HC3 SIMILARITY FORECAST - Radiation values for tomorrow

Last update: September 2019

    Principle - Automatic access

The online access to this service is for FREE. Please help yourself =>


The automatic access to HelioClim-3 Similarity Forecast (data for tomorrow) is for PAY. Please contact us for more details and to receive a quotation.

Access the Web interface - free




  This method explores the HelioClim-3 database to find for similar meteorological events in the past in order to make an estimation of the next day irradiation values.

  • Operational since July 2015
  • Time steps: 1, 5, 10, 15, 30 minutes, hourly and daily
  • Database: HelioClim-3v5 radiation values. 
  • Spatial coverage: Meteosat Second Generation (-66° to +66° both in latitude and longitude)
  • Data availability: Please note that the day d should be over to provide the value for d+1. If a request is launched during day which is running, the service of persistence is applied to complete day d values, and use the solar forecast similarity method to generate day d+1 values. As a consequence, as soon as a new 15 min image is collected, this service provides different values for day d+1.

More information about:

  • + Meteo data : you can now receive Meteo variables (temperature, wind, pressure, relative humidity, rain and snow fall, snow depth) together with your irradiation values by setting to "True" the input parameters "Add Meteorogical data". The origin of Meteo data is GFS (NCEP).
(click on the image to magnify)

The principle of the Solar Forecast Similarity Method algorithm is to search in the HelioClim-3 past irradiance database the closest period to the current day. The closest period is defined by considering the minimum of the square distance. Once the nearest period(s) is(are) determined, the following day(s) is(are) used as a prediction for the day following the current day.
This search for the most suited day could be very time consuming, and a lot of work has been done to reduce this time by a factor up to 50. Different parameters had been adjusted, and the best compromise is given by:

  • a temporal window of 15 days before and after the date independently of the year
  • a search in the previous 4 years is considered
  • the code is searching for the 10 closest days

The days following the 10 selected days in the past are averaged to produce the prediction. With this configuration, the bias is null ; the algorithm outperforms the persistence by 20% and the error is similar to existing methods.

Automatic access

This access is restricted to users who purchased an annual subscription to this service.
You can test this service on the site of Carpentras in France in a Windows environment by using the following command on a single line (pay attention to change the date in red by the date of tomorrow):

wget -O output.csv --header="soda-user: guest" --header="soda-passwd: guest" ...
"http://www.soda-is.com/pub/hc3v5_similarity_forecast.php?geopoint=44.083,5.059&elevation=-999& ...

More information about the automatic access to the HelioClim-3 Similarity Forecast method

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