On track for carbon-free rail traction

On track for carbon-free rail traction

With the world now focused on the need to reduce carbon emissions and improve sustainability, railways around the globe are busy devising smarter approaches to electrification.

Rail electrification has long been seen as a means of improving the energy efficiency of passenger train propulsion in relation to the alternative of diesel traction; more recently, it has come into favour as a means
of removing air pollution at point of use.

These benefits make it easy to see why this form of traction is favoured: on a like-for-like basis, electric trains are lighter in weight, accelerate more quickly, have lower maintenance costs and consume less energy than diesels.

Moreover, electric traction also benefits from the ongoing efforts to decarbonize grid power generation. In the UK, for example, this improvement has been significant. Coal-based power generation, once the predominant source of energy for the power grid, has been dramatically scaled back in favour of renewables such as wind energy and solar. As a result, by2018 the average carbon intensity of the electricity supply in mainland Great
Britain had fallen to just 270 g/kWh CO2e -approximately half the prevailing level at the start of the decade. In fact, the first week of May 2019 saw the country reach the milestone of its first week without coal-generated electricity since the 1880s.

But while electrification may have distinct benefits once in place, it is far from a low-cost option in terms of
upfront capital investment. Installation and commissioning costs vary widely depending on many factors, not least the need to accommodate overhead catenary systems into legacy infrastructure such as overbridges and tunnels. Where height is restricted, the additional cost of lowering the track bed and its foundations to accommodate the increased headroom requirement – or rebuilding those structures completely – can be significant and may also incur financial penalties for line closures during reconstruction.

In the UK there has also been something of a feast or famine approach to electrification strategy over the past
50 years: the length of track completed per year has varied from zero to in excess of 800 single-track kilometres (stk). This compares with an almost constant 200 stk per year in Germany over a similar period. This unpredictability is widely thought to have exacerbated the situation, requiring supply chains to be reconfigured for each major new electrification project. This combination of factors results in a current UK cost of approximately £2.5 million per single track kilometre for electrification as opposed to around £1 million per stk for other majorEuropean networks.

Pragmatic and smarter electrification

Yet while significant efforts are being  made to reduce installation costs, it is almost inevitable that most mixed
networks of urban, intercity and rural  routes will include regions for which the case for conventional overhead electrification cannot be made.

In these circumstances, argues Jon Brown, UK business development manager for Ricardo Rail, a smarter and more pragmatic approach is required: “A key challenge for the rail industry internationally is to look at how we can accommodate gaps in electrification while still maximizing the proportion of electric traction. This might be anything from short section-gaps in overhead line through bridges or tunnels to avoid the costs of reconstruction, to longer sections that remain non-electrified.”

The rationale for allowing such longer gaps in electrification can be varied. As examples, it might be for aesthetic considerations around installing a catenary system for a light rail or tram system in a historic city centre, or it could be the lack of commercial justification for the investment required for a rural route with lower traffic volumes and load factors.

“Either way,” continues Brown, “the key enabling technologies for maintaining zero emissions at point of use are those of on-board energy storage and range extenders: these allow electric trains to operate beyond the reach of catenaries.”

Developing zero emissions rail in the Netherlands

The Ricardo Rail team based in Utrecht was asked to investigate exactly this approach to electrification of the Dutch rail network by the northern Netherlands provinces of Fryslân and Groningen, explains Ricardo sustainability consultant, Martijn Wolf.

“There is a strong regional imperative to reduce emissions, with the provinces having taken the political decision to aim for zero emissions public transport – both in terms of point of use and generation of the energy used – by 2025. This is quite an ambitious target that cuts across both buses and trains,” he says.

“The region is unusual in that its rail lines are part of only 5 percent of the Dutch network that remains unelectrified,” continues Wolf, “but we had previously conducted a study that demonstrated that full conventional electrification of the lines in this region was not cost-effective due to the comparatively light load factors and train frequencies. From the outset of this study, therefore, we needed to explore alternative approaches.”

The study, which was carried out in collaboration with infrastructure consultancy Arcadis, focused in particular
on evaluating different options for range-extender solutions based on hydrogen fuel cells used in the form
of a hybrid propulsion system, or for partial catenaries in combination with higher capacity on-board battery energy storage. With recent improvements and the reduced cost of battery systems, the latter was clearly identified as the more attractive solution.

Initially, a proposal was considered to use charging points at station stops, in a similar manner to some batteryoperated bus networks. However, as Wolf recalls, there were challenges in this approach: “A train has a much higher charging requirement than that of a bus, due to its size and weight. Using the type of discrete charging points that are available for commercial buses would have been impractical due to the positioning
of stations and the length of time that would be required for recharging. Instead, we looked into the options for partial electrification.”

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