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IEC 61345: Photovoltaic (PV) Modules — UV Test for Material Durability
IEC 61345 (1998) specifies the ultraviolet (UV) exposure test procedure for photovoltaic (PV) modules, designed to evaluate the ability of module materials — particularly the encapsulation, backsheet, and front sheet — to withstand long-term UV radiation exposure. UV-induced degradation is one of the primary causes of PV module power loss over time, and this test provides a critical accelerated aging assessment that correlates with decades of field exposure in real-world solar installations.
💡 Test Objective
The UV test serves to identify material incompatibilities and degradation mechanisms that may not be apparent in standard thermal or humidity cycling tests. UV radiation in the 280–400 nm wavelength range causes photochemical degradation of polymers — including chain scission, cross-linking, discoloration (yellowing), and loss of mechanical properties. The test exposes module materials to UV doses that simulate the cumulative effect of years of sunlight exposure, typically 15–60 kWh/m² of UV irradiance depending on the module type and application class.
The UV test serves to identify material incompatibilities and degradation mechanisms that may not be apparent in standard thermal or humidity cycling tests. UV radiation in the 280–400 nm wavelength range causes photochemical degradation of polymers — including chain scission, cross-linking, discoloration (yellowing), and loss of mechanical properties. The test exposes module materials to UV doses that simulate the cumulative effect of years of sunlight exposure, typically 15–60 kWh/m² of UV irradiance depending on the module type and application class.
1. UV Test Procedure and Requirements
1.1 Test Conditions
IEC 61345 specifies the following test parameters: UV irradiance — the sample must be exposed to UV radiation in the 280–400 nm wavelength range at an irradiance of at least 800 W/m² (UVA + UVB component). The UVB component (280–320 nm) should not exceed 5% of the total UV radiation to avoid unrealistic accelerated degradation that would not occur in natural sunlight. Temperature — the module temperature during UV exposure must be maintained at 60 ± 5 °C for crystalline silicon modules (may differ for thin-film technologies). UV dose — the total UV exposure dose is 15 kWh/m² for modules intended for general applications (Class A), with higher doses of up to 60 kWh/m² for modules intended for harsh environments or with specific warranty requirements. Duration — at 800 W/m² UV irradiance, achieving 15 kWh/m² requires approximately 19 hours of exposure; 60 kWh/m² requires about 75 hours.
| Parameter | Requirement | Notes |
|---|---|---|
| Wavelength Range | 280–400 nm | UVA (320–400 nm) + UVB (280–320 nm) |
| UVB Proportion | < 5% of total UV | Prevents unrealistic degradation |
| Minimum Irradiance | 800 W/m² | Measured at module plane |
| Module Temperature | 60 ± 5 °C | For crystalline Si modules |
| Total UV Dose (Class A) | 15 kWh/m² | General application modules |
| Total UV Dose (Class B) | 30–60 kWh/m² | Enhanced durability qualification |
| Ambient Humidity | Uncontrolled (lab ambient) | Typically 30–70% RH |
| Irradiance Uniformity | ±15% over test area | Verified by radiometer mapping |
⚙️ Engineering Insight: The choice between 15 and 60 kWh/m² UV dose depends on the module warranty requirements and the intended geographic installation. A 15 kWh/m² dose corresponds to roughly 1–2 years of outdoor exposure in central Europe (which receives approximately 8–15 kWh/m²/year of UV), while 60 kWh/m² represents 4–8 years. However, for modules installed in high-irradiance regions (desert climates like the Middle East or Atacama), the annual UV dose can reach 20–30 kWh/m²/year, meaning the standard 15 kWh/m² test covers less than one year of real exposure. For these markets, specifying the higher UV dose test is strongly recommended.
1.2 UV Light Sources and Spectral Requirements
The standard accepts several types of UV light sources: Xenon arc lamps — the preferred source, providing a spectral distribution closest to natural sunlight in the UV range when properly filtered; Metal halide lamps — higher UV output per lamp, allowing shorter test durations, but spectral matching to sunlight requires careful filter selection; Fluorescent UV lamps (UVA-340 or UVA-351 types) — commonly used, cost-effective, and providing good spectral match in the 300–360 nm range, but may under-represent the 360–400 nm region. The spectral irradiance must be measured using a calibrated spectroradiometer before each test series, and the lamp output must be monitored continuously during exposure to maintain the required irradiance level.
2. Degradation Mechanisms and Failure Modes
2.1 Encapsulant Degradation
The encapsulant material — typically ethylene-vinyl acetate (EVA) — is the primary UV-sensitive component in a PV module. UV exposure causes EVA to undergo photo-thermal oxidation, leading to several degradation modes: Yellowing/discoloration — formation of chromophore groups that absorb blue light, reducing module current output by 2–10% over time; Acetic acid formation — decomposition of EVA releases acetic acid, which corrodes cell metallization and interconnect ribbons, increasing series resistance; Delamination — loss of adhesion between the encapsulant and the cell or glass surface, creating air gaps that increase reflection losses and provide moisture ingress pathways; and Embrittlement — reduction in elongation at break from >400% to below 50%, increasing the risk of cell cracking under mechanical load. The UV test per IEC 61345 is designed to accelerate these failure modes to assess material suitability before full module qualification (IEC 61215).
