3 rd International Conference on Experiences with Automatic Weather Stations, 19 th -21 st of February 2003, Torremolinos, Spain 1 COMPARISON OF DIFFERENT METHODS FOR MEASURING SOLAR IRRADIATION DATA N. Geuder, F. Trieb*, C. Schillings*, R. Meyer**, V. Quaschning Deutsches Zentrum für Luft und Raumfahrt e.V., Plataforma Solar de Almería, Apartado 39, E-04200 Tabernas, Spain, Tel.: +34 950 38-7908, e-mail: norbert.geuder@psa.es * Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR-Stuttgart, Institut für Technische Thermodynamik, Pfaffenwaldring 38-40, D-70569 Stuttgart ** Deutsches Zentrum für Luft- und Raumfahrt e.V., DLR-Oberpfaffenhofen, Institut für Physik der Atmosphäre, D-82234 Wessling Abstract Knowledge of solar irradiation data is very important e.g. for planning solar power plants. Unfortunately valid data in suitable regions are quite rare. Our investigations at the PSA concern the improvement of irradiation data measured with Rotating Shadowband Pyranome- ters at promising sites. The data show larger deviations compared to real values and need to be revised and corrected after comparison with more precise data we measure with recently installed new thermal sensors. Finally TMY of the sites as well as irradiation maps derived from satellite images will be generated. Key words: irradiation, RotatingShadowbandPyranometer, soiling, satellite data. 1 INTRODUCTION An exact knowledge of solar irradiation data at foreseen locations is very important for planning and installation of solar power plants or other devices using solar energy. Due to in- creased indications of climate changes in the past years, an intensified use of renewable ener- gies in world energy generation is strongly recommended. Solar energy can provide huge amounts of the energy share especially in regions with high solar irradiation. Possibilities to access solar energy are manifold: power plants like those investigated at the Plataforma Solar de Almería (PSA) use solar energy by concentrating direct irradiation, converting it to heat and finally electricity [Geyer00]. But also flat plate collectors or photovoltaic panels, which can be installed decentralized, show promising prospects [Quaschning01]. Solar irradiation can be seen as the “fuel” for these devices and therefore takes strong influ- ence on the costs. Small changes in the annual irradiation sum decide e.g. whether the con- struction of a power plant is either economically reasonable or unattractive. Unfortunately valid meteorological data in suitable regions are quite rare. Furthermore, the weather and sub- sequently irradiation depend strongly on the microclimate and besides vary significantly from one year to another one. Already existing tools, which allow the calculation of the expected irradiation at chosen sites by interpolating some widely spread data [Quaschning00], show rather large uncertainties and cannot be used for valid calculations for projected power plants [Quaschning02]. Methods using satellite data can provide information on the available irra- diation continously in space and time. Exact measurements of the insolation at ground can help to validate these methods. Our investigations at DLR-PSA presented in this paper treat the improvement of meteoro- logical data measurements, which we take with industrial partners at several locations in the south of Spain and Morocco. At already existing stations the irradiation sensors are equipped with simple photodiode sensors having low accuracy. However, the deviations of their signal