High performance does not mean high consumption

Six liters per 100 km. Every driver understands this unit immediately. They know right away whether it’s a lot or a little. It gets more complicated with CNG-powered vehicles, because then consumption is measured in kilograms. And what about electric vehicles? Who knows which drive is efficient and which is not? Usually, only e-car owners. And in which unit is it even measured?

It is safe to say that with electric cars, there are big differences in energy-consumption and driving-range. The range, of course, depends directly on power-consumption. And how much electricity an e-car actually consumes is quite decisive for whether it can be operated economically or whether it will be more expensive than a comparable gasoline, diesel or CNG-vehicle. One thing is immediately apparent about most e-mobiles: they have a very high power output. But is that necessary? And how does that influence power-consumption? JATO Dynamics looked at how electric motors affect the efficiency of battery electric vehicles (BEVs).

However, a direct comparison of vehicles is not easy, because models with different engines often also come with different-sized batteries, which means that the overall weight varies. And this is an important factor for consumption. Nevertheless, certain trends can be identified.

Tesla Model S, Jaguar I-Pace and E.Go Life models are offered with different engines, each with the same overall weight. Amongst other engines, the Tesla offers a 562 hp version, and another one with 796 hp. Remarkably, the fuel consumption of the more powerful Model S with 42 percent more power, is only 3.6 percent higher. The Jaguar I-Pace is available with 320 hp and 400 hp (+25 percent). However, the power consumption is the same for both variants. Things get odd with the E.Go Life. It is offered with 56 hp and 78 hp (+39 percent). But the vehicle with the higher output consumes a whole 12.2 percent less electricity.

E.Go Life: 17 km more range thanks to LED lights

Both E.Go Life models have the same kerb weight and battery capacity. But the 78 hp version has wheels that are two inches larger and one inch wider, which increases rolling resistance – and should actually increase energy consumption. But it is more than twelve percent lower, which increases the range by 14 percent, or 17 km. How can this be? The headlights are responsible. The 56 hp E.GO Life come with halogen lights, while the stronger model gets energy-saving LED lights.

Another example is the Audi E-Tron. Its 313 hp model comes in three trim lines: Basic, “Advanced” and “S Line”. Besides the engine output, the total weight is exactly the same for all three lines. However, the power consumption differs. For the base variant, it is 21.4 kWh per 100 km, while for the other two trims it is 22.5 kWh/100 km which means a 23 km shorter range. The reason is the wheels, which are one inch smaller and 0.5 inch narrower on the base variant.

A few examples of how the overall weight can also influence power-consumption are Fiat 500, Ford Mustang Mach-E, Opel Zafira and Mercedes EQV. All models have several versions with different gross weights and the same engine output. The following applies here: On all models, versions with higher weight also have higher power-consumption.

So, it must be factors other than engine power that are decisive for consumption. To understand this better, we must look at the relationship between engine power, battery capacity and power-consumption. The capacity of a battery is measured in kilowatt hours (kWh). For example, if a battery has a capacity of 100 kWh, an electric motor can produce a constant steady output of 100 kilowatts (kW) for an hour before it runs out. However, cars only need high power for acceleration. Once the vehicle is rolling, it needs significantly less power, and therefore also less electricity, to maintain the speed it has already reached. If a motor has higher power, it simply means that the vehicle can potentially accelerate faster and reach a higher final speed. However, the range can be influenced by the driving style. Thus, if acceleration is moderate, this ensures lower consumption even with a powerful engine.

So, power-consumption of electric vehicles is like fuel consumption of vehicles with internal combustion engines: driving style is a big factor! Certainly, pushing the gas pedal to the floor is more tempting on high-powered vehicles than on lower-powered vehicles. However, the more powerful engine itself does not necessarily result in a higher power-consumption. In addition to driving style, there are other factors the driver cannot influence. These include the overall weight of the vehicle, rolling resistance and energy-sapping features such as air conditioning, heated seats, and outdated technologies such as halogen headlights. These are all factors that can negatively influence both, the fuel consumption of combustion engines and the power consumption of electric vehicles.

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