If there is low yield, modules can be inspected on location with a curve tracer (in line with IEC/EN60891). Calibrated reference cells are a prerequisite for this. This method measures the power and current/voltage curves of the individual photovoltaic modules and of a module string. The values measured are converted to Watt Peak under standard test conditions (STC). (Sunlight strength 1000W/m², ambient temperature 25 °C) 

Determination of the following values:

• Power in Wp (STC and OPC (operating conditions))
• FF (fill factor)
• RS – series resistance
• Determination of characteristic curve under STC 
• Determination of characteristic curve under OPC 

As a rule, analysis on location can be carried out faster and less expensively than a laboratory analysis (such as TÜV Rheinland, Fraunhofer …). But if there are major deviations, it is required to have the modules examined in a laboratory additionally after the measurement on location and the results have been verified. 

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