Weather data
For each hour of a year, the simulation needs irradiance, ambient temperature and wind. Radiaris always works with a year of 8,760 hours in UTC, whatever the source.
Available sources
| Source | What it is | When to use it |
|---|---|---|
| PVGIS · typical year (TMY) | Year built by choosing the most representative months from a multi-year series (European Commission satellite database). It is the default source | The general option for Europe, Africa and much of Asia and America |
| NASA POWER | «Mean year»: each hour of the year is averaged across the downloaded years | Areas not well covered by PVGIS |
| PVGIS · ERA5 | «Mean year» from the ERA5 reanalysis | To cross-check against the TMY |
| Own file | CSV with GHI, DHI, temperature… for 8,760 hours (for example, exported from PVsyst or Meteonorm) | If you have data from another validated source |
| Saved measurements | Your own data, converted and saved; see Your own data | If you have a station at the site |
The engine proposes the most suitable source for the area.
TMY versus «mean year»
A TMY picks real months, so it keeps the typical variability of the climate (extreme days included). A «mean year» averages each hour across years and is smoother, with fewer extremes. With a mean year the balance with batteries and the curtailment may come out somewhat different. Neither is «the real year»: that is why the uncertainty exists.
What the weather year contains
For each hour: global horizontal irradiance (GHI), direct normal (DNI), diffuse horizontal (DHI), ambient temperature and wind speed.
Solar time and offset
By default the engine uses the time of the timestamp to calculate the Sun position. In Advanced settings you can apply an offset in minutes between the hourly data and the time used for the Sun (PVsyst uses +10 min). It only noticeably affects planes facing east or west.
Cold design temperature
The engine can calculate the cold design temperature from the local climate (yearly minimum with a margin) to validate the maximum string voltage. See Electrical validation.
Offline
PVGIS, NASA POWER and the address services need internet. If there is no connection, the application tells you; you can continue with your own file.