STC
The Standard Test Conditions for the specification of PV modules are normalised operating conditions when testing the module. They are defined as:
| 1000 W/m² | Irradiance (global when in outdoor conditions). |
| 25°C | Module temperature |
| AM 1.5 | Spectrum, i.e. a normalised solar spectrum corresponding to the crossing of 1.5 times the "normal" atmosphere (vertical air mass at the sea level). |
For CPV (concentrating modules), the reference irradiance is specified in terms of DNI value (direct component).
Until Spring 2011, it was usually 800 or 850 W/m2 - not always clear.
The present convention has fixed it at 1000 W/m².