Ponencia presentada en: 24th European Photovoltaic Solar Energy Conference and Exhibition celebrada del 21-25 de septiembre de 2009 en Hamburgo.Power generation from photovoltaic systems is highly variable due to its dependence on
meteorological conditions. An efficient use of this fluctuating energy source requires reliable forecast information for
management and operation strategies. Due to the strong increase of solar power generation the prediction of solar
yields becomes more and more important. As a consequence, in the last years various research organisations and
companies have developed different methods to forecast irradiance as a basis for respective power forecasts. For the
end-users of these forecasts it is important that standardized methodology is used when presenting results on the
accuracy of a prediction model in order to get a clear idea on the advantages of a specific approach.
In this paper we introduce a benchmarking procedure to asses the accuracy of irradiance forecasts and compare
different approaches of forecasting. The evaluation shows a strong dependence of the forecast accuracy on the
climatic conditions. For Central European stations the relative rmse ranges from 40 % to 60 %, for Spanish stations
relative rmse values are in the range of 20 % to 35 %
