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III-V multijunction solar cells (MJSCs) operate close to the radiative limit under solar concentration. In this regime, radiative losses from the semiconductor material in one junction of the solar cell can be absorbed by a subsequent junction, thereby transferring charge from one subcell to another. Under blue-rich solar spectra, radiative coupling can improve the electrical performance by lifting constraints imposed by a series connection of subcells. We calculate the practical limit of performance enhancement due to the radiative coupling effect for MJSCs under a wide range of atmospheric conditions encountered in potential sites for concentrator photovoltaic systems. Three-junction and four-junction solar cells with current matched and current mismatched designs under the AM1.5D spectrum were considered. Under realistic atmospheric conditions, the relative enhancement to power due to radiative coupling is found to be 1% or less for current-matched triple-junction solar cells. Enhancement of up to 21% can be expected for noncurrent-matched quad-junction devices. The energy yield improvement over an annual period is shown to be up to 5% for the best combinations of devices and sites.