Involved in hydrogen fuel cell research and development, Gaël Maranzana, a researcher at LEMTA, takes stock of future hydrogen trains.
There are about 20,000 kilometers of railway tracks that allow the circulation of the SNCF’s TER trains, but only 12,000 are electrified to date. The reason? The cost of electrifying a train line is prohibitive, in the order of 1M€/km.
Services on these non-electrified lines are provided by diesel locomotives whose greenhouse gas emissions per passenger and per kilometer are in practice equivalent to the emissions of an automobile. The sustainable maintenance of less frequented lines therefore requires the development of carbon-free traction chains. The SNCF is committed to phasing out diesel in 2035.
For this heavy transport application, lithium batteries used in cars are not suitable because their weight, cost and recharging constraints would be too high. The optimal clean solution, to date, is based on the hydrogen carrier. The first hydrogen-powered trains have been running in Germany since 2018 and the SNCF has just placed an order for 15 trainsets that will enter service in France from 2025. A TER hydrogen train carries about 100 kg of gaseous hydrogen stored in tanks at a pressure of 350 bars. This gives it an autonomy of 1000 km.
HOW DOES A HYDROGEN TRAIN WORK?
In such a train, hydrogen and oxygen from the air are converted by the fuel cell into electricity, heat and water. If the hydrogen is produced by electrolysis from renewable electricity, there are therefore no emissions of fine particles, nitrogen oxides, carbon monoxide, and very few greenhouse gas emissions (limited to emissions related to the manufacturing and recycling of the systems).
The power of the fuel cell is 200Kw. It is supplemented by a 111kWh lithium-ion battery pack that can deliver a power of 450Kw. It is therefore a hybrid locomotive. The presence of the battery makes it possible on the one hand to increase the maximum power for accelerations and on the other hand to recover the braking energy during decelerations.
RESEARCH FOR THE FUTURE
This hydrogen solution for railways is very attractive on paper, but it is still quite expensive. The service life and reliability of the fuel cell system also needs to be improved. At LEMTA, we have been working on these issues for twenty years. At the scale of the fuel cell cell, we are seeking to understand the physical mechanisms that lead to the degradation of the materials constituting the core of the cell. Based on this detailed understanding, we implement control laws and develop architectures that enable us to control the system made up of the cell and its auxiliaries in an optimal way, in order to increase its reliability and durability.
The ageing of fuel cell cells (several hundred cells are stacked to form a stack) is a snowball phenomenon: the more a cell is degraded, the faster it degrades. This is due to the fact that all cells are electrically connected in series: each cell must produce the same current regardless of its state of health. And when a cell is damaged, the whole battery must be shut down. To overcome this problem, we have developed an innovative battery architecture that we have patented [1] and which, thanks to adapted power electronics [2], balances the cell voltages. When a cell begins to age, the system relieves it of part of the current to prevent it from degrading further. And when a cell no longer functions, our system can isolate it, allowing the other cells to continue to function to produce the necessary electrical energy and thus guarantee continuity of service.
This example of multidisciplinary research illustrates how LEMTA is participating in the development of “stationary onboard fuel cell” systems, in particular to put hydrogen on rails.
This article has been written and published by the Conference of University Presidents in the Research Moment N°16: Hydrogen, the essential element of our future. Find this issue on their website.
[1] G. Maranzana, J. Dillet, O. Lottin, S. Didierjean, A. Thomas, IMPROVED FUEL CELL. Patent n° : WO/2014/060198. 2014.
[2] M. Bahrami. J.-P. Martin, S. Pierfederici, G. Maranzana, F. Meibody-Tabar, S. Didierjean, J. Dillet, M. Weber, M. Zandi, R. Gavaksaz, Power equalizer for fuel cell energy management system, IEEE Transaction On Industrial Electronics, 2019