De-carbonising public transport

Transport is a major contributor to greenhouse gases and other harmful emissions worldwide and efforts to reduce these are important for all forms of public transport. Moving from oil to low-carbon energy for transport raises important issues in terms of electrical power generation and distribution systems. 

class 230 train
A Vivarail battery-powered prototype Class 230 unit at Bo’ness station on the Bo’ness and Kinneil Railway during a short visit for demonstration trips on 11th October 2018. Vivarail battery-powered trains have recently been approved for passenger service in the UK and other train manufacturers now have battery-powered and also hybrid hydrogen fuel-cell/battery-electric trains under development. It is perhaps significant for Scotland that Hitachi has made proposals for the addition of batteries to Class 385 electric multiple units to allow operation “beyond the wires”. (Photograph D.J. Murray-Smith)

At our 2019 AGM in Perth, our Vice-chairman and Strategy Officer (and retired engineering professor), David Murray-Smith, gave a presentation on the technical aspects of de-carbonising public transport. Since then, he has written a series of reports which carry these ideas forward.

Developments in Electrical Battery, Fuel Cell and Energy Recovery Systems outlines the current status of batteries, hydrogen fuel cells and short-term energy storage systems for railway and tramway applications, discusses issues associated with regenerative braking and provides a brief account of transport applications in the United Kingdom and elsewhere. This is a rapidly developing field and operating experience with vehicles currently entering service in various countries will provide important additional insight within the next two or three years.

Hydrogen-powered bus in service in Union Street, Aberdeen (May 2019, Photograph D.J. Murray-Smith)

Modelling and Simulation of Hybrid Electric Trains Powered by Hydrogen Fuel Cells and Batteries outlines the development of a train performance model and associated computer simulation software for investigation of some design issues for possible a two-coach hybrid multiple unit, powered by a combination of hydrogen fuel cells and batteries. The chosen mode of operation involves steady-state conditions for the fuel cells, with the batteries being used to provide additional stored energy for use on rising gradients and when the train is accelerating. 
Simulation results are presented for a case study involving a short section of route chosen to be typical of sections of many rural routes in Scotland. Data relating to the performance of a Class 156 diesel multiple unit provides a point of reference in assessing the performance of hybrid multiple unit designs. 
Although other studies of hybrid rail vehicles involving hydrogen fuel cell and battery combinations have been published, those have involved routes that are shorter, with more intermediate stations and no prolonged gradients. Conclusions are presented in terms of fuel cell and battery power levels and battery storage capacity required for the type of route being considered. 

Although energy recovery through regenerative braking is well-established on electrified railways there has, in the past, been no equivalent for conventional diesel traction. However, recent development work by Artemis Intelligent Power using their Digital Displacement® pump technology involves kinetic energy being directed into an onboard energy storage system, thus braking the vehicle. The photograph shows an Artemis Intelligent Power vehicle under test at Bo ‘ness, October 2018. (Photograph D.J. Murray-Smith)

Powering Future Transport in Scotland discusses energy costs and emissions associated with transport in Scotland and reviews options for future power sources for different public transport modes including developments in internal combustion engine technology, battery storage systems, hydrogen fuel cells and systems involving short-term energy storage and recovery of energy otherwise dissipated as heat during braking. The benefits of conventional railway electrification in terms of energy usage, costs and emissions are reviewed.

The Vivarail battery-powered prototype Class 230 unit at Manuel station on 11th October 2018. (Photograph D.J. Murray-Smith).

Design Options for Hybrid Trains Powered by Hydrogen Fuel Cells and Batteries applies the model developed in the previous report to estimate power and stored energy requirements over specific sections of the West Highland line. It concludes that three-coach hybrid passenger train would require three 250 kW traction motors, a fuel-cell stack with a power output of 500 kW together with a 375 kW battery pack providing between 210 kWh and 300 kWh of storage. 

A conventional class 156 DMU close to the summit of the West Highland Line 400m above sea level near Loch Trieg (Photograph N McNab)

Preliminary estimates suggest that the gross weight would be of the order of 135 tonnes. However, restrictions imposed by the UK loading gauge and the dimensions of fuel cell stacks and battery packs available at present  mean that the necessary equipment might not be accommodated without using space normally available for passengers. A pantograph and associated equipment to allow the train to operate in purely electric mode on 25 kV electrified routes have been included in the specification.