Common PV Module Defects: Causes, Detection, and Prevention

AQ Electric inspects solar modules at every stage of their life — in the factory, on arrival at site, at commissioning, and in operation — across the MENA region, and the pattern we see is consistent with what independent laboratories are now reporting: module quality has become more variable, not less. Modules are larger, glass is thinner, new cell technologies are still maturing, and price pressure on manufacturers is intense. This article explains the most common PV module defects, what causes them, how much energy they cost, and — most importantly — which inspection method detects each one, so owners and EPC contractors can find defects while they are still someone else’s responsibility.

What Counts as a PV Module Defect?

A PV module defect is any flaw that reduces a module’s power output, shortens its life, compromises its safety, or breaches its specification or warranty. The common defects in PV modules fall into three groups by origin:

• Manufacturing defects — created in the factory: poor soldering, cell processing errors, contaminated or under-cured encapsulant, badly sealed junction boxes, unsoldered bypass diodes.
• Transport and installation defects — created between the factory and the mounting structure: cell cracks from rough handling, glass breakage, frame damage, and damage from walking on or mis-clamping modules.
• Field-induced degradation — developed in operation: PID, UVID, LeTID, delamination, corrosion, and hot spots that grow from small initial flaws.

Defects can also be grouped by consequence. Some cost energy (cracks, PID, degradation), some create safety risks (junction box faults, insulation failures, severe hot spots), and some are cosmetic at first but signal a problem that will grow (snail trails, early browning). Many defects begin as one kind and become another: a manufacturing flaw can become a field failure years later.

Why Module Defects Are Rising

Independent test data from the past two years points in one direction: module quality has become harder to rely on, and common PV module defects are appearing more often in laboratories and in the field.

• Laboratory failures are at record levels. Kiwa PVEL’s 2025 PV Module Reliability Scorecard reported that 83% of manufacturers and 59% of bills of materials (BOMs) had at least one test failure, both the highest levels recorded. Visual defects — mainly glass breakage in mechanical and hail stress tests — accounted for 60% of failures, and power degradation rose to 19%.
• Factory quality is uneven. Intertek CEA, which has carried out more than 80,000 quality inspections in over 340 module factories, reported that 71% of the factories it audited in 2025 were graded in its two lowest tiers, C or D.
• New red flags are appearing. RETC’s 2026 PV Module Index found damp heat red flags in 11% of modules and UVID red flags in 8%, with RETC linking the rise in UVID to the popularity of TOPCon technology.
• Field data shows the same trend. Raptor Maps’ 2026 Global Solar Report found that small module defects rose 17.4% year on year across its 373 GW dataset.

The causes are partly technical and partly commercial. Modules have grown larger and heavier while glass has become thinner. TOPCon and heterojunction cells have replaced PERC at enormous speed, before their long-term field behaviour is fully understood. And, according to Kiwa PVEL, some manufacturers are using thinner encapsulants and faster lamination to boost throughput — a cost-driven risk rather than a flaw in the cell technology itself. For buyers, the conclusion is simple: brand and datasheet are no longer enough; verification is.

The Common PV Module Defects at a Glance

The table below summarises the common PV module defects covered in this article, where they come from, what they cost, and which method detects them best.

Hot Spots

A hot spot is an area of a module that runs significantly hotter than its surroundings. It happens when a cell or part of a cell cannot produce the current forced through it by the rest of the string; instead of generating power, it dissipates power as heat. Common causes include cracked or defective cells, poor solder joints, partial shading, heavy localised soiling such as bird droppings, and failed bypass diodes.

Hot spots are among the most common PV module defects found in operating plants, and they matter for two reasons. They cost energy, and they damage the module: sustained high temperature can discolour the encapsulant, burn the backsheet, crack glass, and, in severe cases, create a fire risk. Many hot spots also grow over time as the underlying defect worsens.

Hot spot detection on solar panels — one of the most requested inspection services — is done with infrared thermography while the plant operates at sufficient irradiance, because defects only heat up when current flows. Aerial thermography under IEC TS 62446-3 screens every module in a plant; handheld thermography verifies critical findings. AQ Electric explains the method and its anomaly classes in its article on infrared thermography for solar PV, and how a full aerial campaign works in its article on drone inspection for solar PV plants.

