Electric vehicles. You hear about them, read about them, see them in advertisements and follow arguments for and against the technology. But really, what are electric cars?
Understanding an electric car is actually much simpler than it may initially appear because it has a lot of similarities with electrical appliances and gadgets which are a common fixture today. Take a kitchen blender for example. It has an electric motor, actuated by applying voltage to its terminals and to this, a plastic gear is fastened such that the gear rotates with the motor shaft. To this gear, an upper gear is meshed so that the motor shaft and the gear assembly rotate simultaneously. The chopping blades are attached to this upper gear and hence also rotate together and at the same speed as the motor, facilitating the chopping of the contents of the blender jug. Similarly, the electric vehicle has a motor whose shaft is coupled to the wheels which will then rotate with the motor just as is the case with a blender. Whereas a wall socket is used to supply power to a blender’s motor, an electric car’s motor is powered by a battery housed in the vehicle chassis.
So how different is an electric vehicle from a conventional combustion vehicle? The prime mover of an electric vehicle is a motor and not the engine. Similarly, since there is no engine, the cubic capacity (cc) is not a specification applied to electric vehicles because the issue of measuring fuel displacement in the cylinders does not arise.
What about the transmission/gear box which exists in combustion vehicles; do electric cars have it? To answer that question, we need to know what the transmission is used for in conventional vehicles. When fuel combusts in the engine, the energy released applies a turning force (torque) to the crankshaft which transmits motion through a set of gears to the wheels. The torque applied to the crankshaft, known as the engine torque, is dependent on the speed in revolutions per minute (rpm) at which the engine (not the wheels) is running. Torque applied to the wheels is known as transmission output torque responsible for moving the wheels.
If we wish to start a car from rest, the engine must provide sufficient force to propel the entire mass of the car forward. If a gear attached to the crankshaft was meshed with a second gear of the same size and coupled to the wheels, the torque produced at the engine should be the equal to the transmission output torque. Changing the gear ratio to a value greater than 1(by making the driving gear smaller than the driven gear) would raise the transmission output torque, which is the product of the engine torque and the gear. In order to accelerate the car, we shift the gears such that the gear ratio is reduced and the driven gear ends up with a higher rpm, moving the wheels faster at the expense of torque.
What about the torque and speed of electric cars? Electric motors have the capability of generating maximum torque at very low rpm and produce relatively similar torque over a wide range of speeds, making a transmission/gear box generally unnecessary. Furthermore, the gearbox would add non-functional weight to the car. This availability of maximum torque at near standstill gives electric vehicles their impressive acceleration.
Electric cars are also very silent, why? They use alternating current induction motors instead of direct current motors which are characterized by a noisy changing of the magnetic field.
How then do we select an electric vehicle based on its specifications?
Well, the first thing to look at is the capacity of its battery which is the source of power. A battery’s capacity is specified in kilowatt hour (kWh) or Ampere-Hour (A-hr). The battery comprises of several individual cells are grouped together to form modules, which make the battery pack.
The cell modules are wired appropriately to increase their effective output. Nissan leaf, which is arguably the most popular electric car, has battery capacity of 24 kWh in its 2013 version. This version has a consumption rate of 236 Wh/mile when driving at 50 miles per hour (mph). At this speed, this model can be driven for around 70 or so miles before the battery needs a recharge. Simple calculation with the given specifications would result in a range of 100 miles instead of 70 miles. This is because it is not advisable to completely discharge the battery in order to prolong its life which means not the entire 24 kWh is usable. The design of the battery is continually being optimized to occupy the least physical space and minimize weight requirements.
Because the battery is such a crucial component to the electric car, the internal charger should also be considered when purchasing the vehicle. Electric vehicles are widely charged at home when their owners retire from the day’s travels. Simply plugging in your vehicle to a wall socket will charge the battery at a very slow rate adding only about 4 miles of range with every hour of charge. The implication of this charging rate for 2013 Nissan leaf is that it will take you over 20 hours to charge your car! Home chargers are usually Electric Vehicle Service Equipment (EVSE), which allow the car’s internal charger can operate at its rated capacity, that is, restoring 7 and 22 miles per hour for the 3.3 kW and 6.6 kWh internal charger respectively. It will take around 4.5 hours to charge a 24 kWh battery with an internal charger rated at 6.6 kWh using an EVSE. The electric car also incorporates an interesting ability to reclaim energy that would otherwise be lost as heat when braking to charge the battery in what is known as regenerative braking. This concept is very useful, if the battery is not full.
So if electric cars are so serviceable, why aren’t there more of them on the road?
