For 2011 the hybrid rules will change slightly. See
http://www.lemans.org/en/news/2011-L...TIONS_628.html for the main ideas. Only 500 kJ instead of 1000 kJ between braking points and the KERS energy can also be released on the front wheels (like the hybrid 911), but not on both axles.
I don't understand your calculation. Energy = power x time. It is up to Peugeot to decide how to release the 500 kJ of KERS energy. 500 kW (670 hp) during 1 s, 150 kW (201 hp) during 3.33 s, 50 kW (67 hp) during 10 s, 25 kW (34 hp) during 20 s, ...
To give an idea the Peugeot 908HY had a 60 kW electric motor and the Zytek Performance Hybrid system uses a 40 kW electric motor. The Porsche 911 GT3R Hybrid has 2 60 kW electric motors, which can release KERS energy "during approximately 6-8 s"; so around 1000 kJ can be stored in the flywheel battery.
As a final comparison, the hybrid Toyota Supra HV-R that won the Tokashi 24-Hour race in 2007, had 2 10 kW (in-wheel) electric motors on the front and a 150 kW rear axle mounted electric motor. That setup (which is not allowed by the ACO because it drives 3 wheels electrically) would release the 500 kJ in around 3 sec.