On 15 September one of the Alstom Coradia iLint hydrogen powered units from Weser-Elbe-Netz regional passenger services performed a range demonstration run from Bremervörde to Munich. The train covered 1175 km (730 miles) without refuelling. The journey took around 19 hours with some stops, an average speed of 38 mph. It's a reasonable assumption that the train was lightly loaded, and the speed kept down, in order to achieve the 1000 km target. The units have a stated range of 600-800 kms.

The decision on whether to opt for HMUs, BMUs or BEMUs (Hydrogen, Battery or Battery Electric Multiple Units) on the 'rural lines' in Scotland which may never be fully electrified, has yet to be made.

The debate has been going on for quite a while and there is no escape from basic physics. HMUs have to carry batteries, albeit probably smaller and therefore lighter than those in BMUs and BEMUs. Any trains which cover non-electrified sections of route therefore use some of their power to transport their own supply. This is obviously true for diesel traction too.

Logic would suggest that the most economical and resource-efficient long term solution for rail traction without CO₂ emissions must be overhead electrification. The energy efficiency of BMUs is a distant second-best and of HMUs a pretty remote third. However, to meet the Scottish Government's Decarbonisation Plan interim/permanent rolling stock solutions have to be found.

For a (2018, and therefore somewhat dated) breakdown of the practical differences between these solutions Fuel Cell Coradia iLint On Test is worth a read.

Of course in the decision-making processes many factors are in play and it is interesting to read some of the differing views quoted in the railway press.

In Rail Engineer magazine its editor, David Shirres, makes strong arguments about seeing the decision between hydrogen and battery power for trains in the broad context of hydrogen's future role in Scotland:

"Scotland's Rail Services Decarbonisation Action Plan details how rail passenger services will be decarbonised by 2035. By then, the aim is for all core routes to be electrified with services on the remaining less-intensively used routes powered by either battery or hydrogen powered traction.

"For some, Hydrogen trains are an unnecessary distraction. They are considered to be inefficient and more expensive to operate than battery trains and require complex novel fuelling arrangements.

"Such views, however, do not take account of the need to develop a hydrogen economy which will be required if the necessary transition from fossil fuels is to be achieved. In issue 193 (Nov-Dec 2021), Rail Engineer reported on the COP26 hydrogen transition summit. This explained why hydrogen is essential for a low carbon economy as it is the only way to decarbonise things that cannot be directly electrified such as ships, steel production, and heavy mobility. In addition, it can provide grid balancing for renewable power.

"The Scottish Government's Hydrogen Action Plan aims to produce 800,000 tonnes of hydrogen per annum by 2030. This equates to 27 TWh or 17% of Scotland's current energy demand. The plan considers that, by 2045, a strong hydrogen sector in Scotland could support up to 300,000 jobs, many of which could use the skills of those displaced from the oil and gas industries. As part of this plan, £100 million has been committed to develop the hydrogen economy over the next five years."

Meanwhile, in Modern Railways magazine, interviews with Alex Hynes (Managing Director, Scotland's Railway) and Bill Reeve (Director of Rail, Transport Scotland) shed some light on current thinking:

AH: "The current operating costs of hydrogen trains are much higher than for diesel. Most of our rural routes use two-car diesels. In the UK gauge it's likely you'd need space in the train to store the hydrogen, so you might have to buy a three-car hydrogen train to replace a two-car diesel and keep the same capacity. That could create all manner of issues with depots, lengths of loops, sidings and so on. That's why we have a bias to continuous electrification in Scotland."

BR: "Hydrogen trains take longer to fuel, you can't put as much fuel in and you can't put fuel in the same place as passengers. That's why we're working with our partners to understand the practicalities. I don't see a future where hydrogen trains come close to the operating cost of diesel trains, let alone electrics."

Encouragingly, from the FNL viewpoint where possible electrification to Tain is already in the decarbonisation plan, Bill goes on to talk about the West Highland Line, "If you could double the number of passengers^* and do the electrification for £1 million per stk (single track kilometre), you could have a case. The West Highland Line is closer to covering its costs than many routes in Scotland and it's not actually that long. It's likely we'll end up with battery-electric or fuel cell trains, but we don't know for sure yet."

Modern Railways' highly-respected columnist, Roger Ford, has this to say on the subject:

"Hydrogen fuel cell power has been the poster child for alternative traction, promoted heavily by Alstom and Siemens. Hydrogen trains are effectively fuel cell-battery hybrids. In the case of the Alstom iLint, the battery provides power for the traction equipment while the fuel cell charges the battery and powers the train when running at constant speed.

"My critical approach to the rapidly inflating hydrogen traction bubble was not because there was no place for hydrogen traction in future. Rather, that this place was a very small niche and that, despite this, hydrogen was being promoted as an alternative to electrification, as opposed to decarbonising the lightly used fringes towards the end of a rolling programme. In any case, until green hydrogen from renewable sources was available in quantity, fuel cells show little or no advantage in terms of CO₂ emissions over a diesel-battery hybrid.

"All this before you consider the cost of the trains, the cost of the hydrogen and the cost of the infrastructure. This is reflected in a study commissioned for the German state of Baden-Württemberg into the economics of future traction for currently diesel hauled rural routes.

"This study concluded that in terms of total cost of ownership over 30 years, hydrogen fuel cell traction came a poor third after battery hybrids and electrification."

This is a fascinating discussion and decision deadlines for rolling stock procurement are fast approaching - the pressure is on!

^*It is Scottish Government policy to achieve a 20% reduction in car miles - this would result in a doubling of rail passengers.