- Energy consumption depends on the overall efficiency of an EV which is critical to maximizing range.
- There are numerous factors governing the energy it takes to drive an electric car.
- This includes aerodynamics, weight, rolling resistance, powertrain efficiency and more.
With electric mobility taking its roots as the future solution, it becomes critical to acquaint ourselves with the factors on which the energy consumption of an EV depends. Now, everyone is concerned about the range of electric cars which is also the last remaining major issue with electric mobility in conjunction with charging infrastructure. But it looks like if EVs start offering really high range, people might get encouraged to take the plunge.
For this blog post, we shall take into account the incredible feat achieved by the Mercedes VISION EQXX, where it was able to travel over 1,200 km on a single charge with an impressive energy consumption of just 8.3 kWh per 100 km. It completed this journey of 1,202 km from Stuttgart (Germany) to Silverstone (UK) in 14 hours and 30 minutes.
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| Key Figures for this Journey | Value |
| Distance Travelled | 1,202 km |
| Time Taken (over two days) | 14 hours 30 minutes |
| Drag Coefficient (Cd) | 0.17 |
| Energy Consumption | 8.3 kWh per 100 km |
| Weight (unladen) | 1,755 kg |
| Battery | < 100 kWh |
| Voltage | > 900 V |
Energy Consumption of an EV
Aerodynamics
Now, it is not that difficult to understand that aerodynamics can greatly affect the energy consumption of an EV. In fact, that is the reason why the shapes of Formula 1 cars are so distinct. They focus on optimizing the body design to achieve the best aerodynamic efficiency. Essentially, it refers to how efficiently the body of the vehicle is able to cut through wind resulting in the lowest wind resistance.
This becomes important with increased speeds. At high speeds. wind resistance poses the greatest hurdle to the acceleration of any vehicle. In the case of the Mercedes VISION EQXX, its body curves and a retractable rear diffuser aid the aerodynamics tremendously. This allows an overall value to be just 0.17 Cd, which will be the best on any production car when it officially launches beating its own kin, the EQS (which has a Cd value of 0.20 currently). Also, there are additional aero-shutters that open up below the front bumper further contributing to the aerodynamic efficiency at high speeds.
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Energy Consumption of an EV Depends on Wheels
You might have noticed that the tyres of most EVs are very specifically designed. While it is an attempt to distinguish EVs from traditional ICE-powered cars, there is a deeper meaning hidden there as well. There is a way of making a car more aerodynamically efficient but that might make less aesthetic and practical sense. For instance, Mercedes says that they could bring the Cd value down to 0.16 if they cover the rear wheels.
In fact, we see something like that on the Lightyear 0 solar EV. So, while that might theoretically be possible, EV makers also need to consider the fact that the final product must look like a car for them to actually sell as it might not go down too well with the potential customers for whom the looks and design play a key role. The EQXX has a Crr (Coefficient of Rolling Resistance for Tires of 0.0047).
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Rolling Resistance and Weight
Now, the total resistance to the motion of any vehicle takes into account the frontal area of the car, its weight, the rolling resistance of the tires, its velocity, air density and acceleration due to gravity. Out of these, automobile designers can vastly control the frontal area and the weight of the car. For this example, the frontal area of the EQXX is 2.12 m2 and its weight is 1,755 kg (3,869 lbs).
In comparison, the weight of the EQS is around 2,500 kg. The frontal area of the Telsa Model 3 and Toyota Prius is 2.20 m2. The weight of the battery of the EQXX is just 495 kg compared to 537 kg for the 100 kWh battery of the Tesla Model S. Hence, Mercedes has improved on these aspects without compromising the shape of the vehicle too much.
Energy Consumption of an EV Depends on Powertrain and Packaging
Finally, energy consumption is a factor of the efficiency of the powertrain. While the aforementioned factors were a part of the design, the efficiency of the powertrain is what engineers are most engrossed in. That is where the EQXX shines. It has a cell-to-body construction and a passive cooling system for the battery. Note that the motor and inverter have active cooling.
Mercedes also says that the powertrain efficiency during highway runs is around 95%. Also, the peak DC charging capacity is limited to 120 kW. Both these figures inform that the battery heating is not a problem which is why the engineers have decided to go with an air-cooled battery system rather than the more common liquid-cooled ones that we see in most cars.
Hence, these are the most prominent factors that determine the overall efficiency and energy consumption rate of an EV. Mercedes VISION EQXX is an attempt to showcase just how far we can stretch the boundaries with the existing technology without making too many changes to the general aesthetics of a car. We are certain that more carmakers will pursue this method of making cars more efficient rather than slapping them with large batteries. We would love to hear your opinions about this.