Battery-Powered Trains: Examining Their UK Introduction and Safety Considerations

Battery-powered trains may soon become a common sight at stations. As the United Kingdom’s diesel engine fleet nears its operational end, manufacturers are exploring eco-friendly replacements. Currently, trains receive power from overhead electrified lines or, on tracks lacking these, from onboard diesel generators. Many trains are designed to operate using both power sources, switching between them as needed. The adoption of battery-powered trains would eliminate the expense for rail operators of installing overhead wires on the UK’s extensive unelectrified tracks. At Hitachi’s facility in Newton Aycliffe, north-east England, trials have just concluded for a new “tri-mode” train, which features lithium batteries in place of one diesel generator. This modification enables it to consume up to 50% less fuel when operating on non-electrified routes. Following this trial, Hitachi also intends to develop a train model entirely without diesel generators. The company anticipates this model will be capable of covering up to 90km (56 miles) on unelectrified track sections, with the ultimate goal of achieving a diesel-free national rail network. Siemens is also engaged in the development of its own battery-only trains at its factory located in Goole, East Yorkshire. The company reports that it expects orders for over 600 trains from various operators, including ScotRail, Great Western Railway (GWR), and Transport for Wales. GWR conducted tests on its own battery train earlier in the current year. While exclusively battery-powered trains are already operational in Japan and Germany, experts in the UK suggest they could introduce specific fire safety challenges. However, Hitachi engineers have informed the BBC that comprehensive testing has been conducted on the batteries to guarantee passenger safety during an emergency. Contemporary diesel-electric trains are engineered to draw electricity from overhead lines where tracks are electrified. On other sections, they rely on diesel generators positioned beneath their carriages. Hitachi’s new train design substitutes one of these diesel generator units with 16 batteries, similar to those found in electric vehicles (EVs). The company states that these trains can automatically switch between power sources, and that the tri-mode variant would primarily utilize its batteries in station areas and urban environments. Hitachi indicates that these batteries can be recharged while the train is in motion on electrified tracks, or within 10-15 minutes when the train is stationary. The company also suggests that existing diesel-electric trains could be retrofitted with batteries, offering a cost-saving measure. The inaugural train to operate solely on lithium batteries commenced service in Japan in 2016, more than six decades after some limited use of lead-acid battery-powered trains in Scotland. This raises the question of why lithium battery options are only now being developed in the UK. Koji Agatsuma, Hitachi Rail’s technical chief, who oversaw the company’s battery train initiative, attributes the current interest in the UK to a combination of technological advancements and shifts in the political landscape. He notes that the government’s objective is for trains to be “cheaper, greener, more reliable,” while battery technology continues to evolve, making batteries smaller and more potent. Nevertheless, certain limitations persist. Hitachi opted for the tri-mode train design because its batteries currently lack the capacity to cover all unelectrified track sections across the UK. Although further railway areas can be electrified, this process is expensive: in 2020, Network Rail estimated the cost of electrification to be between £1 million and £2.5 million per kilometre of track. Siemens indicates that for its battery-powered trains to operate on the UK’s rail network, specific short track sections would require electrification, and rapid-charging stations would need to be installed along train routes. Hitachi’s test train achieved a range of 70km (44 miles) using only its batteries. This would be suitable for routes such as London to Oxford or Hull, owing to the extent of electrified rail on these lines, but it would not suffice for the entire length of a route like Crewe to Holyhead, for instance. Furthermore, while the train could travel 135km (84 miles) using both diesel and batteries, this performance was observed on relatively flat testing tracks. Routes like those operated by TransPennine – which loaned Hitachi the test Class 802 train – feature inclines that demand greater energy, thereby reducing the overall distance the train could cover without assistance. Jim Brewin, Hitachi Rail’s UK and Ireland chief, states that the government’s objective to achieve net-zero carbon dioxide emissions by 2050 signifies that fully battery-powered trains represent the industry’s future direction, with hybrid trains serving as an interim step. He explains that as battery cells become lighter and more powerful, the company can replace them with newer models to enhance performance. Recent testing also demonstrated that existing trains could be converted to operate fully or partially on battery power. Experts specializing in lithium batteries report that, when utilized in road vehicles, EV batteries are at least 20 times less prone to catching fire than vehicles powered by diesel or petrol. Hitachi’s train incorporates Nissan Leaf cells, which have been implicated in 16 fires over their 14 years of use in road vehicles, according to EV Fire Safe, an organization that compiles global data on battery fires. This figure is out of more than 500,000 cells sold worldwide. “Managed properly, lithium batteries are very safe,” states Jon Simpson, a fire safety consultant and former firefighter. However, if lithium batteries are compromised, they can undergo thermal runaway – a condition where a cell experiences uncontrolled temperature increases, making a fire difficult to manage and extinguish. Jon Hughes, managing director of UK Fire Training, suggests that a “catastrophic event” such as a crash or derailment that damages a cell could trigger such an occurrence. Conversely, Euan McTurk, a consultant battery electrochemist, asserts that Nissan Leaf cells are “far more robust than people give them credit for.” He elaborates: “For them to catch fire, it would take some spectacular lancing of the actual cells themselves, which would mean going through a very strong external structure.” Chris Dautel, a senior electrical engineer at Hitachi, explains that part of Hitachi’s testing involved intentionally destabilizing a cell, including piercing and overheating it. He further notes that Hitachi has installed a heat shield around each cell to prevent the issue from spreading to adjacent cells, ensuring “no danger to passengers in [a] case of thermal runaway.” The train is also equipped with a cooling unit on its roof to regulate battery temperature, and the company has developed software for monitoring and regulating the cells. Mr. Simpson, the fire safety consultant, advises that the immediate response to a lithium battery fire is to douse the cell with as much water as possible to cool it down, though he acknowledges this may not always be feasible depending on the fire’s location. “Tunnels are probably the riskiest area in a rail environment,” remarks Graham Kenyon, an electrical engineering consultant. “If you get a fire, probably the worst things to deal with when you’re evacuating people are smoke and fumes, vapours, gases that are toxic.” In certain scenarios, fire brigades may deem it safer to allow the battery to burn itself out. However, leaving a train on the track could lead to significant operational disruption. Dautel indicates that a carriage experiencing a battery fire could still be moved, even while burning, due to the efficacy of the fire barrier surrounding the cells. “In the case of incidents, we would evacuate the passengers, but they wouldn’t see anything,” he states. He adds that because each unit operates independently, the train would retain the ability to move itself using batteries in other carriages, or it could be towed by another train.