The hybrid system developed by Williams is itself something of a, well, hybrid. Most teams that have used KERS this year have gone with electrical systems using batteries, similar in principal to what is used on road cars. A motor/generator driven off the gearbox provides regeneration/boost. However, instead of storing energy in an electrochemical battery it is stored as mechanical energy in a 40,000 rpm flywheel .
In spite of it not being used on the race cars, team principal Sir Frank Williams believes it has commercial applications. To date, the only automakers that have indicated an interest in a flywheel base system are Jaguar-Land Rover who are testing the completely mechanical Torotrak system. The flywheel system from Williams may be able to provide a more compact and less expensive alternative to batteries for low-cost hybrids. We'll have to keep our eyes open.