Efficiency: electric cars are much more efficient

The efficiency of an electric drive is so high that it is predestined for road traffic. We explain how electric cars, combustion engines, and fuel cell vehicles compare. And where the differences derive from.


  • Sustainability

From the point of view of energy, an electric motor is the most efficient drive technology a car can have. No other drive technology offers a higher degree of efficiency. The term “efficiency” indicates the percentage of the energy supplied that can actually be put to use. This is never 100%, because there are always losses – due to friction and waste heat. Even so, an electric motor achieves an outstanding level of 80% efficiency.

In order to calculate this correctly, it is important not only to consider energy losses in the vehicle itself – especially in the case of electric cars, The major losses occur during the generation and supply of energy, not in the vehicle. The term “well-to-wheel” has become established for this overall consideration – clearly a term which originates from the internal combustion engine.

Applied to electric cars it would be more correct to say “electricity generation to wheel”.

For electric vehicles,   the well-to-wheel efficiency is as follows:

  • 36% of the energy originally used is lost in generating and supplying electricity, and there are also losses when charging the battery.
  • 64% of the energy used is used to power the wheels of electric cars.

How efficient is a combustion engine?

The efficiency of a petrol engine is 20%, while the efficiency of a diesel engine is 45%. The reverse is true of a combustion engine as compared to an electric motor: The major energy losses occur in the vehicle itself, not during fuel production. In an internal combustion engine, a chemical reaction takes place that uses oxygen from the air which involves the fuel being combusted. Combustion generates a lot of waste heat. In addition, valves and gearwheels have to be moved before the useful energy reaches the wheels.

The well-to-wheel  efficiency for petrol engines is as follows:

  • in the case of a petrol engine, 80% of the energy originally used is lost during extraction, production, transport and combustion in the engine.
  • 20% of the energy used drives the wheels of a petrol engine.

Diesels  perform better because their combustion process is more efficient. Their well-to-wheel efficiency is as follows:

  • 55% of the energy originally used is lost in diesel.
  • 45% of the energy used goes towards powering the wheels of the car.

Why is an electric drive so efficient?

Electric motors convert electricity into motion, producing very little waste heat. By contrast, petrol and diesel engines burn fuel, thereby generating a lot of waste heat. Electric drives are extremely efficient by design and because of the existing technical solutions. There are electric motors that even achieve efficiency levels of more than 90%! 

And electric cars offer additional advantages as compared to cars powered by a combustion engine. For example, electric motors do not need a complex “transmission chain” to transfer useful energy to the wheels. This reduces friction losses. Since they are much smaller than combustion engines, electric motors can be installed close to the wheels, for example. What is more, there is no need for a transmission or clutch, because electric motors generate a constant level of torque from a standing start: Here, the power is applied to the wheels instantly. By contrast, a combustion engine can only develop sufficient tractive force to power the car from 800 to 1,000 revolutions per minute. And a gearbox is required to ensure that rotational speed and output are always perfectly matched. The transmission causes friction losses, too.

Electric drives can also generate electric power.

But electric motors can not only convert electrical energy into kinetic energy, they can generate electrical energy from motion, too. In this case, the motor becomes a generator – a power plant. In the case of electric cars, manufacturers take advantage of this when it comes to the braking process: instead of allowing the waste heat to dissipate, the electric motor recovers electrical energy, which is then stored in the traction battery. This increases the range – and therefore the degree of efficiency, too.

One problem that arises with electric drives due to their high level of efficiency is heating the interior in winter. This problem can be alleviated by an in-vehicle heat pump, which – as in the case of a building – extracts heat from the surroundings and then directs it to the occupants. This takes the strain off the traction battery, whose electricity would otherwise have to be used for heating, too.

Combustion engines do not have this problem. Thanks to their low efficiency, they generate far more waste heat than is actually required for heating. But in summer the situation is reversed: here, the waste heat from the combustion engine puts a lot more strain on an air conditioning system than in the case of an electric motor. This is reflected in the fact that the fuel consumption of diesel and gasoline engines is much higher on hot days.

What is the efficiency of a fuel cell vehicle?

The efficiency of a fuel cell drive is between that of a petrol engine and a diesel engine, i.e. far less than that of an electric car. Although a fuel cell vehicle has an electric motor and a (relatively small) traction battery, it ultimately converts electrical energy into motion just like an electric car. But in order to achieve a greater range than an electric car, a fuel cell and a hydrogen tank are on board as well. In order to charge the battery for the electric drive, the fuel cell uses oxygen from the air and hydrogen to generate electricity.

Viewed in isolation, the fuel cell achieves an overall efficiency of more than 80%. But in terms of well-to-wheel efficiency, hydrogen spoils this high figure. In nature, hydrogen doesn’t occur in isolation but has to be produced by way of an energy-intensive process. This is achieved sustainably by means of electrolysers that use renewable electricity to break down water into oxygen and hydrogen. The next step is to store the hydrogen gas at high pressure and low temperatures. Otherwise, the footprint of this type of propulsion would be even worse. The pressure is up to 700 bar. By comparison, a car tyre has a pressure of between two and three bar. The temperature is around –250 degrees Celsius. All of this requires a lot of energy.

So the well-to-wheel efficiency  for FCEV is as follows:

  • 70% of the energy originally used is lost in the production and storage of hydrogen and in the generation of electricity in the vehicle.
  • 30% of the energy used powers the wheels of a fuel cell vehicle.

This also explains why fuel cells are considered a niche technology for road traffic: there is a much less complex and also more energy-efficient solution that can be implemented on a carbon-free basis, namely the electric car.

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