Specialized Irradiation Modeling for Alpine Regions: Clearsky and Diffuse Fraction Estimation

In the data driven performance evaluation of monitored PV systems, offsite irradiation sensors are of great help: either as the only irradiation data source in small residential systems, to estimate dust influence on local reference cells, or to check the calibration of the local irradiation sensors. Thereby, national meteorological measurement network (e.g. TAWES [1]) can be used, that features horizontal pyranometers in more than 250 sites in Austria. By geospatial interpolation, local estimations can be created based on this dense network. For many of these PV evaluations, the hypothetical local clearsky irradiation is of great use, e.g. to filter data for dust evaluations, which is commonly estimated by the Ineichen [2] or King model. Using the historic data of the measurement network, a method is developed to obtain geolocalized correction factors to the Ineichen model. Deviations of more than 10% are observed at altitudes 3500m above sea level, that thereby can be corrected for. As only the total horizontal irradiation is measured in the meteorological networks, an estimation of the diffuse horizontal irradiation is wanted, so that one can then use the Perez model to estimate module plane irradiations. A simplistic methodology is developed that estimates the diffuse irradiation purely based on local total horizontal irradiation, time, and geolocation within Austria. However, the methodology can be transferred any landmass worldwide, e.g. using the data within the GBON of the WMO [2].