⚠️ Important Factor: UV + Temperature Synergy
UV degradation is strongly accelerated by temperature. The standard requires module temperature control at 60 °C, but field measurements show that modules in desert installations can reach 75–85 °C, while those in snow-covered environments operate near 0 °C with reflected UV from the snow surface increasing the effective UV dose. The synergy between UV exposure and temperature means that the standard test at 60 °C may not fully represent the degradation kinetics in the hottest climates. For such applications, consider supplementing the IEC 61345 test with elevated temperature UV exposure (70–80 °C) to better predict long-term performance.
UV degradation is strongly accelerated by temperature. The standard requires module temperature control at 60 °C, but field measurements show that modules in desert installations can reach 75–85 °C, while those in snow-covered environments operate near 0 °C with reflected UV from the snow surface increasing the effective UV dose. The synergy between UV exposure and temperature means that the standard test at 60 °C may not fully represent the degradation kinetics in the hottest climates. For such applications, consider supplementing the IEC 61345 test with elevated temperature UV exposure (70–80 °C) to better predict long-term performance.
2.2 Backsheet Degradation
PV module backsheets (typically multilayer laminates of polyvinyl fluoride/PET/polyvinyl fluoride — Tedlar/PET/Tedlar, or newer polyamide-based formulations) undergo UV-induced degradation that can compromise the module’s electrical safety. Common failure modes: Surface cracking — UV-induced chain scission causes the outer layer to become brittle and develop microcracks, exposing the inner PET layer to moisture and UV; Delamination between layers — loss of adhesion between backsheet layers creates blisters and delamination areas that compromise insulation resistance; Chalking — formation of a white, powdery surface layer of degraded polymer; and Loss of dielectric strength — reduction in the backsheet’s insulation capability, increasing the risk of ground faults. The IEC 61345 UV test is particularly effective at revealing backsheet materials with inadequate UV stabilizer formulation.
3. Engineering Design Insights and Best Practices
3.1 Material Selection for UV Resistance
Based on the failure modes revealed by IEC 61345 testing, engineers can optimize material selection: EVA formulations — use fast-cure EVA with optimized peroxide content and added UV stabilizers (benzophenone or benzotriazole-type absorbers plus hindered amine light stabilizers HALS). The UV stabilizer package must be matched to the encapsulant thickness — too little stabilizer leads to early degradation, while excessive stabilizer can cause outgassing and delamination. Alternative encapsulants — polyolefin elastomers (POE) offer inherently better UV resistance than standard EVA, with no acetic acid generation, and are increasingly used for bifacial modules and high-reliability applications. Front sheet — low-iron tempered glass with anti-reflective coating that also absorbs UV (reducing UV reaching the encapsulant) or quartz glass for ultra-high UV transmission applications.
✅ Best Practice: UV Screening by Glass
One of the most effective UV protection strategies is to use glass with UV-blocking properties. Standard low-iron solar glass transmits approximately 90% of UV radiation at 380 nm but cuts off sharply below 350 nm. Specialty UV-blocking glasses can reduce UV transmission to below 5% at 380 nm, dramatically reducing the UV dose reaching the encapsulant and backsheet. This approach effectively decouples the choice of encapsulant and backsheet from UV durability requirements, allowing the use of lower-cost materials while maintaining long-term reliability. The trade-off is a small reduction in module short-circuit current (1–3%) due to reduced blue-light transmission.
One of the most effective UV protection strategies is to use glass with UV-blocking properties. Standard low-iron solar glass transmits approximately 90% of UV radiation at 380 nm but cuts off sharply below 350 nm. Specialty UV-blocking glasses can reduce UV transmission to below 5% at 380 nm, dramatically reducing the UV dose reaching the encapsulant and backsheet. This approach effectively decouples the choice of encapsulant and backsheet from UV durability requirements, allowing the use of lower-cost materials while maintaining long-term reliability. The trade-off is a small reduction in module short-circuit current (1–3%) due to reduced blue-light transmission.
3.2 Correlation Between UV Test and Field Performance
The correlation between IEC 61345 UV test results and actual field performance depends on several factors. Acceleration factor — the UV test at 800 W/m² and 60 °C provides an acceleration factor of approximately 5–10× relative to central European field conditions, meaning that a 20-hour test corresponds to roughly 100–200 hours of equivalent real exposure. However, this acceleration factor is not constant across all degradation mechanisms — photochemical reactions may have different activation energies, and the absence of diurnal cycling, rain, and soiling in the laboratory test means that certain synergistic degradation effects (e.g., UV + moisture + temperature cycling) may be underestimated. For comprehensive qualification, IEC 61345 should be combined with damp heat testing (IEC 61215) and thermal cycling to capture these synergistic effects.
