Why do electric cars look different?

A short guide to understanding electric cars

Introduction

I’ve liked cars since I can remember. I remember quite clearly when I was 5 or 6 that we travel a lot between a small town where we lived and a village where my parents were building a new house. To shorten my time on that often location changes, I tried to identify each car that was passing by in the opposite direction. Cars became my hobby and I was curious a lot about the car technology as well. The years passed, I have grown up and also the cars and other vehicles changed significantly since then. Today I am a power electronics engineer with PhD and I have been involved in automotive industry for more than 10 years. Powertrain development as well as auxiliary devices within the vehicles are my profession.

Around 15 years ago first modern electric vehicles popped up with sufficient capabilities to travel longer and faster than their predecessors. To me it was quite interesting, how different those cars looked in comparison to conventional ones. Till now, the market of electric vehicles has become enormous and people around the world have really diverse options if they decide to choose this kind of a car. Nevertheless, it is quite easy to distinguish between them and normal cars. Despite this, we can find more and more electric cars – especially of a sport utility vehicle (SUV) type – which don’t look so very different.

In this article I highlighted a few facts about the electric and conventional cars, batteries and liquid fuels in order to clarify the reasons why the electric cars are so different and why there is no straightforward path to the greener environment when talking about personal transportation. Intentionally I will focus only to the passenger cars but some aspects are also applicable to other fields of transportation.

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Chapter 1: It all started with a big bang

The amount of energy/matter in the universe is constant and derives from the mysterious big bang. Over time, energy/matter becomes more and more spread out and less and less useful, even though the actual amount doesn't change.[1]

Energy runs the universe. It cannot be destroyed or created, it only changes forms. But what is it, this energy? To understand it in a practical way, the energy is actually the capacity of doing work. Since it cannot be created or destroyed, it is always stored in one form or another. One form are fossil fuels which are made of decomposing plants and other organic material. These fuels are found in the Earth's crust and contain carbon and hydrogen, which can be burnt to create different forms of energy, such as electricity. Coal, oil, and natural gas are examples of fossil fuels.[2]

The first car running on gasoline was patented by Carl Benz in 1886 and a huge revolution in personal transportation started. Benz developed a single-cylinder four-stroke engine that converted the energy of gasoline into useful mechanical energy which drove his first three-wheeled motor car.

However, the development of electric vehicles didn’t lag behind. It’s hard to pinpoint the invention of the electric car to one inventor or country. It was actually a series of breakthroughs – from the battery to the electric motor – in the 1800s that led to the first electric vehicle on the road.

To understand the popularity of electric vehicles around 1900, it is also important to understand the development of cars and other options available. At the turn of the 20th century, the horse was still the primary mode of transportation. But as people in Europe and America became more prosperous, they turned to the newly invented motor vehicle available in steam, gasoline, or electric versions – to get around.

Steam was a tried-and-true energy source, having proved reliable for powering factories and trains. Some of the first self-propelled vehicles in the late 1700s relied on steam; yet it took until the 1870s for the technology to take hold in cars. Part of this is because steam wasn’t very practical for passenger cars. Steam vehicles required long startup times – sometimes, in the cold, up to 45 minutes – and would need to be refilled with water, which limited their range.

While gasoline cars were promising, they had their share of faults. They required a lot of manual effort to drive - changing gears was no easy task and they needed to be started with a hand crank, making them difficult for some to operate. They were also noisy and their exhaust was unpleasant.

Electric cars didn’t have any of the issues associated with steam or gasoline. They were quiet, easy to drive, and didn’t emit a smelly pollutant like the other cars of the time. Electric cars quickly became popular with urban residents - especially women. They were perfect for short trips around the city, while poor road conditions outside cities meant few cars of any type could venture farther. As more people gained access to electricity in the 1910s, it became easier to charge electric cars, adding to their popularity in all walks of life.

Many innovators of the time took note of the electric vehicle’s high demand, exploring ways to improve the technology. For example, Ferdinand Porsche, founder of the sports car company by the same name, developed an electric car called the P1 in 1898. Around the same time, he created the world’s first hybrid electric car - a vehicle that was powered by electricity and gas. Thomas Edison, one of the world’s most prolific inventors, thought electric vehicles were the superior technology and worked to build a better electric car battery. Even Henry Ford, who was friends with Edison, partnered with Edison to explore options for a low-cost electric car in 1914.

Yet, it was Henry Ford’s mass-produced Model T that dealt a blow to the electric car. Introduced in 1908, the Model T made gasoline-powered cars widely available and affordable. By 1912, the gasoline car cost only $650, while an electric roadster sold for $1,750. That same year, Charles Kettering introduced the electric starter, eliminating the need for the hand crank and giving rise to more gasoline-powered vehicle sales.

