A method for generating mechanical work via a closed-loop Rankine cycle includes heating a working fluid to at least a partial vapor state, generating useful work at a first expansion stage by expanding the working fluid as the working fluid passes through the first expansion stage, generating useful work at a second expansion stage by expanding the working fluid as the working fluid passes through the second expansion stage, generating useful work at a third expansion stage by expanding the working fluid as the working fluid passes through the third expansion stage, and condensing the working fluid to a liquid state.