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We’ve covered much of the Volvo Flywheel KERS (Kinetic Energy Recovery System) when it was first announced in 2011. Now, after lengthy tests on public roads, the Swedish carmaker has confirmed that the technology offers fuel savings of up to 25%, even better than the theoretical 20% boost it initially targeted.

It provides a “light, cheap and very eco-efficient” solution to reducing fuel consumption. Fitted to an S60 with a turbocharged four-cylinder engine, the experimental car returned 25% better economy compared to a six-cylinder turbo engine at a comparable performance level.

With an extra 80 hp available instantly (similar to the output of present-day F1 KERS) and swift torque build up, the test S60 accelerates from 0 to 100 km/h in 5.5 seconds, 1.1 second quicker than a four-wheel drive, 3.0 litre turbo S60 T6 AWD. The performance advantage will be less apparent as speeds rise, as the system is at its most efficient in city traffic.

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The Flywheel KERS is fitted to the rear axle, away from the engine powering the front wheels. Under braking, the engine is switched off while the flywheel harvests the energy, spinning at up to 60,000 rpm. Rotational energy from the six-kilogram carbonfibre flywheel is then used to power the rear wheels via a specially designed transmission.

Despite having the same name, the system is not the same as those used in Formula 1 racing. This one stores the harvested energy in a rotating flywheel and not in electrical capacitors/batteries as per F1’s KERS. It is similar in concept to Williams F1’s stillborn flywheel KERS system from 2009, which was then used to good effect on Audi and Porsche’s R18 e-tron and 911 GT3 R Hybrid racecars.

The latter is said to form the base of a high-tech hybrid system for the upcoming Porsche 918 hypercar, which will go head to head with the Ferrari LaFerrari and McLaren P1, both equipped with its own KERS-like powerplants.

There are no such plans for Volvo of course, but the company is in the midst of evaluating how the technology can be implemented for its future road cars. Less exciting, but much more relevant to us mere mortals.