Other developments also contributed to the decline of the electric vehicle. By the 1920s, the U.S. had a better system of roads connecting cities, so Americans wanted to get out and explore. With the discovery of Texas crude oil, gas became cheap and readily available for rural Americans, and filling stations began popping up across the country. In comparison, very few Americans outside of cities at that time had electricity. In the end, electric vehicles all but disappeared by 1935.[3]

Let’s finish with the history here and take a look at a few physical facts that justify why this happened in the past.

All kinds of vehicles convert energy from one form into movement (mechanical force). Since the idea of a vehicle is to be independent of a non-moving world, it has to have some kind of energy storage on board. But how big? What would be enough? Well, if you are a passenger in a carriage drawn by a horse, you will make 15 to 50 kilometers (10-30 miles) per day before you need to change the horse.[4] But cars are not animals, we can design them in such a way that they will carry us as far as we want. OK, there are limits, too.

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Chapter 2: I feel the need... the need for speed.

In order to move the vehicle with constant speed through the air, we need to counteract force F:

where ρ represents air density (1.293 kg/m3 or 0.0807 lb/ft3), v speed, Cd drag coefficient (shape of the body), and A cross section area of the vehicle. We can see that force is dependent by square value of the speed, meaning that if speed is increased by factor 2, the force which the powertrain of the car needs to counteract will be 4 times bigger. By creating aerodynamic vehicles with lower drag coefficients and smaller cross section area of the vehicle will lead to a more efficient car with better fuel or energy economy. Let’s say that our test car has a drag coefficient of 0.3 and cross section area of 3 m2 (32.3 ft2). If we would like to travel with a speed of 100 km/h (27.8 m/s or 62.1 mph), the powertrain of our vehicle needs to produce at least:

The power P is equal to force F, multiplied by speed v:

If we combine both equations and take a closer look, we will see that the required power to move a vehicle at certain speed depends on its third power:

leading us to the conclusion that if we want to travel faster for factor 2, the required power for that will increase to factor 8. This is huge.

Now we need to define how long we would like to travel without refueling or recharging our energy storage. Let’s say that 1,000 km (621 mi) is enough. With the desired speed v of 100 km/h (62.1 mph), we will manage the distance s of 1000 km (621 mi) in time t:

We can now calculate how much energy is needed to travel that far:

We here neglected the tires rolling resistance but the main energy is used to cover air drag, at least at high speeds. Nevertheless, in many cases the electric cars have narrow tires to reduce rolling resistance which additionally increases overall efficiency. We will see soon why it matters.

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Chapter 3: I feel heavy

In the previous chapter we calculated the energy, with a number and a unit. But what does it actually mean? How much fuel do I need for that? How many batteries?

To calculate this, we first need to investigate what is the capacity of different kinds of fuels or materials. Energy density is a property that tells us how much energy some material carries in one unit of volume (liter, dm3). So it is defined as J/l. If we want to focus on the mass, then Specific energy with the unit of J/kg tells us more. Table 1 summarizes the energy density of different fossil fuels and batteries[5]:

Let’s combine two most used fossil fuels and batteries in today’s cars and see what we get if we have a limited energy storage of 60 liters (Table 2) or a limited energy storage of 60 kilograms (Table 3).

From the tables above we can get a feeling about the energy potential of different materials. There is significant drawback of a Li-ion battery which is widely used in automotive industry. Its capacity to absorb the energy is around 50 times lower than in diesel or gasoline. This is huge. But this is not the end of the story for electric cars. One thing is the potential of one shape of energy (chemical energy) and another thing is how to transform it into useful form (mechanical energy). The transformation process is done with a certain efficiency, which is actually the ratio between the output energy (power) vs. input energy (power). If we also add here the contribution of the car’s shape – which can lead to lower air drag and consequently lower amount of required power – the story becomes quite interesting for the electric car. We will cover this in the following chapter.

Chapter 4: I like to move it

To transform chemical energy into mechanical energy we need to have a machine which can do that. In the car industry there are many types of machines that operate on fossil fuels like gasoline, diesel, compressed natural gas (CNG), liquified petroleum gas (LPG). They are called internal combustion engines (ICEs) and based on the principle of operation we distinguish between: four-strokes engines, two-strokes engines, with or without turbo charger, rotational (Wankel) engine, and others. In the electric vehicles we can find either asynchronous machines or synchronous machines, but in both cases, we need an inverter which converts DC (direct current) power from a battery or fuel cell into AC (alternating current) power that supplies the electric motor. Last but not least, we also know hybrid vehicles with the combination of an ICE and an electric motor with a smaller or bigger battery on board.[6]

In Table 4, we will take a closer look at the efficiency of a few most used machines.

