Solar Panel Failure Modes: PID, LID and Delamination Guide

A solar power plant that performs at 95% of its projected P50 yield in year one may be producing at 82% by year ten, not because of module aging alone, but because of specific, identifiable, and often preventable failure modes that no one detected early enough to correct.

For EPCs, O&M teams, and lenders relying on 25-year yield projections, the difference between 82% and 95% performance can mean crores in lost revenue and potential violation of minimum generation guarantees.

The IEA Photovoltaic Power Systems Programme (PVPS) Task 13 published its 2025 update of the PV Failure Fact Sheets, an international reference on documented PV failure modes drawn from field experience in many climates. Each fact sheet rates a failure mode for safety impact and performance impact.

Quick answer. Solar panel failure modes fall into six practical groups: potential-induced degradation (PID), light-induced degradation (LID and LeTID), delamination and encapsulant failures, junction box and bypass diode failures, soiling and corrosion, and microcracks. Each has distinct causes and detection signatures. Electroluminescence imaging, infrared thermography and IV curve tracing catch most of them early, and many are cheaper to prevent at the design stage than to fix in the field.

This article builds on the IEA PVPS 2025 findings with field engineering context specific to Indian climates (high temperature, monsoon humidity, coastal salt air and heavy dust), where several failure modes manifest faster and more severely than in European temperate reference conditions.

Why PV Failure Modes Matter More Than Module Efficiency Ratings

A module with a 22.5% efficiency rating and a 2% first-year degradation rate looks worse on paper than a 21% module with 0.4% first-year degradation. But efficiency and degradation rate are only two dimensions of module performance risk. What matters for a 25-year asset is the probability of accelerated failure from specific mechanisms that the standard STC efficiency and temperature coefficient tests do not measure.

The IEA PVPS Task 13 risk scoring system rates each failure mode on two axes:

• Safety impact: Does it create fire, electrical shock, structural failure, or toxic exposure risk?
• Performance impact: How severely does it reduce yield, and at what rate?

Potential-Induced Degradation (PID): The Silent Yield Killer

PID (Potential-Induced Degradation) is among the highest-impact performance failure modes documented by IEA PVPS Task 13 and in NREL’s O&M best practices guidance. It occurs when a high voltage potential between the solar cell and the grounded module frame drives ionic current through the module’s encapsulant and anti-reflection coating, leading to progressive shunting of cell junctions.

Root causes of PID:

• High negative voltage on modules at the negative end of long strings (common in 1,500V DC systems)
• High ambient temperature and humidity (both strongly accelerate ionic migration)
• Low-resistivity encapsulant or glass; older EVA formulations are more susceptible than POE (polyolefin elastomer) encapsulants
• Absence of floating or positive grounding of the PV array

In Indian conditions such as coastal Gujarat, Tamil Nadu, Kerala and Andhra Pradesh, with monsoon relative humidity of 70-90%, PID progresses much faster than in dry desert conditions because moisture acts as an electrolyte facilitating ion migration through the encapsulant to the module glass surface.

Illustrative PID progression in a 1 MW Indian ground-mount system (without mitigation, assumed values):

Year	Estimated PID-induced yield loss	Annual Revenue Impact (₹6/kWh PPA)
Year 1	0.5-1%	₹2-4 lakh
Year 3	3-5%	₹12-20 lakh
Year 5	8-12%	₹32-48 lakh
Year 10	15-25%	₹60-100 lakh

PID detection methods:

1. Electroluminescence (EL) imaging, the reference method for PID detection. A PID-affected cell appears as a dark region or completely black cell in the EL image due to shunted junctions. EL imaging must be done at night or in a darkened enclosure.
2. IV curve tracing, a PID-affected string shows a depressed Voc and reduced fill factor. The Pmax loss correlates with the extent of cell shunting.
3. Module-level monitoring, string current monitoring can flag anomalous current reduction that points to PID-affected modules.

