Meteorological data in the Solargis database are derived from numerical weather models. A summary of meteorological models from which Solargis sources data is given below.
| Data Source | Time period | Original spatial resolution | Original time resolution |
| ERA5, the fifth generation ECMWF atmospheric reanalysis of the global climate | 1994 to D-10 | 0.25° by 0.25° | 1 hour |
| ECMWF Integrated Forecasting System (IFS) | D-10 to D+3 | 0.1° by 0.1° | 1 hour |
| Global Forecast System (GFS) | D+4 to D+13 | ~0.11° by 0.11° | 1 hour (D+5) 3 hours (up to D+14) |
Given that the original spatial resolution of the meteorological data from these models is in the range of 0.1 to 0.25 degrees, the data characterize a wider geographic region rather than a specific site. The original spatial resolution of the models is enhanced to 1 km for air temperature and atmospheric pressure by spatial disaggregation and use of the Digital Elevation Model SRTM-3. The spatial resolution of other parameters remains unchanged.
If meteorological measurements are available from the vicinity of a solar project site, the measurements can be used for accuracy enhancement of the historical data derived from meteorological models.
Time step and spatial resolution of Solargis meteorological parameters
| Meteorological parameter | Acronym | Unit | Time resolution | Spatial resolution of model | Final spatial resolution after post-processing | Data source(s) |
| Air temperature at 2 meters (dry bulb) | TEMP | °C | 1 hour | 0.25°, 0.1°, ~0.11° | ~1 km | ERA5, IFS, GFS |
| Relative humidity | RH | % | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | ERA5, IFS, GFS |
| Atmospheric pressure | AP | hPa | 1 hour | 0.25°, 0.1°, ~0.11° | ~1 km | ERA5, IFS, GFS |
| Wind speed at 10 metres | WS | m/s | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | ERA5, IFS, GFS |
| Wind direction at 10 metres | WD | ° | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | ERA5, IFS, GFS |
| Wind speed at 100 metres | WS100 | m/s | 1 hour | 0.25°, 0.1°, 0.25° | ~25 km | ERA5, IFS, GFS |
| Wind direction at 100 metres | WD100 | ° | 1 hour | 0.25°, 0.1°, 0.25° | ~25 km | ERA5, IFS, GFS |
| Wind speed at xxx meters | WSxxx | m/s | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | Derived from WS100 |
| Wind direction at xxx metres | WDxxx | ° | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | Derived from WD100 |
| Wind gust at 10 meters | WG | m/s | 1 hour | 0.25°, 0.1°, 0.25° | ~25 km | ERA5, IFS, GFS |
| Precipitation | PREC | kg/m2 | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | ERA5, IFS, GFS |
| Precipitable Water | PWAT | kg/m2 | 1 hour | 0.25°, 0.1°, ~0.11° | ~25 km | ERA5, IFS, GFS |
| Water equivalent of accumulated snow depth* | SDWE | kg/m2 | 1 hour (GFS 24 hour) | 0.25°, 0.1°, ~0.11° | ~25 km | ERA5, IFS, GFS |
| Dew point temperature | TD | °C | 1 hour | 0.25°, 0.1°, ~0.11° | ~1 km | Calculated from TEMP and RH |
| Wet bulb temperature | WBT | °C | 1 hour | 0.25°, 0.1°, ~0.11° | ~1 km | Calculated from TEMP and RH |
| Ultraviolet radiation A, B* | UVA, UVB | W/m2 | 1 hour | 0.25° | ~25 km | Calculated from UV (UV source ERA5) |
| Water equivalent of snowfall rate* | SFWE | kg/m2 | 1 hour | 0.25° | ~25 km | ERA5 |
| True accumulated snow depth* | TSD | mm | 1 hour | 0.25°, 0.1° | ~25 km | Calculated from SDWE and SDENS |
| Snow density* | SDENS | kg/m3 | 1 hour | 0.25°, 0.1° | ~25 km | ERA5, IFS |
| Cooling Degree Days and Heating Degree Days | CDD, HDD | degree days | Monthly means | N.A. | ~1 km | Derived from TEMP. Base temperature 18°C (64 °F) |
* in the pilot phase, delivery upon request
NOTE:
1. Statistical aggregations (e.g. monthly means, long-term averages, etc.) are calculated from ERA5.
2. The original spatial resolution of the model is enhanced to 1 km for air temperature and atmospheric pressure by spatial disaggregation.
Temperature data derived from the meteorological models are post-processed by Solargis to achieve improved accuracy and homogeneity over a full time period. An overview of the post-processing methods applied is given below.
Elevation correction
The original spatial resolution of temperature data derived from numerical weather models is too coarse to accurately represent the temperature in regions with variations in elevation. This problem can be overcome if the vertical rate of change in temperature is known. This rate is known as the lapse rate. The lapse rate can change with time and from one location to another, it is influenced by weather patterns and local micro-climatic and topographic features. Normally, the temperature decreases as the site's altitude increases. However, near the surface, occurrence of temperature inversion (temperature increase with increasing altitude) is not uncommon. This is the typical case over cold surfaces, for instance.
In addition to temperature at 2 meters over the surface, weather models also provide temperature data at every model layer from the surface to the top of the atmosphere. Using the vertical profiles of temperature, a simplified parameterization of the vertical change of temperature is devised. The calculated lapse rate is then used for spatial downscaling of temperature data to 1 km resolution.
ERA5 and IFS datasets
The historical archive of air temperature data in the Solargis database is derived from 2 numerical weather models – ERA5 (for period 1994 up to D-10) and IFS (D-10 to D+3). It's important to emphasize that even though both models rely on similar numerical frameworks, there may be a non-negligible temperature variation between ERA5 and IFS across various global locations, primarily because of their unique characteristics (ERA5 being a reanalysis model and IFS being a forecast model).
Ground measured temperature data from reliable sources have been used as a reference to calculate accuracy statistics. The local-scale biases can also be corrected by Solargis - however this is a time-intensive exercise and therefore only done on request as part of site-specific resource assessment studies (offered as a consultancy service by Solargis).