Thermal emission (reradiation) limits the efficiency of receivers attempting to produce high-temperature heat from solar radiation. Usually receivers use a working fluid with an inlet temperature significantly lower than the outlet temperature. The authors show that in this case it is desirable to prevent intensive heat exchange or mixing of the working fluid inside the receiver. Rather, it is better to channel the fluid through a path traversing the receiver, gradually heating up the fluid on its way, similar to a cross-current heat exchanger. The receiver aperture then exhibits all the temperature range between the inlet and outlet temperature. The authors show that an ideal non-isothermal receiver subjected to uniform irradiance incurs thermal emission losses typically a factor of three to five lower than an isothermal receiver operating under the same irradiance and the same outlet temperature. For a nonuniform irradiance distribution, the flow should proceed from the location of the lowest irradiance to the highest, exposing the fluid to monotonically increasing irradiance. They calculate the efficiency versus temperature curve on a dimensionless universal scale for isothermal and nonisothermal receivers, under uniform irradiance and under an irradiance distribution described by a Gaussian. The authors find a high potential for reducingmore » reradiation losses, especially for nonuniform irradiance. This may open the possibility to effectively operate at temperatures up to two times higher without reduction in efficiency with non-isothermal receivers in central receiver systems.« less