Fuel-Cell Electric Vehicles
Another type of electric vehicle is now coming into consider-
ation. This is the fuel-cell-powered version (FCEV) in which
hydrogen fuel is stored on board and fed to a fuel cell that
produces electricity to run the electric power train. The only
by-product at the vehicle itself is water.
FCEVs have entered the market later than BEVs because the
underlying technology is much newer, but they are now
becoming commercially available. Toyota’s Mirai sedan and
Hyundai’s ix35 SUV are being sold in small numbers in several
countries, and are both on trial in Australia. Honda’s 2017
Clarity is also on sale outside Australia. More than 10 main-
stream manufacturers have FCEVs in or near production.
This also sounds great, but the same problem as BEVs crops
up: nearly all hydrogen still comes from fossil fuels (by reforming
natural gas), and the associated pollution is released at the
hydrogen production plant, not avoided.
Hydrogen production from electricity – which would need
to be sourced from renewables – by electrolysis of water is a
well-known industrial technology but, like renewable electricity
production itself, is in its infancy compared with the scale
needed to have a major impact on global CO 2 emissions. If the
electricity is generated without CO 2 emissions, then a closed,
sustainable cycle is formed in which hydrogen is extracted from
water using electricity and used to run the FCEV, producing
the same amount of water again. In this scheme, electricity and
hydrogen are the carriers through which the source energy
(solar, wind) is eventually transformed into motive power.
Generating the required electricity at the scale required to
operate a national fleet is feasible. However, significantly more
electricity generation is required than in the BEV case becausethe efficiencies of the electrolyser
(producing hydrogen from water) and the
fuel cell (producing electricity and water
from hydrogen) are both about 50%; in
contrast, the efficiency of the battery in a
BEV is probably above 90% depending on
how the vehicle is driven.
So why would we even consider
hydrogen-powered vehicles, and why are
major automotive manufacturers bothering
to build and sell FCEVs? One answer is their
range, which easily exceeds that of a BEV
(see box: The BEV Range Conundrum).
Another is the different demand for mate-
rials. Whether enough materials can (or
should) be supplied to make the batteries
necessary for a global BEV fleet is a very big
question, since relatively scarce elements
such as lithium are used.
In the FCEV case, pressurised hydrogen is stored in a very
sophisticated tank made from common elements, principally
carbon (in carbon fibre and polymers) and aluminium. The
difference between this and a BEV battery is that the hydrogen
is stored as itself, just compressed, so only a container is required,
not a storage medium. The FCEV does have a battery to smooth
the power demand on the fuel cell, but it’s much smaller than
in a BEV.Electric Trucks and Buses
The BEV–FCEV range comparison holds true for buses and
trucks. Battery-powered buses and trucks, with ranges around
200 km, are excellent in urban situations. For long-haul or
infrequent refuelling, commercially available hydrogen-powered
buses have ranges around 500 km, and the Nikola One and
Nikola Two fuel-cell semi-trailer trucks are claimed to have a
range of 1300–1900 km.
The contrast between the achievable range for current
batteries and fuel cells is starkly illuminated by the Nikola One
and Nikola Two. Their relatively massive 320 kWh battery –
about three times the capacity of a high-end Tesla Model S
battery –can run the 745 kW drive motors at full power for only
about 35 minutes (to 80% depth of discharge), so ~200 km of
level terrain might be crossed on a single battery charge. The
majority of the range comes from recharging the battery on
the fly using the 300 kW hydrogen fuel cell and stored hydrogen.Bumps in the Road
There are several big bumps in the road to electric vehicles.
The lack of refuelling infrastructure is one: vehicle buyers
are wary of the scarcity of refuelling/recharging stations, and30 ||MAY/JUNE 2017
The Toyota Mirai FCEV can achieve a range of ~500 km with its 5 kg hydrogen tank.