Where does discoloration of the backsheet occur?

Crystalline solar modules consist of silicon solar cells that are interconnected and embedded in two polymer films. This composite is either laminated between two module glasses and a front glass and a backsheet. This backsheet is also a polymer that has the task of protecting the solar cells against environmental influences. However, these can discolor over time, which should be noticed during a regular inspection of the solar generator.

How can you recognize discoloration of the EVA film on the module?

Discoloration of the backsheet is easy to recognize. This is because they stand out against the white polymer film as brownish or yellowish spots (Yellowing). They can be spotted very quickly in open-space or elevated roof systems. If the modules are installed parallel to the roof, the panels would have to be dismantled and visually inspected if there is any suspicion. A thermographic image can provide an indication – for example, if areas of solar modules become particularly hot.

What causes the EVA film to discolor?

A common cause of discoloration of the backsheet film is the heating of the solar cells above it. This in turn is due to a high internal resistance, which can be caused by shading, for example. The hot cells discolor the backsheet. Therefore, heavily heated areas of solar modules in thermographic images are an indication that the backsheets are also gradually discoloring. However, discoloration can also be an indication of an inferior film that is attacked by UV radiation.
 

What is the risk of EVA film discoloration?

Even slight discoloration of the backsheet can be a cause for concern, as the discoloration weakens the film. This can lead to cracks forming, which can pose a real electrical safety risk, as the weakening can cause the insulation resistance to decrease. In extreme cases, it is even possible that the backsheet will fail completely, which can lead to the destruction of the entire module.
 

How can discoloration of the EVA film be prevented and can the defect be repaired?

Since the backsheet is an integral part of the solar module and thus firmly attached to it, replacing the backsheet is usually not possible. The repair of backsheets should be considered with caution in the case of discoloration. Because if the cause is a solar cell that has become hot, the repair will not eliminate this and the safety risk may continue to exist. In such cases, it may be worth replacing the module. When replacing the affected module, it is particularly important to ensure that a replacement module matches the other panels in the string and in the system. You can find suitable replacement modules on the SecondSol online marketplace.