Stirling cycle engines with hot and cold gerotor sets separated by an insulation barrier. The barrier has regenerative gas passages to allow gasses to flow therethrough thus connecting displacing chambers of the hot and cold gerotor sets. Each gerotor set has a rotor within a stator and displacing chambers created in an offset space therebetween. The stators may rotate about the rotors, or vice-versa. Either the rotor of the cold gerotor set has an axis of rotation offset with respect to the rotor of the hot gerotor set or the stator of the cold gerotor set has an axis of rotation offset with respect to the stator of the hot gerotor set, and the non-offset rotors or stators rotate about a common axis and are rotationally connected and create an angular phase offset between connected hot and cold chambers. The gerotor apparatuses may be utilized for a Stirling cycle engine for generating electricity, for example.