Mitigation strategies:

• Specify POE (polyolefin elastomer) encapsulant instead of standard EVA when procuring modules for high-humidity coastal sites
• Configure the inverter grounding scheme, per IEC 62548 PV array design requirements, to maintain positive or floating potential on module frames (consult the CEA Grid Code requirements for your connection point)
• Install PID recovery devices that apply a reverse voltage pulse overnight to partially restore shunted cells
• For existing installations showing PID, module replacement is the only permanent fix once degradation exceeds 5% on individual modules

Light-Induced Degradation: LID, LeTID, and What Differentiates Them

Light-Induced Degradation (LID) is a performance loss that occurs during the first hours to days of light exposure on a newly commissioned module. It is a well-characterized phenomenon in standard boron-doped (p-type) silicon cells caused by the formation of boron-oxygen (B-O) defect complexes in the silicon bulk. LID typically causes a one-time loss of 1-3% that stabilizes after the first days of sun exposure. Our PVsyst degradation modeling guide shows how to enter LID and PID in a yield model.

LID vs. LeTID comparison:

Parameter	LID (classic)	LeTID (Light and elevated Temperature Induced Degradation)
Cell technology affected	Standard p-type (boron-doped)	PERC, multi-Si PERC, some n-type
Onset	First hours of light exposure	Weeks to months after commissioning
Loss magnitude	1-3% one-time	5-15% progressive (and potentially partially reversible)
Recovery mechanism	Partial recovery via regeneration annealing	Partial recovery at elevated temperatures over time
Detection at commissioning	IV curve comparison to factory flasher data	Not visible at commissioning, develops in the field
Indian climate relevance	Established, well-modeled	High concern in PERC modules deployed post-2019

LeTID (Light and elevated Temperature Induced Degradation) is a more recently documented and more severe phenomenon affecting PERC cell technology, which now accounts for the majority of Indian solar installations. According to the IEA PVPS Task 13 2025 report, LeTID has been observed in field systems at loss levels of 5-15% developing over the first 6-18 months of operation, with partial recovery thereafter.

For EPCs commissioning large PERC arrays, the DETECT-6 checklist below includes a LeTID monitoring milestone at month 6 and month 18, comparing IV curve Pmax against factory flasher data and the first-month commissioning IV test.

The DETECT-6 Framework for PV Failure Diagnosis

The DETECT-6 Framework is a checklist we recommend to plant owners and O&M teams for diagnosing and prioritizing PV failures in operating plants. It applies the IEA PVPS Task 13 risk categories to field-measured data and ranks remediation by yield recovered per rupee of O&M spend. Heaven Designs does not provide O&M; we use the same failure categories when we design.

Delamination and Encapsulant Failures

Delamination occurs when the adhesive bond between the solar cell, encapsulant, and glass or backsheet layers breaks down. It creates visible air pockets or discolored regions within the module laminate and compromises both optical transmission and environmental protection.

Types of delamination and their causes:

Delamination Type	Location	Primary Cause	Performance Impact
Front encapsulant delamination	Between glass and EVA	Moisture ingress + UV degradation	Increased reflection, 2-8% Pmax loss
Cell-to-encapsulant delamination	Between cell and EVA	Thermal cycling stress	Electrical disconnection, up to 100% cell loss
Backsheet delamination	Between EVA and backsheet	Adhesion failure + humidity	Insulation failure, safety risk
Edge sealing failure	Perimeter of module	Mechanical stress + UV	Progressive moisture ingress, accelerates all other modes

EVA (ethylene-vinyl acetate) encapsulant yellowing, sometimes called “browning” when severe, reduces the optical transmittance of the module and is a common indicator of UV-induced degradation rather than true delamination.

However, advanced EVA browning often precedes delamination in modules operating above 70°C module temperature in high-UV environments. India’s Rajasthan and Gujarat deserts, with peak plane-of-array irradiance above 1,100 W/m² and module temperatures of 65-80°C, are among the most demanding environments for laminates.

Hot Spots, Microcracks, and Cell-Level Failures

Hot spots occur when one or more cells in a module produce less current than the string minimum, typically due to shading, soiling, or a physical defect, causing the underperforming cells to operate in reverse bias and dissipate power as heat. A single shaded cell can dissipate a large share of the string’s power as heat, and severe hot spots can push cell temperatures well above 100°C.

