**2.3. Junction box faults and mechanical breakage**

Junction boxes are attached to the back of modules and protect the connections to the external terminals. Bypass diodes in the junction boxes protect cells in a series when hot spots occur due to partial shadowing of the module [5]. The formation of moisture due to faulty adhesive can lead to wiring degradation that can be the cause of electrical arcing resulting in the potential for fire or threat to human life.

Mechanical breakages usually consist of cracks in the frame produced by poor handling or extreme winter snow loads.

**Figure 2** shows a clear example. Cell cracks may occur during or after production. Major sources of cell cracks are during packaging and transport or during the reloading of PV mod-

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Small cell cracks show a great tendency to develop into larger, wider cracks during operation of the solar module due to mechanical stress [15] from wind or snow load and thermomechanical stress [16] from temperature variations due to changes in weather and intermittent

An inactive cell area of 8% or more is unacceptable. Apart from the risk of power loss there is also the chance of hot spots being formed. This can happen when a cracked cell has a localized

ules and installation in the field.

**Figure 2.** Example of cracks in a PV cell.

**Figure 1.** Examples of (a) EVA discoloration and (b) bubble formation.

cloud cover.

### **2.4. Discoloration of the encapsulation material and bubble formation**

Degradation of the encapsulation material (normally ethylene vinyl acetate or EVA) is an esthetic issue that does not usually affect the performance of a module. It can, however, lead to an average current loss of 0.5%/year or 0.8%/year for Si PV modules [10].

Rising temperatures, the photo-degradation of EVA by UV radiation, and the existence of molecular oxygen lead to the production of acetic acid and volatile gases, that are trapped within the module, and can produce delamination or the formation of bubbles [11].

The presence of acetic acid in a PV module is linked to several PV module failures due to its corrosive effects on cell metal, which may lead to an increased series resistance and hence losses in module performance [12, 13].

Some studies refer to discoloration as degradation rather than failure, as discoloration leads typically to lower performance but not necessarily to failure [6].

On the other hand, inappropriate temperatures or an excessively long lamination procedure [14] during the manufacturing of the photovoltaic module can cause bubbles of gas to be formed either as a direct or as an indirect consequence of melting and solidification processes (**Figure 1**). In **Figure 1(a)** an EVA discoloration can be appreciated while in **Figure 1(b)** we can observe an example of a bubble formed over a metal contact.
