Battery-Electric Trains
Why Battery Electric?
Unlike a conventional electric train, a battery-electric train can operate without a continuous overhead wire or electrified third rail. It can replace a conventional diesel train, on a route without electrification. Full electrification is very expensive. It can cost up to £2 million per track kilometre. Being able to use a train with a battery offers the opportunity to decarbonise the railway without the expense overhead electrification. Battery electric trains need a rapid charging system but this can be provided at a terminus so the train can recharge while it's waiting for its next trip.
A feature of modern traction systems is that a train equipped with electric motors can use these for braking. During braking, the motor becomes a generator and the current produced can be fed back into the overhead line system on an electrified line or back into an on-board battery, if the vehicle has one. This 'regeneration' can be used to recharge the battery while the train is in service.
Challenges
However, the system is not without its challenges. After a long period of gestation, battery-electric trains are now being more widely recognised as a way to decarbonise the railway at a reasonable cost. We can define a battery-electric train as a railway vehicle that stores traction energy in rechargeable batteries and uses it to power electric traction motors.
The engineering challenge is to integrate energy storage, traction, braking, thermal management, structural design and system safety into a vehicle that can carry its own rechargeable batteries, recharge them en route and complete its journey on a finite battery charge. It also has to provide a viable and safe system of battery recharging and the electrical supply system to operate it. None of this will be easy.
Stadler 3-car Battery-Electric Multiple Unit (BEMU) Photo: Stadler
In general terms, the engineering challenge is to ensure that the train has sufficient energy, power, range, acceleration and braking capability while remaining safe, reliable, maintainable and economical throughout its service life. For BEMUs, the jury is still out. They haven't been around long enough to see a whole life. However, the signs are promising with every increasing improvements in battery life and recharge ability.
Progress
BEMU trains first appeared in passenger service in Germany in 2020. They arrived after a long gestation period, but they pointed the way ahead. In the UK in February 2015, a battery-fitted Class 379 Electrostar unit began in trials on the Harwich branch. This was the first battery-powered train in the UK. It ran on battery power up to 77 kms.
Some serious experiments began with the conversion of some former London Underground district line trains, known as D stock and now designated Class 230, that were converted for battery operation. Although a few are in use around the country, the conversion is expensive and the reliability is poor. Conversion of old equipment is always difficult. New builds have proved to be better.
The first purpose-built battery powered passenger train entered service on the extension from Kirkby to Headbolt Lane on 7 October 2023. More recently, Rail Operations Group’s Class 93 locomotives feat Scotture a battery pack as well as diesel power and 25kV overhead line operation and Hitachi tested a tri-mode conversion of a TransPennine Express Inter-City unit train with a battery pack in place of a diesel generator on one car. A fleet of 29 new BEMUs have been ordered for the Trans-Pennine route as a result.
In London, the new 2024 Stock Piccadilly line trains (currently in pre-service testing) have a battery ‘get to the next station’ facility. In Birmingham, some of the CAF trams have batteries added to allow them to serve an extension of the system to Edgbaston Village. All of these are hybrid trains or trams and we can be sure that there will be more to come.
