More On Hydrogen Fuelled Trains

The Search For A Diesel Fuel Substitute

As far as both road and rail transport modes are concerned, there is an endeavour to progressively reduce the amount of fossil fuels used. Different strategies are applied to road transport and to rail transport. Up to now roads, with the exception of those used for trolleybus networks (and two short experimental stretches in Sweden and Germany, for use with lorries), do not have overhead electrification systems to provide a source of power for vehicles. The result is that strategies to provide an alternative source of power for road vehicles focus on equipping them with a means of storing electric energy, usually in the form of a battery. This only provides the vehicle with a limited degree of operational autonomy.

Rail networks have been progressively electrified over the past hundred years and more. This gives them a head start in gaining independence from fossil fuels. By the early 21st century, many countries now have a substantial part of their rail networks electrified, and most trains working on those are dependent traction, i. e. electric vehicles powered using either overhead wire or third rail. They thus deliver high performance and basically have an unlimited operating range under these electrification systems.

Although battery-powered rail vehicles have also been around for over a century, over the past few decades there has not been much interest shown in them by railway companies. Instead, the policy has been to extend the electrification network infrastructure, usually involving important main lines, with heavy traffic. However, with the need for a move away from dependency on fossil fuels, railway is now considering how to replace the dieselpowered vehicles on secondary lines, where the cost of infrastructure electrification might not be justified on account of the volume of traffic.

This procedure is taking place only gradually, since, especially in continental Europe, non-electrified lines are mainly the secondary ones, and in general are not those which carry most traffic. There are not that many non-electrified main lines, where trains are still powered by fossil-fuelled vehicles. The result is that most purchases of new rail vehicles nowadays involve electric vehicles, while those powered solely by diesel fuel are being acquired in smaller numbers. This is occurring now to the extent that some manufacturers have already eliminated diesel-only powered rail vehicles from their product ranges.

Non-electrified lines still exist, however, and some of these carry important levels of traffic. It is therefore necessary to provide them with vehicles which are not dependent on fossil fuels for power, and which generate the minimum possible level of noxious emissions. The result has been the development of various innovative strategies, often financed by subsidies from state sources.

One of these strategies involves the development of rail vehicles powered using hydrogen fuel cells. This has attracted the attention of the media, and of course it is only right to explore different new ways of creating vehicles which do not generate noxious emissions or use fossil fuels. However there is also a need to examine what the real potential of hydrogen powered vehicles is.

Between 3 April and 19 May 2017 Alstom’s Coradia iLint 654 102 visited the VUZ Velim test circuits. This photo shows it on the large circuit on 30 April. The hydrogen canisters are situated in the long pods on each roof, and the fuel cells are housed in the blocks situated near the inner ends of each car. The other two pods on the roof of each car house the air conditioning units.

Hydrogen And Its Production

It is a fact that a rail vehicle powered using a hydrogen fuel cell offers certain advantages over the standard DMU design. The vehicle is quieter, and the only exhaust emissions are steam and condensed water. However, the carbon footprint of any vehicle, road or rail, powered using hydrogen fuel cells is heavily dependent on how that hydrogen is produced. Hydrogen can be derived as a by-product of the chemical industry, being created during the processing of fossil fuels (coal, oil or natural gas). Or it can be generated through electrolysis. The resulting carbon footprint from the latter method depends on the type of energy used in the production of the electricity required for electrolysis.

Taking Germany as an example, the changes in policy regarding energy production will result in the production of hydrogen being „greener“ in 2020 than it is at present. Germany is investing heavily in offshore wind farms, these mostly located at present in the shallow North Sea. At night, during the off-peak consumption period, these wind farms can produce cheap electricity which can be used for other types of demand.

One possibility is its use for the generation of hydrogen for fuel cells. Production of hydrogen is a low-efficiency, yet energy-intensive process, thus overnight processing, taking advantage of reduced nocturnal electricity tariffs, is acceptable. This is one potential use for locally generated and periodically surplus electricity, whose use for other alternatives is also being investigated.

One issue which has to be addressed is the need to convey electricity, via power lines, to where it is required. This could, for instance, be to where batteries in road and rail vehicles are being charged. Electricity can also be stored in complexes such as hydro-gravitational power stations (also known as pump-storage power stations) and in electrochemical storage (battery energy storage) power stations.

Another possibility involves the production of synthetic methane. In this case hydrogen (H₂) produced by the electrolysis is transformed into methane (CH₄), using CO₂ in the atmosphere. The resulting CH₄ is safer and easier to transport than H₂, using the existing network of natural gas pipelines.

