Limit of concentration under extended nonhomogeneous light sources

Static photovoltaic concentrators, which see the sky as an extended distribution of radiance, are analyzed in a general way. The rules for achieving the highest energy on the cell are derived and the appropriate figures of merit are defined. It is concluded that casting increasingly high values of energy on the cell, which would be bifacial, requires collecting a lower portion of the total sky energy. The corresponding figures of merit for the concentrators of the CPC family are analyzed, and it is concluded that a better type of concentrator should be developed for photovoltaic applications.