A novel photometric method for the determination of reflected solar irradiance in the built environment

The urban environment is characterised by diverse structures over an area consisting of buildings, greenery and various ground surfaces. The analysis and modelling of the reflected solar radiation distribution phenomenon in such surroundings are very complex. This paper presents a holistic approach to the analysis of reflected solar radiation in an urban environment. The main body of this work is the presentation and validation of a new method for determining solar irradiance reflected from the surrounding urban elements based on a high dynamic range imaging photometric technique and on-site luminous efficacy measurements. In the proposed method, the effect of the following parameters on the reflected solar irradiance is considered: the characteristics of the surrounding environment, the position of the sun, and the sky conditions. Reflected solar irradiance was determined on selected days throughout the year for two cases differing in urban environment characteristics. The evaluated reflected solar irradiance strongly depends on the surrounding environment, the season of the year, sky conditions and the position of the sun. These discrepancies indicate the complex characteristics of reflected solar irradiance. The proposed method has been validated by comparison of the obtained results with the measured value of solar irradiance incident on vertical surfaces. The convergence of the obtained results and the measurements was very high with a coefficient of determination of 0.95.