HomeElectrificationThe quest for a cleaner railway

The quest for a cleaner railway

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The UK’s railway is eliminating carbon. You must have noticed. The government has pledged to get all diesels off the railway by 2040 and have it “Zero Carbon” by 2050. Scotland, trying to get one over on England as usual, plans to decarbonise its railways by 2035.

But what does that mean? The obvious answer is electric traction, and that means electrifying the railways.

Scotland does indeed have a more developed programme of electrification than England and Wales. But with only 8.4 per cent of Great Britain’s population, and 17 per cent of the railway route miles, to electrify the whole network all will be both an expensive and time-consuming proposition.

Will anyone really electrify the Glasgow to Mallaig and Oban line – the West Highland line – voted the top rail journey in the world by readers of the Wanderlust travel magazine in 2009? How will that look with electrification poles every few hundred metres alongside it?

How clean is your electricity?

And then, of course, there is the question – what is zero carbon? It’s actually a myth, like perpetual motion and the Holy Grail. You can get close but, as they say, “there’s no such thing as a free lunch”. Everything costs something, and part of that cost is in carbon.

True, certain stages of the process don’t generate carbon emissions. Electric trains don’t put out CO2 from their traction motors, but the electricity they are using is likely to have produced carbon when it was generated.

Coal and other fossil fuels produce carbon when burned, that’s obvious. Nuclear power is meant to be clean, but building new power stations uses a lot of resources, and a lot of concrete, and that generates carbon. It’s not much when amortised over the life of the power station, but it’s still not zero.

Wind is carbon free isn’t it? Well, yes, but manufacturing the turbine produced carbon, so that has an impact too. Same for hydro schemes, wave power, solar energy – they all added to industry’s carbon dioxide output when they were made.

The Intergovernmental Panel on Climate Change (IPCC), a United Nations body, publishes figures on the carbon dioxide (CO2) emissions from electricity generation on a whole life basis – including the construction, running and final demolition of the plant. For coal-fired power stations that’s 820 grammes of CO2 per kilowatt-hour (kWh), although, with cleaner coal and more control, the UK government is trying to get that down to 450g/kWh.

Gas-fired power stations do better, at around 250g/kWh.

Then there are the ‘zero carbon’ forms of generation. Taking account of the capital investment and whole-life output, solar energy averages 48g/kWh with a minimum of 18, offshore wind averages 12g/kWh with a minimum of 8, and nuclear also averages 12g/kWh, although Hinkley Point C, which will generate seven per cent of the nation’s power for 60 years, will be around 4.7g/kWh as its start-up emissions are spread over a lot of power produced over its lifetime.

Hinkley Point C (above) will be a base-load station, running all the time. So, what happens when it’s the dead of night and no-one wants electricity? It isn’t wasted – it just recharges the batteries. Huge batteries. A car battery can be rated at about 100 amp-hours, or 1.2kWh. The battery (right) that EDF Renewables has been running at West Burton, near Gainsborough, Lincolnshire, since June 2018 is rated at 24.5MWh, that’s 20,000 times the size! It forms part of National Grid’s 100MWh reserve capacity that is used to correct fluctuations on the grid within less than a second.

Electric traction from batteries

It would seem, then, that electric traction, powered by nuclear or renewable sources, is a close to zero-carbon as we’re going to get. But that doesn’t solve the problem of the cost of electrification.

However, there may be a way to keep that cost down, and a way that’s down to the design of the train, not the infrastructure.

Siemens Mobility makes electric passenger trains. One of its latest orders is for 189 three-Car Desiro ML Cityjet trains for Austrian State Railways (ÖBB). These are electric multiple unit trains, designed to work from ÖBB’s 15kV 16 2/3Hz overhead AC supply.

It’s one of these units that’s particularly interesting. Taken straight off the production line, it has been constructed to incorporate Siemens Mobility’s ‘eco’ technology that will result in an EMU/battery bi-mode. Siemens has fitted a modular LTO battery system to the roof of the train, providing the unit with a range of 50km on batteries alone, with similar ‘off the wires’ performance to it running on AC power. The batteries can be recharged off the AC supply when running on the electrified line, topped up from regenerative braking, and can be fully recharged in as little as 12 minutes.

Battery technology

Lithium-ion batteries were first developed in the 1980s and have been used for mobile devices since the 1990s. On discharge, lithium ions move from the negative electrode (cathode) to the positive electrode (anode) through an electrolyte – the process is reversed on charging. They are quick to charge, have no memory effect (unlike nickel-cadmium batteries) and have a high energy density.

However, the electrolyte is flammable, and early fires caused problems for Samsung Galaxy Note 7 mobile phones and Boeing 787 airliners.

A development of the Li-ion battery, patented in 2001, is the NMC, which uses lithium nickel manganese cobalt oxide for the positive electrode in place of the lithium cobalt/iron/manganese oxides of early examples, with the negative electrode being graphite or another carbon-based material. Electric vehicles such as the Nissan Leaf use this battery technology.

More recently, LTO or lithium-titanate batteries use that material on the surface of their anodes in place of carbon. This allows electrons to enter and leave the electrode more quickly, permitting quicker recharges and giving longer life.

The Siemens X-EMU train uses these LTO battery cells.

The battery packs are part of a fully managed integrated, temperature-controlled system and it is anticipated that they will have a service life of at least 15 years – half of the expected life of the train. They will therefore need only one battery change in their lifetime. A similar arrangement using NMC batteries would typically require three or four changes throughout a train’s life and, although each NMC pack would be cheaper to purchase initially, the LTO battery has a significant advantage in terms of whole-life cost.

