Scientists from the Sapienza University of Rome have created a digital model of a hybrid train powered by hydrogen fuel cells and batteries. This MATLAB-based simulator demonstrates train performance on real railway lines and makes it possible to select the optimal power-to-capacity ratio needed to replace diesel traction with a clean energy source.
The replacement of diesel locomotives with another energy source remains a pressing issue on Europe’s transport agenda. According to researchers, only 57% of the European Union’s railway network is currently electrified, with this indicator falling below one-third in Italy. For many regional routes, it is too expensive and technically challenging to build overhead lines, which is why diesel trains continue to operate on existing lines, increasing the industry’s carbon footprint. Still, rail transport is considered the most environmentally-friendly mode of land transport, and the success of Europe’s decarbonization strategy hinges on how quickly fossil fuels can be phased out. Hydrogen is seen as the most promising alternative, since hydrogen use in fuel cells produces nothing but water, helps reduce noise and improves overall energy efficiency. At the same time, fuel cells are sensitive to sudden changes in power, which is why engineers are seeking balanced solutions, such as hybrid systems in which hydrogen units operate in tandem with batteries.
Such is the hybrid technology proposed by the Italian scientists. In their model, the train receives energy from two complementary sources: a hydrogen fuel cell, which generates electricity, and a lithium iron phosphate battery, which smooths out load peaks and stores energy during braking. The two sources are connected via a common busbar, which powers the traction motor and auxiliary systems. Energy flow control is provided by a special controller, which maintains stable operation of the fuel cell and uses the battery to offset short-term fluctuations in power consumption.
In order to find the optimal balance between fuel cell power and battery capacity, the researchers introduced two parameters. The first parameter (m) reflects the proportion of maximum engine power provided by the fuel cell, while the second one (n) represents the relative size of the battery compared to what could power the entire train. By varying these parameters, the scientists analyzed hydrogen consumption, battery load, equipment wear rate and the final cost per kilometer. Their calculations included capital equipment costs and the cost of hydrogen and electricity, as well as the cost of component replacement during operation.
The simulations were conducted on three real Italian routes: a long, flat route in Calabria, a hilly route in Tuscany and a short, mountainous route in Piedmont. For each section, the program calculated the train’s movement, taking into account the weight of the train, track gradients, the number of stops and speed limits. All energy flows and battery charge levels were monitored at each stage of the journey. The model also accounted for equipment wear, using equations to calculate how frequent load changes reduce fuel cell power and how the depth of discharge affects battery life.
The results showed that if the fuel cell’s power is insufficient or the battery’s capacity is too small, the train can neither recharge quickly nor cover the whole route. If the fuel cell is too powerful, the system becomes more expensive and wears out the battery faster. The optimal ratio turned out to be one in which the fuel cell provides roughly half of the peak demand (m = 0.45–0.50) and the battery has roughly 20% of its full capacity (n = 0.20). With this ratio, the train covers the route safely and the total operating cost goes down to EUR 4.5 per km, while for diesel trains this figure is usually between EUR 6 and 8.
However, the final operating cost depended strongly on the nature of the route. For instance, only five fuel cell replacements would be required over 20 years of service on a flat section, whereas in mountainous conditions more than 20 replacements would be needed. At the same time, fuel accounted for only a small portion of the total costs: up to 80% of the costs went to equipment maintenance and replacement, primarily for fuel cells and batteries.
Therefore, the study shows that a universal solution for hydrogen trains does not currently exist. This means that the configuration of the hybrid system must be tailored to each route. On short and complex routes, it makes sense to increase the proportion of batteries to smooth out power fluctuations and extend the life of the fuel cells, while on long and flat sections, the hydrogen component should be increased to ensure stable system operation with less battery load.
