With cost-effective electrification, we want to decarbonize our “small lines” faster using a new operating mode combined with battery trains. How does it function? What technical challenges need to be overcome? Where is it being deployed? We put these questions, and more, to Vincent Delcourt, Christian Courtois and Thomas Joindot.

Vincent Delcourt: 

head of SNCF’s Performance, Strategy and Tech Intelligence unit, and manager of the SNCF Synapses experts network’s Energy cluster.

Christian Courtois: 

head of SNCF Réseau’s Electric Traction Division

Thomas Joindot: 

Technical Director of SNCF Réseau

Christian Courtois (C.C.): It’s a new traction method that requires fixed installations and rolling stock that can supplement both diesel and electric propulsion. So it’s based on new technologies for trains with onboard energy storage systems. That’s one aspect of the strategy. The other involves what you could call “just enough” electrification, which might be easier to understand than the term “cost-effective”.

C.C.: It means taking a very simple approach—identifying an operating need and meeting it as efficiently as possible.

Vincent Delcourt (V.D.): That’s how you should interpret the meaning of “cost-effective”. But make no mistake, cost-effective does not mean low-cost! It’s more about tailoring the solution to the need. You see, heavy freight trains and low-frequency lines have very different electrification needs—that’s obvious. So, the first question we always ask ourselves is: “How should we rethink the line’s electrification given its power supply needs?”

V.D.: Up until now, if you said “electric train” people would automatically think overhead wires. But recent technological innovations have changed all that. Now, battery technology means a train can have its own power supply onboard. So we no longer need to wire an entire line. That’s a great advantage because the cost of electrifying a line can vary significantly from one place to another. So now we’re thinking that while a battery train might not have the range for hundreds of kilometres, it is definitely capable of covering the short distances on sections that would be very costly to wire. So what we’re really doing here is fleshing out a new business model.

C.C.: Yes, it’s in line with SNCF’s strategy to decarbonize rail. Remember, we aim to reach net-zero emissions by 2050. That’s why discussions about cost-effective electrification concern both passenger and freight trains. Nowadays, it doesn’t make sense to see diesel freight trains running under catenaries, but they often do. That’s because they have to cover a few kilometres to get to their unwired loading or offloading terminals. This final segment is referred to as the “last mile”. To avoid uncoupling locomotives just before they get to these junctions, we’re looking for the simplest way to electrify them.

V.D.: At SNCF Group, everything started to gather speed in 2015 when the French government introduced the National Low-Carbon Strategy (NLCS). This roadmap outlines how we—and all EU countries—are to achieve carbon neutrality by 2050. As the transport sector contributes a significant share of global CO2 emissions, SNCF set itself ambitious targets from the get-go. For example, we aim to cut our greenhouse gas (GHG) emissions by 30% by 2030. Large companies like SNCF have a key role to play and are hard at work charting this decarbonization trajectory. To meet the targets, we’re convinced there’s no silver bullet, but rather a range of solutions. Cost-effective electrification is one, as are hybrid, battery, hydrogen and biofuel trains.

C.C.: France’s regions, which are the local mobility authorities, fully support this decarbonization policy.

C.C.: Only 1,415 km out of 15,000 km are electrified.

V.D.: That’s why it’s essential to roll out other decarbonization solutions—and we’re doing just that with help from local authorities.

C.C.: We’re focusing on two types: freight—we want to double its modal share—and lines “of regional importance”, by which we mean TER regional passenger service. But we also want to develop regional RER commuter rail.

C.C.: In rail freight, the stretches between Chagny and Nevers in central France, and between Amiens and Rang-du-Fliers in northern France, spring to mind. Also, basically all the lines that bypass Paris to the North and South. As far as TERs are concerned, we’re currently introducing battery trains between Marseille and Aix in southern France.

C.C.: First, because it’s a very busy line. The Marseille-Gardanne-Aix project aims to turn this line into a regional express service like the RER. Four years ago, the regional authorities commissioned a study to explore existing ways of operating an electric train off the wire. They went for battery trains. The plan is to use the mid-life refurbishment of the dual-mode high-capacity trains on this line to replace their two diesel engines with batteries.

V.D.: We could have opted for hybrid trains, but the regional authorities preferred a completely carbon-free solution. So we had 3 options: electrify the entire line—which raised funding issues—hydrogen, or cost-effective electrification. We went with the last option, which we felt was best suited.

C.C.: They only need to run along the 6 km of catenary-equipped lines outside Marseille to recharge their batteries. That gives them enough power to reach their destination autonomously. They will also need to use the charging substations we’ve installed in stations.

V.D.: About 20 to 30 minutes at the static charging points. I’d like to clarify that the battery isn’t necessarily flat when the trains get to Aix-en-Provence. The trains have enough time to recharge while they stop/wait at the station.

V.D.: By the end of 2024, a dozen modified high-capacity trains will be running on the Aix-en-Provence - Marseille line. In other words, we can have the trainsets modified, tested and ready for commercial operation within a very short time. We’re also conducting these tests in 4 other French regions.

Thomas Joindot (T.J.): Yes, of course, but the overall cost will come down. It’s not only about decarbonization. Diesel traction also costs. In fact, if you consider the all-in cost per kilometre of rail freight, diesel is 5 times more expensive than electric propulsion. So running trains on thermal power is not in a rail operator’s financial interest, at least not given the price of electricity in France today.

C.C.: There are large and small dual-mode locomotives that run on both electricity drawn from overhead catenaries and a thermal power supply, but they are all still diesel-powered. Powerful battery locomotives for freight don’t exist yet. Freight trains weigh between 1,500 and 2,000 metric tonnes, and you’d need wagon-loads of batteries to pull them.

V.D.: We’re starting to see battery and fuel cell alternatives for shunting and marshalling locomotives. But to date, nothing matches the traction power of a diesel engine. Finding new traction solutions for long-distance freight is something our tech intelligence is focusing on.

C.C.: I’m not sure what “very expensive” means. It’s all relative. For example, a hydrogen train costs €14 million. That’s the same as a 14-kilometre high-speed line that lasts 100 years and needs very little maintenance.

C.C.: Currently, 85% of rail traffic runs on 50% of the network, which is electrified. That means only 15% of rail traffic runs on the remaining 50% of unwired track. Based on this fact alone—not to mention the benefits new technology will bring to rail, or the long-term investment required—it’s difficult to justify electrifying the entire network. And yet, until very recently, the regional authorities were in favour of wiring the network. For example, the Grand Est (Eastern central France) regional authorities decided to electrify the Paris-Gretz-Troyes line. There’s also the issue of improving network connections. A new electrified line means more rerouting options when maintenance work is needed.

T.J.: Well, there are two ways of looking at the issue. Either you see it from a systems perspective, i.e. “electrification equals more maintenance for the infrastructure manager”. And it’s true that catenary maintenance has a cost, but it’s relatively low. Or you can take a more analytical view and compare that cost with the operating and maintenance costs of thermal- or hydrogen-powered rolling stock, which are actually higher than for electric trainsets. So it’s true that it’s about achieving the right balance—hydrogen can’t be the only alternative to electrification.

C.C.: Yes, because you can’t focus on just the infrastructure or just the rolling stock. You have to adopt a holistic approach during the feasibility studies, an approach that encompasses all the issues—investment, operating costs, and carbon footprint.

V.D.: Other regional authorities are watching this project closely. Some of them are already testing battery trains with SNCF and Alstom, and will obviously be actively involved in deploying that solution in their regions.