Useful Car Tips

What is Regenerative Braking?

June 18, 2019
Some energy is wasted whenever you step on your car’s brake pedal, an inevitable outcome due to the laws of physics. Kinetic energy dissipates into heat which effectively cannot be used further, and this occurs with most automobiles on the road excluding those featuring regenerative braking technology. As the name suggests, regenerative braking is a system which takes this kinetic energy generated by braking (and which would normally become useless) and converts it into electricity which is then used to recharge a hybrid or electric car’s batteries. Although the range that fully electric automobiles can achieve has vastly improved since their introduction decades ago, regenerative braking works to add to this figure. Although now offered by many automotive manufacturers with their respective electric vehicles, what is the true viability of regenerative braking technology? Are the benefits worth installation by manufacturers? Will we continue to see this system on road cars in the future? Finally, is an electric car with regenerative brakes right for you?


In order to truly understand the utility of regenerative braking, it’s important to better understand how the system works and the processes which occur. In a conventional car, energy is always wasted when you step on the brakes. Modern brakes do an excellent job of rapidly slowing your vehicle down, but ultimately, the laws of physics become a factor in energy retention. With traditional brakes, all of the kinetic energy due to your car’s momentum is lost to heat due to intense friction generated by the braking process (brake pads pushing down on the car’s disc brakes). Both hybrid and electric vehicles use electric motors to drive and provide power to the wheels. When you let off the throttle and allow the car to coast under its own momentum in these vehicles, regenerative braking begins to work its magic. While coasting, each electric motor essentially becomes a generator that works to capture kinetic energy. This process happens with the electronic throttle closed. In this closed state (with your foot off or at least partially lifted off the throttle), the onboard computer which manages electricity consumption signals the battery to cease sending electricity to the motor. Now, the battery instead receives electricity. At this point, the main battery becomes charged and contributes to extending your driving range, due to the kinetic energy being converted into stored energy in the vehicle’s battery. This process is repeated every time the vehicle is allowed to coast or slow down. Subsequently, much of this stored energy is used the next time you accelerate, instead of tapping into the battery’s regular energy reserve. This is why regenerative braking leads to an increase in driving range. In a nutshell: low throttle input or coasting leads to generators being instantaneously switched on, which leads to them capturing kinetic energy, which is then converted into stored energy and finally used in acceleration without tapping into the battery’s energy reserve.


The ultimate effectiveness of regenerative braking is hard to judge and impossible to narrowly define, as many factors (some of which are extrinsic) affect performance. Firstly, driving conditions have a great effect. Let’s look at a real-world example, the 2019 Toyota Prius. As per Toyota's website, the Prius L Eco hybrid has a city fuel economy rating of 58 MPG and a highway MPG of 53. Some of this difference can be explained by regenerative braking, as the system works better in stop-and-go traffic that is more common in the city than on the highway. This is because frequent braking gives more opportunities for kinetic energy to be captured and then converted into stored energy. Terrain and vehicle size are additional factors which impact the performance of regenerative braking. With uphill sections of road, braking is usually limited. However, downhill sections of road usually require more braking, giving the system yet more chances to convert kinetic energy into usable stored energy. Vehicle size plays a role simply because larger (and subsequently heavier) vehicles have much more momentum and kinetic energy, factors which of course prove conducive to the ultimate application of regenerative braking.


Regenerative braking technology is here to stay, with all hybrid and battery-electric vehicles currently on sale in the United States making use of this system. Additionally, even select gasoline-powered automobiles utilize this system. Manufacturers like Hyundai, Nissan, and Audi offer regenerative braking systems on their Kona Electric, Leaf, and e-tron, vehicles respectively, with many more manufacturers following with contributions of their own. Regenerative braking is simple and effective, and might just be another reason to explore an electric or hybrid car as your next vehicle.
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