With the objectives of energy self-sufficiency and zero emissions in La Reunion, photovoltaics are becoming an increasingly important part of the local energy mix. Installation reliability and safety are crucial to ensure network stability and security, therefore PV system fault diagnosis is an essential tool in the expansion of this electricity production method. The DETECT Project (Diagnosis onlinE of sTate of health of EleCTric systems) is a research project aiming at diagnosis method development. In this way, signal processing provides us with promising tools in the form of decomposition algorithms. Thanks to their low computation cost, empirical mode decomposition (EMD) and variational mode decomposition (VMD) allow undertaking a real-time diagnosis, with on-line PV electrical signal time-series data analysis.