A computational capability that models the operation of any solar energy collector that uses flux concentrators is a valuable aid in the planning, design, construction, calibration, safety analysis, and operation of the system. In addition to the usual optical considerations, the model should treat such imperfections as reflecting-surface slope errors, suntracking and alignment errors, and mirror-focusing errors. It should properly account for the angular distribution of incoming sun rays and the effects of atmospheric transmission on this distribution. A model with these capabilities is described, and two computer programs for implementing it are illustrated.