An energy generator for generating energy from renewable alternative sources, includes: a flotable platform adapted to be partially immersed in a fluid; a tower element arranged on the platform and including at least one wind generator for collecting wind energy and converting the same into electric energy, at least one first energy accumulator and at least one inverter. The energy generator further includes at least one system for storing and converting mechanical energy; the system for storing and converting mechanical energy including at least one charge mechanical accumulator, at least one flywheel balance coupled with the charge mechanical accumulator and a device for converting mechanical energy into electric energy. The wave motion or the stream of fluid where the platform is immersed determines an oscillating movement of the platform, of the tower element and of the at least one balance to charge the mechanical accumulator, which in turn releases the energy produced by its movement to the device for converting mechanical energy.