Abstract
Bypass diodes have been widely utilized in crystalline silicon (c-Si) photovoltaic (PV) modules to maximize the output of a PV module array under partially shaded conditions. A Schottky diode is used as the bypass diode in c-Si PV modules due to its low operating voltage. In this work, we systematically investigated the origin of bypass diode faults in c-Si PV modules operated outdoors. The temperature of the inner junction box where the bypass diode is installed increases as the ambient temperature increases. Its temperature rises to over 70 °C on sunny days in summer. As the temperature of the junction box increases from 25 to 70 °C, the leakage current increases up to 35 times under a reverse voltage of 15 V. As a result of the high leakage current of the bypass diode at high temperature, melt down of the junction barrier between the metal and semiconductor has been observed in damaged diodes collected from abnormally functioning PV modules. Thus, it is believed that the constant leakage current applied to the junction caused the melting of the junction, thereby resulting in a failure of both the bypass diode and the c-Si PV module.
Highlights
The bypass diode installed in the junction box of a crystalline silicon (c-Si) photovoltaic (PV)module is a necessary component used to improve reliability by protecting against hot spots and by reducing losses caused by shading
As c-Si solar cells are connected in series in the PV module, the current and output are greatly reduced when some solar cells among a string are shaded without bypass diodes in the PV module [3,4]
The temperature and applied reverse voltage were carefully chosen in relation was estimated that the leakage current will increase about 35 times in summer when to the temperature the junction box of and to the operating compared to the caseinoperated in winter
Summary
The bypass diode installed in the junction box of a crystalline silicon (c-Si) photovoltaic (PV). A bypass diode fault results in an output loss due to a decrease of the open circuit voltage because the potential (voltage) difference of strings connected with a failed bypass diode is about 0 V It elevates the surface temperature of the solar cells in the PV module, thereby resulting in the lower performance of the PV power plant [26]. According to the characteristics of the PV module with failed bypass diodes, it has been reported that heat may rise to a temperature at which the junction box material can melt, causing a fire when the system is not operated and there is high insolation.
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