The GT3 R Hybrid uses kinetic energy stored up from braking, in a similar way to F1 'KERS' systems. The normally wasted energy instead goes to two 60KW electric motors on the front axle which act as generators, able to then redeploy that energy in six to eight second bursts.
There are no official figures for the amount of extra power the electrical gubbins provides, but with the same 480bhp NA flat-six found in the normal 997 GT3 R as a starting point this is not going to be sluggish.
Porsche boasts that this type of hybrid tech is a real advantage in racing, as it allows them to either run with a smaller fuel tank and save weight, or to run for longer using the existing fuel tank. Presumably with range in mind, Porsche is testing out the new car later this year at the Nürburgring 24 hours race (15-16 May) after its Geneva debut.
As you might expect, our savvy Porsche forum picked this story up this morning, so we've linked that thread to the 'Comment on this story' link below.