ADAC Test: E-cars recover up to 40 percent energy - Advantages in fine dust
Electric cars are efficient, their efficiency is many times higher compared to combustion engines: The simple wisdom has now been tested in practice by the automobile club ADAC with extensive tests in various environments. It turned out that electric cars not only use the energy used for propulsion better, but also recover a lot of energy when braking.
"In conventional gasoline and diesel cars, the kinetic energy is converted into heat during braking – the brake discs get hot. In electric cars, on the other hand, the electric motor can be used in reverse as a generator. It converts kinetic energy back into electrical energy, which is fed into the battery. This energy recovery slows down the car, in some cases to a complete stop. The effect is known from a bicycle with a dynamo: as soon as the dynamo is pressed against the tire, the lights come on, but pedaling becomes more difficult," explain those responsible for the principle.
How effectively a car recuperates depends primarily on three factors:
- Weight: Heavy cars have an advantage in this regard. The more mass is in motion, the more recuperation is needed to decelerate, and the more electricity is recovered.
- Electric motor: What applies to driving also applies to recuperation. The more powerful the motor, the more electricity it can generate.
- Battery: The battery must be strong enough to absorb the recuperated energy, and there must be "space" in the battery. If the energy storage is completely full, recuperation is hardly possible in the first few kilometers.
Dacia Spring versus BMW i7: Extreme case on the mountain
This is clearly illustrated by two examples: Dacia Spring and BMW i7. Both completed a pre-recorded drive on the Kesselberg in the pre-Alps and back down on the test stand at the ADAC Technology Center in Landsberg. The 1,180 kilogram Dacia with a 33 kW (45 hp) engine consumed 26.4 kWh/100 km uphill on the test track. Downhill, consumption was -7.1 kWh/100 km, meaning energy was recovered. This results in a total consumption of 9.7 kWh/100 km. The BMW is significantly heavier and more powerful: It weighs 2830 kilograms and has two motors with a power output of 400 kW (544 hp). Consequently, consumption uphill is high: 59.3 kWh/100 km. Weight and power ensure that 26.3 kWh/100 km were recuperated downhill – resulting in a total consumption of 16.5 kWh/100 km. The calculation was performed as follows: consumption uphill (per 100 km) minus the energy recovered downhill (per 100 km) equals total consumption per 200 km. The result must then be divided by two.
In the city, Nio and Ioniq 6 recover up to 40 percent
Recuperation has a positive impact not only on mountains but also in everyday life. Green NCAP measurements (according to WLTP) have shown that electric cars recover an average of 22 percent of the energy they take from the battery. The leader among the 19 examined vehicles is the Nio ET7, which even recovers an average of 31 percent. The last place goes to the Dacia Spring, which only recovers an average of 9 percent. The greatest potential for savings exists in city traffic, where frequent braking occurs: Both the Nio and the Hyundai Ioniq 6 can recover over 40 percent of the energy used here, with an average of about 30 percent being recuperated in city traffic. On the highway, the recuperation rate drops to around 10 percent.
Fine Dust Pollution Decreases Because Less Braking is Required
In addition to energy recovery, recuperation has another advantage: since the mechanical brake is used much less frequently, fine dust pollution from brake abrasion is significantly reduced; an emission source that will even be limited in the future under the Euro-7 standard. At the same time, the brakes generally last longer due to less wear compared to combustion vehicles - provided they do not corrode beforehand due to insufficient use.
"Recuperation is an important factor for the efficiency of e-cars," emphasizes Dino Silvestro, Head of Vehicle Testing at the ADAC Technology Center. However, the ADAC urges manufacturers to design the interaction between recuperation and mechanical braking intelligently: As much energy recovery as possible and as much mechanical braking as necessary to prevent corrosion. "Furthermore, strong recuperation performance should not be used to justify a high vehicle weight," adds Silvestro. "The energy consumption required to accelerate the large mass still outweighs the benefits of recuperation in the sum. Therefore, looking at resource consumption, automakers should also focus on lightweight construction for electric vehicles."
Tips for Electric Car Drivers:
- Drive Anticipatorily: In many cars, the strength of regenerative braking can be adjusted, for example with paddles on the steering wheel. In urban areas, regenerative braking should be used consciously, while on the highway, so-called sailing, which means coasting with deactivated regenerative braking, is more efficient.
- Use One-Pedal Driving: For more comfort, in some models regenerative braking can be controlled entirely by the accelerator pedal. The car brakes when you take your foot off the pedal, all the way to a standstill.
- Prevent Rust: Since the mechanical brake is used less frequently, there is a risk of rust. Therefore, drivers should regularly use stronger deceleration to free up the mechanical stoppers. Of course, only if the traffic situation allows it safely.
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