Cell Cracks and Microcracks

Cell cracks are fractures in the thin silicon cells inside the module. Microcracks may be invisible to the eye and initially cost little power, but under thermal cycling, wind, and mechanical load they can grow, isolate parts of the cell, and eventually cause hot spots and significant power loss.

Cracks are created at every stage: during cell processing and stringing in the factory, by dropping or stacking modules during transport, by poor handling on site, by walking on modules, and by mechanical loads in operation. Kiwa PI Berlin’s 2025 analysis of its factory inspections attributed around 40% of defects to cell processing and soldering.

Cracks are one of the common PV module defects that thermography handles poorly. Research presented to IEA PVPS Task 13 by DTU found that cell cracks were hard to assess in drone thermography and produced temperature differences of at most about 1 °C. The right tool is electroluminescence imaging, which shows cracked and inactive cell areas as dark regions. AQ Electric explains how EL works and how its results are classified in its article on electroluminescence EL testing for solar PV. For teams that run their own module checks, AQ Electric’s sister company EE Electronics supplies portable EL testing systems in Jordan.

Potential-Induced Degradation (PID)

Potential-induced degradation occurs when a high voltage difference between the cells and the grounded frame drives leakage currents through the module’s materials. Over time, this can cause severe power loss, often affecting the modules at the most negative end of a string first. Heat and humidity accelerate it, and susceptibility depends heavily on the cell, encapsulant, and glass used.

The industry has made progress: Kiwa PVEL reported that 72% of BOMs produced in 2024 degraded by less than 2% in its PID test, an improvement on the previous year. But the picture is changing with new technologies. The IEA PVPS Task 13 report on new module technologies notes that light, especially UV, can influence PID: in one TOPCon case, testing with UV held PID below 3%, while testing without UV produced 28% degradation. The report also identifies a new PID mechanism in heterojunction modules, and recommends combined potential and light testing under the updated IEC TS 62804-1.

In the field, PID shows a characteristic pattern in EL images and a typical signature in IV curves, often concentrated by position in the string. Detected early, some forms of PID can be slowed or partly reversed; detected late, the losses can be large. AQ Electric explains how IV curves reveal this kind of loss in its article on IV curve tracing for solar PV.

LID and LeTID

Light-induced degradation (LID) is an initial loss of power when crystalline silicon modules are first exposed to sunlight. Light- and elevated-temperature-induced degradation (LeTID) is a related mechanism that develops more slowly, over months or years, and is accelerated by heat.

The good news is that these mechanisms are now well understood. The IEA PVPS Task 13 report describes LeTID and LID as largely solved, mainly by replacing boron with gallium as the wafer dopant and by adjusting cell processes. RETC’s 2026 Index found no red flags in its LID and LeTID testing. Even so, buyers should confirm LeTID test results for the specific BOM they are purchasing, because process changes can reintroduce risk.

UV-Induced Degradation in TOPCon and HJT

UV-induced degradation (UVID) has become one of the most discussed module defects of recent years. Some TOPCon and heterojunction (HJT) cells lose power after exposure to ultraviolet light, because UV affects the passivation layers at the cell surface. The issue gained prominence as modules adopted UV-transparent encapsulants that let more UV reach the cells.

The evidence is still developing. RETC’s 2026 Index reported UVID red flags in 8% of tested modules. The IEA PVPS report found UVID pronounced in some TOPCon and HJT modules after accelerated ageing, but called it a solvable problem, since some modules are UV-stable. Research by Fraunhofer ISE suggests that standard UV tests may overstate field losses, because part of the loss recovers under sunlight; on the other hand, researchers at NREL found severe UVID in operational n-type modules in a system flagged for underperformance. Kiwa PI Berlin has noted that limited field data still makes firm conclusions difficult.

Glass Breakage

Glass breakage has become one of the most significant module defects, particularly in large-format bifacial glass-glass modules. Kiwa PVEL reported that module breakage in mechanical and hail stress testing notably increased in its 2025 Scorecard. The IEA PVPS Task 13 report documents cases where thin glass (2 mm or less) in glass-glass modules led to rear-glass breakage of 5% to 10% within two years of installation, and notes that the standard IEC 61215 mechanical load test cannot detect this vulnerability — it only appears in larger-scale testing in the actual mounting position.

