realizing its huge potential. Trendy hydrogen and underrated BioGas are dependent on the development of large-scale production and distribution circuits– which cannot be borne by low-traffic railways services. Rather than gambling to choose one solution, the wiser option sounds like relying on a versatile portfolio and adapt the technology to the rail service’s very needs and to the local power supply opportunities.

Moreover, the “zero-emission” label mostly depends on the electricity mix at the plant where the power source is generated. Zero-emission technologies can then be looked at in a totally different perspective. Considering the possibility to turn electricity into storable and transportable goods, couldn’t they pave the way for an international trading of green, cost-controlled energy ? With zero-emissions trains as first messenger.

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