Creating a fully decarbonised rail network in any country requires deployment of a range of technologies depending on the routes, rolling stock and infrastructure. Electrifying branch lines has long been a challenge due to high costs of overhead powerlines. However, DNV is now observing that battery electric multiple units (BEMUs) are emerging as a potential solution to electrify these routes.

The global transportation sector is steadily advancing toward the objective of achieving net-zero emissions by 2050, and the rail industry is no exception. For road vehicles, there are a plethora of zero emission options for passenger and light commercial vehicles. For the rail industry, electrification is nothing new, with much of the network, particularly main lines already using overhead electric systems. However, such systems are not universally suitable, especially for branch lines, secondary routes, and freight lines. The solution to decarbonise the latter will likely come from a combination of further electrification via use of overhead lines and the implementation of battery electric systems, in the form of battery electric multiple (BEMUs). 

Network Electrification

Current electrification of the rail networks varies from country to country, looking at the 10 largest rail networks in Europe, only two have over 70% electrification, while several have less than 40% [1], including the United Kingdom, as illustrated in Figure 1. The lower adoption rates observed may be attributed to the prevalence of smaller branch and secondary lines, which were initially deemed prohibitively expensive for overhead electrification, however may now be viable candidates for decarbonisation through the use of battery electric solutions.

Looking ahead, Europe is aiming to fully decarbonise and electrify rail transport by 2050. When considering the current rate of electrification, forecasting suggests that by 2050 only 66% of rail lines will be electrified, as shown in Figure 2. This shows the urgency of the challenge, now is the time to ramp up electrification of the sector which will require the deployment of multiple solutions, including investment in infrastructure where feasible, and leveraging battery electric units where most suitable.

Branch/Secondary lines

Battery Electric Multiple Units (BEMUs) are an ideal solution to decarbonise branch/secondary lines which currently operate diesel units. These shorter routes, often serving as direct connections between two points and sometimes used exclusively by passenger services, are particularly well-suited for battery-powered systems. Stationary and relatively isolated locations at one or both termini of a route present ideal opportunities for the installation of charging infrastructure. Some branch lines also feature passing loops that allow upstream and downstream vehicles to pass one another, which can additionally serve as convenient locations for installing charging infrastructure.

Deployment

BEMUs are becoming increasingly prevalent across Europe and the United Kingdom.   Austrian Federal Railways (ÖBB) placed an order to purchase 16 Cityjet BEMUs in 2023 [2]. Stadler has been awarded a contract to deliver 14 Battery Electric Multiple Units (BEMUs) to replace Lokaltog's IC2 trains in Denmark [3]. Bombardier have been working with SNCF deploy BEMUs across France [4]. Germany has been operating its first fleet of battery-electric multiple units (BEMUs) for passenger service in Schleswig-Holstein since 2022 [5].

Equipment Manufacturers (OEMs) and transport operators have introduced, or are planning to introduce, BEMUs into the United Kingdom. Great Western Railway (GWR) have worked to produce BEMUs in the London area for deployment on the GWR network [6]. Class 777 BEMUs were introduced on the MerseyRail network by the Liverpool City Region Combined Authority in 2023 after being successfully trialled in 2021 [7]. These deployments have been enabled by the implementation of innovative technologies, including third rail charging and new battery chemistries.

Battery Electric Multiple Units

BEMUs, are a new type of train that run on electricity stored in onboard batteries, unlike traditional electric trains that need constant power from overhead wires or a third rail. This allows BEMUs to travel on non-electrified tracks, making them ideal for various lines across the network.

Charging

BEMUs can be charged via various methods, including dynamic charging while in motion. The three most common methods are:

1.      Using pantograph system.
2.      In-motion charging while under wire.
3.           3^rd rail system.

Each charging system presents its own advantages and limitations, with suitability largely determined by the existing infrastructure and the specific design of the BEMU. For example, if a branch line includes sections of partial electrification – such as at an intermediate station – a pantograph-based charging system might prove to be a logical and efficient solution. In-motion charging is ideal, as it eliminates the need for dwell time; however, it also requires surplus power capacity on the line and may necessitate a split battery pack configuration on the BEMU. The ultra-fast charging capability of LTO batteries means excessive wait times can be kept to a minimum. Implementing third rail charging solutions is ideal where visual impact and infrastructure costs are key concerns.

Powertrain

At the heart of BEMUs is the electric propulsion system, comprised of lithium-ion batteries, inverters and electric motors. Systems integrators are capable of mounting hardware, underfloor or onboard, dependant on individual requirements. Systems can also be designed to work on both, battery electric and overhead cables, as well as hybrids for traction.

