74 Science & technology The EconomistNovember 23rd 2019
C
ommuters may not have paid them
much attention, but a small array of so-
lar panels next to the railway line at Alder-
shot, 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 Net-
work Rail, the government-owned opera-
tor 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-ener-
gy 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 wereused. In much of the country overhead
lines were installed, but in crowded south-
east England a “third rail” was used in-
stead. 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 over-
head lines, which in Britain run at 25 kilo-
voltsac. As it happens, solar arrays typical-
ly put out dccurrent at 600-800 volts,
which reduces the complexity and cost of
connecting them to the railway line. An-
other convenience is that, to reduce trans-
mission losses, third-rail networks have
more closely spaced substations. These
provide handy feed-in points for lineside
solar power.Plug’n’play
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 besuitable for larger installations.
Apart from green pr, what does Net-
work 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 re-
quired. The “leaves on the line” excuse for
late-running trains is a bit of a joke in Brit-
ain, 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 pow-
er needs might be met this way. Such sav-
ings 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 else-
where, 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 fit-
ting solar panels onto the roofs of some
train carriages. They are still pulled by dirty
diesel-powered locomotives, but the pan-
els 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 dat-
ing 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. 7Trackside solar panels can help power locomotivesSolar-powered trainsLight railways
Furnish’d and burnish’d by Aldershot sun