HC3 Persistence forecast service

HC3 Persistence forecast service - Radiation values for today

  Principle - Automatic access

The automatic access to HelioClim-3 Persistence Forecast (data for today) is for PAY. You need to purchase an annual subscription to this service. Please contact us for more details and to receive a quotation.

Access the Web interface - free



This service provides HelioClim-3 version 4 and version 5 radiation values updated in real time, and forecasts until the end of the current day using a model of persistence. In brief, as soon as a new Meteosat image is available every 15 min, the HelioClim-3 database is updated in real time. To receive a time series covering the whole current day, we decided to complete the time series by applying a persistence model.

  • Operational since March 2015
  • Time steps: from 1 min to hourly data for today
  • Radiation components: all radiation components (horizontal, fix-tilted, any tracker - Diffuse, Direct, Reflected and Global)
  • Version: HelioClim-3v4 and HelioClim-3v5 radiation values in real time (H-15 min) and short-term forecasts using a model of persistence until end of the current day.
  • Start of the service: first values are delivered as soon as the sun elevation is above 2° (before March 2016, the threshold was 12° as for the HC3 Archives)
  • End of the service: last image is acquired at 20:45 UT. After that time, the radiation values are not updated anymore. At approximately 23:00 UT, the HelioClim-3 Persistence Forecast service and the HelioClim-3 Archives service delivers the same radiation values.

Figure 1: Illustration of the principle of the HC3v4 and v5 real-time and short-term forecast service

More information about:

  • Validation results
  • Automatic access (for pay)
  • + 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).

In depth:

The principle of the HC3v4 and HC3v5 real-time and short-term forecast service is the persistence of the clear-sky index Kc, defined as the ratio of the GHI by the GHI in clear-sky conditions. Figure 1 illustrates this principle by giving an example of 15 min slots available until 11:25 AM (Figure 1 a)) for a given day d. The last slot available gives half-cloudy half-sunny weather; the main assumption of the Kc persistence states that the same type of weather will be available until the end of the current day, modulated by the sun position (Figure 1 b). Finally, a new MSG image is acquired, and finally, the weather is nicer than planned 15 min ago. The prevision is consequently adjusted (Figure 1 c)). Every 15 min, the service provides the data until the end of the day, with estimates based on all the slots available until the current instant, and forecasts based on local persistence afterwards.

The HelioClim-3 (version 4 and version 5) Persistence Forecast is based on the "persistence of Kc". We remind that the Kc index corresponds to the Global Horizontal component divided by the GHI in clear sky conditions (GHI/GHI_cls). You may see it as the "percentage of clouds". This method computes the last available Kc value and extend this value for the remaining slots of the day, taking into account of course the time of the day. As a consequence, at least one slot of the day should be available. The HelioClim-3v5 Persistence Forecast predicts the current day and is available only after sunrise.

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 today):

wget -O output.csv --header="soda-user: guest" --header="soda-passwd: guest" ...
"http://www.soda-is.com/pub/hc3v5_persistence_forecast.php?geopoint=44.083,5.059&elevation=-999& ...

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

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