Damages at Solar Panels

Solar modules are designed to produce electrical power at least for 20 years. However, solar modules are technical products and damages can occur during their life time.

We illustrate some of the defects, their causes and impact on the electrical output.

Questions about damages at your module? Please contact us.


1.Hotspots

Reasons of Hotspots: 

If a part of the solar cell is shaded the cell can heat up to such extreme temperatures that the cell material as well as the encapsulation (EVA) and backsheet will be permanently damaged. A so called hot spot develops.

Under normal operation condition the cell generate current. In contrast, a shaded cell not produce any electricity any more but uses the current from the other cell. The current from the other cells of the strings is driven through the darkened cell. The current flow is then converted into heat.

To prevent the cells from hot spots bypass diodes are used in all standard modules nowadays. If a cell is shaded, the bypass diodes get into operation and redirect the current for the full cell string via a bypass and prevent the cells from the hot spot effect.

Hotspots may still occur. For example, if the bypass diodes are faulty, or if only a very small part of the cell is shaded and thus the bypass diode is not enabled.

Other reasons for hotspots can be high contact resistance at the busbars of the cells (bus bars are the silver coloured lines connecting the cells). Reasons for high contact resistance can be cracked solder joints on the busbars.

The power loss of a module with a hotspot is often very low. Unless there are already big areas with hotspots. Nevertheless, these modules should be replaced, especially when not the cell only but also the surrounding encapsulation material burned.

HotspotHotspot

Hotspots at Solar Cells

Quelle: www.photovoltaikforum.com


2. Delamination

In a PV module, the solar cells are encapsulated with the so-called EVA (ethylene vinyl acetate). The EVA protects the sensitive cells from weather influences such as moisture and UV radiation.

During manufacturing the module composite is laminated under a precisely defined pressure and process temperature. It is important to keep the defined process temperature and time to ensure that the EVA cures correctly during the lamination process. Wrong process parameters or cheap material can result in a delamination of the EVA later in lifetime. The layers of EVA dissolved and get a "milky" colour.

Delaminated solar modules should also be replaced. Due to the delamination, moisture can get to the cells which leads to cell corrosion and an ongoing performance loss. Further, the light transmission is reduced.

Delaminierung - Delamination

Delamination of the EVA: White ("milky") parts. In this case around the busbars.

Quelle: www.photovoltaikforum.com

 


3. Cell cracks and micro cracks

Already during the production but also due to external influences, such as transportation and installation microcracks in the cells can occur. In general microcracks can not be completely avoided and usually not lead to a loss in performance. Although there is always a potential risk that a micro-crack progresses to a cell fraction with a performance lost.

Furthermore, in some cases "snail tracks" on the modules develops from microcracks. "Snail tracks" are a relatively new phenomenon. These always occur in the first months after the installation, due to certain combinations of material combination and having micro-cracks in the cells. From current state of knowledge snail tracks have  no negative influence on the energy output and lifetime. Just considered as an optical defect.

Cell breaks itself can lead to a loss of yield. A broken corner or a small local plan does not result in yield loss. However, when an entire cell area was separated from the bus bars, a yield loss is expected. In this case, the module should be replaced.

Unkritischer Zellbruch

 Uncritical Cell crack (Source: Own Picture)

Schneckenspuren Monokristallines Modul Schneckenspuren Monokristallines Modul EL Aufnahme

Called worm or snail tracks (Right: Snail tracks under EL test). Generally it is not accepted as a warranty case by the manufacturers because from current state of knowledge it not leads to a full lost in power.


4. Markings shown on Edge of cell

Cells from some manufactures show dark markings on the edge of the cell. These spots are due to the specific production process and not have any negative influence to the performance or life time of the cell.

During the cell production a process called PECVD is used. Objective of PECVD is to form a blue
layer, the anti reflex film, on the wafer. The anti reflex film increase the performance of the cell. The process is a chemical reaction under high temperature. During the process the cells are hold by the fingers of the robotic (contact points) on the edge of the cells. Under the contact points the anti reflex film is skipped resulting in small dark coloured markings in the edges of the cell. 

 

Roboterfinger auf Zelle

Markings at the contact points of the robotic fingers. Non critical and no negative influence on life time (Source: Own Picture)

 


5. Glass Breaks

In most cases glass breaks are caused by external conditaions such as poor packaging during transportation, during installation or by hail and stone throwing. Very rarely, the glass breaks due to manufacturing or material defects.

Especially for frameless modules, typically thin-film modules, glass breakage can also occur through the module clamps. Becasue of the missing frame, the clamps must be fixed directly on the glass. Thermal expansion during operation can cause cracks.

Modules with broken glass should always be replaced.

 Steinschlag SolarmodulHagelschlag SolarmodulGlasbruch Dünnschichtmodul

Broken glass solar modules. From left to right: (a) Stone's throw, (b) Hail, (c) Thin film module, clamps are fixed on the glass


6. Defect Connectors

Today's standard are connectors from type MC4. The original connector was developed by the Swiss company MultiContact AG.

Chinese manufacturers mostly not using original MC4 connectors, but MC4 compatible. These connectors have same specifaction as MC4 but not produced by Multi Contact. However, the connectors are TUEV tested as well and quality standard is good at least for those connectors used by the high end chinese solar manufacures.

Low quality connectors can lead to problems such as breaking during assembly, especially at cold ambient temperature, or to poor electrical contact.

Also an unclean crimping results in a poor contact connection with the risk of sparks and eventually a burned connector.

Connector

Connector

 

Picture Left: Burned connector.

Picture Right: Broken connector during assembly of the photovoltaic system


8. Burned Solar Junction Box


The junction box contains the bypass diodes of the solar module. Bypass diodes are electric components that in case of need - for example, partial shading of the modules - bridge a part of solar cells and thus cut it off.

If shadow meets only a part of all cells, the shadowed cells working very weak. Comparable to a water channel which gets narrowed. The narrowing results in a high resistance. As a consequence of the high contact resistance the output yields of the entire module strings goes extremely down and the cell itself can  overheat whcih results into hotspots (see above). In case of such need the bypass diodes starts to work and will avoid hot spots and power loss. The current now flows freely through the bypass diodes with minimal resistance rather than through the shaded cells with very high resistance.

However, badly contacted bypass diodes dues to a manufacture failure can now also overheat itself and lead to a fire in the junction box. In photovoltaics, however, fire-resistent materials are always installed, so usually the fire does not spread out in most cases.

Brand Anschlussdose Photovoltaikmodul

Burned Junction Box Photovoltaic Module (source: Customer picture)


9. Browning

Browning is a yellow or brown discoloration of the EVA (cell encapsulation).

The EVA contains additives to improve the UV resistance and to prevent it from the Browning effect. If low quality EVA is used, if the EVA be stored under improper conditions or too long before manufacturing, the additive in the EVA partly dissapears and due to UV radiation and heat the EVA starts to get yellow or brown colour.

As a result of browning cell bleaching, bubble formation at the EVA and backsheet and also cell corrosion can happen.

The heat absorption increases with browning. Higher heat absorption enforces further browning.

Modules showing browning should be replaced.

 

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