An energy harvester comprising a mass that is subjectable to environmental forces for bringing it into the status of a moving mass, and means linked to the mass for converting and storing of energy embodied in the moving mass, which means are arranged for subsequent release of said energy, wherein the mass is part of a compliant system comprising a frame and first and second elastic beams connecting the mass to the frame, wherein the first and second elastic beams are provided with opposite stiffnesses so as to arrange that in a predefined range of excursions of the moving mass, said mass experiences a preselected stiffness.