Load Flow Calculation of a Low Voltage Transformer using Satellitebased Irradiance Data

A scheme using satellite-derived irradiance measurements to model the load flow of a medium-to-low voltage transformer in a low voltage distribution grid area is described. This scheme is validated by comparison with measurements at the transformer from a test site with 21 residential PV systems in the city of Ulm, Germany. The irradiance data are provided by the SOLEMI, the Helioclim 3 and the MACC-RAD services. The load flow simulation model is based on a PV model taking into account nominal power and location of the PV systems as provided by the distribution system operator and orientation angles taken in high resolution from aerial laser-scan data. The load data are assumed using load profile time series from standard load profiles and measured profiles. Modell quality is assessed by a comparison of modelled and measured power. Average mean errors of power are found in the range of 14.0 % to 16.6 % and the RMSE is between 41.1 % and 42.3 % for the different input data sources. Relative values are related to the total average loading of the transformer. Overall, the study indicates the usefulness and applicability of satellite-derived irradiance data for utility applications like load flow monitoring of transformers in areas with a high amount of residential PV systems.