Abstract: A method for assessing solar insolation potential upon existing building rooftops in a given region comprises: (a) computing Global Horizontal Insolation values based on topographical Digital Elevation Model (DEM) data for the region; computing a Sky Transmissivity parameter as it affects Global Horizontal Insolation based on available climate and cloud cover data for the region; (c) applying an Albedo parameter for ground reflectivity and scattering to determine Diffuse Insolation values; (d) applying a Shading Coefficient based on measuring shadow surface areas in relation to total area from aerial photographs of the region over defined times and periods; (e) determining Total Building Roof Area based on image analysis of aerial photographs of the region, and applying a typical roof slope factor; (f) estimating typical Roof Slope, Type, and Orientation (azimuth) selected from a defined set (vocabulary) of rooftop types based on a visual survey of the region; and (g) calculating Total Building Rooftop Insola