The biggest challenge lies with the net calorific value or the energy per volume of electricity as a fuel compared to petrol used in conventional vehicles. The energy per volume of a lithium ion battery used by the electric car is 280 Wh/liter compared to 9,700 Wh/liter for petrol and 10,700 Wh/liter for diesel. Take the 2013 Nissan leaf which consumes 236 Wh/mile. Assuming the mass of the car remains the same, a liter of petrol would take the car 41 miles compared to the 1 mile that a liter of electricity from the battery would take it. In other words, for a single car battery to drive a car an equivalent of 41 miles between charges, it would require to be around 41 times bigger! How much weight would such a heavy battery add to the car? Of course, additional weight would mean that more power has to be drawn from the battery because the mass to be propelled is now larger necessitating an even bigger battery and the power requirements would just keep growing. The problem becomes comparable to an ouroboros!
The practical limit to the weight of battery that can be installed in the vehicle means the battery has to have a much higher energy density than a normal battery, making the battery pack the single most expensive component of the electric car, driving its price much higher above a corresponding engine vehicle. In 2012 for instance, Ford’s company electric vehicle, the FOCUS EV, was retailing at about $39,200. Its 23 kWh battery, cost between $12,000 and $15,000, which is about a third of the total cost! This represents a cost of $500 – $650 per kilowatt which is very high. Currently, the price of batteries is steadily falling with General Motors disclosing that its cells now cost $145 per kilowatt. A reduction in the price of batteries means the price of electric vehicles can also come down.
An additional cost is replacement of batteries, which can only withstand a certain number of charge/discharge cycles before they start deteriorating. Newer gadgets take longer between charges but as they grow older, frequently charging is required because of the loss of capacity. Reduction in battery prices would be very favorable to electric car owners.
The other big challenge faced by electric cars is charging. Generally speaking, there are two ways to charge an electric vehicle. One is to use an EVSE which charges either at the rating of the on-board charger or rapidly charge the battery with high DC power. EVSE charging is widely known as level 2 charging, utilizing 240 V at 30 A. Rapid charging models itself after the fuel filling stations that are available for engine powered cars. The on-board charger is bypassed and the battery is fed directly with very high DC power. One of the most common fast charging protocols, the CHAdeMO from Japan, deploys chargers that can supply beyond 50 kW per hour, which means that it would take about 30 minutes to charge a 24 kWh battery.
Fast charging stations are costly and require a large amount of power that is not employed in residential establishments. These stations are located in public places where the electrical grid has the capability of delivering such power. The cost of putting up a new fast charging stations is anywhere between $50,000 and $100,000 due to the high cost of hardware and more often than not, the need to install a transformer at the site. This figure does not even include the running and maintenance costs. An investor wants reassurance of a reasonable payback period, which might be in question if the numbers of electric vehicle on the roads remains small. On the other hand, some potential buyers are dissuaded by the long home charging hours seeing as fast charging stations are still few and far between.
A big selling point for electric vehicles has been the reduction of pollution due to the absence of carbon dioxide tail pipe emissions produced by engine vehicles and also because the electricity used for charging can be produced from green sources such as wind and solar. If this is true, why are these freely-available, renewable energy sources not utilized to produce electricity as the car moves in an attempt to increase the vehicle’s range? Solar technology has not achieved efficient conversion from heat to electricity that would make it a viable source for powering the electric car for everyday use. Installing wind turbines in a car would mean that the power consumed to facilitate the electricity generation is more than the power that can be generated for the car. And this is why: an object moving in an enfolding fluid induces a force known as the drag that tends to oppose the movement of the object, which is exactly what the turbines would be subject to because of the moving blades. Overcoming drag force means drawing even more power from the battery. Wind turbines also require special tuning and must be mounted at the right height and orientation. The extra controls to achieve this positioning would increase the complexity of the central control system as well as the cost of the car. We must also not forget no matter how functional a car is, we all want to drive an instrument of aesthetic distinction. Hardly anyone wants to be seen with a car that looks like a sail boat on wheels!
So, are there other different types of electric cars?
An efficient category of electric cars are those powered by fuel cells instead of electrochemical cells. In a fuel cell, hydrogen is stripped of its electrons by a chemical process and as these electrons travel from the anode to the cathode of the cell, they form an electric current which is used to power the motor in fuel cell electric cars.
The hydrogen fuel cell vehicle holds the title of most eco-friendly vehicle, with the only exhaust emission being water, which is the by-product of the chemical processes in the cell. Hydrogen fuel cell vehicles are quite promising and may become a staple on the roads if the unit price drops and more charging infrastructure is available. A hydrogen fuel cell vehicle currently in the market is the Toyota Mirai which boasts an impressive 312 mile range on a full tank, a figure positively comparable with engine driven vehicles. This vehicle was introduced with a price tag of $57,500 in the United States in 2015.
