Meteonote6_Annual variability

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Meteonote6_Annual variability

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The distribution of yearly Irradiation values  for several years (at least 10-15 years) is evaluated using a Gaussian distribution.

The year-to-year variability is the width  (RMS) of this gaussian function.


-The year-to-year variability is now provided by the Meteonorm database.
It is displayed in the "Geographic site" dialog, page "Monthly Meteo", after importing the data from Meteonorm 7.2.  
-If you get multi-years data from a meteorological data provider, you can evaluate the variability of these data using  the tool  "Databases > Compare Meteo data". Here you can choose the years to be accumulated, and choose the "Histo and probabilities"  option to see the corresponding plot.  
-The variability of the meteo data has been studied in detail by Pierre Ineichen for about 30 different sites, in a document available from our web site  (cf Ineichen_2001)
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 table 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 the evaluation of the P90 values, we have established an upper estimate which is used as default value.