Individual module test with the Z200 PV Analyzer
Z200 PV Analyzer - a multifunctional PV tester also able to detect PID
PV Module Test
This application is based on measuring various parameters, when 1 module in a string of modules, is shaded during measurements. This particular approach has the peculiarity that it can reveal latent and complex faults, while still being rather simple to carry out.
Solar Cell shunting resistance RSH
The shunting resistance RSH can be quantified by measuring the low frequency impedance of the whole PV string, while the PV module under test is being 100% shaded. Simply cover the PV module, and measure the impedance of the whole string. If the “low frequency impedance” has a relatively low value when compared to other PV modules in the same string, be aware that a low shunting resistance is indicated, and hence the module could likely be caused degraded e.g. by Potential Induced Degradation – PID, if there is a trend towards a terminal or a grounding point.
During the Z200 PV Analyzer “PV module test” a baseline is first measured under irradiation. Then each PV module is shaded one by one, and measurements are carried out while the PV module under investigation is shaded. This procedure lead to valuable data, that are normally only possible to obtain when PV modules are examined in the PV test laboratory away from the installation.
Module voltage measurement
The module voltage drop caused by shading modules, one by one, is measured in the string of modules under test. Under normal circumstances, the string voltage drop thus corresponds closely to the voltage of the shaded module. The result of this testing procedure, is an overview of the individual modules voltages in bar diagram form. Modules with a low voltage, relative to the majority of the string modules, may then be identified in a convenient manner.
If a single module voltage is found to be about 2/3 or 1/3 of the normal open circuit module voltage, the problem could be caused by 1 or even 2 bypass diodes, that are in a short circuit state. Short circuited bypass diodes are often seen as a damage following lightning strikes, but please note that many types of damage could lower the voltage of a solar PV module installed in the field.