PV Faults: Causes & Resolutions

Defect 

What is it? 

Cause 

Resolution 

Open Circuit 

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Open circuit in module sequence 

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Module Open Circuit

Interruption in the flow of electric current. 

One group of PV modules has a temperature of a few degrees higher compared to another similar group. However, within the affected group, the temperature remains uniform. 

Loose connections, broken cables, or a panel failure. 

The entire string is disconnected, causing the modules to become hotter as solar irradiance is not being converted into energy. The affected modules absorb sunlight without dissipating this energy in the form of electricity, which results in a higher temperature compared to neighboring strings. Causal factors: 

• Damaged fuse 

• Disconnect Rope 

• Damaged or burnt weld spot 

• Physical problem in the junction box or inverter 

• Any fault that causes electrical disconnection or prevents current from passing through the string. 

Inspect cables and connections, test electrical continuity, and replace damaged components. 

These failures may result in significant energy losses and are often easy to fix. They should be treated as a top priority. 

Potential Induced Degradeation (PiD) 

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Suspected of PiD

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PiD Detection 

Performance degradation caused by electrical potential differences between the photovoltaic cells and the panel structure that prove unwanted electrical currents. 

PV modules feature an anomalous heating pattern that starts at the edges and extends along the string, starting at the negative pole and advancing toward the positive pole. This degradation leaves no visible marks on the surface of the modules. 

This anomaly does not occur in isolation at a single point in the plant; it is necessary that several strings present this same pattern for the problem to be characterized as PID. 

High humidity, high tension and unsuitable materials.  

Potential Induced Degradation (PID) occurs due to the voltage difference between the photovoltaic cells and the module structure. This variation can generate a residual leakage current, significantly reducing the efficiency of the system.  

This effect is influenced by several factors, including: 

• Grounding of the structure of the photovoltaic modules, including brackets and fixings. 

• Type of inverter and its mode of operation, especially the potential difference between the supports and the ground of the inverter. 

• Design of the photovoltaic module, considering aspects such as the type of insulation used, the silicon wafer technology, and the mechanical design of the structure. 

Characteristics of environments with high humidity and temperature 

Install PID recovery systems, use inverters with PID mitigation, and choose modules with PID protection. 

• Check the grounding of the modules, rows, and inverter structure to assess whether it can be improved. A detailed inspection of the affected strings and rows can help identify the source of the problem. 

• Alternate the position of the modules in the string, moving the modules from the positive extreme to the negative extreme, as a stopgap measure to avoid permanent damage over time. 

• Adjust the operating mode of the inverters (if possible) to modify the potential difference between the ground and the inverter poles. 

• Use commercial solutions that inject a small reverse current overnight to offset the effects of PID. 

Improve Environmental Conditions – Reducing the humidity and temperature around the modules can help minimize the impact of PID. 

Bypass diode activated 

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Bypass diode activated on a module. 

The diode protects the string of a faulty module. 

PV modules with multiple cells at high temperature can be classified as Multi Hot Spots. However, if these cells are located in the same substring, the cause of the problem lies in the diode of that substring. Normally, a large temperature variation is observed between the cells in one third of the photovoltaic module, while the rest has a homogeneous temperature. This phenomenon is known as single-diode failure. 

Shadows, dirt, or cell failures. 

The diode responsible for diverting the current from the substring is damaged and allows electricity to pass through continuously. This type of failure usually occurs due to an excessively high current going through the PV module, often caused by lightning strikes, resulting in a permanent defect in the diode. 

Clean the panels, remove shadows, and test the diodes to identify faults. 

If diode replacement is not feasible, it will be necessary to replace the entire PV module. 

Two bypass diodes active 

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Two bypass diodes activated in two modules 

Larger part of the module compromised. 

As with single-diode failure, the multi-diode problem affects more than one substring. The main difference from a Multi Hot Spot is that, in this case, the anomalies follow the alignment of the substrings, forming a linear pattern. 

Physical damage, extreme dirt, or serious failures. 

Test modules individually and replace faulty panels. 

Cell Hotspot 

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Hotspot in a module cell 

Cell heats up beyond a delta of T > 10°C. 

Hot Spots indicate a cell-level defect in which one or several cells have a higher temperature than neighboring cells. 

Depending on the temperature difference between the cells, a Hot Spot can indicate a defect with different levels of severity. 

Manufacturing defects, dirt on site or micro-cracks. 

• Dirt buildup  

• Bird droppings  

• Overgrowth of Light-Blocking Vegetation in Modules  

• External shadows  

• Physical defects – include micro-cracks, delamination, back film problems, and cracked glass. 

The most common reasons are related to external elements that cast a shadow on the PV module. When a cell is shaded, it behaves like a resistor, dissipating the energy generated by the other cells in the string. 

Clean the modules, monitor HotSpot severity, and replace faulty cells. 

• Dirt and bird droppings: cleaning the modules may be enough to restore power generation. 

• Vegetation: Mowing the grass or plants near the modules usually solves the problem. If not treated quickly, an initially reversible Hot Spot can cause permanent damage. 

• Shading: Remove external obstacles and monitor affected modules. Evaluate a new plant layout. 

• Physical defects: Depending on the severity of the Hot Spot, the age of the plant, and the underlying cause, it may be possible to claim the manufacturer's warranty. Review acceptance criteria vary between manufacturers. Change of module, if necessary. 

Multi Cell Hotspots 

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Hotspots in multiple cells 

Several cells in the module overheat. 

Partial shading, internal module failures, or manufacturing defects 

Replace damaged modules and avoid constant shading. 

Object shading the modules  

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Shading + Butterfly Effect

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Shading by tall vegetation 

Obstruction of sunlight on the panels. 

Butterfly or mirror effect: 

Partial blockages or defects on one side of the module can cause a mirroring effect, making it appear that another region of the module is affected, even if the problem is only in one part. 

The cause can be physical obstructions such as trees, tall vegetation near or between the panels, and suspended objects. 

Remove objects 

Overheating of the junction box 

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Junction box defect with bypass diodes activated 

Junction boxes naturally heat up a bit due to the high density of current they pass through. However, very high temperatures can indicate problems with the connections, resulting in energy losses or even a risk of fire. 

The heat generated in the junction box dissipates through the back of the module, the PV cell, and the glass before it is detected. Based on this, we evaluate whether there are any faults in the junction box. 

Overheating of the junction box in a solar module can be caused by: 

• Faulty connections – Loose, oxidized, or poorly soldered terminals increase electrical resistance, generating excessive heat. 

• Damaged bypass diodes – If a diode fails, it can prevent the correct deviation of current, causing abnormal heating. 

• Excessive current – A current flow greater than supported can overload the junction box components. 

• Module design flaw – Structural problems in the junction box or low-quality materials can make it difficult to dissipate heat. 

The exact cause can be identified by visual inspection and electrical measurements. 

To resolve the overheating of a junction box in a solar module: 

• Inspection – Check for loose connections, faulty solders, and damaged bypass diodes. 

• Replacement – Change diodes or the junction box if necessary. 

• Monitoring – Keep track of the temperature with thermal cameras to prevent further problems. 

If overheating persists or compromises the safety of the system, it may be necessary to replace the PV module to avoid greater risks.