Boom time for
battery traction
Techno Talk
Mark Nelson
We’re back with batteries this month, but batteries of a very different kind – specifically, traction batteries
for cars, buses, trams and trains. Not the sort you are likely to use in electronics hobby projects, but
they may well trickle down into broader fields, cross-fertilising into much smaller types. In any case,
many of us may be driving electric cars soon and we’ll definitely want to know what makes them tick.
T
oday’s urgent need to reduce
carbon emissions and energy
costs means that traditional petrol
and diesel-engined road vehicles are
no longer flavour of the month. Fully
electric cars, having zero tailpipe emissions are greener, cleaner and better
for the environment. New technology
is creating even more environmentally
friendly batteries, as well as focussing
research into more efficient, quieter
electric vehicle (EV) motors.
Existing electrified railways and tramway systems will continue to employ
their overhead wires or conductor rails
to deliver power to the traction units,
but even here battery power has a significant role to play. Not all main-line
railways are electrified, and on lines
that have not yet been ‘wired’, battery
traction offers a far greener option than
choking diesels. It also avoids the visual intrusion of the ‘electrical Meccano’
and ‘wire knitting’ used for suspending the overhead line.
On relatively short routes, batterypowered trains are a very viable option,
with a ten-minute battery charge giving
a range of 50 miles. The British company Vivarail makes battery-driven
passenger trains that are under consideration for use on the Valley Lines
in south Wales. These would run from
Cardiff under overhead wires to the
outskirts of the city, simultaneously
recharging their batteries, before continuing on battery power to destinations
including Rhymney and Merthyr Tydfil.
Visual impact reduction applies
also in cities, which is the reason why
trams on a new route extension in
Birmingham will run partially on batteries. Overhead wires are taboo in
certain historic areas of the city, which
is why trams will use their on-board
batteries to protect the visual aesthetics of Birmingham Town Hall (built
in 1834), the 1879 Council House and
historic buildings in Paradise Street.
Perils of prediction
Atom physicist and Nobel laureate
Niels Bohr famously said, ‘Prediction
is very difficult, especially if it’s about
10
the future.’ So far, people have rather
assumed that electric cars, buses, trams
and trains will charge their on-board
batteries before and after making every
journey, which may sound logical, but
it may also prove to be highly inconvenient. Recharging batteries is not an
instantaneous process, and in an ideal
world it would help if batteries could
also be topped-up along the way.
Wireless charging
Experiments are already underway in
which wireless power transfer (WPT)
methods are used to charge the batteries of electric vehicles while they are
in motion. The system is not totally
wireless; the electric conductors that
transfer the power are laid beneath
the road surface. For this reason, some
proponents use the term ‘contactless’.
Magnetic resonance is currently the
preferred WPT method, on account of
its efficiency and its extended charging distance, but this may well change.
After all, the first domestic radio receivers used inconvenient crystal detectors
and headphones, but these were soon
supplanted by valve receivers fitted
with loudspeakers.
Is the concept feasible? Yes, and already in 2016 Berlin became the first
capital city to introduce wirelessly
charged electric buses in a one-year
experiment. Four Solaris Urbino 12
electric vehicles operated on route
204, their 90 kilowatt-hour batteries being recharged on the move in
a matter of minutes. This was a topping-up process, as the batteries were
charged to full capacity overnight with
cables at the bus depot. The charging
was carried out with metal plates under the road and it was claimed that
the wireless charging system was so
well shielded that the electromagnetic radiation was lower than that of a
conventional induction cooker in your
kitchen. It must be conceded that this
first implementation was not entirely
successful, but practice makes perfect
and the experiment provided valuable
experience for further development.
Meanwhile, electric trams using the
same Primove technology are operating successfully around the world.
All’s fine now?
Well not quite. Mass replacement of internal-combustion engines will require
a vast number of traction batteries, together with the mining and extraction
of huge amounts of lithium. This in itself carries high environmental costs,
and the problems don’t end there either,
because lithium-ion batteries cannot be
recharged indefinitely. Their useful life
is between seven and ten years, and to
quote The Engineer magazine, action
must be taken now to avoid a potentially
massive waste management problem in
the near future. Research work led by
the University of Birmingham in collaboration with Newcastle and Leicester
universities estimates that the one million electric cars sold in 2017 alone will
produce 250,000 metric tonnes (half a
million cubic metres) of unprocessed
battery waste at life-end.
Landfill and storage of spent batteries
is not an option, as they are flammable
and might release toxic materials into
the environment. On the positive side,
recycling spent batteries could present
a massive opportunity, as the manufacture of replacement batteries requires
access to strategic elements and critical materials for key components in
electric vehicle manufacture. On that
basis, recycling exhausted lithium-ion
batteries could provide a valuable secondary source of materials.
There is also another option, as explained by Prof Andrew Abbott of
Leicester University, who was involved
in the research. This would be to use
batteries that are no longer powerful
enough for vehicles to perform less-demanding tasks, such as storing electricity
from wind turbines and solar farms. The
team also said that devising better ways
to gauge the health of a battery would
make it easier to assess whether they
could be reused or repaired. But most
important, he stressed, would be to develop recycling techniques similar to
those for lead-acid batteries, in which
100% of the materials are recycled.
Practical Electronics | March | 2020
