Considering that the current through all the PV modules of a same string is constant, any differences in the electrical behaviour of the modules give raise to differences in the corresponding operation voltages. That opens the door for careful observations of the PV array functioning carried out under normal operation conditions, that is, with the inverter delivering energy and, thus, without the need for disconnection as required for more standard PV array analysis methods: measuring I-V curves, open-circuit voltages and so on. This in-routine operation observation procedure is relatively easy implemented in practice, by means of “T” shaped quick connectors to connect PV modules to each other, which are widely commercially available. In fact, this has been successfully applied to in-the-field PID detection on commercial PV plants, by monitoring the voltage differences between the modules at the extreme poles of the string. This time, we have applied such observation procedure to all the 21 PV modules comprising a 5 kW PV array connected to the grid at the IES-UPM terrace. Moreover, we have also glued a PT1000 in the back of each module. Together with a PV reference module for measuring in-plane irradiance, this set-up allows for continuous and simultaneous monitoring of, both, the operation conditions (irradiance and temperature) and the electrical response (current and voltage) of all the PV modules.