The transport industry is currently responsible for around a quarter of GHG emissions worldwide, with a forecasted increased share for the next coming years. The rail industry is one of the most energy efficient and less polluting transport mode. In European Union (E.U.), for instance, the rail sector currently accounts for 1.5% of E.U. transport GHG emissions, with over 8.5% of total market share, while on the United States (U.S.), it accounts for 1.9% of transport GHG emissions (0.6% for freight railroads, with a share of around 40% of long distance freight volumes, in a ton-mile basis).
Despite this remarkable environmental and energetic performance, the rail sector is also strongly committed with the compromise of a continuous reduction of its specific GHG emissions, for both the passenger (passenger-km) and freight (tone-km) services, to comply with the world effort, to keep the overall increase in average global temperature below 2 °C, compared to pre-industrial levels.
One of the main strategies to reach these ambitious targets is to increase the rail electrification share, with the massive use of electric powertrains, with their inherent improved efficiency and zero local emission performance, compared to the internal combustion engines powered counterparts.
The conventional rail electrification, based on a third-rail or overhead line, might be cost and environmental effective for city and inter-city intensively used routes. However, secondary lines and regional routes, lack the required traffic density for conventional electrification, given the high infrastructure costs required.
In this context, alternative rail electrification routes, such as the use of Battery Electric Rail (BER) powertrains, have been seen as a promising electrification alternative to comply with rail industry compromises, to reduce its GHG share and efforts to improve energy efficiency, especially in the low density traffic rail segments.
It is noteworthy that alternative rail powertrains have launched the debate around traction technology selection for rail fleet renewal, given the average 30 year lifetime of rail equipment, which ultimately require immediate policies and actions to guarantee the long term rail environmental and efficiency targets.
In the E.U., BER has been evaluated as alternatives for non electrified low density rail segments (mainly for inter-regional passenger transport), with extensions in the 40–80 km range, given the medium term strategic decision to ban the diesel powertrains, currently used on Diesel Multiple Units (DMU). In the rail freight segment, there are some U.S. preliminary BER initiatives, focused on both shunt/switch locomotives (given their low power and range requirements, compared to road locomotives), and even line-haul locomotives, the later with a limited potential, given their large power and range requirements.
However, prior to the widespread use of BER, there are some challenges to be taken up, such as battery technologies improvement (basically the battery chemistry, to meet the harsh rail operational requirements), charging infrastructure, sustainable electricity cost and availability, as well as operational impacts (such as the required charging intervals and the use of battery tender cars on rail productivity).
This work presents an unbiased assessment of battery rail technology (for both the passenger and freight sectors), based on the state of the art technical sources, with a focus on battery technology and infrastructure topics, weighted against rail operational requirements.
Finally, there are presented some case studies, with BER experiences and prototypes, showing preliminary BER outcomes, followed by the technological and operational challenges to be faced, prior to its commercial use in specific rail niche segments.