COMMUTERS MAY not have paid them much attention, but a small array of solar panels next to the railway line at Aldershot, a town 50km (30 miles) south-west of London, could herald a greener future for train travel. The site is an experiment to supply electricity generated from sunlight directly to a railway line. It is the “directly” bit that is novel. In Britain, as in many places, solar power is already fed into the grid, and it is the grid which train operators plug into. So, in a sense, many electric trains already use some solar power. But by connecting the panels to the line itself, trains can be powered more efficiently.
Admittedly, it is not at present a lot of power. At around 37 kilowatts the site could easily top up the battery of a Tesla electric car, but it might not move an electric train very far. That does not matter at this stage, because it is there to test a concept rather than run a railway. And the concept is working, says Stuart Kistruck, director of engineering for the southern region of Network Rail, the government-owned operator of railway infrastructure in Britain.
Network Rail is working on the project in collaboration with Imperial College, London, and Riding Sunbeams, a not-for-profit company set up by climate activists to promote locally owned renewable-energy projects. The plan now is to scale up the idea and roll it out elsewhere.
Connecting up the Aldershot site was made easier by a quirk of history. When the electrification of Britain’s railways began in the late 19th century, two systems were used. In much of the country overhead lines were installed, but in crowded south-east England a “third rail” was used instead. This consists of a conductor rail placed alongside the track on insulated brackets. A pickup shoe near the wheels of the train draws power from this rail.
Third-rail systems tend to be employed in urban railways because they are easier and cheaper than making tunnels and bridges large enough to accommodate overhead cables—and the railway lines of southern Britain have plenty of low bridges and tunnels. For safety and other reasons, third-rail systems typically operate at 750 volts DC, a much lower voltage than overhead lines, which in Britain run at 25 kilovolts AC. As it happens, solar arrays typically put out DC current at 600-800 volts, which reduces the complexity and cost of connecting them to the railway line. Another convenience is that, to reduce transmission losses, third-rail networks have more closely spaced substations. These provide handy feed-in points for lineside solar power.
One problem facing groups like Riding Sunbeams is that electricity grids are rarely designed to accept power from small and varied sources, so feed-in arrangements can be hard to set up. A passing railway line, however, provides an alternative, says Leo Murray, the company’s director. Along with Network Rail, Riding Sunbeams has drawn up a list of other sites that might be suitable for larger installations.
Apart from green PR, what does Network Rail get out of this? First, there is a lot of unused land next to railway lines, where solar panels could be placed. Those panels would also shade vegetation, reducing its growth and the amount of cutting-back required. The “leaves on the line” excuse for late-running trains is a bit of a joke in Britain, but the slippery conditions leaves cause for train wheels are a big problem.
Second, it is a good deal. Lineside solar electricity will be cheaper than that from the grid, Mr Kistruck calculates. Overall, he reckons, 10% of the southern region’s power needs might be met this way. Such savings are not to be sniffed at. With around 40% of the country’s rail system electrified, Network Rail is Britain’s biggest single user of electricity. It has an annual bill of around £300m ($390m) just for traction.
The idea could also be employed elsewhere, and not just on urban lines. With additional work it might be adapted for overhead-powered systems as well. It looks particularly promising in countries beyond cloudy Britain. India, for instance, is keen on using solar power to electrify its rail system. Indian Railways has been fitting solar panels onto the roofs of some train carriages. They are still pulled by dirty diesel-powered locomotives, but the panels run the lights, fans and information displays, which saves some fuel.
The limited space available for solar panels on train roofs means that not enough power could be produced to propel an entire train. However, the Byron Bay Train, a heritage railway near Brisbane, Australia, comes close. It is a two-car unit that runs entirely on energy from solar panels on its roof and on the roof of its shed. The converted train, originally dating from 1949, can carry 96 passengers on a route just 3km long—but in a part of the world blessed with plenty of sunshine. London’s commuters have no such luck.■
This article appeared in the Science and technology section of the print edition under the headline “Solar-powered trains could make rail transport greener”