Method and device for identifying low-output PV modules in a PV system

A measurement method for determining a reduction in output of a PV (Photo-Voltaic) unit within a photovoltaic system comprising a plurality of PV units electrically connected in parallel, wherein each PV unit is associated its own fixed current sensor, and each PV unit is removable from the parallel circuit by a switching device, the method comprising:

• i) measuring a direct current through one of the PV units by the associated fixed current sensor;
• ii) measuring substantially simultaneously with the measurement under i), the direct current with a reference ammeter;
• iii) evaluating, for the PV unit, a difference between the current value measured by the current sensor and the current value measured by the reference ammeter;
• iv) storing the evaluated difference;
• v) repeating steps i) to iv) for each of the plurality of PV units electrically connected in parallel;
• vi) combining the evaluated differences between any two desired PV units into data and calculating such in a ratio (V) to one another;
• vii) providing the combined data, in particular the ratios (V), to an analysis unit;
• and
• viii) ascertaining, via the analysis unit, an output capacity of the relevant PV units.