investors won’t bankroll the needed
infrastructure unless there are vehicles to
use it. This affects FCEVs more than
BEVs, since the roll-out of BEVs and
charging points is further advanced. BEV
charging points are simple and cheap
compared with a high-pressure hydrogen
refuelling station, but more are needed
because of the BEV’s range problem.
Another bump is cost, but that is the
case with all new technologies. Early
adopters pay more, but high-volume
production brings down the price dramat-
ically – look at the example of photovoltaic
panels – and this bump will vanish. In
January 2017 there were 274 hydrogen refu-
elling stations around the world, and the
number is growing at about 50% per year).
The biggest bump –of major concern
in relation to lowering CO 2 emissions to
zero to minimise global warming, and
fundamentally the reason to change to
electric vehicles – is really the need for
sustainably produced electricity to
recharge BEVs and generate hydrogen for
FCEVs. The associated lesson is that solu-
tions to a complex problem that ignore
the connected nature of the problem never
work.
BEVs or FCEVs?
Which type of electric car to go for
amounts to “horses for courses”. For short
trips, modest performance and a daily
distance travelled of 100 km or so, a small
BEV recharged at home or work will be
convenient for many drivers. For long
trips in a modestly sized vehicle with
decent performance and a quick refuel,
FCEVs are the logical choice.
Either way, as long as the electricity or
hydrogen is sourced from renewable
resources rather than fossil fuels, we can
buy electric cars in the knowledge that we
really are doing something positive for the
planet.
Evan Gray is Professor of Physics in the School of Natural
Sciences at Griffith University. Information about hydrogen
filling stations from H2stations.org was provided by Ludwig-
Bölkow-Systemtechnik GmbH.
MAY/JUNE 2017 | | 31The BEV Range Conundrum
BEVs generally have a small driving range: the Nissan Leaf’s range is approximately
150 km, depending on how you drive it. However, the top-of-the-range Tesla
Model S has a claimed driving range of up to 500 km.
Among FCEVs the small Toyota Mirai and the medium-sized Hyundai ix35s both
have a claimed range around 500 km on a single 5 kg tank of hydrogen.
What’s going on here? Why can’t all BEVs have a 500 km range. How does a
small FCEV manage this trick? To understand what’s going on, we should first
remember that power (measured in kilowatts) is the rate of production or use of
energy (measured in kilowatt-hours).
The key point about the FCEV is that the energy-containing hydrogen fuel is
retrieved from the fuel tank at the rate needed by the fuel cell to provide the
required electric power to the traction motors. The maximum continuous power of
the vehicle is set by the fuel cell and the motors. The range is set by the volume of
the fuel tank, just as in an ICEV.
In other words, power production in a FCEV is decoupled from its energy
storage capacity. As long as the volume of the fuel tank can be accommodated
within the vehicle’s envelope, the range can be extended to match an ICEV with
very little need for increased fuel-cell and motor power, because the hydrogen tank
constitutes a small proportion of the vehicle’s weight.
Now let’s think about the BEV in the same way. Vehicle batteries are very heavy
compared with a hydrogen tank for the same stored electrical or electric-
equivalent energy. The BEV battery pack is modular, so to make a bigger battery
that stores more electrical energy we just add more modules. This sounds simple
and obvious, but the consequences are far-reaching for our BEV’s design.
The maximum power of the vehicle is set by the traction motors, so the battery
pack should supply this power, but greater power cannot be used unless the
traction motors are upgraded. That’s the point: the power rating and energy
storage capacity of a modular battery pack are proportional, so adding more
batteries to increase the driving range also adds more power rating, whether or
not it is needed. It also adds more weight to the vehicle.
To get a big driving range requires a big, heavy battery pack, and this big,
heavy battery pack can deliver awesome power. This big, heavy, awesomely
powerful battery pack is also very expensive, so we end up with a big, heavy,
awesomely powerful and expensive luxury vehicle as the logical outcome of
wanting a 500 km driving range.
If we opt for a small battery pack with modest power output, we end up with a
small, relatively cheap BEV with a restricted driving range. The driving range
problem of current BEVs comes down to the fact that the power production and
energy storage are naturally coupled in modular battery packs.The top-level Tesla Model S is a BEV with a claimed range of up to 500 km.