Portable IV Curve Tester: Key Tool for Photovoltaic Module Performance Testing and Fault Diagnosis

In the daily operation, maintenance, and performance evaluation of photovoltaic power plants, the Portable IV Curve Tester is an indispensable device. By testing the IV curve of photovoltaic modules/strings, it provides important basis for evaluating their electrical performance, judging quality, and troubleshooting.

The Portable IV Curve Tester is a core means to evaluate the electrical performance of photovoltaic modules/strings. Through this test, the relationship between current and voltage of photovoltaic modules/strings under different illumination and temperature conditions can be obtained, including parameters such as open-circuit voltage (Voc), short-circuit current (Isc), maximum power point voltage (Vmp), maximum power point current (Imp), maximum power point (Pmax), and fill factor (FF). These parameters directly reflect the power generation capacity of photovoltaic modules/strings, as well as their adaptability and stability under different environmental conditions, and serve as important criteria for judging their quality. During the operation of photovoltaic power plants, photovoltaic modules/strings may suffer from faults or performance degradation due to environmental factors, equipment aging, or human operations. By analyzing the deformation of key points in the IV curve, abnormal conditions can be identified, causes can be analyzed, and fault points can be quickly located, helping maintenance personnel repair in a timely manner, reducing system downtime, and improving the operating efficiency and stability of the power plant.

The principle of photovoltaic IV testing is based on the photoelectric effect and circuit analysis. During the test, it is first necessary to ensure the correct connection between the solar cell module and the testing equipment, and use standard cells and temperature sensors to collect the irradiance received by the module and the backsheet temperature. Then, the solar cell module is placed in an open-circuit state to measure its open-circuit voltage (Voc). The tester starts from 0V and gradually increases the working voltage, while synchronously measuring the corresponding output current. Finally, these voltage and current data are plotted into an IV curve.

According to NB/T 11222-2023 Technical Specification for Photovoltaic String I-V Detection and Diagnosis, the key points and shapes of the IV curve include open-circuit point, short-circuit point, maximum power point, step inflection point, flat arm, vertical arm slope, etc. The faults of modules/strings can be preliminarily judged through the deformation of these key points.

When there are steps or depressions in the IV curve, it indicates that there is a mismatch in different areas of the tested array or module. This is usually caused by the conduction of the bypass diode, with part of the current being shunted. Possible reasons include partial shading, pollution, or covering of the array or module, damaged cells/modules, or short-circuit of the bypass diode. Even shading a single cell may cause such curve deformation.

When the expected current differs from the measured current due to low current, if caused by the array, it may be due to uniform pollution, banded shading, dust deposition, or attenuation of photovoltaic modules; if caused by the module, it may be due to incorrect import of module information, incorrect connection or mismatch of the number of parallel strings; problems with the calibration or installation of the irradiance sensor, changes in irradiance, reflection effects, and excessively low irradiance may all cause this situation, and the measured current may also be higher than the expected current.

Low voltage can also be caused by multiple factors. It may be due to the conduction or short-circuit of the bypass diode, incorrect number of modules in the string, potential induced degradation (PID), or overall shading; it may be due to incorrect information import or incorrect import of the number of parallel strings; during measurement, inaccurate measurement of cell temperature or a substantial deviation between the measured value of the string and the predicted value may cause voltage changes, and the measured voltage may also be higher than expected.

A smooth curve in the IV curve may be a sign of aging. It is necessary to check the slope of the parallel and vertical arms, as changes in slope may lead to similar changes in curve shape.

If the slope of the vertical arm decreases and is located at the rear part of the curve, between the maximum power point voltage (Vmp) and the open-circuit voltage (Voc), it may be due to damage or failure of photovoltaic wiring, failure of connections between modules or arrays, increased series resistance of modules, etc. Longer cable connections may also affect the curve shape. The slope change in the upper part of the IV curve may be caused by the shunt circuit of photovoltaic cells, mismatch of short-circuit current (Isc) of modules, gradual shading or dirt, etc. Shunting is usually caused by local defects in cells or cell connections, which can be detected by infrared testing. Production differences and different degrees of shading can also affect the curve.