Abstract: There is provided a method for fault diagnosis on a solar module in which electrical potentials are checked within the solar module to provide the possibility for carrying out the fault diagnosis even when the solar module is not exposed to sun light. Specifically the solar cell module is excited by both a DCBIAS and an AC voltage over a wide frequency range, and the impedance of the solar cell module is measured as a function of the frequency response. There is also provided an embodiment, wherein time domain reflectometry (TDR) is used in combination with the DC BIAS and AC voltage based fault diagnosis. Based on the method safety operations can be carried out as a part of the integrated electric functionality.