The I-V curve provides a quick and effective means of accessing the true performance of solar PV modules or strings. In a correctly performing PV system the shape of the curve should follow the normal profile and the measured values of Is/c, Impp, Vo/c, Vmpp and Pmax should be as expected for the environmental conditions at the time of measurement.
As part of the manufacturing process, modules are tested under standard conditions (STC) at an irradiance of 1000W/m2, a temperature of 25oC and air mass of 1.5. Measurements of irradiance and temperature captured at the same time as the I-V curve data can be used to convert field I-V curve measurements to STC. Corrected measurements can then be used for a direct comparison with the rating plate figures.
At the factory stage, the testing is used to identify any manufacturing problems and also to verify the power rating of a particular module for inclusion in product datasheets and specifications.
Once a module or string has been installed on site, I-V curve tracing can be carried out to create an operational I-V curve to confirm that the actual power output is close to the predicted value of the new system.
If there is a discrepancy, analysis of the I-V curve shape can be used to help identify the root cause for the under-performance and remedial measures can be implemented.