**2.5. Cell cracks**

PV cells are made of silicon so they are very brittle. Cell cracks are formed in different lengths and orientations in the substrate of the photovoltaic cells and often cannot be seen easily.

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

Backsheet failures include yellowing, brittleness that leads to cracking, and delamination within the multilayer composite. Delamination and cracking allow water vapor and oxygen into the PV module and are considered to be the worst kind of failures within backsheets as they cause problems with isolation and subsequently can cause safety issues [9]. Water vapor critically affects degradation phenomena such as decomposition of the encapsulation, corrosion of the metal parts, and potential induced degradation (PID) of the PV modules. Such failures impact on the performance of a PV module and shorten its lifespan. Yellowing, on the other hand, has not been reported as having an influence on the electrical performance of

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 poten-

Mechanical breakages usually consist of cracks in the frame produced by poor handling or

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

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

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

Some studies refer to discoloration as degradation rather than failure, as discoloration leads

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

PV cells are made of silicon so they are very brittle. Cell cracks are formed in different lengths and orientations in the substrate of the photovoltaic cells and often cannot be seen easily.

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

to an average current loss of 0.5%/year or 0.8%/year for Si PV modules [10].

typically to lower performance but not necessarily to failure [6].

observe an example of a bubble formed over a metal contact.

within the module, and can produce delamination or the formation of bubbles [11].

modules.

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

tial for fire or threat to human life.

losses in module performance [12, 13].

**2.5. Cell cracks**

extreme winter snow loads.

96 Solar Panels and Photovoltaic Materials

**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 modules and installation in the field.

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 cloud cover.

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

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

reverse current path in the still active cell part. The cell may reverse bias and the full current will be able to flow along the localized path as a consequence of the missing cell area. This can cause hot spots and subsequently burn marks [17].

Recently, a new maximum power point tracking (MPPT) method was proposed to avoid the consequences of hot spots. It is based, firstly, on a bidirectional buck converter to control the operating point of each module and uses a boost converter to control the terminal voltage of each branch. Secondly, MPPT is modeled as an large-scale global optimization (LGSO), and a novel, multicontext, cooperatively coevolving particle swarm optimization (PSO) algorithm

Degradation Monitoring of Photovoltaic Plants: Advanced GIS Applications

http://dx.doi.org/10.5772/intechopen.75650

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Potential-induced degradation gives rise to power losses owing to the presence of eddy currents in the PV modules. Its effect can potentially reduce the power of the equipment [22].

The principal cause of these currents is reported to be voltage gaps between the ground and the module. In photovoltaic systems without a grounding system, this effect occurs when modules have a non-zero voltage, which is normally negative especially under high ambient

Cell strings can become disconnected if string interconnected ribbons are weak, which may be caused by large deformations, by the quality of the welds during the production process, or by weak connections between the string and the ribbon. Small distances between cells can

The consequences of this may be a broken cell interconnected ribbon and a subsequent decrease in maximum power point current [24] or a shunt by a cell interconnected ribbon and a subsequent

(CCPSO-m) is proposed to solve this large-scale problem [21].

humidity and/or temperatures and high voltage conditions [23].

**2.9. Disconnected cells and string interconnected ribbons**

also contribute to interconnected ribbon breakage [5].

**2.8. Potential-induced degradation**

decrease of open circuit voltage.

**Figure 4.** Example of a burn mark on a PV cell.
