Normalization of the Solar Radiation Data obtained from Images of Geostationary Satellites for a Medium Geographical Region, with Data measured in a Single Solar Earth Station. - Case of Galicia (Spain)

摘要

In order to obtain the maps of the daily average monthly global solar irradiation for Galicia (Spain), the daily average monthly values of solar irradiation, that were calculated from the Meteosat-6 satellite images using the Heliosat-II method, were normalized for all the pixels in the region using, as normalization reference, the solar data measured in the pixel where the meteorological station of the University of Vigo is located. Normalization consists in calculating for each month a coefficient, that is obtained by dividing the daily average monthly irradiation measured in the station by the daily average monthly irradiation from the Heliosat in the pixel of the station, and multiplying the daily average monthly irradiations obtained from Heliosat for all pixels in the region by the coefficient. This simple technique proved very efficient as the comparison of values obtained this way with unrelated solar data measured in other stations in the region showed differences lower than 0.5%. From this experience, we decided to apply a similar proceeding to obtain the monthly solar maps for the diffuse and the beam solar radiation. Using global and diffuse daily data from the station of the University of Vigo for the 2002-2004 period, twelve monthly correlations of the daily diffuse coefficient (diffuse/extraterrestrial) versus the daily clearness index (global/extraterrestrial) were obtained for each month of the year. These relations were applied to the daily clearness indices obtained from the daily global irradiations obtained with the Heliosat-II method for all the pixels in the region and for each corresponding month in order to obtain first the daily diffuse coefficients and by difference (clearness index minus diffuse coefficient) the daily beam coefficients. From these coefficients, the daily diffuse and direct solar irradiations were obtained that, in turn, let to obtain the daily average monthly values of diffuse and direct solar radiation for each month and each pixel. The last values were in turn normalized in a similar way as the global values using multiplying coefficients obtained for the diffuse and the direct components in the pixel of the Vigo station. Finally, the monthly diffuse and direct solar maps were obtained. In the paper, a detailed discussion of the work is shown together with some examples of the maps.