Availability of Solar Energy on Vehicle Roofs in German Road Network; Validation of Surface Structure Data for Shadow Loss Modelling

Solar potential maps for static applications like PV power plants have improved much in data quality in recent years. For moving objects like vehicles with potential solar applications the situation is different. Studies are available but measurement data is scarce. Therefore, Fraunhofer ISE has applied for and won a citizen science research project (PV2Go) supported by the German federal ministry for economic affairs and energy to assess, model and validate the solar potential on the German road network. ISE developed a high precision solar radiation measurement device with in-house calibrated reference cells producing its own energy supply. Equipped with an electrical energy storage device charged by a solar module it can keep recording data for about two weeks of darkness. Fiftyseven units have been sent to chosen citizen scientists and project partners, including a description on how to properly mount the sensor on a vehicle. The unit logs timeseries data with a time resolution depending on the moving state. It transfers the data through the mobile radio network including high precision global horizontal irradiance (GHI) and GPS location. This allows for comparison with satellite image derived GHI. The comparison with satellite data does not only provide information on the measurement uncertainty but is also used to derive shading information for when the vehicle experiences a shading event, therefore satellite data in turn can be used to estimate potential shading losses for a vehicle mounted PV installation. In a first approximation for the data evaluation a fixed threshold (satellite and measurement data relative to clear sky irradiance values) between measurement and satellite data has been established for shadow detection. Applied to all available data, this lead to a cumulated energy loss of 34% relative to satellite data derived irradiance. In addition to the citizen science campaign the PV2Go Project entails a detailed analysis of potential shading for major streets in Germany. This was done using a digital surface model combined with geometric analysis. The result are solar driving profiles describing the solar potential for roads in Germany. The validity and accuracy of this satellite data derived solar driving profiles is evaluated by the measurement values of the citizen science campaign.