Energy is stored in the Flywheel Energy Storage Systems by accelerating a rotor or flywheel to a very high speed and maintaining that energy as rotational energy. When electricity is needed, the flywheel decelerates and the stored kinetic energy is converted back into. . A flywheel-storage power system uses a flywheel for grid energy storage, (see Flywheel energy storage) and can be a comparatively small storage facility with a peak power of up to 20 MW. ESSs store intermittent renewable energy to create reliable micro-grids that run continuously and efficiently distribute electricity by balancing the supply and the load [1]. 2 m diameter x 7 m deep, 6 m of which buried. No flammable electrolyte or gaseous hydrogen release. Power conversion components on 10-year replacement cycle. £750k per 1 MW, 2 MWh system. Equipment installation up to low voltage connection point.