If you're wondering why we (or anybody else, for that matter) didn't note that the energy storage system used on Porsche's new 911 GT3 Hybrid racer was developed by Williams in our original post, that's because the Germans 'conveniently' forgot to mention it in their official press release...
Thankfully, Williams issued a separate release informing us about their collaboration with Porsche while the company also noted that the energy storage system was originally developed for use in Formula One by the AT&T Williams team (the KERS system), but now it is focusing on applying the technology in road vehicles through its Williams Hybrid Power subsidiary.
The firm's patented electromechanical composite flywheel system is an electric motor that can spin to speeds of up to 40,000 rpm, storing energy mechanically as rotation energy and then supplying it to the electric motor(s) that drive the wheels.
In essence, it replaces the battery pack found in conventional hybrid cars with obvious gains in space and weight savings. The system's weakness is that it cannot store large quantities of energy.
In the case of the 911 GT3 R Hybird racer, the system releases up to 120kW of electricity for short bursts of around 6-8 seconds after each charge process that can be used either for additional power or to increase fuel economy.