Batteries

Development and widespread adoption of battery technology across various industries has demonstrated their reliability and safety to such an extent that even the highly regulated rail sector is now beginning to integrate them into its operations. As packaging is less of a constraint, unlike in the road vehicle sector, lower energy density and safer batteries chemistries can be used. This enables the deployment of lithium iron phosphate (LFP) or even lithium titanate oxide (LTO) batteries, capable of delivering several hundred kilowatt-hours of energy, thereby supporting operational ranges extending to tens or even hundreds of kilometres.

Unlike road vehicles, which must operate across a variety of duty cycles, trains typically follow consistent operational patterns throughout their service life. Selecting appropriate battery units during the initial design phase enables systems to achieve a service life exceeding 15 years, without the need for mid-life replacement of critical components such as motors and batteries.

The challenges

Implementation of Battery Electric Multiple Units (BEMUs), alongside expanded overhead electrification, presents a promising path toward full rail decarbonisation. However, several critical challenges must be addressed to ensure successful deployment:

·       Site Selection and Suitability - Identifying optimal routes and regions where BEMUs offer the greatest operational and environmental benefits.

·       Assessment of Long-Term Viability - Evaluating the enduring performance, maintenance needs, and potential limitations of BEMU technology over time.

·       Cultural and Operational Change - Shifting away from traditional practices and embracing new workflows, training, and operational models.

·       Financing and Investment - Securing funding for infrastructure, rolling stock, and supporting systems, while ensuring cost-effectiveness.

·       Lifecycle Management - Planning for the full lifecycle of BEMUs, including reuse, recycling, or disposal at end-of-life.

·       Charging Infrastructure and Strategy - Developing efficient, scalable charging solutions that align with service schedules and energy demands.

How DNV can support

DNV’s world leading knowledge in transport electrification and battery systems puts it at the forefront of net-zero technologies.

DNV has worked to enhance safety, quality, energy efficiency, and environmental performance across all sectors. DNV assesses vessel types and offshore structures within maritime transport. Within the automotive sector, DNV focuses on the transition to electric vehicles (EVs) and the broader decarbonisation of transport while looking at sustainable technologies such as transport electrification, biofuels and hydrogen. For rail transport, DNV offers a range of services to improve rail asset performance, including advisory and assurance.

DNV has years of experience forecasting battery systems, which can be found in DNV’s Energy Transition Outlook (ETO) [8] and Battery scorecards [9]. The ETO predicts the long-term battery storage technology trends and determines the electrical storage capacity till 2050.

Authored by Brian Lambert (Principal Consultant Sustainable Transport) and Robert Camm (Principal Consultant Sustainable Transport)

References

[1] ‘Length of railway lines by number of tracks and electrification of lines’. Available:https://ec.europa.eu/eurostat/databrowser/view/rail_if_line_tr/default/table?lang=en

[2] D. Briginshaw, ‘ÖBB orders first batch of battery EMUs from Stadler’, International Railway Journal. Available: https://www.railjournal.com/fleet/obb-orders-first-batch-of-battery-emus-from-stadler/

[3] R. Preston, ‘Danish battery fleet order confirmed’, International Railway Journal. Available: https://www.railjournal.com/fleet/danish-battery-fleet-order-confirmed/

[4] ‘SNCF and Bombardier convert diesel to battery trains’, Urban Transport Magazine. Available: https://www.urban-transport-magazine.com/en/sncf-and-bombardier-convert-diesel-to-battery-trains/

[5] K. Fender, ‘First German BEMU fleet enters service’, International Railway Journal. Available: https://www.railjournal.com/news/first-german-bemu-fleet-enters-service/

[6] ‘GWR to start operating battery Class 230 train’, ROLLINGSTOCK. Available: https://rollingstockworld.com/passenger-cars/gwr-to-start-operating-battery-class-230-train/

[7] ‘Liverpool City Region’s new trains scoop National Transport Award’. Available: https://www.liverpoolcityregion-ca.gov.uk/news/liverpool-city-regions-new-trains-scoop-national-transport-award

[8] ‘Energy Transition Outlook 2024’, DNV. Available: https://www.dnv.com/energy-transition-outlook/download/

[9] ‘2024 Battery Scorecard’, DNV. Available: https://www.dnv.com/publications/2024-battery-scorecard/

 

04/06/2025 09:50:00