Abstract
A standard thermodynamic theory of energy conversion is corrected by including the return fluxes from the sink to the converter and from the converter to the pump. By also allowing for the limited solid angle subtended by the pump at the converter and for general photon distributions (not only black-body), one obtains a better theory than has so far been available. It yields maximum conversion efficiencies as a function of solid angles and entropy generation rates. Comparison is made with earlier work where available.