We could not find a better teacher than Dr.-Ing. Daniel Armbruster, project manager of the Porsche hybrid (without a helmet and standing on the photo), to explain this technology which had it's second race Petit Le Mans.

The first race for the hybrid was the 24 Hours Nürburgring back in May, it ended in a retirement from the lead after more than 22 hours of racing. This first trial was cut short due to falure the conventional petrol engine. The primary objective at Road Atlanta was to finish the race to gain the maximum amount of data. This mission was more than fulfilled. It crossed the line in a notional eighth place but the car was entered 'out of classification' so could not score points in the LM GT2 category. With a best lap time in the same second as the fastest GT2, it might even have raced to victory if two flat tyres early in the race had not delayed it.

There were no built-in advantages for the hybrid to exploit at Road Atlanta, far from it. The extra weight of the energy recovery system in place of the passenger seat, is more than 105 kg compared to a normal Porsche 997 GT3 RSR in the LM GT2 category. On a circuit with an impressive climb, weight can only be a handicap, and the extra load is like having a substantial passenger on board. There are many fast corners on this circuit where drivers just lift a little or dab the brake, and the system needs heavy braking to recharge.

The hybrid system used by Porsche is better known in Formula One as KERS (Kinetic Energy Recovery System).

Under braking this system recovers a proportion of the energy absorbed in slowing a car down, hence the importance of the individual track. This kinetic energy is stored in an flywheel accumulator. When the driver brakes, the energy is converted to electrical energy and sent to the flywheel via high voltage cable. The flywheel rotates faster because of the energy supplied. When the driver wants to use energy to get a power boost, he presses a button that sends the energy to the two electric motors located in the front wheels via two cables. The speed of rotation of the flywheel decreases gradually as the energy is sent to the front wheels and flywheel can be recharged at the next corner.

To simplify the driver's life, already busy in managing traffic, the system can be automated. Depending on several parameters, the system triggers itself. When, for example, the driver is overtaking a slower car, the driver can regain control of events and trigger manually. Similarly, the energy can be used to "assist" the combustion engine, reducing fuel consumption. The Porsche hybrid is penalized by being overweight, so has a larger tank capacity than normal LM GT2 at Road Atlanta with 120 liters.

The system seems so simple, so why has it not been developed before? The safety problems posed by KERS are numerous: remember the mechanic electrocuted by touching the car of Juan Pablo Montoya during winter testing in Formula One a few years ago. Safety was a major concern of Dr.-Ing. Daniel Armbruster and his team: "One of the engineers, who is familiar with high voltage systems, has been appointed to start the hybrid system. In addition, each engineer has received specific training and we have several mechanical and electronic systems to cut-out the KERS in case of trouble. "

Why not use a simple battery instead of a flywheel? Again, for safety: such a high rate of charging could cause uncontrolled chemical reactions in a battery.

No problems were reported during the 1000 miles of Petit Le Mans, which allowed engineers to come away with valuable data in order to adapt this system for road cars, the main motivation of the German manufacturer, including the magnificent 918 Spyder.

Sceptics might want to analyze the free practice session on Thursday held in deluge conditions. The fastest car on track during the greater part of the hour of testing was the Porsche hybrid, also one of the few cars braving the elements. Why? Simply because with two electric motors mounted on the front wheels and supplied by the kinetic energy of the flywheel, the car turns in the equivalent of four-wheel drive.

According to the drivers, the system provides a real advantage, especially when they want to overtake for position. The extra power in the "push to pass' makes overtaking easier, and without increasing fuel consumption.

Will there be more such cars in the future? The regulation of hybrids at the 24 Hours of Le Mans is in its infancy and for the moment only prototypes. From 2011, the hybrid prototypes will be allowed to compete officially, and presumably large manufacturers will be interested. Is this the hybrid the technology of the future? The answer will possibly come next year ...

Cecile Bonardel - Translated by Dave Davies