Method and Apparatus for determining possible deliverable power for given irradiation conditions

The method involves calibrating radiation signal (10) of a radiation sensor (9) using associated measured values without power output limitation of a photovoltaic system (2) by a feeder line (11). The radiation signal is supplied when the photovoltaic system is after-calibrated without power output limitation using the associated measured values of the actual feeder line. An independent claim is also included for a device for determining a feeder line of a photovoltaic system achieved under actual radiation conditions.