NOVELTY - The system is for use of sea wave energy and uses a generator fixed to the sea bottom driven by buoy lifting force, where the buoy size must be flexible as must also the resistance in the generator, so as to optimize the lifting force of the buoy in relation to the size of the waves. The buoy incorporates a central tube (1) containing an electric motor (2) which drives a movable part (3) positioned in the central tube upwards and downwards and thereby by means of cogged bars drivse fixed gearwheels (4) and chains (5) which push out and draw in three or more double stays (6) which run out from the central tube from an upper and lower point and are divided into two or more parts so that the outer parts can run in the interior and top wires (7) which are fixed in the outer buoy sheet and run in through holes in the central tube uppermost part and are fixed in the movable part in the central tube and thereby draw in the buoy sheet when the movable part is driven downwards and at the same time draw in the double stays, and stay wires (9) which run between the two stays in each double stay but outside the buoy sheet and are fixed in the central tube below the buoy sheet and run upwards around the buoy sheet and in through holes in the central tube uppermost part and are fixed in the movable part in the central tube and thereby draw in the buoy sheet between the two stays in each double stay when the inner movable part is driven downwards.    USE - To make use of sea wave energy, with a generator fixed to the sea bed driven by a buoy lifting force.    DETAILED DESCRIPTION - The buoy sheet upper opening hole is covered by a protective cover (10). The top wires and/or stay wires are not drawn inwards when the movable part is lowered in the central tube, unless directly by the electric motor (2) or by a separate electric motor.    DESCRIPTION OF DRAWING(S) - The figure presents the buoy whose lifting force is optimized in relation to the size of the waves. The technical solution comprises a metal construction which can expand or draw inwards and wires which tension the buoy sheets against the metal construction. The positioning of the metal stays and wires is designed to minimise losses when the buoy sheet is tensioned in different positions.    Central tube (1)    Electric motor (2)    Movable part (3)    Gearwheels (4)    Chains (5)    Stays (6)    Top wires (7)    Stay wires (9)    Protective cover (10)    Chains (5)    Stays (6)    Top wires (7)    Stay wires (9)    Protective cover (10)