what is the reason for solar panel junction box failure

In recent years, with the continuous reduction of the cost of photovoltaic power generation, photovoltaic power generation has gradually become the main energy source in the new power system. Module products are the core power generation equipment of photovoltaic power stations, and their safety and reliability will directly affect the power station long-term stable operation. Ensuring the quality and reliability of solar panel products is the core element to ensure the safety of power generation systems, and it is also the key to escorting the value of end customers.

There are various factors that affect the risk of module reliability. Among them, the junction box installed on the back of the module plays an important role in current output and bypass, and its quality and reliability are the most important. Looking at the current terminal market, the failure and burning of junction boxes have become the number one killer affecting the safety hazards and power generation of power stations.

The common quality problems of the junction box mainly include the hot spot problem caused by the false welding of the bus bar lead-out wire, the diode failure or breakdown, the cable connection is loose and falls off or the quality of the crimping is not good, resulting in the thermal effect of the resistance or even fire, and the connector is cracked or corroded.

At present, the mainstream technology adopts the way that the lead wires are soldered to the metal part of the box body. If the lead wires are soldered or have other welding quality problems, poor contact will occur in the subsequent operation of the power station, forming a resistance heating effect. The position of the weak soldering continues to generate heat and high temperature, causing the junction box to deform. In severe cases, the junction box will be burned and even cause a fire.

Cables are another important component of junction boxes. The connection quality between the cable and the box body and the connection quality between the cable and the connector, such as the riveting part, will directly affect the size of the contact resistance. Poor connection quality will cause excessive contact resistance, resulting in loss of power generation, severe cases will cause loosening, or lead to resistance heating effect, which may easily cause high temperature burnout and other situations.

Another common failure mode is that when part of the cell area of the module is blocked, the diode is turned on, the forward current is large, and the diode heats up rapidly and is easy to be broken down; the basic test standard for photovoltaic modules IEC 61215 includes a diode junction temperature test The standard is used to test the long-term reliability of diodes, but this test is not comprehensive enough to reduce the failure of diodes. In recent years, some professional leading photovoltaic manufacturers such as Longji have conducted extended research on some failure modes, such as the breakdown of diodes after some shading is removed. The reason is that the diode changes from forward conduction to reverse cut-off state at the moment when the shading is removed. At the same time, the temperature of the diode itself is relatively high, and it continues to generate heat under the reverse leakage current. At this time, if the heat dissipation of the junction box is good, the temperature of the diode will gradually decrease to normal, otherwise the temperature will continue to rise until the diode fails due to thermal breakdown, which is also called "thermal runaway" phenomenon (also known as thermal runaway). For this reason, LONGi took the lead in incorporating the IEC62979 thermal runaway test standard into the mandatory standard specification for junction box imports, further reducing the risks of diode failure, junction box deformation and burning during power station operation.

To sum up, the seemingly inconspicuous junction box on the back of the module hides a "big article" related to the reliability risk of the module. A high-quality module must have a junction box with reliable materials, reasonable design, and high safety factor as a guarantee. In the development and design of components, we should beware of various risks that may appear in the junction box, so as to avoid irreversible damage to the components in the terminal application, which will adversely affect the long-term safe and reliable operation of the power station and the benefits of customers.

Related tags: off grid solar system,on grid solar system.