HelioClim-3 version 4 sOLAR SIMILARITY FORECAST service
time series at d+1

Last update: Dec. 2015

    In brief - Methodology - Access - Validation

Access the interface - free -

 

In brief

  • Operational since July 2015
  • Access: graphical user interface at http://www.tsv.soda-pro.com/web-services/radiation/helioclim-3-forecast and automatic (see below)
  • Time steps: 1, 5, 10, 15, 30 minutes, hourly and daily
  • Database: HelioClim-3v4 radiation values provided at d+1. 
  • 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.
  • NB: the version  5 can not be available in real time since the input data are only available at d-2.
(click on the image to magnify)

Methodology

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

On Windows, you have first to download the executable wget.exe in a directory. In the same directory, create a .bat file with the following wget command. On Unix, wget is a standard tool, so just create a .sh file with the following wget command.

Request:
wget -O output.csv --header="soda-user: your_login" --header="soda-passwd: your_password"
"http://server/pub/hc3v4_similarity_forecast.php?geopoint=latitude,longitude&elevation=altitude ...
&firstday=yyyy-mm-dd&lastday=yyyy-mm-dd&duration=time_step&time=time_reference&slope=tilt_of_panels ...
&azimuth=az_of_panels&albedo=ground_albedo&horizon=boolean_horizon&soda-user=your_login"

  Inputs:

  • HelioClim version is "4"
  • latitude and longitude: in degrees, with at least 3 digits after comma, e.g. "geopoint=45.563,7.25"
  • altitude: in meters. Set "elevation=-999" to let SoDa get the elevation from Nasa SRTM database
  • yyyy-mm-dd: the firstday and lastday MUST be identical and equal the date of the next day
  • time_step: "1", "5", "10", "15", "30" (minutes), "h" (hourly), "d" (daily)
  • time_reference: "TU" (universal time) or "TST" (True Solar Time)
  • tilt_of_panels: from "0" (horizontal) to "90", and "-999" (sun tracking)
  • az_of_panels: from "0" (North), 90° (East), 180° (South) to 270° (West), and "-999" (sun tracking)
  • ground_albedo: from "0.0" to "1.0". A usual inland value is "0.2" (default).
  • boolean_horizon: takes into account "1" or not "0" the far horizon. If not set, default value is "0".

  Outputs:

Compared to the output column content available in the standard HelioClim-3 services, two points differ:

  • the header is by default available
  • a column of code is available before the last column of Top of Atmosphere irradiation values:
    Code: 0: no data; 1: sun below horizon; 2: satellite assessment;  5: interpolation in time; 6: forecast

NB: For the SoDa Customers who already exploit the output format of hc3v4_request.php, it is possible to get back to this format by adding the following parameters "rely=0&header=0"

  Error messages

  • ERROR -1: Incorrect tilted plane parameter
  • ERROR -2: Cannot open file
  • ERROR -3: Cannot write to file
  • ERROR -4: Cannot read file
  • ERROR -5: Not enough memory
  • ERROR -6: Cannot access remote data
  • ERROR -7: Helioclim service is corrupted
  • ERROR -8: Unregistered IP address
  • ERROR -9: Incorrect location parameter
  • ERROR -10: Incorrect time step parameter
  • ERROR -11: Incorrect date parameter
  • ERROR -12: Incorrect horizon parameter
  • ERROR -13: Incorrect elevation parameter
  • ERROR -14: Incorrect stations file
  • ERROR -15: Subprogram failed with no error message
  • ERROR -16: Incorrect calibration parameter
  • ERROR -17: Incorrect user/password parameters
  • ERROR -18: Incorrect albedo parameter
  • ERROR -19: Incorrect time reference parameter
  • ERROR -21: Incorrect rely parameter
  • ERROR -22: Incorrect header parameter
  • ERROR -23: HC3 database is not updated
  • ERROR -24: This service is out the scope of your SoDa subscription
  • ERROR 1: No data available with these input parameters
    (generic message if the error is unknown)

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Validation

Please find below the validation results corresponding to the validation results for the Global Horizontal Irradiation values and for different time steps (monthly, daily, hourly and 15 min data). To produce these results, the HelioClim-3 version 4 Solar Similarity Forecast data at D+1 have been compared to the BSRN stations (see illustration below).
NB: we adopted the validation protocol and the quality check procedure described on the SoDa website.