Given that fact that many rail networks only consume a limited amount of diesel fuel nowadays, the potential for large quantities of hydrogen to be consumed by rail vehicles are comparatively small, especially when one considers the amount of electricity generated by wind farms. At present many of the latter are designed for, and generate, more electricity than do standard-sized nuclear power stations (around 2 GW).

Therefore, for quantitative reasons, it is impossible for hydrogen-powered vehicles to make any greater contribution to the balance of power between global consumption rates at saddle periods and wind farm output. It is therefore essential to look for more efficient means. In fact the reason why Germany is interested in developing hydrogen powered rail vehicles is because public funds have been made available for the use of the surplus hydrogen generated at night as a by-product of wind farm operation in the North Sea.

Readers will recall that in Railvolution 5/16, pp. 76 - 78 we stated that hydrogen is not a sustainable replacement for hydrocarbon-based fossil sources of energy. Hydrogen is not a naturally occurring fuel, and has to be produced either from fossil fuels or from electricity. Therefore it is not possible to develop a project for a large fleet of hydrogen trains in the future, quite simply because the whole objective behind looking for alternative sources of energy for trains used on non-electrified lines is to liberate them from their dependency on fossil fuels.

To supply the iLint with hydrogen gas during the tests at VUZ Velim a mobile fuelling point, provided by Air Products, was installed within the complex.

So again we emphasise that it is not correct to compare a hydrogen-fuelled rail vehicle with one powered by an internal combustion engine - the latter type of vehicle does not have a long term future. Neither it is possible to make a direct comparison with a conventional EMU, which is of course unable to run on non-electrified lines. The only real comparison that can be made is between a hydrogen fuel cell-powered rail vehicle and one which is powered by batteries.

The diagrams below show driveline layouts for various types of rail vehicle. The addition of a second source of power should be regarded as a means of extending the operating range of the train, see Fig. 4 - Overhead electric line, Fig. 7 - Diesel engine and genset, Fig. 9 - Fuel tank and fuel cell.

At present the on-board energy storage device usually comes in the form of an electrochemical accumulator, this usually nowadays a Li-ion battery. However, if there is a need for fast charging or discharging, two-level supercapacitors can be used. A combination of the latter and a battery is also possible.
A paradox is that while hydrogen with a high specific energy provides a vehicle with an ample operating range and the fuel cells take only a short time to be refilled in comparison with an electrochemical accumulator, battery-equipped vehicles do not necessarily need to have a great large operating range. This is because recharging a battery is often possible and is an easier matter than arranging for the refilling of hydrogen fuel cells.

The way to a future, cleaner transport environment has had its ups and downs. Efforts using CNG or rapeseed oil methyl ester have proven disappointing (this photo shows a field with a rapeseed crop in flower). Researchers have been forced to back-track and start again, down a different path. To predict what will happen in the future is difficult. However, given our current knowledge of the subject, it looks as though the use of hydrogen fuel cells for powering rail vehicles may not be a very realistic future option.

Legislative Updates

On 30 November 2016 the European Union issued what is known as the Winter Energy Package. This follows on from the Paris Climate Protocol of 12 December 2015, and proposes an update of the conclusions of the 23/24 October 2014 European Energy Summit, as recorded in the European Council’s document SN 79/14 „Conclusions on the Climate and Energy Policy Framework By 2030“. The proposals essentially tighten up the EU’s targets for increasing energy efficiency (or reducing energy consumption) strategies.

The October 2014 document establishes an indicative target of increasing energy efficiency by 27 %, whereas the November 2016 proposal sets a new, binding target of 30 %. This is not exactly an unrealistic target. For example, on railways and on urban transport systems it has been achieved in the past by replacing resistance control of traction drives with pulse converters and using regenerative braking. However that has been done on electrified rail networks.

In transport systems in general it can be achieved relatively easily by extramodal savings - by reducing the quantity of transport realised using energy-intensive modes (the private car) and transferring it wherever feasible to less energy-intensive modes (collective public transport modes, and in particular electrified rail transport. A necessary condition is the creation of a high quality and attractive public transport, including a massive switch to the use of electricity to eliminate the dependency on fossil fuel consumption and the resultant damaging emissions.

Conclusion

Prompted by the enforcement of these legislative measures, there is a high probability that vehicles powered by internal combustion engines will disappear not only from our roads, but also from our rail networks. All the indications are that, in the case of railways, the extension of conventional electrified networks will continue. Perhaps on lines where there is no economic justification for electrification, vehicles fitted with batteries will be used. Thus there appears to be no overriding factor which justifies the use of hydrogen fuel cell-powered vehicles, together with the provision of their required infrastructure.

