Electric cars can recover some of the energy used to drive through recuperation. The has determined how much this can be under what conditions and which cars are particularly good or not so good.
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Mountain journey: three electric cars in comparison
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City/country/highway: How high is the recuperation there?
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Vehicle weight of electric cars: a problem?
What is recuperation?
Anyone who climbs a pass in an electric car will be amazed at the rapid rise power consumption a bit queasy at times. The good thing is: you can go down the mountain again at some point. And it is precisely in this driving situation that the advantage of regenerative braking becomes most visible to the driver.
But the Recuperation Fortunately, the use of an electric car is not limited to driving downhill. It always works when the car slows down: in front of an intersection, a traffic light or a speed limit. Here, too, the electric motor becomes a generator that is driven by the rotating wheels – just as a dynamo used to generate electricity for the lights on a bicycle.
How much braking energy The conducted a study to determine under what conditions recuperation takes place, which cars are particularly good or bad and what role the vehicle weight plays. The most important part was an evaluation WLTP measurements through Green NCAP. But the engineers also conducted their own Measurements when driving uphill through – with some surprising results.
In the mountains by electric car
For the Measurements of a mountain journey The chose the Bavarian Kesselberg between the Kochel and Walchensees. For this purpose, its route and incline profile was recorded and stored in the test bench recreated, since all disruptive influences from weather, weather and traffic can be excluded on the test bench and so the measurement accuracy is higher than in a real drive. The 5.5 kilometer long route was driven uphill and then downhill again, with sections of up to ten percent incline or decline.
The test vehicles were a Dacia Spring Electric Extreme 65, a Tesla Model Y and a BMW i7 – electric vehicles with very different engines and different weights.
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Dacia Spring Extreme 65: 33 kW | 1180 kg test weight | Front wheel drive
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Tesla Model Y Max Range: 387 kW | 2186 kg test weight | all wheel drive
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BMW i7 xDrive 60: 400 kW | 2830 kg test weight | all wheel drive
Result of the measurements: Once in the valley, he has Dacia Spring 35 percent the energy used uphill is recovered Tesla 40 and the BMW 50 percent.
Why the Dacia recuperates the least can be explained by its weight and the motor-generator performance: the light Spring with its small motor charges the battery with a maximum of 15.9 kW when driving downhill. The much heavier Tesla Model Y with its two engines (all-wheel drive) achieves a peak of 52.7 kW, and the BMW i7, which is also all-wheel drive, even achieves 55.1 kW – a value that the Dacia does not even reach at the charging station.
The two extremes are particularly interesting in the measurements: As the heaviest and most powerful vehicle, the BMW i7 recovers the most energy and therefore recuperates best. The extremely light and almost underpowered Dacia Spring, on the other hand, recuperates the worst. The reverse also applies: the heavy BMW requires the most energy uphill, the light Dacia by far the least.
So that’s what’s crucial Balance between consumed and recovered energy. And it looks like this: This one Dacia consumed on average during this up and down journey 9.65 kWh/100 kmthe Tesla 15.57 kWh/100 km and the BMW was included 16.54 kWh/100 km. When it comes to power consumption, the picture changes: despite the lowest level of recuperation, it shows up Dacia During the ascent the bottom line is overall than that most efficient vehicle.
WLTP: Recuperation in lowlands
Away from the special case in the mountains, towards everyday life in the lowlands. The has Measurements from Green NCAP evaluated how much energy current electric cars recuperate. The measurements are taken in a driving cycle based on the official WLTP. The 19 examined electric cars from different manufacturers are a good cross-section of the market. Since all vehicles are tested under identical conditions at 23 degrees with a battery that is not fully charged were tested, a representative and comparable picture of the recuperation performance of current electric cars emerges.
Result: Current electric cars win in the WLTP cycle an average of around 22 percent the energy they previously invested in driving. The Nio ET7 (31 percent) and the Hyundai Ioniq 6 (29 percent) perform remarkably well. In the normal traffic conditions of the WLTP, the Dacia Spring recuperates by far the least amount of energy (9 percent). The Cupra Born tested also ranks well below average with a rate of 16 percent.
The other two electric cars from the VW Group can do this much better. The Audi Q4 e-tron achieves 23 percent, the VW ID.5 26 percent. The two Teslas tested are on par with 23 (Model 3) and 24 percent (Model S).
Division city/country/highway
A look at the different route profiles of the WLTP shows that in the City with 33 percent on average most energy recovered becomes. Even the worst vehicle in the study still recovers 15 percent in urban areas. On average, the recuperation performance outside of town is 21 percent, while on the highway (with a maximum speed of 130 km/h) it is only twelve percent.
How can these differences depending on the route profile be explained? While in City cycle through traffic lights, intersections and obstacles frequent braking operations are made, we are dealing with fairly evenly flowing traffic on the country road and motorway cycle. Stopping processes are hardly taken into account in the simulations for country roads and expressways (only one stop outside of town). So there are far fewer situations for the car to recover energy.
In addition, as the speed increases, Air resistance and whose own braking effect becomes more important.
This is how you save electricity in the city and increase the range of your electric car
Video: Recuperation in electric cars
Do hybrid cars also recuperate?
With the same principlewhich is used to charge the battery of purely electric cars, hybrid cars also recuperate – regardless of whether they are plug-in hybrids, whose battery is also charged via a plug, or mild or full hybrids, which have a small battery to support the additional E -Have motors on board.
Conclusion: recuperation and weight
What can be derived from the measurements? Are crucial for recuperation Speed and weight of the vehicle (moving mass) as well as the Electric drive performance, which converts the braking energy into electricity and stores it. Just as high weight is a hindrance to the energy consumption required to get a car moving, it is just as beneficial in situations where braking energy can be recovered.
Simply put, all measurements show: Light electric vehicles use less energy, but also recuperate less, heavy electric vehicles consume more, but recuperate better.
From this it follows: This Problem of weight of heavy electric vehicles relativizes itself a little given its potential for energy recovery. In cars with combustion engines that cannot recover braking energy, the problem remains 1:1. For them, any form of braking energy is lost.
Conclusion: The bottom line is that despite better recuperation, heavy electric vehicles still have disadvantages in terms of energy efficiency – not to mention the increased consumption of resources. With Lightweight construction the car manufacturers could in matters Efficiency control against it. The extremely high costs that BMW once had for the i3 with carbon fiber were not worth it for the manufacturer. The cost-benefit ratio of carbon fiber lightweight construction was less good than was assumed at the beginning of the development of modern electric cars. This realization may also be the reason why BMW has long since said goodbye to the i3 concept.
It is also important to know that: cold battery the possible recuperation is reduced. Recuperation also becomes noticeably less or even impossible if the Battery fully charged is. So if you charge an electric car at the top of the mountain, you should not fully charge it and leave a buffer for the braking energy while driving downhill.
Project management and technical advice: Luis Kalb, Matthias Vogt, Technik Zentrum
