A system for generating electrical energy from the wave motion of the sea, comprising: - a floating body, designed to oscillate about a main axis of oscillation; and - an electrical-energy generating device which is set on said floating body and which comprises a body that is configured to move as a result of the oscillation of said floating body about said main axis, and electric-generating means configured to generate electrical energy as a result of the movement of said body; wherein: - said floating body comprises equipment provided with at least one chamber containing a variable volume of liquid material controlled by a regulation device in order to vary the frequency of the resonance peak of said system with respect to a movement of oscillation of said body about said main axis; and - said system comprises a control unit configured for controlling said regulation device so as to regulate said frequency of the resonance peak towards or on a value substantially corresponding to the frequency of oscillation of the wave motion, said system being characterized in that: - said equipment comprises a first chamber and a second chamber, which contain said material and are hydraulically connected together so that, as a result of said movement of oscillation about said main axis, said liquid material displaces at least partially from said first chamber to said second chamber, and vice versa; and - said regulation device is configured for regulating the flow of said material from said first chamber to said second chamber, and vice versa, wherein said control unit is configured for controlling said regulation device as a function of said frequency of oscillation of the wave motion, and wherein said system comprises at least one acceleration sensor, and said control unit is configured for controlling said regulation device on the basis of an acceleration signal transmitted by said sensor. - a floating body, designed to oscillate about a main axis of oscillation; and - an electrical-energy generating device which is set on said floating body and which comprises a body that is configured to move as a result of the oscillation of said floating body about said main axis, and electric-generating means configured to generate electrical energy as a result of the movement of said body; - said floating body comprises equipment provided with at least one chamber containing a variable volume of liquid material controlled by a regulation device in order to vary the frequency of the resonance peak of said system with respect to a movement of oscillation of said body about said main axis; and - said system comprises a control unit configured for controlling said regulation device so as to regulate said frequency of the resonance peak towards or on a value substantially corresponding to the frequency of oscillation of the wave motion, - said equipment comprises a first chamber and a second chamber, which contain said material and are hydraulically connected together so that, as a result of said movement of oscillation about said main axis, said liquid material displaces at least partially from said first chamber to said second chamber, and vice versa; and - said regulation device is configured for regulating the flow of said material from said first chamber to said second chamber, and vice versa, wherein said control unit is configured for controlling said regulation device as a function of said frequency of oscillation of the wave motion, and wherein said system comprises at least one acceleration sensor, and said control unit is configured for controlling said regulation device on the basis of an acceleration signal transmitted by said sensor.