Electric Traction Drivelines

Electric traction drivelines have been in evolution now for well over a century, as far as rail vehicles are concerned, and they form one of the three basic energy usage advantages of rail transport.

An electrified railway, using either an overhead contact wire or a third rail, enables the use of electric traction motors. Compared with internal combustion prime movers, these are around 2.5 times more efficient. This, for the future, is a highly valuable energy-related advantage. The other two energy advantages possessed by rail transport are the low rolling resistance of a vehicle with steel wheels on steel rails, and the low aerodynamic resistance of a train of vehicles, where the ratio of length to cross-sectional area can be very high.

As a result of all three of these positive factors is that railway has a very low ratio of energy consumed per unit of transport work done (for example, the haulage of a long rake of freight wagons behind just one locomotive, compared with a single HGV with semi-trailer). Bearing in mind current international concern over fossil fuel usage, environmental protection and climatic change, this is a very important consideration.

When we refer to vehicles with electric traction, we are considering the drivelines involved. Electric traction covers not only electric vehicles, those which receive an electric power supply, but other types as well, the three categories being:

• dependent electric traction vehicles. These rely for their power either on an overhead power line (using a pantograph) or a third or fourth rail (using a current collection shoe). The infrastructure consists of electricity substations which transform the electricity from the national grid into a form (voltage) suitable for use by the vehicles. Such vehicles are not equipped with any means of storing electrical power.
• independent electric traction vehicles. Such vehicles are fitted with an autonomous power source, such as an internal combustion engine, which drives an electricity generator. No electric traction infrastructure is necessary.
• semi-dependent electric traction vehicles. These vehicles are fitted with an electric energy storage device, for example an electrochemical accumulator (battery) or a two-layer supercapacitor. These give them a limited range of autonomous operation, but recharging must take place from time to time. A recharging point infrastructure has to be provided.

In the future it is likely that the main direction for rail transport will be in the continued development of electrification, and thus of dependent electric traction. That means the systematic electrification of non-electrified railways, because all rail-based urban transport systems - tram and metro networks - are already electrified. However, the economic returns from an electrification strategy are proportional to the amount of traffic a line or network carries, so the busiest non-electrified railways will be the first to be electrified.

Rail Transport: Semi-Dependent Electric Traction

As the size of the electrified network increases, favourable conditions are created both for the development of dependent electric traction vehicles, and also for semi-dependent electric traction vehicles:

• as the length of the electrified network increases, the length of remaining non-electrified lines decreases. This means that the operating requirements for the action radius (range) of vehicles equipped with means of energy storage (semi-dependent electric traction vehicles) decreases.
• an increase in the length and number of electrified lines also results in an increase in the number of locations where recharging of the energy storage systems of semi-dependent electric traction vehicles can take place while in motion (under catenary) or while at rest (at stations or depots).

It should also be recalled that the low rolling resistance and low aerodynamic resistance of rail vehicles, which result in the economic use of energy, also favour the use of systems of semi-dependent electric traction systems, extending the vehicles’ operating range compared with that possible with road vehicles.

At present there is considerable focus on developing road vehicles with electric energy storage systems. The reason here is not related to any suitability of road transport for the use of electric energy storage, but is on account of the fact that roads (except those used for trolleybus networks) are not equipped with catenary. The one possible option available is the battery-powered road vehicle.

The introduction of these is still being furthered in spite of the physical fact mentioned at the beginning of the article that battery in a road vehicle has to be used for a greater amount of traction work (high rolling resistance and high aerodynamic resistance) consumed per unit of transport work done than one
in a rail vehicle. Hence the amount of electricity consumed from a road vehicle battery is proportionately greater than that used by a battery-powered rail vehicle.

In the near future, railways will have to address the question of how they can provide zero-emission transport on non-electrified lines. First, it is necessary to be aware of what benefits are derived from modern electric traction. It uses not only certain long-established features (traction motors, traction transformers, current collectors and suchlike), but also new electrical engineering technologies (new types of energy storage systems and semiconductor converters for their charging and discharging, microprocessor control systems, data communication devices, and suchlike). On these two pages nine possible basic configurations for an electric traction driveline are summarised.

