Solar Panel Defect: Common Types, Warning Signs, and How to Identify Them

Solar panels are designed to operate outdoors for decades, enduring heat, cold, humidity, wind, rain, snow, and continuous exposure to sunlight. But like any manufactured product, photovoltaic (PV) modules can develop defects or experience failures during manufacturing, transportation, installation, or long-term operation.

A solar panel defect does not always mean a panel will immediately stop generating electricity. Some defects cause gradual power loss, while others can remain hidden until specialized testing is performed. In certain cases, defects can also create reliability or safety concerns.

The U.S. Department of Energy (DOE) identifies hot spots, cell cracks, water intrusion, and module delamination among the issues that can require repair during the operating life of a PV system.

Understanding the most common defects, and how they are detected, can help installers, EPCs, developers, asset owners, and solar equipment buyers protect system performance and make better procurement decisions.

What Is a Solar Panel Defect?

A solar panel defect is a physical, electrical, or material problem that affects, or has the potential to affect, the module’s performance, reliability, durability, or safety.

Defects can originate at several stages of a panel’s life.

Some begin during cell or module manufacturing. Others can occur when modules are transported or handled improperly. Installation errors can cause additional damage, while environmental exposure can contribute to degradation over many years.

The International Energy Agency’s Photovoltaic Power Systems Programme (IEA PVPS) identifies numerous PV module failure modes, including delamination, cell cracks, junction-box failures, broken frames, discoloration, burn marks, potential-induced degradation, failed interconnections, defective bypass diodes, and broken front glass.

Not every visible imperfection has the same impact, however. A defect needs to be evaluated according to its location, severity, progression, and effect on electrical performance.

1. Cell Cracks and Microcracks

Cell cracking is one of the better-known solar module defects.

Crystalline-silicon solar cells are thin and relatively fragile. Mechanical stress during manufacturing, transportation, installation, or operation can create cracks within a cell.

Some cracks are visible, but many microcracks cannot easily be identified through a normal visual inspection.

Their impact also varies.

A small crack may initially have little measurable effect on output. If a crack electrically isolates part of the cell, however, it can reduce the active area producing electricity and contribute to power loss.

DOE has supported research specifically examining how cell cracks affect PV module degradation and power loss.

For buyers receiving large quantities of modules, careful transportation, unloading, storage, and installation practices can therefore be important even when panels appear undamaged externally.

2. Delamination

Solar modules are constructed from multiple layers bonded together to protect the cells and electrical components from the outside environment.

Delamination occurs when these layers begin separating.

DOE identifies delamination as one of the module-damage issues that can require repair or attention in operating PV systems.

Loss of adhesion can compromise the protective structure of the module. Depending on its location and severity, it may also increase the potential for moisture intrusion and subsequent degradation.

Visible bubbling, separation, or changes around module edges can be warning signs that deserve closer inspection.

IEA PVPS similarly recognizes delamination as an established PV module failure mode.

3. Hot Spots

A hot spot is an area of a solar module that operates at an abnormally high temperature compared with surrounding cells or module areas.

Hot spots can develop for several reasons, including cell defects, electrical mismatch, damaged interconnections, or partial shading.

NREL research has documented manufacturing-related causes of hot spots including crystalline defects, cracks, high-resistance solder points, and current mismatch between cells.

External shading can also contribute. Leaves, dirt, snow, nearby structures, or other obstructions may cause a cell or group of cells to operate differently from the rest of the module.

Hot spots deserve attention because concentrated heating can contribute to additional module damage. DOE lists module hot spots among the common problems requiring PV system maintenance.

Infrared thermography is one method used to identify abnormal temperature patterns that may not be apparent during a standard visual inspection.

4. Potential-Induced Degradation

Potential-induced degradation, commonly called PID, is an electrical degradation mechanism that can reduce PV module performance.

PID can occur when voltage differences between solar cells and grounded components contribute to leakage currents and changes within the module.

Environmental conditions can influence the risk. DOE notes that high-humidity and salt-containing marine environments can present additional challenges associated with potential-induced degradation.

The effects may not be visually obvious.

NREL research identifies PID-related shunting among degradation mechanisms that can cause module power loss while remaining difficult to identify through visual inspection alone.

