In one embodiment, a turbine includes a first shaft rotatable in a first direction and a second shaft rotatable in a second direction; the second direction is generally opposite the first direction. A first propeller is coupled to the first shaft for rotating the first shaft in the first direction, and a second propeller is coupled to the second shaft for rotating the second shaft in the second direction. An armature is operatively coupled to the first shaft for rotation with the first shaft, and a field component is operatively coupled to the second shaft for rotation with the second shaft.