A method of determining and responding to an overcast sky condition during daylight hours in a solar tracker installation utilizing a single, fixed-position irradiance sensor associated with a set of solar tracker assemblies of the solar tracker installation and, if a series of irradiance levels communicated by the irradiance sensor to an array controller of a solar tracker control system of the installation indicates that an overcast sky condition has been present for a predetermined overcast sky duration period, the array controller transmitting control signals to a set of solar tracker controllers associated with the set of solar tracker assemblies to deviate from a normal solar tracking mode to an overcast sky mode by pivoting respective tables of the associated set of solar tracker assemblies to one or more predetermined overcast sky condition angles of inclination, and a solar tracker control system for implementing the foregoing method.