?We can see that the electric engine despite the need for an inverter can reach far the best overall efficiency. Not only the peak but also the average efficiency is outstanding, which means that the energy consumption will be pretty much equal throughout the speed range (excluding harsh accelerations). On the other hand, the ICE needs to cover much higher losses, including exhaust energy, heat losses, brake work, transmission losses, etc. Also, the powertrain in an electric vehicle is simpler in terms of mechanical parts. There is no need to lubricate parts with oil, no need for filters. Often, there is also no need for transmission or there is only one fixed gear (we also know of in-wheel drive with a rotor directly attached to the wheel), they don’t consume energy in idle mode since an electric motor can provide nominal torque at 0 rpm. Moreover, an electric powertrain is able to recuperate energy while decelerating and the use of mechanical brakes is rarely needed.

Here is the comparison of two types of powertrains in terms of torque, shaft speed, and delivered power. Figure 1 shows characteristics of ICE and Figure 2 represents characteristics of an electric motor.

From the charts above we can see that the powertrain of an electric car has a flatter curve of torque which is very useful to cover the speed demand through all the range. Besides that, an electric motor can reach speeds above 20,000 rpm and a single fixed gear can cover the entire vehicle speed range. There is no need for transmission with a clutch which is a must for ICE vehicles.

Chapter 5: 1 + 1 = 2

Let’s summarize a few numbers to get the whole picture, shall we? In the previous chapter, we saw that electric machines are the best in terms of efficiency. But on the other side, energy density of the battery is pretty poor compared to fossil fuels. In other words, it means that the energy storage of vehicles with ICE can be much smaller and lighter despite poor overall efficiency. Table 5 shows the comparison of three different cars with the autonomy of 1,000 km:

This is a pretty ideal example of travelling by car with constant speed and neglecting other factors like tire rolling resistance. In reality, the consumption of a vehicle with ICEs would be at least double the value, and for an electric car about 20% higher. With this modification we get the following table:

We can see that we need around 50-60 kg (110-130 lb) of fossil fuel and around 600 kg (1300 lb) of batteries in order to travel 1,000 km (621 mi). The benefit of an electric car is that its powertrain weight is lower in comparison with ICE, so the drawback of a huge battery in an electric car is slightly reduced. With additional battery weight reduction (and range autonomy) in electric cars, the total mass of all vehicles is comparable. This is also the main reason why most of electric cars are shaped in a way that they produce the lowest air drag possible. In many cases the electric cars also have narrower tires to reduce rolling resistance and have limited maximum speed (electronically or by optimized motor design). The car manufacturers are trying to extract as much as possible from these heavy weight batteries in order to manage decent distances with an electric car. On the other hand, the vehicles with ICEs can be much more wasteful with energy and still reach decent range. At the expense of ecology, of course... It is also true that conventional cars need bigger cooling systems due to bad efficiency, leading to bigger openings in the front in order to catch more air stream.

Chapter 6: Please stop, I am thirsty

The convenience of car ownership has quite an important role in the modern world. We want the things we own to contribute to our efficiency and commodity. We do not want to spend much time repairing the car or even refueling it. For electric cars, this aspect is another drawback, despite the fact that there are better and better options for them nowadays. Have you ever asked yourself what is the power flow during refueling gasoline or diesel? Well, it is pretty remarkable: around 40 MW (at a flow rate of 1 l/s (0.26 US gal/s or 0.22 UK gal/s)). This is the value of a quite decent hydro power plant. On the other hand, the charging power for batteries achieves up to 350 kW at fast charging stations. And this is really the maximum at the moment. Normal power rates (with on-board chargers) are much lower and charging times are measured in hours. Not a huge problem for over-night charging, but otherwise it can be quite a limitation.

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Chapter 7: Why is an electric car different?

Let’s try to compare overall advantages and disadvantages of two real cars from the market: the first one with a diesel engine and rated power of 150 kW and a battery powered electric car with rated power of 168 kW. They are not exactly the same in terms of performance, but useful to see the physical limitations and where are the main differences. We put a few most important parameters into the table 7. The drag coefficient numbers confirm that electric cars are shaped much more efficiently, which is the main reason why you are able to distinguish them from normal cars.?

At this stage, we will not make a judgement about which car is better. What does it even mean? You can decide for yourself based on the importance of each parameter, including the price of the ownership, which we didn’t discuss. The point of this article is to give a clear understanding of physical properties of both cars, including advantages and disadvantages. What is really important is which one looks better. And why the electric car is uglier. Ups, different.

[1] Ross, K. (2022, March 9). If energy cannot be created or destroyed, where does it come from? Newscientist.

[2] National Geographic Society (2022, May 20). Fossil Fuels. National Geographic.

[3] Matulka, R. (2014, September 14). The History of the Electric Car. Energy.gov

[4] Stanek, A. (2021, September 19). How Fast & Far Can a Horse-Drawn Carriage Travel? HorseyHooves

[5] Wikipedia, (2023, January 23). Energy density. Wikipedia

[6] Febiac, (2021, November 19). The different types of engine. Febiac