3.3 UV Test for Emerging PV Technologies
With the rapid evolution of PV technologies, the applicability of IEC 61345 to non-standard module types requires careful consideration. Bifacial modules — require UV exposure on both front and rear sides, with the rear-side UV dose potentially higher due to albedo reflection from the ground (especially snow-covered or light-colored surfaces). Thin-film modules (CdTe, CIGS) — may have different temperature sensitivity and UV degradation kinetics; the standard test temperature of 60 °C may need adjustment. Perovskite and organic PV — these emerging technologies are inherently more UV-sensitive than silicon; the standard UV test is still relevant but may need modification (e.g., lower UV dose thresholds, different pass/fail criteria, or testing under controlled atmosphere to prevent oxygen-induced degradation).
❌ Common Pitfall
A critical mistake in UV test interpretation is assuming that passing the IEC 61345 test with the minimum 15 kWh/m² dose guarantees 25-year field durability. The test is a screening tool — it identifies gross material incompatibilities but does not simulate the combined effects of UV, temperature cycling, humidity, and mechanical load that a module experiences over its lifetime. A module that passes the UV test may still fail in the field due to synergistic degradation modes. The UV test results should always be evaluated together with damp heat (1000 h at 85 °C/85% RH), thermal cycling (200 cycles, −40 °C to +85 °C), and humidity-freeze cycling tests to build a complete reliability picture.
A critical mistake in UV test interpretation is assuming that passing the IEC 61345 test with the minimum 15 kWh/m² dose guarantees 25-year field durability. The test is a screening tool — it identifies gross material incompatibilities but does not simulate the combined effects of UV, temperature cycling, humidity, and mechanical load that a module experiences over its lifetime. A module that passes the UV test may still fail in the field due to synergistic degradation modes. The UV test results should always be evaluated together with damp heat (1000 h at 85 °C/85% RH), thermal cycling (200 cycles, −40 °C to +85 °C), and humidity-freeze cycling tests to build a complete reliability picture.
4. Frequently Asked Questions
Q1: What is the difference between IEC 61345 UV test and the UV preconditioning in IEC 61215?
IEC 61345 is a standalone UV exposure test specifically for evaluating material UV resistance, while IEC 61215 (the PV module qualification standard) includes UV preconditioning as one component of a comprehensive test sequence. The IEC 61215 UV exposure (15 kWh/m², same as IEC 61345 Class A) is applied before damp heat and thermal cycling tests to pre-stress the module and reveal UV-dependent failure modes in subsequent tests. IEC 61345 allows more flexibility in test conditions (higher UV doses, variable temperatures) and is often used for materials development and qualification, while IEC 61215 UV preconditioning is a fixed part of the type approval sequence.
Q2: Can a PV module pass the UV test but still experience UV-related failures in the field?
Yes, and this has been documented for several backsheet materials that passed IEC 61345 but experienced field failures after 5–10 years. The reasons include: (1) the test duration (~75 hours for 60 kWh/m²) does not capture long-term stabilization effects in polymer formulations; (2) the absence of diurnal temperature and humidity cycling may slow certain degradation pathways; (3) the UV spectrum of laboratory lamps may not precisely match sunlight, particularly in the UVA region; (4) field modules experience additional stressors (soiling, cleaning chemicals, hail impact) that create microcracks allowing moisture and UV to penetrate to deeper layers.
Q3: How does UV exposure affect the electrical performance of PV modules?
UV exposure primarily affects module performance through optical degradation of the encapsulant and backsheet. Key effects: (1) encapsulant yellowing reduces blue-light transmission, decreasing short-circuit current (Isc) by 2–10% over 25 years; (2) backsheet degradation can lead to increased series resistance (Rs) due to moisture ingress and cell metallization corrosion; (3) delamination creates air gaps that reflect light, further reducing Isc; (4) in severe cases, insulation failure due to backsheet cracking can cause ground faults and safety hazards. UV exposure generally has minimal direct effect on the silicon cells themselves, which are inherently stable under UV.
Q4: Is the UV test required for all PV module types and applications?
The UV test per IEC 61345 is part of the type approval sequence for flat-plate PV modules per IEC 61215. It is required for all crystalline silicon and thin-film modules seeking IEC certification. For building-integrated PV (BIPV) modules, additional UV testing may be required per the construction product regulation. For CPV (concentrator PV) modules, UV testing per IEC 62108 is applicable. Small modules intended for consumer electronics may use a reduced UV dose (7.5 kWh/m²) per the relevant product standard. Modules intended for extreme environments (high altitude, desert, tropical) should be tested at the higher UV dose level (30–60 kWh/m²) to ensure adequate long-term durability.