The hot spot phenomenon is particularly damaging because it creates a positive feedback: the initial temperature rise degrades the cell further, increasing current mismatch, which increases heating, which further degrades the cell. Without bypass diodes, a single hot-spotting cell can destroy an entire module in hours. With bypass diodes, the diode activates and bypasses the affected cell group, protecting the module but reducing its output by approximately 30%.

Cell microcracking is documented in the IEA PVPS Task 13 fact sheets and is one of the most underdiagnosed failure modes. Microcracks develop from:

• Transport and handling damage: forklift shock, improper stacking, inadequate packaging
• Installation stresses: stepping on modules, improper clamping torque
• Thermal cycling: daily expansion and contraction stresses over years of operation
• Wind and snow loading, fatigue cracking from sustained dynamic loading

The critical distinction is between inactive microcracks (cracks that are structurally present but do not cause immediate cell isolation) and active microcracks (cracks that propagate to isolate a portion of the cell from the current collection grid). Inactive cracks may convert to active cracks under continued thermal cycling, particularly at the module corners and edges where stress concentrations are highest.

Detection of microcracks requires EL imaging. Visual inspection misses most microcracks because they are sub-millimeter scale and invisible under normal light. IR thermography identifies hot spots caused by active microcracks but misses inactive cracks. Only EL imaging, which passes current through the module and images the resulting light emission pattern, reliably maps both active and inactive microcrack states.

Soiling and Corrosion: India-Specific Failure Patterns

Soiling loss is not a structural failure mode in the IEA PVPS classification, but it is the single largest source of day-to-day performance gap in Indian solar installations. Published field studies put soiling losses in Indian systems in the low single digits with regular cleaning, rising sharply in high-dust locations such as Rajasthan during pre-monsoon periods. Our regional guide to solar soiling loss in India covers the ranges by region.

Distinct soiling profiles affect different Indian regions (indicative ranges; measure on site where possible):

Region	Primary Soiling Type	Loss Range	Optimal Cleaning Frequency
Rajasthan / Gujarat desert	Wind-blown mineral dust	8-18% without cleaning	Every 7-14 days
Coastal Tamil Nadu / Kerala	Salt spray + dust	5-12%	Every 10-21 days
Agricultural states (Punjab, MP)	Agri-residue + dust	4-10%	Every 14-28 days
Urban industrial (Delhi NCR, Mumbai)	Industrial particulate + carbon	6-15%	Every 7-14 days

Beyond routine dust soiling, India-specific chemical corrosion failures include:

• Frame corrosion in coastal installations: aluminum frames exposed to salt spray can lose structural integrity within 5-8 years without appropriate anodization or coating specification
• Connector corrosion: MC4 connectors that are not properly crimped or that have been exposed to condensation develop contact resistance increases that show as heating on IR surveys
• Backsheet chalking: UV degradation of non-fluoropolymer backsheets produces a white chalky surface that indicates compromised UV protection and approaching insulation failure

Junction Box Failures: The Fire Risk Nobody Talks About

Junction box failures carry a high safety impact rating in the IEA PVPS Task 13 fact sheets because they can start module-level fires. The junction box houses the bypass diodes and is the electrical interface between the module and the string wiring. Failure mechanisms include:

• Bypass diode failure: diodes that fail short-circuit (most common) permanently bypass a third of the module’s cells, causing 30% module power loss and overheating. Diodes that fail open-circuit remove bypass protection, creating severe hot-spot risk.
• Solder joint failure: thermal cycling loosens solder connections within the junction box, increasing contact resistance and generating localized heat that can ignite the encapsulant or the cable sheath.
• Potting compound cracking: the silicone or polyurethane potting compound that seals the junction box interior cracks under thermal stress, allowing moisture ingress and accelerating corrosion.
• Cable gland failure: improper torque on cable glands during installation allows cable movement under wind loading, fatiguing the insulation at the entry point.

Junction box thermal failure is a recognised fire source, particularly in ground-mount installations where the junction box operates at ground level in environments with leaf litter, grass, and other combustible material. Annual thermographic surveys that specifically scan the junction box area at maximum current conditions are the primary preventive measure.

