Car recuperation: How does it work?
Formula 1 fans know it as part of the KERS, where the Kinetic Energy Recovery System is used, especially when overtaking. In roadworthy cars, it is known as recuperation. What is meant is energy recovery during braking. This system is usually found in all e-cars as well as some hybrid vehicles. However, this process has not been reinvented for electromobility. Rail vehicles such as cogwheel railways or some electric locomotives already use this so-called utility brake to feed braking energy back into the power grid. In the case of electric cars, recuperation recharges the battery.
What is recuperation?
The term recuperation comes from the Latin word "recuperatio", which means "recovery" or "reacquisition". It is a technical process for recovering energy. Recovery serves to increase energy efficiency. Recuperation can be found in many applications – especially in combustion plants, cars and trains. Braking energy does not always have to be used. Hot exhaust gases can also be converted. They are also heat energy. Heat exchangers are used for this purpose, which can convert and store the energy from the exhaust air.
How does recuperation work in electric cars?
In the case of the electric car, this is referred to as recovery of braking energy that would otherwise be lost as heat. For this purpose, the car has a regenerative braking system. The driver doesn't even have to step on the brakes. It is enough to take your foot off the accelerator pedal and the car brakes quickly.
In order for the energy to be recovered, it must first be generated. This is done via the engine of the car. Electrical energy is converted into kinetic energy. If you step on the brakes while driving, the kinetic energy is converted into braking energy – i.e. frictional heat. In the combustion engine, this energy is normally lost as heat. Thanks to recuperation, the electric car can convert the kinetic energy back into electrical energy and feed it into the electric car battery. This is made possible by the special feature of electric motors: they can also serve as generators and reverse their function – similar to what we may still know from bicycle dynamos.
If the driver takes his foot off the accelerator pedal, the kinetic energy is transferred to the generator. The electric car brakes and the motor generates electricity through electromotive resistance. This is stored in the vehicle's battery. How strong the recuperation is in the car depends on the system used. On the one hand, there is the medium recuperation. In this variant, energy recovery is controlled automatically – based on the position of the accelerator pedal and brake pressure. The strength of the recuperation depends on the braking behaviour. The harder you brake, the more energy is recovered. On the other hand, drivers of a car with variable recuperation adjust the strength of the recovery themselves. Depending on the model and manufacturer, there are menu options for this purpose, which the driver can use to select the strength of the recuperation.
Good to know: In cars with combustion engines, there is also a system to use recuperation. This includes, for example, the alternator. It generates electricity for the starter battery while driving and also generates the electricity for the ignition spark in the gasoline engine.
What are the advantages and disadvantages of brake energy recovery in electric cars?
Recuperation in the electric car increases the range of batteries – an unmistakable advantage for electric cars. Around 70 percent of the kinetic energy that would be lost during braking can be recovered as a battery charge. The remaining 30 percent is emitted as heat. Another advantage of a brake system with a recuperation system is that the brake discs are not subjected to as much stress. This in turn increases the service life.
However, there are also disadvantages. On the one hand, you have to adapt your driving and, in particular, braking behavior when you drive an electric car for the first time, because the car brakes by itself. In most cases, the normal brake pedal only has to be used for emergency braking. During such an emergency stop, the energy is then lost as heat. On the other hand, recuperation in an electric car can cause brake writing to rust more quickly. The reason is that they are used less and residues of moisture are not removed.
Advantages
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Increased reach
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Brake system less stressed
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More dynamic driving style
Disadvantages
- Switching from combustion engine to electric car requires getting used to
- Brake discs can rust faster
- Energy recovery depends on braking
How to use recuperation in the car correctly
Even if recuperation in the electric car already works well from the factory, you can optimize energy recovery with a few tips. Your driving style and road conditions have a big influence. If you often drive in mountainous areas, recuperation is particularly efficient, as you can let the car roll downhill – it brakes automatically when you take your foot off the accelerator. But be careful: If the battery is fully charged, there is no recuperation.
In normal road traffic, you should drive with foresight and use recuperation instead of the brake pedal as often as possible. When you brake, brake more gently, because this way you can recover more energy and don't lose it as heat.
Recuperation checklist
To help you make the most of the full potential of recuperation, here are the most important tips:
- Roll on downhill rides
- Driving with foresight
- Using recuperation for braking
- Gentle braking for more energy recovery
Can you fully charge the battery through recuperation?
No need to search for a charging station and simply charge while driving – unfortunately, this is not possible with recuperation. Energy recovery is used to reduce the energy consumption of the electric car. The power is not large enough for a full charge of the battery. This is limited to 50 to 90 kW to protect the lithium-ion battery. Nevertheless, the range can be increased: With optimal use of recuperation, between 20 and 30 percent of the range can be gained – enough to reach the nearest charging station in an emergency and reduce the charging time.
Attention: Some people have already come up with the idea of towing an empty Tesla Model S and using the recuperation of the electric car to charge the battery. E-car owners should urgently refrain from doing so. This can damage the on-board electronics under certain circumstances.