Range Extenders

The technology of electrochemical accumulators is evolving rapidly. In the 20th century the main product was the lead battery which for traction purposes had a specific energy of 25 kWh/t. Then around a decade or so ago came developments aimed at producing batteries which needed only infrequent charging, for use in personal electronic devices, such as laptops and mobile phones. Subsequently the first lithium batteries for vehicles (especially for electric buses) were also produced. These had a specific energy output of around 100 kWh/t. Further refinement, particularly for use in private cars, gives the lithium battery a specific energy output of as much as 200 kWh/t, and its evolution will not stop there.

While developments in battery technology involving higher specific power outputs and higher specific
energy serve to increase vehicle range, other developments are aimed at reducing the need to have large quantities of energy stored on board vehicles and reducing the size of installed energy storage. A typical example - in the past battery vehicles were maintained on a 24-hour cycle, being in use during the day, and being recharged at night. The modern trend is to realise fast top-up battery charging at intermediate stops or at the termini of routes.

There are also various ways of extending operational range without direct recourse to the battery: energy can be drawn from other sources than the battery both for the powering of main and auxiliary drives. What sort of range extenders are available for vehicles fitted with batteries?

• a dependent electric vehicle on an existing electrification system (see Fig. 4), which directly supplies the traction equipment and the auxiliary drives, and can also recharge the battery, both while the vehicle is in motion and when it is at a standstill. It is a cheap, widely available source of recharging energy, with conventional electrification networks still being extended.
• a hybrid vehicle with an internal combustion engine, with a battery and the ability to also recharge its battery from fixed installations (see Fig. 7). The provision of an internal combustion engine with an electric generator acts as a range extender. This configuration, however, still relies on fossil fuel technology, and can no longer be regarded as having a long term future.
• a vehicle with a hydrogen fuel cell, an electric energy accumulator and with the ability to recharge the battery from fixed infrastructure (see Fig. 9). The hydrogen storage tank together with the hydrogen fuel cell serve as a range extender. The one advantage of this configuration is that the hydrogen delivers a high level of specific energy. The main disadvantages are the low energy efficiency of the conversion of electricity to hydrogen and back to electricity, and also the need to provide a new infrastructure of refuelling points.

Electric Energy Storage Devices

The function of mobile electrical energy storage is usually realised by means of electrochemical batteries. At present the most popular battery used on board both rail and road vehicles is the lithium battery, whose design is being progressively modified and enhanced, to improve performance. Among the desired characteristics are high specific energy, high specific discharge power, high specific charging power, long service life and low cost. For some specific applications, like rapid discharging, or rapid charging when the vehicle is stationary at stops, an alternative form of energy storage can be double-layer capacitors, or a combination supercapacitor and battery. Both Li-Ion batteries and double-layer capacitors are maintenance-free.

Hydrogen production by electrolysis and the subsequent conversion of hydrogen into electricity via fuel cells, viewed as a chain activity, can also be regarded as an open-circuit electrical battery.

Although thanks to its high specific energy, hydrogen used as a fuel provides a vehicle with a much wider geographical operating range than do electrochemical accumulators, which means that refuelling locations need only be few and far between, a vehicle with electrochemical accumulators does not need such as a great range, while the recharging of a battery is a much easier procedure, since this can be done using the electrification infrastructure either while the vehicle is in motion or at standstill.

1. An electricity-dependent (catenary-dependent) vehicle, such as a conventional electric locomotive. Its traction equipment consists of a power supply (P) drawn from the catenary (L), the input circuit (V), the pulse inverter (S) and the traction motor (M). Braking energy can be recuperated into the power grid or dissipated as heat in the brake resistors (R), if the vehicle has these.

2. An electricity-independent vehicle with an internal combustion engine, such as a conventional diesel locomotive with electric power transmission. Its traction equipment comprises a fuel tank (T), the internal combustion engine (D), a traction generator with a rectifier (G), a pulse inverter (S) and a traction motor (M). Braking energy can be dissipated in the brake resistor.

3. An electric semi-dependent (battery) vehicle, such as the prototype Class A 219.0 battery-powered two-axle shunter, built by ČKD in 1993, or conventional electric road vehicles. The traction equipment consists of a power supply (P) from a fixed location (Z), the charging converter (N), the electric energy storage or battery (B), the pulse inverter (S) and the traction motor (M). The battery is used both to store energy drawn from the external power supply and to store braking energy regenerated by the traction motor.

