For the next few months, an old London Underground train can be seen running along a length of National Rail track in west London, as it tests a new battery technology that could replace diesel trains on branch lines.

Test train at West Ealing (c) ianVisits

The former London Underground train had been bought by a start-up firm created by Chiltern Railway’s former managing director, the late Adrian Shooter, as a way of providing affordable trains for use on branch railway lines. However, that firm, Vivarail, went into administration in December 2022, but GWR bought much of the intellectual property, rolling stock and equipment as they were interested in its fast-charging technology.

If it works, they aim to swap polluting diesel trains for emissionless battery trains on short shuttle services, of which GWR is “blessed” with many examples.

The main advantage of battery trains over electrification of the railway is cost – as the cost of electrifying the railway is considerable, and often more considerable than originally expected. It’s not just the cost of adding the infrastructure to consider, though, but also the months of disruption for the people who live alongside the railway and have to put up with the noise and muck from the installation work.

Then you need to consider the long-term visual impact at the ends of their gardens.

Pragmatically, the main benefit of electrifying the track vs electrifying the trains would be faster trains, but on branch lines, that’s not really a factor, so battery trains could be an answer to removing polluting diesel trains from the network.

Hence, these battery-powered trains.

After a couple of weeks of testing, the first of the new trains has started trial running in between the existing timetabled service in west London. The aim of the trials is to build up the mileage for the regulator to certify the train and also build up real-world experience and understanding of the issues that might arise.

One of the other issues with fast chargers is that batteries heat up when charged, and the faster the charge rate, the hotter they get. To remove the heat, the batteries are air-cooled by fans that blow air through the battery packs while they’re being recharged at the station.

The other issue that often arises from the electrification of a transport service is getting the necessary amount of power to the site for energy-guzzling services. When these trains arrive at West Ealing station, a fast charger that’s installed between the railway tracks delivers a sharp burst of energy to the train’s batteries. To take that amount of power from the local grid in just a couple of minutes would have needed expensive and time-consuming upgrades to the power supply.

So, to avoid heavy spikes in power demand, a separate bank of batteries next to the tracks is trickle-charged, and it is those that provide the burst of energy to the train when it pulls in.

The fast charger (c) ianVisits

If the technology is rolled out elsewhere, using trickle-charge batteries to store power for the train could avoid the cost of upgrading the local electricity grid and the lengthy delays in securing planning permission for the upgrade.

Although the train has only been used on the Greenford branch so far, GWR has carried out computer simulations of its expected performance on other branch lines, and they’re confident it would work on the Slough-Windsor, the Maidenhead-Bourne End and the Tyford-Henly branch lines.

At the moment though, you might be able to see them out on trials running between Greenford and West Ealing.

Apart from the physical difference between the old and new trains, if you watch both in action, the difference between them is obvious—the smell and the noise. The battery trains are nearly silent, but the diesel is noisy and really quite smelly when you’re standing next to it.

Admittedly, the quiet train is nearly drowned out by the noise of the mainline services rushing past, but once away from West Ealing station and onto the branch line, the trains’ quietness will benefit the people living next to the railway.

Existing diesel train (c) ianVisits

Test battery train (c) ianVisits

Although the tests are needed to prove the technology is reliable, they’re also needed to carry out real-life experiments, such as determining how long the batteries last if the train also has the in-carriage heating on during winter months or, if fitted, air conditioning in the summer months.

There is a whole range of demands on what’s called “hotel power” for customer facilities—from lighting to phone chargers—that need to be evaluated.

The test train already has a proven range of over 80 miles, which is vastly more than is needed for the Greenford branch, but also comfortably within the UK’s average branch line length of about 25 miles. When you get to longer branch lines, the extra power drain from heating and the like becomes more concerning; hence the tests to verify performance.

Inside the drivers cab in test mode (c) ianVisits

One of the other issues with switching from diesel to battery is that the battery trains have a top speed of 60mph, compared to the 75/90mph of the existing trains. However, electric trains accelerate faster, and on branch lines with modest gaps between stations, the acceleration offsets the slower mileage speed.

