The FIA Formula One World Championship visits the Autodromo di Monza this weekend, near Milan, Italy. Often referred to as the sport's theatre of speed, it has a rich racing history dating back to 1922 and a reputation as one of the fastest circuits on the calendar. A key ingredient in creating the pace of a modern F1 car is its KERS unit.

Ever since its reintroduction, KERS has been far less of a controversial subject than it was in its first incarnation. Under today's regulations, and having had time to bed itself into the core design of an F1 car, KERS is very much here to stay. As Renault Sport F1 head of track operations Remi Taffin explains, it is hard to think of an F1 car these days without such a device.

"The Kinetic Energy Recovery System was reinstated last year. It is an electric motor which is run onto the internal combustion engine and is able to provide a maximum of 60kW power, 400kJ of energy. To make it simple, you can deliver just below seven seconds at 60kW boost over a lap, or about an extra 80 horsepower.

"The system now is so well integrated, and simple. The driver pushes a button two or three times a lap. It's just like being able to shift gears at the right time. There's no more confusion or issues about braking stability or anything like that. In the early days it was adding a lot of mass to the car, maybe 40kg, but today the whole system is nearly half that weight and fully integrated into the car."

So how does the unit actually work?

"It is connected at the front of the engine, straight driven onto the timing gear. It is functioning both ways, so under braking the inertia of the car/engine runs the electrical motor and generates energy into the battery, so we are charging the battery. When we are accelerating, especially at low gears, we are going to put that energy back on the engine, drawn from the battery and run through the electric motor, which will add an extra boost straight onto the crankshaft.

"It is always a challenge to know how best to deploy the boost, and it becomes tactical. If you look at overtaking and the specificity of Monza then you would probably activate before the start-finish line and then you can keep on pushing on the KERS for the remainder of the straight which means that actually you could have up to 13 or 14 seconds of KERS if you were in a race situation and you wanted to overtake. At this point you could be up 12kph, which is a substantial difference."

There remain two teams in Formula 1 however who do not run KERS. Although in its original form, there were doubts raised about the advantages of running KERS, in the present day, the benefits far outweigh the disadvantages.

"It is very simple. In qualifying you gain four tenths of a second per lap with KERS. Sometimes it will be three tenths, sometimes five, depending on the track layout, but the average is four. In the race it is a bit different because you use it to overtake. We saw that in Spa very graphically when Kimi overtook Michael Schumacher: he actually used all of his KERS going down to Eau Rouge to try and be as close to him as possible. It can be very useful in the race to attack someone where they would not expect you to attack."