Car features Brake energy regeneration

The 'KERS' system will be used in F1 next year

The 'KERS' system is also used in Formula 1 racing

When a car is moving, it has what is known as kinetic energy, but when you slow down, you lose some of that. 

The theory behind brake energy regeneration is to harness the energy lost when lifting off the throttle or pressing the brake pedal, and to convert it into electricity. 

Electric and hybrid cars already use such systems to recharge their batteries: their electric motors ‘reverse’, turning into generators which convert kinetic energy into electrical current. 

This is fed into the batteries, extending their range free of charge.

BMW has a more subtle form of brake energy regeneration: the alternator is only connected to charge the battery during braking.

Reduced engine load

This does not harness kinetic energy as such; but, because the alternator only draws current when there is no other demand for power on the engine, it reduces the load on the engine overall. 

BMW says this reduces CO2 emissions by 3%. Audi will also introduce a similar ‘intelligent energy management’ system on newer models.

This isn’t just for road cars, either. Kinetic energy recovery is also used in F1 motor racing. 

The ‘KERS’ system will take excess energy and store it either electrically or in a flywheel, to provide extra performance for limited periods.

Other sections in this guide

  1. Overview
  2. Green cars explained
  3. Hybrid cars
  4. Diesel hybrid cars
  5. Hydrogen hybrid cars
  6. Hydrogen fuel cell cars
  7. Stop-start systems
  8. Brake energy regeneration
  9. Gearbox and aero tweaks