Long-Term Monitoring of Degradation and Defect in High-Voltage Strings through Dark I-V Measurements

For on-site monitoring of photovoltaic (PV) strings, most traditional techniques, such as daylight I-V measurements, thermography, and electroluminescence, require stable weather conditions and are often time-consuming. Dark I-V measurements, conducted at night under consistent environmental conditions, provide a reliable alternative. To continuously monitor the degradation trend and detect potential faults in PV systems, a dark I-V measurement system (DIVMS) was developed. During measurements, the PV string is disconnected from the inverter and connected to a high-voltage source, where a controlled reverse current is injected to record the I-V curve. However, in 1500V systems, a single string may require up to 30 kW of instantaneous peak power, making traditional high-voltage power supplies both expensive and impractical for industrial use. As a cost-effective alternative, a local energy storage system charged by a low-power flyback converter was developed.