Talking KERS with the Renault F1 Team

KERS is the new buzzword of Formula 1. We know that it's supposed to encourage overtaking and lead the sport towards a greener future, but just how does it work and how effective is this new technology? The ING Renault F1 Team is here to explain…

Let's start with a definition: KERS stands for Kinetic Energy Recovery System and was introduced by the FIA to direct the Formula 1 engineering community towards developing greener technologies. Kinetic energy is energy stored in motion and can be thought of as the energy that is required to stop that motion. For example, stopping a bicycle, a car or a train is all about removing its kinetic energy.

Most commonly kinetic energy is removed using friction brakes, turning the kinetic energy into heat energy that goes towards warming up our planet that little bit more. With KERS, that energy is not lost but stored somewhere to be used to drive the car – that somewhere could be in a battery (chemical energy) in a flywheel (mechanical), in an accumulator (hydraulic) and in many others ways too. This stored energy can then be reused to give extra power to the engine with the regulations allowing maximum KERS power of 60kW and energy release of 400kJ in any one lap. In simple terms this means 60kW for a little over 6 seconds to ‘boost' the car each lap.

When the KERS project began, the first priority was to study all possible energy store solutions.
It was a tough call deciding between batteries and a pure mechanical flywheel, but the battery solution was more promising and offers the potential for adapting this technology for road cars over the next ten years. Renault's KERS device therefore uses chemical storage in a Lithium-ion battery provided by SAFT, a French company with a track record of providing cutting-edge battery solutions.

KERS needs more than just energy storage to be a complete system – it needs devices to ‘translate' the energy between its various forms of kinetic, electrical and chemical. This energy ‘translation' comes from an electric motor-generator unit (MGU) which can turn the kinetic energy of the car into electrical energy and vice versa.

However, such translation devices normally weigh in the region of 50kg and require a lot of space: two things which Formula 1 teams go to great lengths to avoid. It was therefore paramount that the MGU weighed as little as possible, which is where the involvement of Magneti Marelli came in and by working together we have been able to produce a compact, lightweight solution to meet our particular needs.

The resulting MGU is very small as it is active only during braking and for six or so seconds of acceleration, while for the rest of the lap it can relax and dissipate the heat generated in the active moments. The more efficient the KERS system is, the lower the heat losses, with the Renault F1 system achieving over 70% round-trip efficiency from capturing energy at the rear axle, converting it to electricity, storing it in the battery, pulling it out of the battery and then finally converting it to energy at the rear axle again.

Well, the additional 60kW boost (which equates to 80HP), limited to 400kJ per lap, will reduce lap times by between 0.2-0.3 seconds and, as demonstrated by Fernando Alonso's and Nelson Piquet's starts in the Malaysian Grand Prix (gaining six and four places respectively), there are clear benefits in using the system from a standing start. But to get the most from KERS, the whole system needs to be as lightweight and compact as possible; otherwise this advantage can quickly disappear. The weight of each team's solution is therefore a closely guarded secret, but when you consider that every 10kg of unnecessary weight can cost 0.35 seconds per lap, it's no wonder so many cars have been on diets over the winter.

In reality, though, there are other more subtle effects that get in the way of achieving the theoretical 0.2-0.3 second lap time reduction, such as weight distribution, not just longitudinally (front to rear) but also vertically. It would be easy to lose all of the KERS lap time potential if these points are not well considered. But, provided you can settle upon the ideal solution and get the gearing of your car right, the 60kW boost to the engine should aid overtaking, at least between KERS cars and non-KERS cars. Of course, it's still in the earliest stages of development and as the teams learn how to optimise KERS as a racing tool, the advantages are likely to become more apparent as the year unfolds.