Calculating solar radiation for inclined surfaces: Practical approaches

Various practical approaches to calculating the solar irradiation for an inclined surface are reviewed. All assume that the direct and diffuse irradiation for an inclined surface are available, either as measured or calculated values. The paper distinguishes numerous categories of model on the basis of time scale of applicability (hourly or daily or longer time intervals) and on the basis of the radiant flux that is modelled (direct, diffuse or reflected irradiation). The relative performance of the various models is assessed using the results of several studies. Superior models are identified.