Maximizing the output of a solar module requires proper siting and placement (tilt and east-west orientation), of the module. In addition, it also depends on parameters outside of human control, such as, number of daylight hours and local climatic conditions. To predict the performance it is necessary to know the instantaneous solar flux incident on the surface. This is also relevant to predicting the incident radiant energy striking the wall or window of a building which then subsequently penetrates into the building contributing to its heating load. The goal of this work was to develop an empirical model to predict the variation of incident solar radiation on surfaces of different orientations. A series of empirical predictive equations for the average daily variation of incident solar radiation were developed for different months of the year for a surface located at a specific latitude. These were then combined into a single global model that can be used for any month of the year. The model was validated against measured data.