Comparing Failure Mode Risk: A Decision Matrix for O&M Prioritization

Knowing which failure modes need immediate attention and which can be monitored is the core of an effective O&M program. The following matrix applies the IEA PVPS Task 13 risk scoring to the Indian context:

Failure Mode	Safety Risk	Performance Risk	Detection Tool	Indian Priority
PID	Low	Very High (3-10%/yr)	EL imaging, IV curve	Critical in coastal/humid
Hot spot from bypass diode failure	High (fire)	High	IR thermography	Critical all regions
Junction box thermal failure	Very High (fire)	Medium	IR thermography	Critical all regions
LeTID (PERC)	None	High (5-15% one-time)	IV curve + EL	High for PERC arrays
Microcracks (active)	None	Medium (1-5%)	EL imaging	High, transport damage common
Delamination (front)	Low	Medium (2-8%)	Visual + EL	High in desert locations
Backsheet failure	Medium (insulation)	Low-medium	Visual + IR test	High in coastal installations
Soiling	None	Very High (8-18%)	Visual + yield monitoring	Immediate, ongoing
Connector corrosion	Medium (arcing)	Low-medium	IR thermography	Medium in coastal
Frame corrosion	Medium (structural)	None	Visual inspection	Low inland, High coastal

How Bankable Engineering Design Reduces Failure Risk

The most effective point to address PV failure risk is the design stage: before procurement, before installation, and before the first kilowatt-hour of generation. Our list of common solar installation defects caused by design errors shows where those decisions go wrong. Design choices made in the engineering phase directly determine which failure modes a system is vulnerable to and how severe their impact will be.

Key design decisions that affect failure risk:

• Module technology selection: POE encapsulant versus EVA, fluoropolymer backsheet versus non-fluoropolymer, PID-resistant cell architecture for coastal sites
• String voltage configuration: limiting negative frame-to-ground voltage on humidity-exposed sites, guided by the module maker’s PID test data
• Grounding scheme: positive, negative, or floating array grounding affects PID risk and requires alignment with the inverter’s ground fault detection design
• Tilt angle and ground clearance: affecting soiling accumulation rate, moisture retention under the modules, and hotspot risk from grass or debris contact
• Cable management and strain relief: preventing fatigue failure at junction boxes and connector points under long-term wind loading

The bankable PVsyst reports guide covers how yield models should incorporate degradation curves that reflect specific failure mode risks for the project site, not just the manufacturer’s standard 0.4%/year degradation assumption.

For utility-scale projects where lenders require an Independent Engineer (IE) review, the IE assessment commonly includes module technology risk, soiling loss methodology and degradation rate assumptions.

Module qualification tests per IEC 61215 and IEC 61730 establish minimum reliability baselines, but these standard tests do not replicate the extended thermal cycling and combined stress conditions that drive real-world failure modes in harsh Indian climates.

Projects using outdated degradation assumptions risk IE rejection or require additional performance guarantee buffers. See the advanced PVsyst analysis guide for how to structure a bankable degradation model.

How Heaven Designs Integrates Failure Mode Risk into Engineering Deliverables

Heaven Designs addresses failure mode risk in its engineering deliverables, from pre-design through commissioning documentation. This is part of the design scope, not a separate O&M service. For the acceptance tests that close out a project, see our guide to IEC 62446 PV acceptance testing.

• Solar Rooftop Detailed Engineering Design, Module technology specification guidance for climate zone, string voltage optimization for PID risk, grounding scheme design.
• Solar Ground Mount Design, Inter-row spacing and tilt angle optimization for soiling accumulation and cleaning access, cable management design to prevent hot-spot and junction box failure.
• Site Survey and Land Feasibility, Soiling loss assessment using ground-level dust and aerosol data, humidity and salt-spray risk profiling for module specification.
• STAAD Pro Reports, Structural analysis that includes wind fatigue load calculations to assess microcracking risk at mounting system interfaces.

Contact us to discuss how failure mode risk analysis integrates into your next project’s engineering scope.

FAQ

What is the most common solar panel failure mode in Indian installations?

Soiling is the most common day-to-day cause of performance loss in India, and losses climb fast in high-dust locations without regular cleaning.

