In this study, a first-order environmental impact study of a large-scale deployment of solar energy-installed technologies in a complex coastal urban environment is conducted. The work is motivated by the positive prospects of building-integrated solar technologies as a sustainable alternative to energy demands and reduction of green house gases. Large-scale deployment of solar technologies in rooftops of densely populated cities may have the potential of modifying surface energy budgets resulting in cooling or heating of the urban environment. To investigate this case, a mesoscale simulation (regional atmospheric simulation system (RAMS)) effort was undertaken, with a horizontal grid resolution of 4 km on an innermost grid over Southern California (South Coast Air Basin (SoCAB)). The simulation period was selected in summer 2002 where strong urban heat islands (UHIs) were observed for the region. The urban landscape was modified to represent a percentage of the rooftops with optical and thermal properties corresponding to solar PV and thermal collectors. Results show that the large-scale presence of solar technologies in rooftops of SoCAB may have a net positive thermal storage of the buildings, an effect enhancing the existing UHI by up to 0.2 °C. This additional heat is advected inland as the sea breeze develops warming further inland areas. The net environmental effect of solar technologies when compared with solar energy production was not investigated in this study.