Detailed balance method for ideal single-stage fluorescent collectors

It is shown that fluorescent collectors where radiation is confined with the use of selective reflectors can be modeled as converters of blackbody radiation. By decreasing the temperature and frequency of the radiation, the effective etendue of the emitted beam can be reduced substantially in the conversion process without violating the second law of thermodynamics. This type of collector can, in principle, achieve surprisingly high efficiencies: the output from a silicon solar cell operating with an ideal collector can exceed 90% of the output from a directly illuminated solar cell.