A thermo-electric engine with a working fluid operative in a closed Rankine cycle to enable a harvesting energy from an external source of thermodynamic energy, such as an internal combustion engine or solar energy. The thermo-electric engine can have an evaporator; a turbine fluidically coupled to the evaporator; a heat exchanger comprising a condenser for receiving working fluid from the turbine; a hot liquid input for coupling to a source of heated liquid coolant from an internal combustion engine to the evaporator; a liquid return for returning liquid coolant to the internal combustion engine; a cooling liquid input to the condenser for receiving cooling liquid from a radiator; and a cooling liquid return for returning the cooling liquid to the radiator. Alternatively, a solar energy collector can power a turbine fluidically coupled to the solar energy collector for receiving working fluid.