What is the function of junction boxes?

The junction box is a small box that is usually attached to the back of the solar module. In some semi-transparent double-glazed modules, they can also be attached to the side. But they all have the same function. This is because electrons are released in the solar module, which lead to the flow of electricity. These electrons are then conducted via soldering ribbons or cell grids, the cell connectors and the electrodes to the junction box. There, the electrodes are connected to the external connection cables, which establish the connection to the next solar module in the string via plug systems. Furthermore, bypass diodes are housed in the junction boxes to protect the cells of a string in the event of a hot spot, i.e. a hot area on one or more of the cells, or shading.
 

How can faulty junction boxes be detected?

Several faults can occur on or in junction boxes. For one thing, they can be poorly attached. This can be recognized if the junction box can be easily moved on the back of the module. In addition, the lids of the junction boxes can come off, which is also easy to see during a visual inspection. Furthermore, the junction boxes can become deformed, which shows that the box has become too hot.

What causes faulty and charred junction boxes?

The causes can be very different. Junction boxes that peel off can be traced back to the use of an unsuitable adhesive in module production. This happens especially when the adhesive systems hold well in the short term but are not suitable for long-term adhesion. Open or poorly closed junction boxes are usually manufacturing defects as well.
Deformation of the junction boxes may indicate that they are getting too hot. This can have various causes. Either moisture ingress causes corrosion at the connections or the string connection cables. This increases the resistance at these solder joints, causing the junction box to heat up. Poor or missing wiring or soldering can also cause heat to build up inside the junction box.
 

What are the dangers of faulty and charred junction boxes?

Junction boxes that come loose can eventually fall off completely and it is possible that the backsheet will be damaged. This in turn can lead to a decreasing insulation resistance of the module and thus to touch voltages. Moisture can penetrate open or poorly closed junction boxes. This leads to corroding solder joints, which in turn can result in heat build-up within the junction box. In extreme cases, this can even cause a fire within the junction box. This can also happen if the wiring or soldering inside the box is poor or missing. This is because arcing can occur between the loose contacts, which can cause a fire.

How can faults and fires in junction boxes be prevented or repaired?

Since the faulty junction boxes are usually manufacturing defects, prevention is often hardly possible. However, consequential damage can be avoided – through regular maintenance of the system. This includes inspecting the modules and often also taking a thermographic image. This can be used to detect hot junction boxes. But loose or poorly closed junction boxes can also be detected by a visual inspection. It may be possible to replace or repair defective or deformed junction boxes. Loose junction boxes can also be reattached. However, this process can be time-consuming, so replacing the entire module might be a better option. The system operator should make sure that any replacement module is electrically compatible with the other modules in the string. Suitable replacement modules can be found on the SecondSol online marketplace.