An apparatus includes an electric generator having a stator and a rotor. A first turbine wheel is coupled to a first end of the rotor to rotate at the same speed as the rotor. A second turbine wheel is coupled to a second end of the rotor opposite the first end, and configured to rotate at the same speed as the rotor. The first and second turbine wheels may rotate in response to expansion of a working fluid flowing from an inlet side to an outlet side of the turbine wheels.