Keywords: hybrid, battery, sizing, discontinuous electrification, zero emissions.

There is currently significant pressure on the transport sector to reduce CO2 emissions. Rail vehicles are currently one of the most efficient forms of transport, particularly when electrically propelled. However, the requisite infrastructure enabling this limits flexibility, with electrification of the whole network prohibitively expensive. One alternative is the use of on-board energy storage systems, such as batteries, which enable vehicles to operate on discontinuously electrified, or even completely non-electrified, lines. There is, however, a multitude of possible battery configurations. Thus, a high-level battery configuration tool for batterification of rail vehicles is presented. This tool allows a comparison of different chemistries, cell formats and cell sizes for known energy, power and voltage requirements. The tool can be used to prioritise solutions based on combinations of number of cells, mass, and volume. The benefit of the tool is that it allows a quick and early investigation into the feasibility of hybridisation and/or batterification of rail vehicles. Herein, this is used to compare the performance of four potential lithium-ion batteries, developed using currently available automotive technologies: lithium iron phosphate (LFP), nickel cobalt manganese oxide (NCM), nickel cobalt aluminium (NCA) and lithium titanate (LTO). Whilst NCM and NCA offer potential in the automotive sector due to their higher discharge rates, this is less important in the rail sector due to symmetry in the acceleration and deceleration rates. Meanwhile LFP offers lower volume and mass than other chemistries. LTO offers up to 10 times cycle life, with the total cost of the battery over the life of the pack an important consideration for vehicle manufacturers. It should be noted that detailed modelling of the energy and power requirements, considering the exact vehicle and route parameters, is required to specify the battery system further. The battery pack configuration tool presented in this paper provides a methodology for comparing the technical parameters of different cells, whilst also offering manufacturers considerable learning opportunities. However, the specific choice of cell/configuration can ultimately be guided by other factors, including battery lifetime and economic viability.

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