We’ve all seen the news... the internal combustion engine is dead; the future is electric! We live in exciting times as far as automotive propulsion is concerned, it used to be that the choice was either gasoline or diesel (some limited LPG/CNG). Just a few years later and there is a much wider choice; including cryo-engines, clean 2-stroke, clean diesel, fuel-cells, hydrogen as a fuel, even compressed air engines. Some of these technologies clearly have a place in specific applications but the big investments are being made in electric vehicles. We’ve all read the news, or know someone with one, so it seems a foregone conclusion that the future is electric right? Well maybe, but it’s not that simple. Many people do not realise there is a choice of electric architecture or agree on the best path to take for the future. So let's take an armchair view of what ‘electric car’ means by exploring the different architectures competing for the pound in your pocket.
These vehicles have been mainstream for several years. The vehicle uses a conventionally sized internal combustion engine (ICE) but replaces the starter motor & alternator with one unit – an ISG (integrated starter generator). These vehicles have no means of electric propulsion, the engine always drives the wheels. However, when stationary the ISG allows the engine to be turned on and off again quickly without the use of the ignition key. When in the off position the vehicle is using no fuel and producing no emissions. This means that average fuel consumption and average emissions are decreased when a homologation driving cycle is run. The frequent stop/start system can cause batteries to discharge quicker and so some form of regenerative braking is usually employed to convert wasted kinetic energy into useful stored battery power.
Advantages: Conventional technology, limited change in architecture needed, inexpensive solution, some improvement in emissions and fuel economy.
Disadvantages: Stop/start can be confusing at first, improvements in economy and emissions are limited and sceptics argue benefits are negligible in real-world driving.
PARALLEL HYBRID (SELF CHARGING)
These vehicles have a conventional (usually gasoline) ICE plus an electric motor. Both the motor and engine can drive the wheels either separately or together. When pulling away, electric power only is used until the vehicle reaches approximately 20mph. Thereafter the ICE provides all of the propulsion and in addition charges the battery (regenerative braking is usually employed too). Under full load, the electric motor kicks in and provides additional power alongside the gasoline engine. An example of this technology being applied is the Toyota Prius.
Advantages: True electric vehicle in that electric power does propel the vehicle under certain conditions, no need to manually charge the vehicle, no range anxiety, offers greater fuel economy, performance and lower emissions.
Disadvantages: If used on shorter runs the battery never charges, as such it is propelled exclusively by the ICE. With the additional weight of the electric motor and engine, fuel economy and performance are reduced if in this mode. More costly to produce and more likely to fail due to ICE and electric motor.
PARALLEL HYBRID (PLUG-IN PHEV)
Propulsion architecture is the same as above, but the battery is replenished by plugging into a charger. With the ability to charge the vehicle, it can run for longer on electric power thus improving economy and emissions further. Examples of this technology being applied is the Mitsubishi Outlander PHEV.
Advantages: Increased fuel efficiency, lower emissions, longer all electric range and thus cost/mile of motoring reduced.
Disadvantages: Overall 'greenness' of using and ICE and e-motor is questionable; recyclability an issue as battery packs need more frequent changing, extra strain on national grid, no standardised charger, extra infra structure required.
RANGE EXTENDED HYBRID
Range extended hybrids have both an electric motor and small displacement ICE (500-700cc), but only the electric motor is connected to the wheels meaning all propulsion is electric. The ICE is used solely as a generator to charge the battery and as such can be optimised for this duty cycle (i.e. minimal changes in load/speed). This solution is really for those users where range anxiety is an issue. An examples of this technology being implemented is the BMW i3 range extender.
Advantages: Reduced running cost per mile, high performance from electric motors, range anxiety reduced as engine can charge the battery, reduced weight compared to parallel system. Fuel economy and emissions can be zero depending how driven.
Disadvantages: More complex and costly to produce than full electric; more a psychological fix than an ideal technical solution.
BATTERY ELECTRIC VEHICLE
These vehicles have only an electric motor for propulsion– there is no ICE engine. As such they must be plugged-in to charge. These are pure all electric vehicles. Batteries are usually built as structural members, closely packed and fitted wherever there is space (usually floor to reduce centre of mass and thus vehicle handling). Examples of this technology includeTesla.
Advantages: Zero emissions, lowest running costs, exhilarating performance, simple compared to ICE and thus price will fall with economies of scale, no local pollution.
Disadvantages: Range is limited to 150-200 miles in good conditions, require owner to have charging point, long time to charge, pollution moved to power stations, investment in infra structure required, recyclability, battery flammability, architecture of vehicle significantly changed to reduce weight/improve dynamics.
THE FUTURE OF BATTERY
It seems most investment is going into pure BEV although several Japanese manufacturers see self-charging or PHEV as the winning solution. Regardless the race is on to increase range and decrease charging times. Here are a few changes we may see on battery vehicles of the future:
More intelligent use of power: New heating/cooling technologies for HVAC, greener driving modes, intelligent connectivity that builds in charging stops (or reserves charging) into satnav.
Solar cells (PV) cannot capture enough sunlight to propel a vehicle (at the moment) but could potentially be used to power ancillary systems and provide a trickle charge.
Connected autonomous vehicles: The connected and self-driving car – if a car can navigate and drive itself, it can drive itself to local communal charging points while the owner is sleeping.
Charging: Batteries that can accept a higher charge rate and an infrastructure than can deliver more power per hour, use of inductive charging, standardised plugs.
Improved battery chemistry: Current lithium battery technology uses a 'slush' electrolyte, this is flammable and uses cobalt which is toxic. Improvements in battery technology include solid state, low cobalt electrolytes with ion carrying capability on par with slush. These will allow more tightly packed cells and thus overall higher energy densities and improved flammability safety. Chemists are also looking at sodium or even magnesium-based cells.
WHAT ABOUT OTHER TECHNOLOGIES?
Even with the improvements in battery technology, they will still have inherent disadvantages – time to charge, range, safety, additional infra structure. So are there any alternatives?
Fuel cells: The use of electrolysis to combine oxygen (from air) and hydrogen (stored on vehicle) have been talked about since the 1950’s. They produce no noxious emissions and can be refilled like a traditional gasoline car and so surely this is the future? On paper they offer a lot, but in reality there are the following challenges to overcome – hydrogen infrastructure does not exist (volume production, storage and distribution), safety of storing hydrogen, reliability and durability are much lower than ICE. Very little R&D investment is going into fuel cells for cars (Hyundai excepted) and no government legislation has been shaped to hasten adoption. Its seems therefore that hydrogen is a dead end...or is it?
Hydrogen as a fuel. Hydrogen is the most abundant element in the universe, has a higher energy density that gasoline or diesel and burning it as a fuel can be done in a modified ICE with no carbon pollutants (NOx may still be an issue). Furthermore, some vehicle by their nature eg PSVs, have duty cycles very unfavourable to current battery technologies (frequent stopping/starting, large volumes to heat, pressure to minimise down time. The challenges of hydrogen distribution and storage still remain, but some manufacturers are actively researching workable hydrogen fuel engines.
So, there you have it! The future is electric we’re told. Unless it’s hybrid...or then again... is it hydrogen? Join the debate andlet me know what you think.