The invention relates to a kinetic energy accumulator, comprising a plurality of rotatably mounted accumulator members (100, 198) positioned adjacent one another, an input drive mechanism (116) arranged to impart rotational drive to a first of the accumulator members, and velocity responsive coupling members (106, 192) arranged to provide for magnetic coupling of successive ones of the accumulator members when respective ones of the accumulator members are caused successively to rotate with an angular velocity equal to, or greater than, a predetermined velocity. The accumulator can store kinetic energy and thereby act as source of rotational drive. Hence, there is also provided a kinetic energy transfer system, comprising the kinetic energy accumulator (118), an energy transmitter mechanism arranged to apply drive from a kinetic energy source to the input drive mechanism (116) of the energy accumulator; and a load device coupled to, and arranged to be driven by, the energy accumulator when each of the accumulator members is rotating with an angular velocity equal to, or greater than, the predetermined velocity. The load device can be an electric generator or other device.