A generic model for the simulation of solar rectangular photobioreactors (PBR) is presented. It combines the determination of the time-varying solar radiation intercepted by the process with the theoretical framework necessary for PBR simulation, namely modeling of the radiant light energy transport inside the culture volume, and its local coupling to photosynthetic growth. Here, the model is applied to illustrate the full dependency of PBR behavior on solar illumination regimes, which results in a complex, transient response. Effects of day-night cycles, culture harvesting, and the interdependency of physical (light) and biological (growth) kinetics are discussed. It is shown that PBR productivity is the result not only of light intercepted on the illuminated surface but also of light attenuation conditions inside the bulk culture as influenced by incident angle and beam/diffuse distribution of solar radiation. Results are presented for a location in France for 2 months representative of summer and winter. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 1947-1960, 2011