Broken glass exposes the cells to moisture, creates insulation and safety risks, and leads to power loss. Causes include thin glass, stress from clamps and mounting structures, hail, and handling damage. Because breakage often depends on the combination of module and mounting system, the IEA recommends testing several thin-glass modules in their final mounting position. Breakage is easily visible in drone RGB imagery and visual inspection.

Delamination and Encapsulant Degradation

Delamination is the separation of the module’s layers — glass, encapsulant, cells, and backsheet or rear glass. It allows moisture to enter, which can corrode cell metallisation and interconnections, reduce insulation resistance, and cause power loss and safety faults. Related encapsulant problems include discolouration (browning or yellowing) and bubbles.

Kiwa PVEL has linked delamination to poor material choice, thinner encapsulants, and poor lamination processes, and has found that different BOMs from the same manufacturer can produce different results. RETC’s damp heat red flag rate of 11% in 2026 points to the same family of moisture-related weaknesses. Delamination is visible on inspection; its safety consequence — reduced insulation resistance — is measured electrically. For the insulation testing side, AQ Electric’s sister company EE Electronics explains how to choose the instrument in its article on how to choose an insulation resistance tester.

Snail Trails

Snail trails are dark, discoloured lines across a module’s cells that resemble the trail of a snail. They typically form along cell cracks, where moisture reaches the cell surface and reacts with materials in the silver paste and encapsulant. The discolouration itself costs little power, but it is a visible indicator of the cracks beneath it. A module with snail trails should be checked with EL to understand the extent of the underlying cracking.

Junction Box and Bypass Diode Failures

The junction box connects the module’s internal circuit to the string cables and houses the bypass diodes that protect cells from reverse bias when part of the module is shaded or defective. Failures here are among the most dangerous module defects because they combine high current, heat, and proximity to flammable materials.

Kiwa PVEL reported that about one-third of manufacturers had junction box failures in its 2025 testing, including falling covers, exposed wiring, diode issues, and melted connectors, and that safety failures — mainly insulation problems from poor junction box sealing or pottant application — affected 7% of BOMs. The IEA PVPS report warns that incorrectly soldered contacts can leave bypass diodes unconnected, which can cause fires and power losses and is hard to detect after installation; it recommends 100% bypass diode checks in production.

In the field, a failed or conducting bypass diode produces a characteristic thermal pattern — typically one-third of the module running warm — and a step in the IV curve. Overheating junction boxes and connectors show up clearly in thermography. Connector problems at module level are closely related to string wiring quality, which AQ Electric covers in its article on solar string wiring.

Frame and Mechanical Damage

As modules have grown larger and heavier, frames and edges have come under more stress during transport, handling, and installation. Kiwa PI Berlin’s 2025 report identified frame damage as the second most common defect category in its inspections, linked to ever-larger module formats. Bent or cracked frames weaken the module’s resistance to wind and snow loads and can lead to glass breakage. Frame damage is found through visual inspection at the factory, on arrival, and during installation.

PV Module Defect Detection: Which Test Finds What

PV module defect detection depends on choosing the right method for each defect. No single test finds everything, which is why a robust inspection programme combines several.

In practice, the most efficient sequence for finding common defects in PV modules on an operating plant is aerial thermography and RGB imagery of 100% of modules, followed by targeted EL and IV curve tracing on the strings and modules that the aerial survey flags. On new supply, factory and arrival inspections add flash testing, EL, and visual inspection before modules are installed.

Where to Catch Defects in the Project Lifecycle

The cost of a defect rises sharply the later it is found, and that is true of all common PV module defects. A cracked module rejected at the factory costs the manufacturer; the same module found after installation costs the EPC; found after acceptance, it costs the owner — together with the labour and downtime to replace it.

1. In the Factory

Factory inspection verifies the BOM, the production process, and the finished modules through pre-shipment checks, flash testing, EL imaging, and visual inspection. It is the only stage at which the buyer can confirm that the agreed materials are actually being used. AQ Electric explains the factory and site acceptance process in its article on FAT vs SAT in solar PV projects.

