Unlike the Williams F1 developed electrocmechanical flywheel system that we saw at PLM in 2010 http://www.popularmechanics.com/cars/alternative-fuel/hybrids/porsche-911-gt3r-hybrid-flywheel, the Flybrid is completely mechanical with no electrons involved. As such the system is lighter although it may not be as flexible because it has to be geared into the conventional drive system. The system that was used by Porsche and in this years Le Mans winning Audi R18 e-tron sends electricity back to a pair of electric motors driving the front wheels. 

This isn't Dyson's first foray into alternative energy in ALMS. Since 2010, the Mazda-powered Lolas have been fueled by isobutanol produced from biomass.