A device for generating electricity comprising: - an electricity generator having a rotatable generating shaft for generating electricity; - a floating frame designed to at least partly support said electricity generator; - a first roller portion wound around a respective first winding body and a second roller portion wound around a respective second winding body, the winding bodies being mounted on the floating frame and the roller portions (6, 8) being configured to rotate the respective winding bodies (7, 9); wherein each winding body (7, 9) is supported by a respective portion of the shaft (12, 13) and is rotatable about an axis of rotation (X1, X2); wherein said first roller portion has an end connected to a sea bed or to a fixed structure and said second roller portion has an end connected to a counterweight; wherein said winding bodies are mechanically and/or kinematically connected in such a way that when said floating frame is lifted, with the end of the first roller portion fixed to the sea bed or to the fixed structure, a corresponding lifting of the counterweight follows and a lowering of the floating frame is followed by a corresponding lowering of the counterweight; wherein said portions of shaft (12, 13) are mechanically connected to said generating shaft for transmitting mechanical power to the generating shaft; and wherein each of said winding bodies (7, 9) is connected to the respective portion of shaft (12, 13) by at least one free wheel designed to transmit a torque between the winding body and the corresponding portion of shaft (12, 13) in a direction of rotation and a free rotation of the winding body relative to the respective portion of shaft (12, 13) in the other direction, in such a way that when the first winding body transmits a torque to the respective portion of shaft the second winding body, kinematically coupled to the first winding body, is freely rotatable on the respective portion of shaft, and vice versa. - an electricity generator having a rotatable generating shaft for generating electricity; - a floating frame designed to at least partly support said electricity generator; - a first roller portion wound around a respective first winding body and a second roller portion wound around a respective second winding body, the winding bodies being mounted on the floating frame and the roller portions (6, 8) being configured to rotate the respective winding bodies (7, 9); wherein each winding body (7, 9) is supported by a respective portion of the shaft (12, 13) and is rotatable about an axis of rotation (X1, X2); wherein said first roller portion has an end connected to a sea bed or to a fixed structure and said second roller portion has an end connected to a counterweight; wherein said winding bodies are mechanically and/or kinematically connected in such a way that when said floating frame is lifted, with the end of the first roller portion fixed to the sea bed or to the fixed structure, a corresponding lifting of the counterweight follows and a lowering of the floating frame is followed by a corresponding lowering of the counterweight; wherein said portions of shaft (12, 13) are mechanically connected to said generating shaft for transmitting mechanical power to the generating shaft; and wherein each of said winding bodies (7, 9) is connected to the respective portion of shaft (12, 13) by at least one free wheel designed to transmit a torque between the winding body and the corresponding portion of shaft (12, 13) in a direction of rotation and a free rotation of the winding body relative to the respective portion of shaft (12, 13) in the other direction, in such a way that when the first winding body transmits a torque to the respective portion of shaft the second winding body, kinematically coupled to the first winding body, is freely rotatable on the respective portion of shaft, and vice versa.