Panel - Cracked vs Delaminating vs Discolored Decision Tree

Why this matters

A panel that looks bad on the roof can be one of three things: cosmetic-only and harmless, a manufacturing defect under warranty that the customer is entitled to replacement for, or an active safety risk that needs immediate isolation. Telling a customer "it is fine" on a backsheet that is actively delaminating exposes them to a fire risk. Sending a panel back to the manufacturer for an aesthetic browning that does not affect production wastes everyone's time. The tree below sorts the field-typical defect modes, ordered by what tech sees in the field.

Symptom presentation

Pattern A: visible glass crack, shattered or web pattern across one or more cells. Pattern B: bubbling, peeling, or whitish patches on the back of the panel (visible from underneath). Pattern C: brown, tan, or yellow patches on the cells visible from the front. Pattern D: snail trails (thin dark squiggle lines following cell boundaries). Pattern E: hot spot visible as a discolored cell with surrounding burn pattern.

Quick checks - 10 minute pass

1. Confirm panel model and manufacturer. Sticker on the back of the panel. Manufacturers stand behind 25-year power warranty and 10-12 year product warranty - the warranty type matters for the claim.
2. Determine date of install. Less than 10 years: usually product warranty applies. 10-25 years: power-warranty only on output.
3. Test the affected panel's output. Open-circuit voltage (Voc) and short-circuit current (Isc) at noon, full sun, compared to spec sheet. A 5-10 percent deviation indicates a degraded panel.
4. Per-panel monitoring data if available. Compare the suspect panel against same-string neighbors.
5. Visual inspection from underneath (through skip-light gaps or by removing one panel as a check). Backsheet condition is the key safety signal.

Isolation tree

Step 1 - Pattern A: visible glass crack

Glass cracks split into three causes:

Hail or impact damage: spider pattern centered on impact point. Repair is replacement; if hail event was recent and documented, homeowner insurance covers under property loss. File claim.

Thermal stress crack: hairline crack across multiple cells in a wave pattern, usually around year 8-15 of life. Manufacturer defect of laminate. Warranty claim.

Walking damage during install or service: linear cracks in a path. Installer liability if recent. Not a warranty claim - workmanship.

Action: cracked panel cells continue producing at reduced output if encapsulated. If the glass is shattered to the point that EVA or backsheet is exposed, isolate the panel (open the string disconnect) and replace. Hot spots can develop on cracked cells, creating fire risk.

Step 2 - Pattern B: backsheet delamination

Bubbles, blisters, white patches, or peeling on the back of the panel:

Identified in some model lines as a known defect (DuPont Tedlar PVF-based backsheets installed 2010-2014 had a class-action settlement). Confirm panel model against industry-known defect lists.

Severity gates:

• Minor surface haze, no exposed laminate: monitor annually, document.
• Bubbles or blisters not yet ruptured: report to manufacturer, schedule replacement under warranty.
• Ruptured backsheet with EVA visible: ACTIVE FIRE RISK. Isolate panel immediately, replace, file warranty claim.
• Conductor exposed: shut down string, lock out, replace.

Backsheet failure is a safety-critical failure mode. Backsheet integrity is the dielectric barrier between live cells and roof structure. Once breached, leakage current can ignite the substrate.

Step 3 - Pattern C: discoloration of cells (front view)

Browning, yellowing, or tan patches on cells visible through the glass:

EVA encapsulant yellowing - common in panels older than 15 years. Cosmetic, not safety. Production drops slightly (1-3 percent). Not warranty replaceable unless power output is below the warranty line.

Cell hot spot discoloration - usually with halo of darker color around a cell. Caused by mismatched cell in series, shaded cell with bypass diode failure, or microcrack on cell. Safety concern. Investigate further (Step 5).

Anti-reflective coating degradation - even pattern, uniform appearance change. Cosmetic.

Step 4 - Pattern D: snail trails

Thin dark squiggle marks on cells, following microcracks. Cosmetic in most cases - the cells continue to produce. Snail trails are a marker of microcracking, which is a product-quality indicator. If snail trails appear across many panels in the first 5 years, document for warranty claim. The actual production impact is small (1-3 percent) unless paired with significant microcracking confirmed by electroluminescence imaging.

Step 5 - Pattern E: hot spot

A localized hot spot is a serious failure mode:

• Caused by reverse-biased cell (shaded or microcracked cell forced to dissipate current rather than produce).
• IR thermography during full production identifies hot spots above 80 C as urgent.
• Bypass diode failure removes the safety mechanism and the hot spot escalates.

Severity:

• Mild hot spot (less than 70 C IR): monitor.
• Moderate (70-90 C): replace panel under warranty.
• Severe (above 90 C, or visible scorch on backsheet from underneath): immediate isolation, replace, possible roof structure inspection.

Step 6 - PID (Potential Induced Degradation)

Bulk shift in production across many panels (10-30 percent drop in months) with cells appearing dim or with abnormal blue cast. Caused by leakage current across encapsulant under negative-grounded string. Some inverters offer PID-recovery routines (SMA, Fronius). Older systems may need ground-reference change or panel replacement.

Confirming the diagnosis

IR thermography during peak production for hot spot confirmation. Electroluminescence imaging (specialty service) for microcrack confirmation. Voc and Isc measurements vs spec. Photographs from above and below. Power output measured against panel's individual datasheet at standard test conditions.

Remediation

• Glass crack (impact): homeowner insurance claim plus replacement.
• Glass crack (thermal): manufacturer warranty.
• Backsheet minor: monitor.
• Backsheet ruptured: isolate, replace urgently.
• EVA yellowing (cosmetic): no action unless power below warranty line.
• Hot spot mild: monitor.
• Hot spot severe: isolate, replace.
• Snail trails alone: cosmetic.
• PID-affected: PID recovery program if available, otherwise replace.

References

• IEC 61215 Crystalline Silicon PV Module Design Qualification.
• IEC 61730 PV Module Safety Qualification.
• IEC TS 62804 PID Test Methods.
• NREL Photovoltaic Module Reliability Workshop publications.
• Manufacturer warranty terms (typically 10-12 year product, 25-30 year linear power).