4. An electricity-dependent vehicle with an auxiliary battery, such as a partial trolleybus or an EMU fitted with a battery. The traction equipment consists of a power supply (P) drawn from the catenary (L), an input circuit (V), a pulse inverter (S) and the traction motor (M). There is also a circuit with a charging and discharging converter (N/V) and an electric accumulator (A), used for operation away from the catenary. The accumulator also serves as a store for energy drawn from the overhead wire and for braking energy regenerated by the traction motor.

5. An electricity-dependent vehicle with an internal combustion engine, such as an electric locomotive with a Last Mile auxiliary diesel for shunting. The traction equipment consists of a power supply (P) drawn from the catenary (L), the input circuit (V), the pulse inverter (S) and the traction motor (M). There is also a curcuit with the fuel tank (T), the internal combustion engine (D) and a traction generator with a rectifier (G), used for operation away from the catenary. This configuration always works using only one of the energy sources (catenary or diesel engine). It is not possible to combine their performance.

6. A hybrid vehicle with an internal combustion engine and a battery, such as the ČKD-built Class TA 436.0 four-axle shunter, or hybrid cars. The traction driveline consists of a fuel tank (T), an internal combustion engine (D), a traction generator with a rectifier (G), an accumulator (A), a pulse inverter (S) and a traction motor (M). The accumulator serves to compensate the vehicle’s energy balance: it stores energy supplied by the internal combustion engine and braking energy regenerated by the traction motor. Both the battery and the internal combustion engine can work together and their outputs are thus combined. This results in the vehicle’s performance being increased over and above the rated power of the internal combustion engine.

7. A hybrid vehicle with an internal combustion engine and a battery, which can be charged from the electricity grid, such as plug-in hybrid cars. The traction equipment consists of a fuel tank (T), an internal combustion engine (D), a traction generator with a rectifier (G), an accumulator (A), a pulse inverter (S) and a traction motor (M), and is supplemented by a power supply (P) from a fixed location (Z) and a charging converter (N). The battery serves to equalise the vehicle’s energetic balance, storing the energy supplied from the generator powered by the internal combustion engine, storing the braking energy regenerated by the traction motor, and storing energy obtained from the national grid by plugging in to power sockets.

8. A vehicle with fuel cells and an accumulator for electric energy storage, such as hydrogen fuel cell cars and rail vehicles. The traction equipment consists of a fuel tank (H), a fuel cell (F), a charging and discharging converter (N/V), an accumulator (A), a pulse inverter (S) and a traction motor (M). The battery serves to equalise the vehicle’s energetic balance - to store the energy supplied by the fuel cell and the braking energy regenerated by the traction motor. Both power sources (battery and fuel cell) can work together, and as a result their outputs can be combined.

9. A vehicle with fuel cells and a storage accumulator, with the ability for recharging from a fixed point via the national grid, such as hydrogen fuel cell plug-in road vehicles. The traction equipment consists of a fuel tank (H), a fuel cell (F), a charging and discharging converter (N/V), an accumulator (A), a pulse inverter (S) and a traction motor (M) and is supplemented by the plug-in power supply (P) taken from the fixed source (Z) and the charging converter (N). The battery serves to equalise the vehicle’s energetic balance - storing the energy supplied by the fuel cell, storing the braking energy regenerated by the traction motor, and storing energy obtained by plug-in recharging.

Conclusion

It is envisaged that in the future present trends in the field of electric traction will continue. The primary type of electric rail vehicle will be the dependent electric traction type - in other words, dependent on fixed electrification infrastructure. Electrification of rail networks will continue, and in the future will expand considerably.

There will of course be some railways where electrification is deemed unsuitable, either because of low traffic levels, or because of economic or physical non-viability, and there will also be lines awaiting electrification as programmes evolve. On these lines, it is understandable that efforts will be made to find some environmentally friendly form of traction. A highly rational option is the use of battery-powered vehicles.

These can be considered the definitive option for lines on which electrification infrastructure is deemed infeasible or uneconomic, and also as the most suitable stop-gap measure for lines for which electrification infrastructure is proposed at some future date. The main objective must be to ensure the compatibility of the rolling stock and traction fleet with that of the rail infrastructure energy subsystem.

Electrification of more stretches of the rail network does not necessarily work against developing of battery-powered vehicles for the remaining non-electrified stretches. On the contrary, electrification is a measure which should encourage their use, since the more electrification infrastructure that exists, the more opportunities that exist for battery charging.

Moreover, if vehicles designed for dependent electric traction are built, and are also fitted with batteries, to extend their autonomy, as the electrification network increases in length or is completed, it will only be necessary to remove the batteries, an operation which does not require the vehicles to be scrapped or extensively rebuilt.