Japan Rail introduced the first fleet of battery trains between 2016 and 2019, converting 18 Dencha trains from diesel power. The model converts AC electricity from overhead lines to charge onboard batteries.
Nearly a decade after that revolution began, the UK still has few options – but that could be about to change. As old trains go out of service, operators are looking at battery-powered alternatives for the next generation of transport.
Last year, Hitachi Rail replaced the diesel engine in one of its intercity Class 802 trains with a single 700kW battery. The trial included a 70km journey powered entirely by the battery.
Following the successful test, Jim Brewin, chief director for the UK and Ireland at Hitachi Rail, said: “Everyone should be immensely proud of creating battery technology that had zero failures during the entire trial. Using our global expertise, Hitachi Rail has created new technology, which means the greenest mode of transport just got greener.” The next step for the company was a full intercity battery-powered train, which it believed could have a range of 100-150km.
Some experts are unsure if battery trains will become a frequent sight on the network, however. “I’m slightly sceptical about it, but people I talk to are very confident,” said transport commentator Christian Wolmar.
The additional weight that trains would have to carry throughout entire journeys could scupper their chance of becoming economical, he said. “It seems like a lot of weight for not much power.”
He added: “I can’t really see it having widespread use… In Suffolk or Norfolk, there might be places like branch lines where it could be useful technology, but I don’t think it’s a gamechanger.”
There could nonetheless be marginal use cases, he said. Merseyrail is using battery technology on its Class 777/1 IPEMUs (independently powered electric multiple units), which expanded the network to include areas without overhead powerlines. The initiative has been hit with frequent delays to journeys, however, with some saying the rollout was too quick to be effective.
Merseyrail isn’t the only operator dabbling with batteries: Great Western Railway set a UK record for the longest distance travelled on battery power alone in February 2024. But that journey was only 86 miles (138km), about half the distance from London to Manchester by train.
Manufacturers are also making strides in improving battery technology. In the North East of England, Hitachi’s tri-mode train switches between a single diesel generator and lithium batteries, reducing the amount of fuel used.
Siemens is also developing battery-only trains in Yorkshire. The company said battery-powered trains could “consign diesel trains to history” and save £3.5 billion, plus 12 million tonnes of CO2 emissions, in the next 35 years.
The Hitachi experiment is among the most advanced and highlights the potential of the technology for the future of rail travel. But it needs a whole-industry response to come to reality.
Wolmar pointed to slow progress in electrifying the rail network itself as evidence of challenges ahead. The network remains stuck at about 38% electrified, although the Railway Industry Association (RIA) released a report in April 2024 suggesting more than half could be electrified in the next decade. With further tweaks, the RIA said it would be possible to fully decarbonise all passenger services and almost all freight services.
That would require new innovations and more work on safety. Some battery-sceptic engineers worry about degradation of the cells that will power the next generation of trains, and fear they could cause fire risks. Supporters of the electric train movement point to positive safety data from electric vehicles on the road as evidence that those worries are overblown.
The main issue is not necessarily the technology, according to Wolmar, but the challenging financial environment. “Electric trains have been around for more than 100 years and [are] clearly a more efficient way of doing things,” he said. “But they require initial investment. It’s particularly difficult at the moment because there are so many stakeholders.”
The arrival of Great British Railways could help unite the industry’s disparate initiatives into a concerted effort, he added.
Want the best engineering stories delivered straight to your inbox? The Professional Engineering newsletter gives you vital updates on the most cutting-edge engineering and exciting new job opportunities. To sign up, click here.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.