Stuttgart was connected to the town of Horb am Neckar by a railroad line built between 1874 and 1879. Since 24 January 2022, a battery-powered train has been running on this 67.2 km line in Baden-Württemberg and on the 16.8 km line between Pleinfeld and Gunzenhausen in Bavaria. The latter is one of 450 lines in Germany that have been used only by diesel locomotives so far. But now a four-month test is underway to see if battery trains could replace them. The choice of these two lines is based on a thorough analysis by the TU Berlin Chair of Railway Operations and Infrastructure and the Chair of Methods for Product Development and Mechatronics.
"Our task was to collect requirements for the trains and the rail infrastructure so that the battery being developed would become a viable alternative to diesel," says Ulrich Zimmermann, a research associate at the Chair of Railway Operations and Infrastructure. Pavel Boev, research assistant at the Chair of Methods for Product Development and Mechatronics, also did a profitability analysis and lifecycle assessment.
The analysis of the rail network showed, among other things, that as many as 360 lines used by diesel locomotives already have varying shares of electric overhead lines. Moreover, most diesel-run lines are 80 to 90 km long. The range of the battery must be designed for this. One technical challenge is that while charging shouldn’t take too long, fast charging can damage the battery over time. "A diesel train can resume driving after its stop after three or four minutes. A battery-run train also needs to resume operations fast to keep the schedule," says Zimmermann. If this isn’t solved, the battery train won’t be able to replace the diesel locomotive. "Our department developed a tool to answer important questions on electrifying a rail network, such as feasibility on the chosen line, the number of required battery trains when taking into account charging times, the number of charging stations, or the operational integration of the charging process," says Boev.
Replacing diesel trains with battery-powered trains may help reduce changeovers, which are always a weak point in the schedule. The reason is that diesel trains end at electrified main lines, where passengers then need to switch to electric trains. One result of our investigations is that, although generalized statements are difficult, lines between 40 and 45 kilometers in length are generally suitable for battery operation and require minor infrastructure adjustments at most," says Zimmermann. Pavel Boev's feasibility analysis showed that, under certain conditions, battery trains can be 20 to 30 percent cheaper than diesel locomotives, if the expected service life is between 25 and 30 years. "And if 100 percent of the electricity used for charging comes from renewable sources, carbon emissions can be reduced by 80 to 90 percent," says Boev. The test will run with passenger traffic till early May. Two different charging scenarios are tested: through overhead lines during operation or charging at the terminal stations. The researchers are also expecting data on how reliable their models are, so they can apply them to other lines without having to test them in practice.
Author: Sybille Nitsche