This is one reason electrical performance testing can be necessary when a system is underperforming even though its modules look normal.

5. Backsheet Cracking and Damage

On many module designs, the backsheet provides an important protective barrier on the rear of the panel.

Over time, environmental exposure and material degradation can lead to cracking, separation, or other backsheet problems.

Backsheet damage can compromise protection of internal components and potentially contribute to moisture intrusion or electrical reliability issues.

DOE research programs have specifically identified backsheet cracking alongside corrosion, delamination, and encapsulant discoloration as PV module reliability concerns.

Visible cracking or deterioration on the back of a module should therefore be investigated rather than treated purely as a cosmetic issue.

6. Moisture Intrusion and Corrosion

Solar panels spend their entire operating lives outdoors, making protection against moisture essential.

If water or moisture reaches areas that should remain protected, corrosion and other electrical problems can develop.

DOE identifies water intrusion into the module laminate or junction box among typical causes of PV system problems.

Corrosion can also affect connections elsewhere in a PV system. DOE notes that corrosion at electrical connection points can increase resistance and create potential safety concerns.

Projects in coastal or high-humidity environments may require particular attention to environmental exposure when selecting equipment.

7. Junction Box and Bypass Diode Failures

The junction box mounted on the back of a solar module contains important electrical connections.

Problems with junction boxes can include poor connections, moisture intrusion, mechanical damage, or component failures.

Bypass diodes are another important component. They allow current to bypass portions of a module under certain conditions, such as when part of the module is shaded.

IEA PVPS identifies both junction-box problems and defective bypass diodes among documented module failure modes.

Failures involving these components may contribute to reduced production or abnormal heating and can require electrical testing to diagnose accurately.

8. Discoloration

Changes in the appearance of module encapsulation materials can also indicate degradation.

Encapsulant discoloration has historically been used as one indicator of PV module reliability issues. DOE research notes EVA yellowing or discoloration among degradation mechanisms evaluated in module-reliability work.

Discoloration can reduce the amount of light reaching the underlying cells depending on its extent and location.

However, visual discoloration should not automatically be used to determine exact power loss. Electrical testing is required to understand its actual performance impact.

9. Broken Glass and Frame Damage

Some defects are much easier to see.

Cracked front glass, damaged frames, impact marks, or severely deformed components should be identified during receiving or routine inspection.

Damage can occur during:

• Manufacturing
• Freight transportation
• Unloading
• Warehousing
• Installation
• Severe weather
• Impact events

Even when a damaged module continues producing electricity, its long-term environmental protection or mechanical integrity may have been compromised.

IEA PVPS includes frame breakage and front-glass breakage among recognized module failure modes.

How Are Solar Panel Defects Detected?

A standard visual inspection is a useful starting point, but it cannot identify every solar panel defect.

Professional inspection can use several methods.

Visual inspection

Visual inspection can identify problems such as broken glass, delamination, discoloration, damaged frames, burn marks, damaged backsheets, and junction-box issues.

Infrared thermography

Thermal imaging identifies temperature differences across operating modules.

Unusually hot areas can indicate hot spots, damaged cells, connection problems, or other abnormalities.

IEA PVPS identifies steady-state thermography as one of the commonly used methods for detecting module failures.

Electroluminescence imaging

Electroluminescence, or EL, imaging can reveal defects that are difficult or impossible to identify visually.

IEA PVPS describes EL as an increasingly established laboratory method for identifying PV module failures, including cell-level problems.

It can be particularly useful for detecting cracks and electrically inactive areas within cells.

I-V curve testing

Current-voltage, or I-V, curve testing evaluates the electrical behavior of a module or string.

NREL notes that I-V analysis has long been an important tool for degradation research and can provide information through measurements such as open-circuit voltage, short-circuit current, fill factor, shunt resistance, and series resistance.

Combining electrical testing with imaging can provide a more complete understanding of a suspected defect.

Does Every Solar Panel Defect Require Replacement?

Not necessarily.

The appropriate response depends on the type and severity of the problem.

A defect may have little immediate impact, require continued monitoring, justify a warranty claim, or require the module to be removed from service.

The key questions include:

• Is power output affected?
• Is the defect getting worse?
• Does it create an electrical or mechanical safety concern?
• Has the module’s environmental protection been compromised?
• Is the issue covered by the manufacturer’s warranty?

