Significant technical, regulatory and media attention has recently been given to the use of electrical storage batteries onboard a line-haul (long-distance) locomotive or “energy storage tender” (coupled adjacent to a locomotive) as a means of improving railroad fuel efficiency and reducing freight locomotive exhaust emissions. The extent to which electrical energy stored onboard could supplement or replace diesel generated power has yet to be quantified or proven. There are significant technical design, maintainability, logistical and safety challenges to making this technology commonplace, especially for over-the-road (line-haul) freight trains.

The use of electrical batteries to provide some amount of point-source fuel- and/or emissions-free locomotive power is not a new concept. Recent claims that onboard storage of locomotive propulsion energy is “new locomotive technology” are unfounded. The world’s first all-battery-powered locomotive was built in 1838 only 34 years after the world’s first steam locomotive operated. A total of 126 identifiable locomotives using onboard batteries to store propulsion energy have been built and operated to some extent in the United States (US) since 1920. Almost all were low-power switching locomotives and none are currently in revenue freight service. Two high-horsepower line-haul experimental engineering test locomotives with an experimental battery design and regenerative dynamic braking have been built (in 2004 and 2007) but very little revenue service testing has occurred.

This paper reviews propulsion battery-equipped locomotives over the past 95 years in the US, and discusses future options and possibilities including the technical and logistical challenges to such propulsion.

Capturing dynamic braking energy (developed by locomotive traction motors during deceleration or downhill operation) could be a source of onboard battery recharging, but will require significant additional locomotive control system development work to achieve practicality. New battery technologies are being developed but none are yet practical for large-scale locomotive applications. Retrofitting of large amounts of onboard battery storage on existing (or even future) diesel-electric locomotives will be limited by onboard space constraints. The development and use of energy storage “tenders” will bring complications to locomotive and train operations to make effective use (if commercialized) practical and safe.

This paper is also intended to provide technical background and clarity for various regulatory agencies regarding battery energy storage technologies for future locomotive propulsion.

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