System for converting kinetic energy of a fluid to electric energy, the system comprising: a generator coupled to a shaft for producing electric power upon rotation of the shaft; mechanical means being adapted to convert fluid motion into a torque exerted upon the shaft; a controller for controlling the turning speed of the shaft; characterized in that the controller is adapted to monitor the magnitude of the torque exerted upon the shaft, the turning speed of the shaft and an indicator value of the mechanical power fed to the generator and: to increase shaft turning speed acceleration respectively decrease shaft turning speed deceleration, if, during a preceding period either: a turning speed increase was accompanied by a torque decrease and an indicator value increase; or a turning speed decrease was accompanied by a torque increase and an indicator value decrease; or a turning speed increase was accompanied by a torque increase; and to decrease shaft turning speed acceleration respectively increase shaft turning speed deceleration, if, during a preceding period either: a turning speed increase was accompanied by a torque decrease and an indicator value decrease; or a turning speed decrease was accompanied by a torque increase and an indicator value increase; or a turning speed decrease was accompanied by a torque decrease. a generator coupled to a shaft for producing electric power upon rotation of the shaft; mechanical means being adapted to convert fluid motion into a torque exerted upon the shaft; a controller for controlling the turning speed of the shaft; characterized in that the controller is adapted to monitor the magnitude of the torque exerted upon the shaft, the turning speed of the shaft and an indicator value of the mechanical power fed to the generator and: to increase shaft turning speed acceleration respectively decrease shaft turning speed deceleration, if, during a preceding period either: a turning speed increase was accompanied by a torque decrease and an indicator value increase; or a turning speed decrease was accompanied by a torque increase and an indicator value decrease; or a turning speed increase was accompanied by a torque increase; and to decrease shaft turning speed acceleration respectively increase shaft turning speed deceleration, if, during a preceding period either: a turning speed increase was accompanied by a torque decrease and an indicator value decrease; or a turning speed decrease was accompanied by a torque increase and an indicator value increase; or a turning speed decrease was accompanied by a torque decrease. to increase shaft turning speed acceleration respectively decrease shaft turning speed deceleration, if, during a preceding period either: a turning speed increase was accompanied by a torque decrease and an indicator value increase; or a turning speed decrease was accompanied by a torque increase and an indicator value decrease; or a turning speed increase was accompanied by a torque increase; and a turning speed increase was accompanied by a torque decrease and an indicator value increase; or a turning speed decrease was accompanied by a torque increase and an indicator value decrease; or a turning speed increase was accompanied by a torque increase; and to decrease shaft turning speed acceleration respectively increase shaft turning speed deceleration, if, during a preceding period either: a turning speed increase was accompanied by a torque decrease and an indicator value decrease; or a turning speed decrease was accompanied by a torque increase and an indicator value increase; or a turning speed decrease was accompanied by a torque decrease. a turning speed increase was accompanied by a torque decrease and an indicator value decrease; or a turning speed decrease was accompanied by a torque increase and an indicator value increase; or a turning speed decrease was accompanied by a torque decrease.