Modules with suspected electrical or safety problems should be evaluated by qualified solar professionals rather than handled or repaired without appropriate training.

How Buyers Can Reduce Solar Panel Defect Risk

Defect management should begin before modules reach the project site.

Purchase certified equipment

For the U.S. market, buyers should verify applicable product certifications.

UL Solutions identifies UL 61730-1 and UL 61730-2 as PV module safety qualification standards and provides performance testing against the IEC/UL 61215 series. Testing can also cover factors such as potential-induced degradation, mechanical loading, corrosion, and other stresses.

Certification cannot guarantee that an individual module will never fail, but it provides an important baseline for safety and product qualification.

Review warranties

Buyers should understand both product and performance warranty terms, including exclusions and the documentation required to make a claim.

Inspect shipments

Modules should be checked when they arrive at the warehouse or project site.

Document damaged packaging, broken glass, bent frames, and other visible problems before equipment is installed.

Handle modules correctly

Improper transportation, storage, carrying, or installation can damage modules even when the damage is not immediately visible.

Monitor system performance

DOE emphasizes the importance of maintaining monitoring systems that track PV performance. Unexpected reductions in production can help operators identify problems that require further investigation.

 

 

Compare available modules and equipment from established suppliers on the Sunhub Marketplace.

Why Module Quality Matters in Solar Procurement

For installers, EPCs, developers, and distributors, module procurement is about more than price per watt.

Solar systems are expected to generate electricity for decades. DOE notes that reliable PV equipment can reduce maintenance expenses, financing risk, and unexpected outages while spreading initial project costs across a longer operating lifetime.

Procurement teams should therefore evaluate:

• Applicable certifications
• Manufacturer track record
• Product warranties
• Performance warranties
• Supplier reliability
• Quality-control documentation
• Shipping and packaging
• Warranty support
• Product traceability

A lower equipment price can quickly lose its advantage if modules arrive damaged, experience excessive failures, or create additional labor and replacement costs after installation.

Conclusion

A solar panel defect can range from a small cell crack with limited immediate impact to a serious electrical, mechanical, or environmental failure.

Common problems include microcracks, delamination, hot spots, PID, backsheet damage, moisture intrusion, corrosion, junction-box failures, discoloration, and broken glass.

Some are visible. Others require thermal imaging, electroluminescence, I-V testing, or other diagnostic techniques to identify.

For solar businesses, preventing problems begins with procurement. Certified equipment, reputable suppliers, proper transportation, careful receiving inspections, correct installation, and long-term performance monitoring can all reduce risk.

And when performance does change, identifying the underlying defect early can help determine whether the module needs monitoring, repair, a warranty claim, or replacement.

Frequently Asked Questions

What is the most common solar panel defect?

There is no single defect that is universally the most common across every module technology, climate, and system age. Documented failure modes include cell cracks, delamination, hot spots, backsheet problems, discoloration, junction-box failures, PID, and damaged interconnections.

Can a defective solar panel still generate electricity?

Yes. Some defects reduce only part of a module’s output or have little immediate measurable effect. Others can progressively worsen or create reliability and safety concerns.

Can you see microcracks in solar panels?

Not always. Small cell cracks can be difficult to detect visually. Electroluminescence imaging and other diagnostic methods can reveal defects that are not readily visible from the outside.

What causes hot spots in solar panels?

Hot spots can be associated with cell defects, cracks, electrical mismatch, poor connections, or partial shading. Thermal imaging can help identify abnormal heating patterns.

How can solar panel defects be prevented?

Not every defect can be prevented, but risk can be reduced through appropriate product qualification and certification, careful supplier selection, proper transportation and storage, correct installation, routine inspection, and ongoing system monitoring.

Sources

• U.S. Department of Energy – Optimizing Solar Photovoltaic Performance for Longevity
• U.S. Department of Energy – Photovoltaic Reliability and Standards Development
• U.S. Department of Energy – Managing and Mitigating Solar PV Corrosion
• IEA PVPS – Review of Failures of Photovoltaic Modules
• IEA PVPS – Photovoltaic Failure Fact Sheets 2025
• UL Solutions – PV Module Certification
• National Renewable Energy Laboratory – PV Module Hotspot Detection