Among structural failure modes, PID is the highest-impact concern in coastal and high-humidity states (Tamil Nadu, Kerala, coastal Andhra Pradesh, Gujarat), while hot spots and junction box failures carry the highest safety risk across all regions. Track performance ratio against solar plant performance ratio benchmarks to spot when a failure mode starts to bite.

How does electroluminescence (EL) imaging differ from infrared (IR) thermography for fault detection?

Infrared thermography measures surface temperature differences during operation. It identifies active faults where current mismatch is generating heat (hot spots, active microcracks, junction box overheating, bypass diode failures).

EL imaging passes current through the module in darkness and images the photon emission. It reveals both active and inactive structural faults (all microcracks, PID-affected cells, inactive cell areas from LID/LeTID) that do not yet generate heat anomalies. The two techniques are complementary: IR surveys are faster (drone-based, daytime) and identify immediate actionable faults; EL imaging is more thorough and captures latent faults before they become performance problems.

Can PID be reversed or recovered in the field?

Partial PID recovery is achievable using PID recovery units that apply a reverse bias to the affected modules overnight. Recovery depends on the severity of degradation: lightly affected modules often recover much of the lost power, while heavily degraded modules may not.

Modules with more than 10% PID loss show partial recovery but rarely return to full rated power. The preferred approach is prevention: PID-resistant module specification, appropriate grounding scheme, and annual EL monitoring to catch PID before it becomes severe.

What degradation rate should be used in a PVsyst model for PERC modules in India?

The appropriate annual degradation rate for a bankable PVsyst model of PERC modules in Indian conditions depends on the site. For dry inland locations (Rajasthan, Gujarat, Maharashtra plateau), a degradation rate of 0.5-0.6%/year is defensible with standard PERC modules and a well-maintained cleaning program.

For coastal or high-humidity locations (Tamil Nadu, Kerala, Andhra Pradesh coast), where PID risk is elevated, independent engineers commonly require 0.65-0.80%/year for PERC without PID-specific mitigation measures, or 0.5%/year with documented POE encapsulant specification and PID-resistant inverter grounding. TOPCon and HJT modules, which have lower PID susceptibility and lower LID, can be modeled at 0.4-0.45%/year in IEA-aligned analysis.

How frequently should IR thermography surveys be conducted on operational plants?

Common practice is at least one full-array IR thermography survey a year, with semi-annual surveys for larger plants or high-risk environments (coastal, high-humidity, or a documented hot spot history).

In Indian practice, the monsoon season creates a natural inspection opportunity immediately after the rains, when accumulated moisture may have triggered or worsened junction box sealing failures, and an annual pre-summer inspection in February-March checks for soiling patterns and early hot spots before peak generation season.

Drone-based IR surveys cost a small fraction of a plant’s annual revenue, so annual surveys are easy to justify for most MW-scale plants. Get local quotes before budgeting.

What is the risk of solar panel fires from junction box failures?

Junction box failures, particularly bypass diode failures that cause sustained local overheating, are a recognised cause of module-level fire incidents in the IEA PVPS Task 13 fact sheets. The risk is highest in ground-mount installations where vegetation or combustible materials are present under and between rows.

The fire risk from a single failed junction box depends on the diode failure mode (short-circuit versus open), the ambient temperature, and whether the failure is caught during routine monitoring. Annual IR thermography specifically targeting junction box temperatures, combined with immediate replacement of any module showing junction box temperature above 15°C above adjacent modules, substantially reduces fire risk.

How does module microcracking at installation affect long-term performance?

Cell microcracks introduced during installation (from improper handling, clamping over-torque or transport shock) may be inactive at commissioning (no immediate performance impact) but convert to active cracks under 2-5 years of thermal cycling.

Active microcracks isolate cell areas from the current collection grid, causing proportional power loss. A module with 10% of its cell area isolated by active microcracks will show approximately 8-12% Pmax loss relative to its factory flasher certificate.

Systems with transport damage or poor installation practice show noticeably higher microcrack-related losses over time. Pre-installation EL testing of a sample of received modules (5-10% sampling rate) is the recommended procurement quality control measure.