Our childhood memories of trains are romantic: black metal monsters heaving themselves down the track, huge white billows of smoke trailing behind. “Everybody loves the sound of a train in the distance,” Paul Simon mused. “Everybody thinks it’s true.” What’s true about trains today, though, is that we need to electrify railway lines. That’s because the transportation sector is the major emitter of GHG and other harmful gases. Our contemporary dreams must now focus on a battery train in the distance for the health of the planet.
So when news emerged about a fine battery train achievement in late February, lots of renewable energy advocates were jazzed. Great Western Railway’s (GWR’s) innovative fast charge battery train trial broke records for UK distance without recharging. Then, a few days later, it set another UK record — this one of 86 miles (138 km) travel on battery power without recharging. That meant the battery train operated in a real-world environment at speeds of up to 60 mph, stopping and starting over a hilly route, with elevation changes of up to 200 meters.
As if those milestones weren’t enough, more recently that Class 230 battery train tested a 70-mile transit that drew upon only 45% of its battery capacity. Onboard specialist engineers insisted it could have traveled more than 120 miles on a single charge. Until now, such efforts have been limited by range.
The GWR successes offer hope for future battery train applications.
The Backdrop to a Battery Train & a Look to its Future
A primary measure to achieve long-term decarbonization goals is to reduce transportation levels of climate pollutants, which are nearly unchanged since the 1990s. As a large energy consumer, railway systems in many countries have been electrified gradually for the purposes of performance improvement and emissions reduction.
The source that powers an electric train could be in the form of an overhead line, battery, or third rail. The electricity to power the train may come from a source like wind turbines, hydroelectric power, or diesel. The electric locomotive uses alternating or direct current and stores it in huge batteries or ultracapacitators, which is then used to power the train forward. The wheels move using this stored electricity.
Today, hybrid versions of the electric trains are most often used: a diesel engine produces electricity which, in turn, runs the train. An example is Hitachi Rail, which runs 20 tribrid trains across Italy. The trains switch among battery power, electricity, and diesel and can travel about 10 miles on battery power. The batteries replenish themselves whenever the train is braking or by drawing electricity from an overhead apparatus that connects the train to a power line. The hope is to be able to eliminate the need for overhead electric lines, which are expensive, are time consuming to install, and impact the landscape.
The traction demands of the railway network are characterized by their rapid variations depending on the trains’ operational conditions and timetables. Battery specifications, the battery energy, mass, and cost all contribute to the viability of battery trains. The challenges with higher energy requirements are mass and volume constraints within the locomotive and the train to carry the energy onboard. Rapid battery technology improvements are continuously increasing energy density, improving durability, and reducing production costs.
Battery trains, which are powered by an external electrical supply, are lighter and more powerful than diesel trains, but they have higher initial capital and maintenance costs. The implementation of batteries in heavy-haul rail presents an excellent opportunity for decarbonization. GWR’s fast charge technology has been designed to solve the problem of delivering reliable, battery-only trains capable of fulfilling timetable services on branch lines, eliminating the use of diesel traction, and helping to meet government and the wider rail industry’s target to reach net zero carbon emissions by 2050.
The Key is the Regenerative Braking
When a railway vehicle is braking, its induction motors function as generators that convert the kinetic energy into electrical energy. The produced regenerative braking energy is transmitted to and stored in a stationary or on-board energy storage system (ESS). Commercially viable solutions for the use of ESSes in high-speed railway systems are relatively new areas of research. Various forms of ESSes — such as flywheels, electric double-layer capacitors, batteries, fuel cells, and superconducting magnetic energy storage devices — are being tested in electrified railway systems.
Energy storage devices with high energy and power density are suitable for applications where weight and size are among the main considerations. Batteries that take on the role of reversible storage systems allow an extensive use of regenerative braking on railway vehicles. Electric railway vehicles are able to convert the kinetic energy in the braking phase into electric energy for the purpose of energy reuse.
Generally, there are 3 solutions to manage regenerative braking energy in railway vehicles:
- Synchronizing the loads along the traction power supply lines;
- Feeding the regenerative braking energy back to the external grid; and
- Storing the regenerative braking energy in an ESS.
Among a range of batteries, Li-ion batteries are one of the most popular types used for regenerative braking energy recovery. For current Li-ion battery technology, there will be a continued push to increase the energy density, according to an Australian team of researchers in the Journal of Energy Storage. Active research areas in LIB technologies include Ni- and Li-rich cathode materials, Si-rich anode materials, and solid-state batteries. The development of these new electrodes could push LIB energy density to over the current 350 Wh/kg barrier. Solid-state batteries may further extend this to ∼500 Wh/kg if the solid-state electrolyte is coupled with a metallic Li anode.
US Steel converted two of its diesel switcher locomotives at the Mon Valley Works’ Edgar Thomson and Clairton Plants to battery trains late in 2023.
Fortescue was able to develop its “Infinity Train” that runs on 100% electrical power yet never needs charging. The EDumper, a massive all-electric mining truck developed by eMining AG, rolls downhill fully loaded, riding the brakes, then powers itself (empty) back up to the top of the mine on the energy it gained from the regenerative energy system, with loads to spare.
Final Thoughts
At West Ealing, where the GWR technology will be trialed in a real-world environment for the first time this spring, the UK train will charge for just 3 ½ minutes before restarting its journey on the Greenford branch line. GWR has already carried out simulations on other branch lines in the Thames Valley to explore how it could be rolled out even further in the future. This could reduce GWR emissions alone by over 1,700 tons of CO2e per year. It is hoped the technology could one day see battery trains in operation across the UK’s approximately 2,000 miles of 80-plus branch lines.
