A power compounder is disclosed. The power compounder comprises a working fluid configured to receive thermal energy from waste heat of a prime mover, a working fluid collector, an evaporator configured to transfer waste heat to a working fluid producing a phase change to vapor (or gas) in the working fluid, a double screw expander configured to receive the working fluid for creating rotational mechanical energy, and a condenser configured to produce another phase change in the working fluid to liquid. The double screw expander transfers the rotational mechanical energy via a shaft to the prime mover.