Abstract: A flywheel energy storage device containing at least one rotary element (1) which is capable of floating and rotating on liquid and/or in liquid, at least one element which is capable of transferring energy onto the rotary element (1) and at least one generator (3) which is capable of transferring the energy from the rotary element (1) wherein the rotary element (1) is axleless. A method of use of the flywheel energy storage device in such manner that the energy is accumulated as kinetic energy of at least one rotary element (1) that floats and rotates on liquid or in liquid.