2. On Arrival at Site

Transport damage is a major source of cracks and breakage. Arrival inspection on a statistical sample of pallets — visual checks, EL, and flash or IV testing — identifies damaged consignments before they are installed and while the claim is still straightforward.

3. During Installation and Commissioning

Handling and mounting introduce their own defects. Commissioning tests, string IV curves, EL sampling, and thermography under load create the baseline at handover and catch defects while the EPC is still responsible. AQ Electric covers this stage in its article on the solar PV commissioning process.

4. In Operation

Periodic thermography, followed by targeted EL and IV testing, catches field-induced defects such as PID, hot spots, and diode failures as they develop. AQ Electric explains how this fits into a full programme in its article on solar PV plant operation and maintenance.

Defects and Warranty Claims

Module warranties protect owners only if common PV module defects can be proven to be covered. Manufacturers typically require evidence that a defect is covered, that it exceeds the warranty threshold, and that it was not caused by transport, installation, or operation. That makes inspection records central to every claim.

• Baseline records — factory flash data, arrival inspection results, and commissioning EL and IV data show the module’s condition before operation.
• Quantified loss — IV curve tracing and calibrated measurements establish how much power has been lost.
• Defect evidence — EL images and thermograms show the type of defect and help distinguish manufacturing from handling damage.
• Scale — aerial surveys establish how widespread a defect is across the plant, which matters for serial defect claims.

Timing matters as much as evidence. Raptor Maps’ 2026 report found that losses rose 55% between years two and three of operation, coinciding with the end of EPC warranties that often last one to two years. An inspection before that window closes is one of the best investments an owner can make. When a plant is bought or refinanced, the same evidence feeds the asset review described in AQ Electric’s article on solar PV technical due diligence.

Module Defects in the Gulf and MENA

The region’s climate shapes which common PV module defects matter most, and it makes some of them develop faster than in temperate markets.

Heat

High module temperatures accelerate many degradation mechanisms, including LeTID and encapsulant ageing, and intensify the damage from hot spots. Temperature-related stress also makes thermal cycling more severe for solder joints and interconnections.

High UV

The region’s strong sunlight means high UV exposure, which raises the stakes for UVID in TOPCon and HJT modules and for UV-related encapsulant and backsheet ageing. BOM-specific UV test evidence is particularly valuable for Gulf and MENA projects.

Dust, Sand, and Soiling

Heavy soiling creates partial shading that can trigger hot spots, and sand can abrade glass and coatings. Uneven soiling, such as dust accumulating along the lower frame edge, produces thermal patterns that analysts must distinguish from genuine module faults.

Coastal Humidity

Coastal sites around the Gulf and Red Sea combine heat, humidity, and salt, increasing the risk of moisture-related defects such as PID, corrosion, and delamination. AQ Electric’s work in two of the region’s largest markets is covered in its articles on solar PV testing services in Saudi Arabia and solar PV testing services in the UAE.

Imported Supply at Scale

Almost all modules in the region are imported over long supply chains, often in very large volumes. Factory inspection and arrival inspection are therefore the most cost-effective defences against both manufacturing and transport defects.

AQ Electric’s PV Module Inspection Services

AQ Electric for Power Solutions, founded in Jordan in 2019 and expanded to Egypt in 2021, provides PV module defect detection across the full project lifecycle in the MENA region, covering all of the common PV module defects described in this article. Its services combine the methods described in this article: electroluminescence testing through its EL testing services, string and module power analysis through its IV curve tracing services, thermal and EL scanning from the air through its drone inspection services, and factory and arrival inspections through its FAT and SAT quality assurance services.

Because AQ Electric performs aerial screening, EL, IV curve tracing, and thermography in-house, a defect found by one method can be confirmed and quantified by another, and turned into a repair plan or a warranty claim. Independent verification for owners and lenders is also available through AQ Electric’s third-party inspection services. AQ Electric operates under an ISO 9001, ISO 14001, and ISO 45001-certified management system from offices in Amman, Jordan and New Cairo, Egypt, with more than 1.0 GW of PV project experience. The full portfolio is on AQ Electric’s projects page.

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