Illustration: locations of the BSRN stations

Quality assessment results of GHI values

HelioClim-3 v4 Solar Similarity Forecast service -- GHI Quality assessment results vs. the BSRN stations
MONTHLY SUM OF 15 MIN IRRADIATION
Station Number of values Mean
- BSRN -
(kWh/m2)
Bias HC3v4
(kWh/m2)
(relative in %
)
Bias Forecast
(kWh/m2)
(relative in %
)
RMSE HC3v4
(kWh/m2)
(relative in %
)
RMSE Forecast
(kWh/m2)
(relative in %
)
Correl. coeff.
HC3v4
Correl. coeff.
Forecast
Toravere 50 86.9 -2.8 (-3.2%) -2.4 (-2.8%) 8.3 (9.6%) 11.1 (12.8%) 0.987 0.974
Cabauw 65 88.2 -3.1 (-3.5%) -3.7 (-4.2%) 7.3 (8.3%) 12.0 (13.6%) 0.994 0.980
Palaiseau 54 103.7 3.5 (3.4%) 2.6 (2.5%) 6.0 (5.8%) 11.9 (11.5%) 0.998 0.981
Payerne 29 107.8 -8.5 (-7.8%) -11.0 (-10.2%) 10.1 (9.4%) 16.2 (15.0%) 0.996 0.985
Carpentras 61 130.0 1.3 (1.0%) -0.4 (-0.3%) 3.8 (2.9%) 9.2 (7.1%) 0.999 0.990
Sede Boqer 44 166.9 -11.7 (-7.0%) -12.9 (-7.8%) 13.9 (8.3%) 14.2 (8.5%) 0.992 0.995
Tamanrasset 65 159.9 0.1 (0.1%) 0.2 (0.1%) 8.1 (5.1%) 10.6 (6.6%) 0.973 0.953
Brasilia 27 144.8 5.7 (4.0%) 8.5 (5.8%) 7.7 (5.3%) 12.6 (8.7%) 0.989 0.958
Sao Martinho da Serra 32 141.2 -1.9 (-1.3%) -3.5 (-2.5%) 4.2 (3.0%) 10.9 (7.8%) 0.997 0.978

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HelioClim-3 v4 Solar Similarity Forecast service -- GHI Quality assessment results vs. the BSRN stations
DAILY SUM OF 15 MIN IRRADIATION
Station Number of values Mean
- BSRN -
(Wh/m2)
Bias HC3v4
(Wh/m2)
(relative in %
)
Bias Forecast
(Wh/m2)
(relative in %
)
RMSE HC3v4
(Wh/m2)
(relative in %
)
RMSE Forecast
(Wh/m2)
(relative in %
)
Correl. coeff.
HC3v4
Correl. coeff.
Forecast
Toravere 1481 2795.3 -82.1 (-2.9%) -56.4 (-2.0%) 445.3 (15.9%) 1140.4 (40.8%) 0.978 0.843
Cabauw 1946 2940.1 -103.6 (-3.5%) -123.1 (-4.2%) 378.1 (12.9%) 1106.9 (37.6%) 0.987 0.868
Palaiseau 1639 3412.4 114.2 (3.3%) 101.1 (3.0%) 332.4 (9.7%) 1144.7 (33.5%) 0.991 0.867
Payerne 877 3558.8 -278.9 (-7.8%) -360.5 (-10.1%) 467.7 (13.1%) 1263.8 (35.5%) 0.987 0.862
Carpentras 1824 4359.2 43.5 (1.0%) -14.4 (-0.3%) 319.3 (7.3%) 1168.1 (26.8%) 0.992 0.881
Sede Boqer 1287 5647.8 -398.2 (-7.1%) -418.3 (-7.4%) 553.4 (9.8%) 741.6 (13.1%) 0.981 0.949
Tamanrasset 1723 5624.6 6.3 (0.1%) 25.3 (0.4%) 566.3 (10.1%) 902.5 (16.0%) 0.908 0.762
Brasilia 761 5073.7 194.7 (3.8%) 306.4 (6.0%) 583.5 (11.5%) 1046.0 (20.6%) 0.911 0.662
Sao Martinho da Serra 970 4721.2 -67.2 (-1.4%) -148.5 (-3.1%) 405.3 (8.6%) 1742.7 (36.9%) 0.986 0.672

