A Kinetic Energy Recovery System or KERS collects or 'harvests' waste energy during braking, and allows that energy to be re-used later to help accelerate the car.

KERS can be an electrical system using motor/generators and an electrical battery, or the energy can be stored in a flywheel and used by either an electrical or mechanical system.

Formula 1 cars use KERS to promote overtaking, and Porsche has run a 911 GT3 racing car with a flywheel KERS.