Efficiency of antenna solar collection

Antennas with rectifiers, "rectennas", have been proposed for high efficiency conversion of solar energy and high efficiencies have been demonstrated for quasi-monochromatic microwaves. Antennas receiving black body radiation may be modelled as a pair of resistors at the black body temperature, each supplying electrical noise power. Extraction of that power from a load as heat is feasible at the same limiting efficiencies as solar thermal converters. Rectennas, relying on rectification of the broadband electrical noise, appear to have lower efficiency limits due to the unavailability of a design for the Carnot conversion of the noise from a hot resistor.