Hybrid Vehicle Range Extenders: Goodbye
Pistons
By Dr Peter Harrop, Chairman, IDTechEx
Hybrid vehicles are already big business from hybrid cars, buses
and trucks to outdoor forklifts, even hybrid tugboats. Indeed, many
hybrid aircraft will soon appear. An increasing majority of hybrid
powertrains are series hybrids where the engine only charges the
battery: it never drives the wheels. As explained in the IDTechEx
report, Range Extenders for Electric Vehicles Land, Water & Air
2015-2025
www.idtechex.com/range, the conventional engines
with pistons that are used as range extenders are now being questioned
because they are not a good starting point in making a lowest cost,
weight and size power source that is very reliable and lasts the life
of the vehicle.
Development of these "reciprocaurs", as opponents
describe them, is being questioned because many simpler alternatives
are beginning to look feasible. That said, the hold-up of such piston
engine advances as the single cylinder Polaris range extender and the
in-line free piston engines that directly provide electricity seems to
be more a reluctance to invest than a technical problem.
One example of the potential escape from pistons originates from
the fact that jet airliners have Auxiliary Power Supplies APU that are
used on fairly steady load in the tails of jet aircraft for hotel
facilities etc not flight. Derivatives of such Capstone turbines have
had modest success as range extenders in buses and trucks, Total Cost
of Ownership being one of the limitations.
Bladon Jets in the UK is developing tiny jet engines you can hold
in your hands, cost reduction being promised from miniaturisation,
having only one moving part and selling them in volume for home and
office electricity supplies in countries such as India. The blades and
shaft are spark eroded as one piece.
In an alternative approach, Monash University in Australia, in
collaboration with Safran Microturbo of France, has made a small jet
engine using 3D printing. Being additive, this wastes very little
material, potentially taking costs of gas turbine range extenders even
lower. Indeed Rolls Royce in the UK is already making jet engine parts
this way that will fly later this year. They are both achieving more
complex shapes and showing how to reduce costs. Monash uses laser 3DP
but Rolls Royce used electron beam 3DP.
Microturbo is a member of the Safran group and a subsidiary of
Turbomeca and it designs, develops and manufactures low-power gas
turbines. Microturbo has become a global reference in small robust,
reliable turbines and turbojets. It works on two lines of products.
They are on-board APU for airplanes, helicopters and ground
applications and starting systems and secondly turbojet engines for
missiles and targets.
Change of course with fuel cells
Fuel cells are another "new" range extender if we
ignore the fact that they have been around for 175 years and
concentrate on the fact that they are yet to be successful in
vehicles. Enthusiasts keep talking about five years from now, when the
problems of cost, maintenance, size, charging infrastructure and so on
start to be overcome to the point of volume production being
contemplated, for example with Toyota expecting to produce up to tens
of thousands of fuel cell cars.
Fuel cell materials developer ACAL Energy points to, "a
number of breakthrough technologies that will be bought into the
second generation fuel cell vehicles between 2020 and 2025 that
overcome all of these issues and ACAL Energy's liquid catalysts will
be part of this. ACAL liquid catalyst technology addresses the
problems of:
• Instantaneous response to load
• Removal of all cathode degradation mechanisms
• Ruggedness - ability to operate with pin-holes in the
membrane
• Simplified balance of plant
• And a 50% reduction on catalyst cost when compared with
the Pt cost target required to get to <$35/kW system cost.
Battery/Supercapacitor technology is complementary to FC
powertrains as all the auto OEM's we are engaged with plan some form
of hybrid drive system".
Proton Motor has developed fuel cell vehicles for 20 years with
its own fuel cell stack and system design know how. It is currently
developing a range extender fuel cell bus system with a fuel cell
performance of 25kW and a battery on board between 80 to 120 kWh,
depending on the drive cycle. This concept will allow a 12m 18 tonne
city bus to run at a two shift operation with a refuelling time of
hydrogen in 10 minutes. Cost for the bus is in line with the EU target
for 2020, they told IDTechEx.
The advantages are fast refuelling, full range of operation, less
weight and higher payload compared to a pure battery bus, less
batteries on board (reduction of resources and problems to recycle
large amount of batteries), low maintenance compared to a bus with a
large fuel cell system, long lifetime of the fuel cell based on
optimized operation mode and longer lifetime of the battery as it can
be operated in an optimized SOC. Will cost be competitive? The BYD B9
is this size of bus and it is selling in many thousands already but
its recharging time is 30 minutes or more.
Certainly more fuel cell cars are now appearing albeit in tiny
quantities, though trials of fuel cell buses peaked ten years ago and
the architecture is hybrid with the fuel cell as range extender, there
being a large NiMH or Li-ion battery or a supercapacitor with
conventional battery, these doing start-up, accepting energy
harvesting electricity and managing load variations. Also see the
IDTechEx report "Electric Buses 2015-2025"
www.idtechex.com/ebuses.
Given the slowness of improvements and growing competition from
improved pure electric vehicles, which are greener, attitudes have
changed this year, with developers realising they must be open and
accept help from any quarter. At the recent World Smart Energy Week in
Tokyo, GM, which did a partnership with Honda for fuel cell
development out of necessity to reduce risks and required investments,
now called for suppliers to approach them.
Toyota recently threw its fuel cell patents open for a limited
time to try to accelerate progress - Its Mirai fuel cell car being
sold in very limited quantities presumably due to cost. In Japan,
Toyota told IDTechEx that they can warranty 200,000 km of fuel cell
durability - big progress with one former problem - but they do not
know how the car resale market will evolve. Very low resale prices for
battery electric cars have inhibited sales and the same will probably
be true of fuel cell cars for some time.
Volkswagen said their position on fuel cells is that they are not
fully convinced that fuel cell cars will be widely deployed. They will
not invest highly and will use a petrol car platform for their fuel
cell car development. They are concerned about how zero carbon fuel
cells cars will ultimately be, given hydrogen from fossil fuels and
the complexity of manufacture. Indeed, a hydrogen fuel cell typically
emits one kilowatt of heat for every kilowatt of electricity
used.
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