Comparison to maps derived from satellite data
Differences between global solar radiation interpolated from ground level measurements (Fig. 2 values) and published in  were shown on Fig. 6. As it is observed, a non-homogeneous distribution of significant relative differences (from +25 to -60 %) indicates the high dependence of solar radiation from the local conditions in every location. Therefore, it should be recommended a calibration of satellite data from a number of ground level measurements (ideally, from all of the available stations) that can represent these local effects.
From the 34 students registered in the Solar Radiation subject, 32 started their work selecting a meteorological station to process. 31 students passed the subject in the first attempt (including a written exam by 60 % of the total qualification); just one student required to repeat the written exam, in order to pass the subject. The other two students abandon the subject.
The interest of the students in this work was higher than the theoretical issues and practical problems of the subject. Specially, processing meteorological datasets from real stations selected by the students was an extra incentive. And, in addition, processed datasets result very useful to get a solar resource evaluation in the region over the studied period, as only minor revisions of students’ calculations were required.
In this work an estimation of the annual solar resource over Galicia was developed, in the framework of a self-learning experience with the collaboration of students of the MSc in Renewable Energies and Energetic Sustainability. This educational experience was very successful, as the interest of the students was very high and their results were very useful to achieve the solar resource maps.
From the solar global irradiation distribution, solar resource in this region is extremely connected to the local conditions (local cloudiness, rain, fog), that are very variable because of the changeable weather and complex topography of this region. Although the validity of these results is limited to an annual period, irradiation distribution shows the necessity to consider local conditions in the application of any methodology to estimate solar resources at Galicia.
As the main conclusion, satellite data processing has to be completed with a high number of ground level measurements. Other techniques, as Digital Terrain Models (DTM) , allow to estimating ground level irradiation considering topographic effects; these technique can help to cover complex terrain zones with lack of ground level data.
Meteorological dataset provided by MeteoGalicia (Xunta de Galicia) from its web page is acknowledged. Dataset processing was partially developed by the students of the MSc in Renewable Energies and Energetic Sustainability of the University of Santiago de Compostela (2007-08 academic year).
This work was partially funded by Galician regional R&D Programme (Xunta de Galicia) under project 07REM02CT.
 Vera Mella N. Atlas climatico de irradiation solar a partir de imagenes del satelite NOAA. Aplicacion a la peninsula iberica. PhD Thesis. Universitat Politecnica de Catalunya, Barcelona, Spain; 2005.
 Sharmer k. Towards a new atlas of solar radiation in Europe. International Journal of Solar Energy, 1994; 15: 81-87
 Baldasano J. M., Soriano C., Flores H. Atlas de radiacio solar a Catalunya. Institut Catala d’Energia. Barcelona, Spain; 2001.
 Alnaser W. E., Eliagoubi B., Al-Kalak A., Trabelsi H., Al-Maalej M., El-Sayed H. M., Alloush M. First solar radiation atlas of the Arab world. Renewable Energy 2004; 29: 1085-1107
 Font Tullot I. Atlas de la radiation solar en Espana. Instituto Nacional de Meteorologia, Ministerio de Transportes, Turismo y Comunicaciones. Madrid, Spain; 1984.
 Nrnez, M., Reyes, J. J., Marroquin, A., Ramiro, A. Mapas de valores medios mensuales de irradiacion solar estimados para Extremadura a partir de otros datos meteorologicos. XXVIII Jornadas Cientlficas de la Asociacion Meteorologica Espanola. Badajoz, Spain, 2004.
 Vazquez Vazquez M., Santos Navarro J. M., Prado Cerqueira M. T., Vazquez Rios D., Rodrigues Fernandes F. M. Atlas de radiacion solar de Galicia. Universidad de Vigo. Vigo, Spain; 2005.
 Rigollier, C., Lefevre, M. and Wald, L. The method Heliosat-2 for deriving shortwave solar radiation from satellite images. Solar Energy 2004; 77: 159-169.
 Pettazzi A., Souto J. A. Analysis of the incoming solar radiation and other significant parameters to estimate the solar resource at eight sites in Galicia (NW Spain), Proceedings of EUROSUN 2008, 1st International Conference on Solar Heating, Cooling and Buildings., Lisbon, Portugal, 2008
 Salson S., Souto J. A. Automatic weather stations network of the department of environment of Galicia: data acquisition, validation and quality control, Proceedings of the 3rd international conference on experiences with automatic weather stations, Torremolinos, Spain; 2003.
 Pettazzi A., Souto J. A., Salson S. EOAS, a shared joint atmospheric observation site of MeteoGalicia. Proceedings of 4th ICEAWS - International Conference on Experiences with Automatic Weather Stations, Lisbon, Portugal; 2006.
 Davies J. A. Validation of models for estimating solar radiation on horizontal surfaces. Report available from the IEA, Downsview, Ontario, Canada; 1988.
 Iqbal M. An introduction to solar radiation, Academic Press, San Diego, CA; 1983.
 Instituto Nacional de Meteorologia. Guia resumida del clima en Espana 1971-2000. Instituto Nacional de Meteorologia, D25.3, Ministerio de Medio Ambiente. Madrid, Spain; 2001.
 Batlles F. J., Martinez-Durban M., Miralles I., Ortega R., Barbero F. J., Tovar-Pescador J., Pozo - Vazquez D., Lopez G. Evaluation de los recursos energeticos solares en zonas de topografia compleja. XII Congreso Iberico y VII Congreso Ibero Americano de Energia Solar. Vigo, Spain; 2004.
 Martinez Cortizas A., Perez Alberti A. Atlas Climatico de Galicia, Xunta de Galicia, Santiago de Compostela, Spain; 1999.
 Tovar-Pescador J., Pozo-Vazquez D., Molina A., Batlles F. J., Lopez G. Mejora en la estimation de la irradiancia solar en zonas de topografia compleja mediante modelos digitales del terreno. XII Congreso Iberico y VII Congreso Ibero Americano de Energia Solar. Vigo, Spain; 2004.