Which Solar Module Glitches are the Most Usual, the Most Fatal, and the Most Intriguing?

Overheated spots are the most usual

Overheated spots: Overheated cells in a module that are mostly caused by dust accumulation or avian excrement. Overheated spots show damage at the cell level where one or more cells have elevated temperatures than the surrounding cells. An overheated spot indicates damage of different severity levels depending upon the temperature difference between the overheated cell and a normal cell.  At FUTR OS, our solar software solutions can spot the difference between overheated spots (where only a single cell is affected) and multi-overheated spots (where more cells are affected).

Reasons:

The sources of an overheated spot are many. Some of them can be avoided while others are unavoidable. Usually, thermal images are unable to identify the sources of overheated spots, but with the use of visual (RGB) photos, it is possible to identify the main reason for overheated spots.

The most common reason for this damage can be any outside element that is casting on the solar cells. A cell turns into a resistor when it is covered by shade and begins dissipating the energy that is being produced by other cells of the string. At FUTR OS, the sources of overheated spots are identified by the following categories:

• Dust accumulation: accumulation of dirt, rust, etc. 
• Avian excrement: Excretory material of birds. It is more common at the seaside and near food processing plants

• Plant growth: Plants and grasses that grow between the panels or near the panels.
• Shade: Outside elements casting shade on the solar cells. For example, electric poles, cables, wires, trees, bushes, fences, etc.
• Physical anomalies: Deteriorated cells will show overheated spots but the actual reason may not be identified by the naked eye. These include cracks, delamination, shattered glass, back sheet issues, snail trails, etc. 

Solutions:

Overheated spots act as resistors and dissipate the energy produced by normal cells. Therefore, the affected cell can depreciate the energy production of the entire string that the cell is a part of.

Generally, the energy loss is proportional to the temperature difference and only one overheated spot on a string can result in the loss of  90 % of the production of a panel.

1. String issues are the most fatal : When a group of cells gets disconnected from the inverter, due to a bad connection or a blown fuse, then this issue is called a string issue. 

Signs:

A group of cells has a higher temperature as compared to other cells and the temperature of the affected group of cells is uniform. 

Reasons :

An entire string gets disconnected and as a result, gets hotter because light intensity is not converted into electricity. This is due to different issues like

• Short circuit 
• Unattached wire
• Burnt or damaged joint
• Defect in the inverter or the connection box
• Any malfunction that prevents current flow or causes any wire disconnection.

Solutions:

Check all connections of the string thoroughly. The treatment of string issues should be prioritized because such issues cause more loss but are very easy to fix. 

Shortfalls:

When the string of cells gets disconnected, energy production reduces and remains less as long as the string issue exists. 

Voltage-Induced Degradation (VID) and suspected VID are the most intriguing :

Voltage-induced degradation and suspected VID are early-stage malfunctions that occur due to voltage differences between the frame and cells of the panel. 

Signs:

The definition and cutoff for the classification of VID differ throughout the market. At FUTR OS, we not only distinguish VID but also the panels that show early-stage VID-like behavior. In this case, the panels close to the borders are warmer, indicating that voltage difference can be the reason for the temperature increase. 

Our criterion is that we mark panels that have more than one border affected by such a kind of effect.

Panels show a grid pattern on infrared images. Proper temperature differences can be seen between the cells. This anomaly affects several adjacent panels mostly at the end of the string or close to the negative pole of the string.

Reasons:

Voltage-induced defects are due to voltage differences between the frame and cells of the panel. This difference results in the flow of residual leakage current through cells. This impacts the yield greatly. 

This impact is mostly affected by the following characteristics

• Stability of the panel skeleton, poles, etc. 
• Type of inverter and its settings, like the voltage difference between the ground that the inverter is set and the poles. 
• Design of the system, such as type of silicon wafer, insulation type, frame’s mechanical design, etc. 

Solutions:

All the reasons for VID can not be rectified. Therefore, the operator has a limited choice in this case. 

The following actions can help in avoiding VID:

1. Check the stability of the cell rows, poles and inverter to decide whether the grounding can be upgraded. A deep examination of affected rows and strings can lead you to identify the main causes of VID.
2. For short-term treatment, switch cells from positive to negative ends to avoid further anomalies.
3. Change the voltage difference between the inverter poles and the ground by changing the inverter’s working mode, if possible.
4. Take those commercial solutions into consideration that introduce a small amount of reverse current at night to counteract VID. 
5. In case of suspected VID, no short-term solutions are advised.

These issues can also imply the simple wearing of the cells because of their installation age. In any case, a proper examination of the system is necessary to see how the situation turns out. 

Shortfalls:

Overheating of cells and leakage of current cause loss of energy which the inverter has to convert. A normal estimate in the research community is that 30% of the losses per panel can be rectified. However, VID issues normally get worse over time. 

In the case of suspected VID, the temperature differences point to losses, but such cases result in lower losses as compared to actual mature VID. 

Get in touch to learn how FUTR OS upgrades your solar system.  of include inverter problems, voltage instability, and temperature disparities.

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