HC3 Real time
HC3 Persistence forecast service - Radiation values for today |
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 | |
Principle
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.
|  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& ...
firstday=2017-07-29&lastday=2017-07-29&duration=15&time=UT&slope=25&azimuth=180&albedo=0.2&horizon=1&format=unified"
More information about the automatic access to the HelioClim-3 Persistence Forecast method