Fitting batteries to an EMU like this gives two possibilities. An X-EMU can run off the main electrified routes down an unelectrified branch line on batteries alone. For longer range ‘off-wire’ operation, a recharging station can be provided at the end-of-line terminus or even en-route.

In addition, the train can run through ‘extended neutral sections’ on a main line, electrified using a discontinuous electrification scheme without loss of performance. With this approach, railways could potentially be electrified at a significantly lower cost, resulting from the fact that difficult infrastructure (tunnels and bridges with inadequate clearance) would not be wired, instead relying on the train’s batteries for that portion of the route, with the batteries being recharged when the train reconnects to the AC supply.

The ÖBB Cityjet train completed homologation in August and entered passenger service on 2 September 2019 in the Linz area of Austria. Passengers throughout Austria will have the chance to ride on this exciting train in the coming months.


Siemens Mobility’s ‘eco’ battery technology could also be fitted to a brand-new fleet of 20 Siemens Mireo trains (above) for Ortenau Network 8 in the German state of Baden-Württemberg, to operate both on and off electrified routes, giving the batteries ample time for recharging. The local government wanted an ‘emissions-free’ solution, so the electric/battery units could work well, but the contract award is currently under appeal by another bidder, meaning the award may not be confirmed as planned.

In the United Kingdom, where the more restricted loading gauge probably precludes the batteries being mounted on the roof, existing four-car units could be upgraded to include underfloor mounted Siemens Mobility ‘eco’ battery technology, increasing the potential of existing EMUs by turning them into battery EMU bi-modes.

Graeme Clark, head of business development for Siemens Mobility Rolling Stock in the UK, is keen to point out that, even when running on batteries, these are still electric trains. “Off-wire, they still have EMU acceleration,” he emphasised, “so they will have faster journey times than the diesels they replace, as well as being lighter, far more efficient and significantly cheaper to maintain.”

Improvements in technology are helping all the time. Electric regenerative systems can brake an electric train significantly and efficiently, with energy being returned for re-use to the infrastructure or (to recharge train battery systems), but friction brakes are still needed to bring it to a complete stop. As technology has advanced, the proportion of braking done electrically has increased, significantly reducing brake pad and disc wear and minimising maintenance cost.

The industry’s gradual move from asynchronous electric motors to permanent magnet motors will make a big difference in this area. They will be capable of braking the train to a complete stop, meaning that potentially, mechanical braking can be removed completely and replaced with a simple parking brake!

And there’s more

The other ‘clean’ fuel that’s much touted these days is hydrogen. Like electricity, its cleanliness depends on how it was made.

If it’s made by the ‘steam reformation’ of fossil fuels, particularly natural gas and methane, then significant quantities of both carbon monoxide (CO) and dioxide (CO2) are produced, so it’s not a zero-carbon process.

Some industrial processes produce hydrogen as a waste product. It wasn’t produced by a zero-carbon process, but it would otherwise be burned off and wasted, so using it to power trains is, essentially, recycling.

Then hydrogen can be produced by simply passing an electric current between two electrodes submerged in water. Oxygen comes off at one electrode, hydrogen at the other. There are no other waste products and no pollution.

Once again, the cleanliness of the electricity can be called into question, but if it comes from a wind turbine at 3am when the world is asleep and using very little electricity, then the power is both clean and essentially free, meaning that the hydrogen is also clean and is produced for only the infrastructure cost of the plant.

It can also come from nuclear power. EDF Energy R&D, in partnership with Lancaster University, Atkins, European Institute for Energy Research (EIFER) and EDF Group’s Hydrogen subsidiary Hynamics, is looking to design a hydrogen gas generation plant at Heysham power stations. The project, which is funded as part of the Department for Business, Energy and Industrial Strategy’s £20 million Hydrogen Supply programme, runs in two phases – the first is a feasibility study, which will be completed by September 2019, and the second (subject to selection by the UK government) will be the pilot demonstration, starting in 2020 and running for two years.

To use this ‘free’ hydrogen, Siemens, which makes both wind turbines and the electolysers that produce hydrogen, has designed the ‘eco’ concept to include an option for hydrogen fuel cells that will charge the batteries, giving extra range ‘off the wires’ or even allowing it to run on non-electrified long distance non-electrified routes.

Siemens is working with Canadian company Ballard, a market leader in fuel-cell production, to develop compact, lightweight high-power fuel cells that can be fitted easily onto trains. The fuel cells will recharge the batteries, which then power the train. This approach reduces noise, as the fuel cells are running under constant load, reduces hydrogen consumption and leads to longer fuel-cell life.

Will the future of passenger trains be overhead/battery/hydrogen hybrids? Quite possibly. The first Siemens ‘eco’ train powered by a hydrogen fuel cell will be on test in the near future and offers an excellent solution to the replacement of diesel trains and an alternative environmentally friendly approach to lines which could never justify electrification.

But all of this development leaves one unanswered question – what to do about freight trains? Here in the UK, the freight-only lines are not electrified, the trains are heavy, and batteries, with no overhead wires to recharge them, would not last long.

Is electrifying the whole network the only solution? Time will tell…

Thanks to Graeme Clark of Siemens Mobility and to Martyn Butlin and Andrew Cockroft of EDF for their help in preparing this article.


  1. Good see some positive reporting on the energy alternatives available to the rail industry for the future in decarbonising the rail network. I had the opportunity to travel on the Desiro on the 31st October 2019 when it ran from Linz to St Nikola Struden and return. In Transport Scotland we are taking a good look at these alternative energy sources for traction power in conjunction with the rail industry, enabling us to be an informed client for the future.


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