Porsche has flywheel generator

In the 911 GT3 R Hybrid the front wheels will be driven by two electric motors, each developing 60kW. These will supplement the 480hp naturally aspirated four-litre engine that drives the rear wheels.

But instead of powering the motors with batteries — a technique common in many hybrid road cars — an electrical flywheel power generator will deliver the energy to the electric motors.

The flywheel generator — which can rotate at up to 40,000rev/min — will be charged whenever the brakes are applied to the vehicle, as the two front-axle electric motors reverse their role and act as generators.

Then, when the car accelerates out of a bend or overtakes another car, the energy stored in the flywheel will be used to power the electric motors. The additional power will be available for approximately 6-8 seconds.

By increasing the efficiency and, accordingly, the performance of the car, Porsche engineers claim that either reductions could be made to the weight of the fuel tank or the car could make less frequent pit stops for refuelling.