Solar irradiance on flat-plate collectors in urban environments

A numerical climatic model has been developed in order to simulate the solar irradiance that would be available to a flat-plate collector sited at street level within a typical urban setting. Results confirm that the available irradiance can be substantially reduced by the presence of horizonal obstructions. It is additionally evident that the optimal collector azimuth may vary by as much as 60° from due south-in the mid-latitude northern hemisphere. Losses of available irradiance, associated with the popular practice of facing collectors due south and tilting them as a simple function of latitude, appear to be as high as 10-15% when compared to the total solar irradiance available at an optimal collector orientation as determined by simulation.