Approaches to computing irradiance on building surfaces

This article compares alternative options to generate sky radiance maps based on a limited scope of measured radiometric data (such as global and diffuse horizontal irradiance). Two options made use of both measured global and diffuse horizontal irradiance values. Two other options used only measured global horizontal irradiance. A fifth option used calibrated digital photography to derive the sky models. These sky models can be used in simulation applications to compute irradiance values on arbitrarily oriented surfaces. In the present contribution, we compared computed irradiance values on four vertical surfaces with corresponding measurements. The two options, which use both global and diffuse horizontal irradiance values for sky radiance generation delivered better results. However, the range of errors was rather high for all options.