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HelioClim-3 v4 Solar Similarity Forecast service -- GHI Quality assessment results vs. the BSRN stations
HOURLY SUM OF 15 MIN IRRADIATION
Station Number of values Mean
- BSRN -
(Wh/m2)
Bias HC3v4
(Wh/m2)
(relative in %
)
Bias Forecast
(Wh/m2)
(relative in %
)
RMSE HC3v4
(Wh/m2)
(relative in %
)
RMSE Forecast
(Wh/m2)
(relative in %
)
Correl. coeff.
HC3v4
Correl. coeff.
Forecast
Toravere 18095 221.9 -6.0 (-2.7%) -3.3 (-1.5%) 60.3 (27.2%) 126.5 (57.0%) 0.958 0.800
Cabauw 22886 249.6 -9.0 (-3.6%) -10.8 (-4.3%) 56.7 (22.7%) 126.9 (50.8%) 0.968 0.821
Palaiseau 19680 285.1 9.3 (3.3%) 6.6 (2.3%) 51.4 (18.0%) 134.1 (47.1%) 0.978 0.830
Payerne 10167 306.7 -24.3 (-7.9%) -31.6 (-10.3%) 67.3 (22.0%) 144.3 (47.1%) 0.970 0.839
Carpentras 21959 362.3 3.5 (1.0%) -1.9 (-0.5%) 47.2 (13.0%) 133.7 (36.9%) 0.986 0.878
Sede Boqer 14417 505.6 -35.3 (-7.0%) -39.0 (-7.7%) 69.2 (13.7%) 98.0 (19.4%) 0.982 0.957
Tamanrasset 20996 479.2 0.7 (0.1%) 0.4 (0.1%) 71.7 (15.0%) 120.6 (25.2%) 0.974 0.926
Brasilia 9428 417.1 16.4 (3.9%) 24.2 (5.8%) 110.4 (26.5%) 154.2 (37.0%) 0.933 0.860
Sao Martinho da Serra 11567 396.3 -5.8 (-1.5%) -13.0 (-3.3%) 73.3 (18.5%) 190.6 (48.1%) 0.971 0.787

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HelioClim-3 v4 Solar Similarity Forecast service -- GHI Quality assessment results vs. the BSRN stations
15 MIN IRRADIATION
Station Number of values Mean
- BSRN -
(Wh/m2)
Bias HC3v4
(Wh/m2)
(relative in %
)
Bias Forecast
(Wh/m2)
(relative in %
)
RMSE HC3v4
(Wh/m2)
(relative in %
)
RMSE Forecast
(Wh/m2)
(relative in %
)
Correl. coeff.
HC3v4
Correl. coeff.
Forecast
Toravere 71550 61.6 -2.0 (-3.2%) -1.7 (-2.8%) 20.4 (33.2%) 36.0 (58.5%) 0.935 0.779
Cabauw 88643 64.7 -2.3 (-3.5%) -2.7 (-4.2%) 19.0 (29.4%) 35.3 (54.6%) 0.944 0.787
Palaiseau 76660 73.4 2.4 (3.3%) 1.8 (2.5%) 18.1 (24.7%) 37.5 (51.1%) 0.957 0.795
Payerne 39758 78.6 -6.2 (-7.8%) -8.0 (-10.2%) 21.3 (27.1%) 39.2 (49.9%) 0.951 0.814
Carpentras 84383 94.4 1.0 (1.0%) -0.4 (-0.4%) 15.6 (16.5%) 36.2 (38.3%) 0.975 0.856
Sede Boqer 56695 130.7 -9.2 (-7.0%) -10.1 (-7.7%) 20.7 (15.8%) 27.2 (20.8%) 0.970 0.943
Tamanrasset 80956 128.4 0.1 (0.1%) 0.1 (0.1%) 23.0 (17.9%) 34.8 (27.1%) 0.958 0.903
Brasilia 36273 110.2 4.6 (4.2%) 6.7 (6.0%) 37.1 (33.7%) 45.7 (41.5%) 0.881 0.807
Sao Martinho da Serra 44186 104.3 -1.4 (-1.4%) -3.2 (-3.1%) 24.7 (23.7%) 51.9 (49.8%) 0.949 0.749

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