Besides satellite images, the Solargis model also requires atmospheric data i.e. water vapour and aerosols as inputs.
In order to deliver solar radiation data with latency of one
day we are required to use atmospheric data inputs derived from forecast models,
as final atmospheric data are not available at the time of solar radiation
calculation. After some time, usually with delay of 12 hours, we receive
updated, final atmospheric data inputs. When we receive updated atmospheric
data, we recalculate solar radiation data using the updated inputs.
Typical timeline of calculation of solar radiation data is as follows:
1) Every day, solar radiation data is calculated for DAY-1 and DAY-2.
2) At beginning of each month, solar radiation data for previous month is re-calculated using final atmospheric data inputs. Atmospheric data are homogenized with historical data records to avoid abrupt changes due to atmospheric models changes.
Example: Solar radiation data (based on satellite observations, not forecast) for 15th January will first become available on morning of 16th January. The data for 15th January will be updated on 17th January and then again on 2nd or 3rd of February. The data received on 2nd or 3rd of February can be considered as definitive or archive. From time to time, there is also need to recalculate whole historic periods because of model updates. However, important to note is that differences introduced with every update is typically small. Every model change is recorded in version number.
In case of meteorological parameters (TEMP, WS, RH...) the DAY-1 and DAY-2 values are taken from NOAA GFS data source (forecasted value). The meteorological data from GFS model are later updated with data from the NOAA CFS v2 data source (re-analysed archive data). Meteorological data for period DAY-3 or earlier can be considered as definitive.