André Mermoud Posted September 12, 2013 Posted September 12, 2013 The variability of the meteo data has been studied, namely by Pierre Ineichen, in a document available from our site (Global Irradiation: average and Typical year, and year-to-year annual variability, University of Geneva, 2011 ). He has collected data from different sources, and analyzed time series of 10 to 30 years for each of the 30 sites studied. The main results are gathered on the plot given below. It appears that the variability is dependent on the annual irradiance: this may be explained by the fact that with sunny climates with many clear days, the possibility of middle or bad days is lower.Therefore for use of these data in theevaluation of the P90 values, we have established an upper estimate which is used as default value. Meteo year-to-year variability, and default estimation for the P90 evaluation
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