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Long-term average

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Long-term averages provide a basic overview of solar resource availability and its seasonal variability. Such information is useful during the site selection and pre-feasibility phase of a solar energy project. GeoModel Solar offers access to monthly and annual long-term averages representing solar resource and meteorological data from a historic period of 22/17/9 years.

Sample data

  • Download ZIP files and examine SAMPLE DATA:
  • Long-term monthly and yearly averages (ZIP, 2 kB), sample data refers to a site: Plataforma Solar de Almería (PSA), Spain.
  • ASCII GRID, Global horizontal irradiation, yearly long-term average (ZIP, 834 kB), data covers the region of Central Slovakia, Europe
  • ASCII GRID, Global horizontal irradiation, yearly long-term average (ZIP, 954 kB), data covers the region of Central Slovakia, Europe

SolarGIS GRIDed data of Solar radiation characteristics for GIS analyses
A snapshot of the ASCII GRID sample data provided above

Purchase data

Long-term averages for any location can be accessed via SolarGIS iMaps or pvPlanner.

Limitations of long-term averages

Long-term monthly and annual averages are suitable for a quick overview of a site's solar potential in terms of seasonal climate characteristics. Once candidate sites have identified, further detailed evaluation is required using time-series data to determine whether the site is suitable for development.

Average values do not offer an insight into inter-annual variability, which is required to evaluate the performance of a solar energy system. Inter-annual variability is the reason why one year of data does not adequately represent solar radiation climate. Moreover, average monthly values do not represent typical weather fluctuations in a particular month. Other popular simulation software is able to generate synthetic hourly time series from long-term monthly averages. However, this representation of the time series is distorted and may be highly misrepresentative.

GIS analyses on SolarGIS GRIDed data
A snapshot from spatial analyses od SolarGIS ASCII data in ArcMap (ESRI Inc.)

Data available


Direct Normal Irradiance/Irradiation


Global Horizontal Irradiance/Irradiation


Global Tilted (in-plane) Irradiance/Irradiation


Diffuse Horizontal Irradiance/Irradiation


Air temperature at 2 m


Relative humidity


Wind Speed at 10 m


Wind Direction


Terrain, Landcover, Population

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