The challenges facing fuel cell electric vehicles are akin to those faced by battery electric vehicles. The obstacles can be categorized in terms of technology, cost and infrastructure. Technology aspects include the energy density of hydrogen, which has thankfully improved over the last few years, so that a 50 kW hydrogen cell fuel cell is now the size of a microwave whose compact dimensions can easily be integrated into a car. There is also the issue of a hydrogen storage tank inside the car. In operation as a fuel, hydrogen has to be pressurized to achieve a viable energy density. With progressive research, the storage pressure has increased allowing storage of more fuel in the car, thus extending the range. The operating temperature of hydrogen for use as fuel is also very low requiring very large radiators for cooling which presented a challenge. Owing to intense research in fuel cell technology, many of these challenges are continuously being overcome. With regard to cost, although hydrogen is the most abundant element in nature, it does not occur stand-alone and an intermediate operation must be carried to liberate hydrogen from other compounds. One must also consider the cost of producing the fuel cell which is still understandably high, the cost of putting up a hydrogen refueling station as well as that of specialized storage of hydrogen at the stations. Just as with the fast charging stations, investors are reluctant to pour money into infrastructure whose return in uncertain while potentials customers are conscious of the scarcity of hydrogen fueling stations. One country in which hydrogen fuel cell vehicles have a large uptake is Germany and this can partly be attributed to an ingenious benefit they offer electric utilities and the increased uptake of renewable energy sources. As of 2011, power from wind energy in Germany accounted for over 7% of the total power produced with the figure rising steadily in the ensuing years.
Are there other forms of electric transportation apart from vehicles?
Electric mobility also encompasses electric two wheelers such as push bikes and e-scooters. In 2012, over 25 million units of electric two wheelers were sold worldwide and over 90% of these were push bikes sold in China. Hybrid cars, which combine a combustion engine and an electric motor drive, are more popular because the engine can kick in after the electric battery dies, eliminating the range anxiety associated with pure electrics.
So, what are the market opportunities presented by the electric mobility industry?
The biggest areas of investment is the supply chain, for example in the manufacture, sale and installation of home chargers and fast charging stations. There is also the unique battery market that will exploit second life use of vehicle batteries after they are retired as well recycling trade. This particular venture may not pick up for a few years because there are as yet not many aged electric vehicles. The prospect of car sharing or carpooling services that use electric vehicles or taxi services that use electrics is also a potentially profitable venture. This is especially viable for travel around a city where distances are short and the presence of public charging stations would be higher than in rural areas.
Because an electric car is basically a complex electric gadget, app developers have a rich environment for which to cultivate products. An app developer can create platforms to inform drivers of nearby charging stations, billing data, communicate state of charge of the vehicle and so on. Car manufacturers actually update the vehicle operating systems wirelessly and owners should, therefore, be able to communicate with their cars using apps.
Electrical utilities can also use the vehicles for load balancing because of the sizeable capacity of their batteries, noting that especially for personal vehicles, a large percentage of time is spent with the car parked. Why not organize for a profitable exchange of electricity during these idle moments? Perhaps the most comprehensive opportunity would be served by entities that act as integrators or aggregators of all these services. An integrator can facilitate the installation and maintenance of charging stations, coordinate the vehicle and grid interaction for load balancing which would require an extensive IT infrastructure with built in communication protocols to authorize and synchronize events.
It will also be interesting to see how car manufacturers evolve their business models to sell electric vehicles. Because of their relatively high cost, an enticement is required to woo potential buyers. Perhaps settle for cutting down the deposit and instead opt for a monthly payment schedule with a package that includes subsides for fast charging at particular stations or certain online service such as free access to certain phone applications for use with the cars.
The electric vehicle has been around for a long time; it actually was the first automobile ever produced. However, the discovery of oil, hence surmounting the insufficiency of the energy density of electricity as a fuel relegated electrics to the back burner wistfully watching while the internal combustion engine took over the world. Although the industry has gained momentum in recent times, it is still too early to tell whether electric vehicles can reduce the engine vehicle market share. New trends in urbanization such as the development of mega cities and mega corridors may probably play a great part in increasing the uptake of these vehicles. For instance, governments may introduce low emission zones in such large metropolises and impose congestion charges in an effort to mitigate traffic. Electric vehicles would thrive in such cities. The increased population would also mean that infrastructure investment would not be such a daunting venture and novel ventures such as the car sharing mentioned earlier would find their niche.
There are still a lot of maybes in the tale of the return of the electric vehicle. We are earnestly watching to see if the electric mobility age finally arrived!
About the Author:
Esther Wangui is a Ph.D student in Electrical Engineering at the University of Botswana. Her areas of interest are power distribution, specifically from renewable energy sources.