Analysis of the incoming solar radiation and other significant. parameters to estimate the solar resource at eight sites in Galicia (NW Spain)
Department of Chemical Engineering, University of Santiago de Compostela, Lope Gomez de Marzoa St.,
Campus Sur. 15782 Santiago de Compostela, Spain
Corresponding author, ia. souto@,usc. es
The evaluation of the solar resource in a region needs the characterization of different meteorological parameters. In this work, an analysis of global irradiation, clearness index and sunshine hours has been carried out in Galicia (NW Spain). Mean values of irradiation are compared with those derived from satellite images. The analysis is completed with the evaluation of other related parameters: precipitations, temperature and relative humidity. A complete characterization of the solar resource has been achieved in eight areas of Galicia. Results show high variability in the solar irradiation values, describing a more complex pattern than that derived from satellite observations. Evidences of the presence of local atmospheric phenomena, that overlap the diurnal evolution of solar radiation, drive to the conclusion that the distribution of the solar resource in this region cannot be explained without the consideration of climatologic and topographical features.
Keywords: solar resource, ground-satellite comparison
The development of technologies for renewable energies is a priority target in the policy from different fields. Between the renewable energies, solar thermal and solar photovoltaic energies have a great potential in Spain and in Galicia too . In Spain, the only official reference of the solar radiation climatology is the Atlas of Solar Radiation  that collects monthly means of sunshine hours and global irradiation between 1951 and 1983. Unfortunately, the low resolution of its results and their oldness may not represent a valid reference for estimating the solar resource in the present. Other works  applies satellite images to obtain solar maps for Spain, but they lack of homogeneous validation with ground measurements.
In Galicia, only an attempt was done, by Vazquez et al. . Using the method Heliosat-2 , they collected in an atlas the results of monthly means of solar radiation from observations by satellite Meteosat-6. Nevertheless, the analysis covered a short period of time and the results obtained were only compared with the measurements proceeding from one station. Finally, no information about other relevant parameters was provided.
This work is focused on the evaluation of the solar resource in Galicia from the ground. Over a 5- years period, the surface meteorological parameters that affect the performance of thermal and photovoltaic systems are analysed, keeping in mind the peculiarities of the Galician region. To accomplish this task, global irradiation, sunshine hours and clearness index have been evaluated at
eight locations, using daily measurements. Mean values of global irradiation proceeding from the stations have been compared with those derived from satellite observations. The evaluation is completed with the analysis of the time series of complementary parameters, such as precipitation, temperature and relative humidity, in order to obtain the most complete information about solar resource at these locations.