An apparatus includes an outer structure body having a cavity and an inner structure body rotatably supported within the cavity. The inner structure body has a central bore. Movable elements are positioned along the inner surface and movably coupled to the outer structure body. Ball elements are positioned along the outer surface and coupled to the inner structure body for movement with the inner structure body. The ball elements are positioned to releasably contact and impart motion to the movable elements in response to relative motion between the inner structure body and the outer structure body. A plurality of triboelectric energy harvesters are positioned to generate electrical charges when motion is imparted to the movable elements by the ball elements.