The method comprises determining that the clear day exists in response to the apparent diameter of the solar disc being similar to the expected diameter of the solar disc on the clear day and determining that an overcast condition exists in the camera image in response to the apparent diameter of the solar disc being distorted. The method may further include receiving a camera image of a sky section from a camera at a first location; segmenting the camera image into a first portion around a known position of a solar disc and a second portion of the remainder of the sky section containing an horizon; determining that the solar disc is obstructed by the horizon; and establishing that the first location is experiencing shadow conditions based on the determining.