The best way to harvest what is essentially free engine power, for example when braking or running on a trailing throttle, has challenged engineers for decades.The most common solution is “brake energy regeneration” - capturing kinetic energy (the energy generated by a vehicle when it moves) that would otherwise be lost when slowing down. This energy is used to recharge batteries in electric and hybrid cars, for example, or to power the on-board electrical network and save engine power and therefore save fuel.MAZDA6 'THE FIRST'Such systems have been in use for some years – on F1 race cars since 2009 – but Mazda’s system is unique. i-Eloop (short for “intelligent energy loop”) claims to be the world’s first car system to use a capacitor (they used to be called 'condensers') to store the electricity.The all-new Mazda6 is the first of Mazda’s Skyactiv technology models to be available with the system.Mazda Motors UK managing director Jeremy Thomson said: “The i-Eloop capacitor is a unique solution to the challenge of how to harvest free engine power.Watch the video“One of the benefits of energy recovery systems is that they allow ancillary systems such as aircon to be used without a detrimental effect on fuel consumption.“i-Eloop was launched with Mazda’s ‘building block’ strategy, a step-by-step introduction of auxiliary electrical systems to Skyactiv technology, allowing breakthrough initiatives to be added as and when ready.”A typical vehicle deceleration phase lasts only about 10 seconds. Realising that the effectiveness of regenerative braking systems to date has been limited by the charging and storage drawbacks of conventional lead-acid batteries, Mazda engineers adopted an electric double-layer capacitor (EDLC) which recharges fully in only a few seconds.GONE IN 60 SECONDSAn efficient 12V-25V variable voltage alternator generates the electricity and charges the EDLC; a converter then steps down the voltage to power electrical components such as aircon and audio systems, with any surplus going to the car’s main battery.A full capacitor charge is enough to run the vehicle’s electrical systems for a minute or so. This makes i-Eloop the perfect companion for i-stop - launched as standard on the Mazda CX-5 and the all-new Mazda6 – as there is no need to use to battery power, even when Mazda’s stop/start system has stopped the engine.During stop/go city driving charging often resumes before the capacitor is discharged so i-Eloop can produce most, if not all, of a vehicle’s electricity needs, whereas normally some of the engine’s output is required just to drive the alternator.By freeing up this engine capacity, i-Eloop reduced fuel consumption under everyday driving conditions.