Sustainability
Rail drives in transition
Considerations on alternative drive concepts for multiple units
Rail vehicles with drive concepts that are based on fossil fuels are getting shelved! In most relevant markets, there are already legal regulations that leave no doubt about this outcome. The roadmaps for the decarbonization – in other words, saying goodbye to fossil fuels such as diesel – were already finalized some time ago. In the second half of the 21st century, large parts of the international community will mostly set emissions of harmful greenhouse gases to zero. A fundamental shift in transportation is key to implementing these plans. Of course, this also affects rail transport. Of the 1.3 million kilometers of routes worldwide, only around 375,000 kilometers are electrified – which is barely 30 percent. This is why locomotives and multiple units with combustion engines – usually powered with fossil diesel – still tend to be the rule rather than the exception in many parts of the world. At least coal-fired steam locomotives are used almost only as nostalgic relics for tourism at this point.
Degree to which the rail networks are electrified
The degree to which the rail networks are electrified varies considerably. In North America, it’s about one percent. In Asia, it increased from 34 percent in 2013 to just over 55 percent today. And in Europe, about 46 percent of the entire rail network is used by diesel vehicles. Despite many efforts to bring more electricity to the railways, an electrification rate of 100 percent even by the beginning of the second half of the century is utopian, if only because of the enormously high expenditures that rail network operators would have to invest in the expansion in a relatively short period. Furthermore, from an economic perspective, electrification only tends to be worthwhile in cases of medium to high traffic densities.
Therefore, operators of rail vehicles must already take a closer look at the innovative drive concepts of a post-diesel generation. After all, it isn’t rare for rail vehicles to be used for 30 years or more. So, if anyone is putting a new vehicle into operation in 2022, they must pay some attention to the emission rules for the year 2050. In principle, there are three concepts to consider for sustainable propulsion: Fuel cells, battery-electric drives and combustion engines with alternative fuels. All of these systems fundamentally require the climate-neutral production of energy, for example with photovoltaics, wind or hydropower. Otherwise, nothing will be gained in terms of climate protection.
Concept 1: Alternative fuels
The advantage of this concept is obvious: The existing vehicles can continue to be used, since nearly all combustion engines can handle the sustainably produced e-fuels without problems. Voith is already working on solutions designed specifically for e-fuels or hydrogen. The use of state-of-the-art drive concepts can optimize efficiency and thus also the emissions reduction even further. At least as a bridging technology, biodiesel and e-fuels are therefore conceivable alternatives on the way to the zero-emissions target.
Concept 2: Battery-electric drives
As part of its Update Fleet Strategy 2035 initiative, for example, the Austrian Federal Railway has already been using the Cityjet Eco prototype since 2019. And in 2023, Deutsche Bahn plans to use battery-powered trains to bridge non-electrified sections on several routes. Here, the crux of the matter lies in factors such as the weight of the storage systems or range of the vehicles. With a range of about 120 kilometers, today’s batteries are mainly sufficient for local transport or for bridging operations. Then the train either has to go to a charging station – with long idle time – or it draws energy from running on track sections with an overhead line. In addition, the drive motors will switch to generator mode if the locomotive driver gives an electric brake signal. This principle of recuperation is similar to electric cars. It is only possible to achieve longer ranges with more batteries, which adds significantly to the weight of the vehicle. For this reason, it is currently hard to conceive of economic operations on long routes.
Despite these limitations, a first step has been taken and thanks to even greater energy density, future battery generations will enable significantly longer ranges.
With a wide range of gear units, Voith already has a very high level of expertise for all future-oriented drive concepts, also in the segment of electromechanical drives. Electrically powered rail vehicles are already using these systems worldwide.
Concept 3: Fuel cells
The prerequisite for this is a sufficiently large and reliable storage system. The Voith technology group presented an innovative H2 storage system last year and is in the process of getting it ready for serial production. The current focus is on high-performance applications for roads. However, the system is designed so that it can be easily scaled. The structure of the pressure vessels is particularly exciting. They consist of CFC material developed and produced by Voith. The production of the tanks utilizes pre-impregnated fibers, so-called TowPregs, for the first time. The energy carrier is refueled at a pressure of 700 bar, which is significantly higher than with the currently common tank systems. The filling takes only a few minutes. In other words, it could be carried out while the train is on a regular break.
Summary
- e-fuels likely offer the least complicated way to make the switch, because operators wouldn’t be forced to invest in an entirely new vehicle fleet. At the moment, however, the limited availability of these fuels is holding further development. The development of production capacities is progressing in the meantime. The infrastructure for e-fuels will soon be expanded to the same extent.
- Battery-electric systems are already an option today, especially on short routes. Long-distance transport requires more powerful batteries, but these will take at least a few more years to go into series production.
- Fuel cell drive systems already have production maturity. Because of the long ranges enabled by hydrogen and the relatively short refueling times, fuel cells have become a favorite option for developers at present. Here as well, the breakthrough is held in check by the currently available capacities. But in this area, the expansion is also progressing, and some traditional oil-producing countries such as Saudi Arabia, Norway and Brunei plan to significantly advance the production and export of hydrogen in the near future. At the same time, plans regarding transport capacities and hydrogen filling stations are progressing at an accelerating pace.
This means that that fleet operators will have to consider an entire bundle of influencing factors when choosing the right energy carrier for their vehicles in the future: The climate, topography and route length; available primary energies and their costs; weight and safety; operational requirements such as schedules and passenger volumes; and idle times for recharging or refueling are just a few of the important issues that will determine which energy source is used. Voith reflects this openness of systems in its portfolio of drive systems. The technology group thus offers its customers the opportunity to select the optimal drive concept for every requirement.
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