Solar Irradiance Data

Solar Irradiance Data is Vaisala Xweather's satellite-derived solar resource dataset for solar project developers, operators and financiers. It is produced by Solar Model 3, Xweather's proprietary model, which applies the Heliosat-V cloud-index method to 15-minute imagery from several geostationary satellites at 3 km native resolution. The model launched on Meteosat 0° imagery, and Xweather states that its coverage now spans multiple geostationary satellite footprints. A McClear clear-sky model sets the baseline irradiance for each location, and adaptive calibration accounts for each satellite sensor's spectral profile.

The dataset provides global horizontal (GHI), direct normal (DNI) and diffuse horizontal (DHI) irradiance and albedo, with air temperature, wind speed and humidity, as 15-minute, hourly, daily and monthly time series from 2004. It is delivered through Weather API endpoints for archive, recent monitoring, summary and typical meteorological year (TMY) data, in JSON, GeoJSON, CSV and TSV formats. The API documentation lists coverage of Africa, Europe and North, Central and South America.

Against ground-based measurements Xweather reports a mean bias error of 0.86% and a bias standard deviation of 2.72%, and 38% greater GHI accuracy than ERA5. An optional Model Output Statistics (MOS) correction combines on-site pyranometer observations, the long-term satellite data and NWP weather data into a site-specific, bias-corrected dataset; Xweather states that 12 months of on-site observations reduce uncertainty by 57%. Typical uses are site assessment, bankable resource assessments for project finance, and operational performance monitoring.