On branch lines with much longer gaps between stations, then that’s a potential trade-off to consider.

At the moment, they are testing the train, and a decision about commissioning live passenger trains is still to be made. However, considering the alternatives available and the investment going into this trial, it’s pretty certain that a battery-based train will be replacing the diesel trains in the near future.

Further ahead, GWR would consider the trains for other branch lines it operates, where diesel needs to be phased out by 2040 anyway.

(c) ianVisits

There’s also the tantalising possibility that one of the problems when trying to reopen an old railway in the future will be the mandatory use of zero-emission trains. Campaigners may find battery locomotives a viable alternative to expensive rewiring of the line.

But that’s for the future. In the meantime, look out for a battery test train running along the Greenford branch line in west London.

(c) ianVisits


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  1. Brian Butterworth says:

    I wonder if this is also the solution to “heritage steam” railways. Put the engine (and a kettle for show!) on the front but actually use this system to drive the train?

  2. Paulo says:

    “Then you need to consider the long-term visual impact at the ends of their gardens.”

    You really don’t. People who chose to live next to rail lines should expect that the nature of the rail infrastructure may change over time.

  3. Bob says:

    To all the nay sayers that the green revolution can’t happen because of blah blah blah. The only thing that limits their tiny brains is their imagination.

    Time and time again they are proven wrong and that these problems are solvable. This is prototype 1 operating for the first time ever. We didn’t stop at Stevenson’s rocket and we won’t stop here. The future is bright. The future is clean energy.

  4. Keith says:

    For some branch lines I imagine that adding fast charging points at some intermediary stations may be required, even if they only charge for just a minute. That may also mitigate for trains being held at red signals for a long period of time, to ensure they can still reach a charging point.

    I can see the fast charging having a lot of potential for smaller lines in reducing the need for diesel trains.

  5. Alex Mckenna says:

    Maybe even longer diesel lines could benefit from this system? The Marshlink line from Hastings to Ashford, and even the Uckfield line for example.. both about 25 miles..

  6. Mike Jones says:

    And, of course, all those lithium batteries are compostable…

    • Keith says:

      Companies are working to improve lithium batteries. One of the winners of last year’s earthshot prize is aiming to do just that, ref

    • ianVisits says:

      Batteries are a lot easier to recycle than desiel that’s been combusted to provide fuel and gas.

    • Geoff says:

      It’s a lot easier to recycle batteries than it is to recycle the tonnes of diesel that a train burns every year

    • simhedges says:

      Not compostable. Reusable after many years in service, for grid storage and the like. They can also be broken down into their components and new batteries made from those.

      All in all, they have much longer life and are much more resuable than the vast amounts of diesel that will no longer be required.

  7. Alan O'Connor says:

    Electric trams in some European cities currently operate with the power source/battery charger buried along the centre of the track for the entire route length. No wires visible at all. This could easily be adapted for trains.

    • Anton says:

      Many branch lines with diesel powered traction are suburban if not rural. Are the embedded/ground level electrical pickups “nature proof”?

      i.e. prevent rodents from nesting inside, shorting power or interfering with the mechanics of the power pickups. Also, how to ensure that animals and leaves/branches etc doesn’t caught in or otherwise foul the electrical pickup?

    • ianVisits says:

      The same way existing 3rd-rail power supplies aren’t affected by those problems — and anyway, the whole point of running trials is to iron out any problems that might crop up.

  8. Andy T says:

    If this technology is able to be expanded for the road network at some point in the future, for example large underground battery stores in filling stations, it would be a game changer for electric road transport

    • Geoff says:

      This is already a thing, a fast electric charger with a battery attached, that can charge slowly. It can be rolled out in rural areas, where the grid would need upgrading, and there are less cars to recharge.

  9. ChrisBCN says:

    Thank you for explaining about the trickle-charged batteries, never knew that.

  10. Brian says:

    Excellent article, saw one of the battery powered trains parked up at the weekend.

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