Photovoltaic Materials Combustion Performance Testing: Standards, Methods and Applications

Photovoltaic (PV) materials combustion performance testing evaluates the ignitability, flame spread, heat release, smoke production, and dripping behavior of polymer-based components used in solar modules and balance-of-system products. Testing to internationally recognized standards such as IEC 61730, IEC 60695, UL 94, ISO 4589-2, and ISO 5660-1 is a prerequisite for product certification, building-code compliance, and fire-risk management of PV installations. This article explains the sample types, test items, test methods, and practical applications of combustion performance testing for photovoltaic materials.

Technical Overview

Although a photovoltaic module is often perceived as a non-combustible assembly of glass and aluminum, it contains a substantial share of polymeric materials: encapsulant films such as EVA and POE, multilayer backsheets based on PET, PVF, and PVDF films, engineering plastics in junction boxes and connectors (polyamide, polycarbonate, PPO blends), cable insulation and sheaths based on cross-linked polyethylene and halogen-free polyolefins, as well as adhesives, sealants, and potting compounds. These components can be ignited by sustained internal electrical faults such as hot spots and DC arc faults, by external fire exposure from wildfires or adjacent burning structures, or by lightning-induced surges. Once ignited, burning encapsulants and backsheets can propagate flame across the module, release significant heat and toxic smoke, and generate flaming drips that threaten the roof assembly beneath the array.

Combustion performance testing provides quantified, reproducible evidence of how PV materials behave under defined fire scenarios. It supports material selection during product development, demonstrates conformity with safety standards for module certification, and establishes the fire classification required for building-integrated photovoltaics (BIPV). Testing is typically performed at two levels: material-level tests on plastics, films, and compounds, and module- or component-level fire tests that assess the finished product as installed. Key objectives include:

• Characterizing ignitability, self-extinguishing behavior, and flame propagation tendency of polymeric materials
• Quantifying heat release rate, total heat release, and smoke generation under radiant fire exposure
• Verifying the absence of flaming drips and particles that could spread fire beyond the point of origin
• Supporting certification of PV modules to safety standards such as IEC 61730 and UL 61730
• Establishing fire classes for BIPV products under construction product regulations
• Enabling fire-risk assessment of rooftop and ground-mounted PV power plants

Testing Samples

Backsheet Films

Multilayer backsheets (for example PET-based cores with fluoropolymer outer layers) are tested as representative laminates or as individual film layers. Specimens are cut to the dimensions required by each method, typically 125 mm × 13 mm bars for UL 94 burning tests and 100 mm × 10 mm strips for oxygen index testing, at production thicknesses from 50 µm to 350 µm.

Encapsulant Films

EVA and POE encapsulant films are inherently combustible thermoplastics. Testing determines their limiting oxygen index, UL 94 classification, and heat release characteristics, often in the cured (cross-linked) state to reflect the condition inside a laminated module. Comparison of neat, cured, and laminated specimens helps evaluate how lamination additives and degree of cure influence flammability.

Junction Boxes, Connectors, and Engineering Plastics

Molded plastics used in junction boxes, cable connectors, and bypass diode housings are tested in the form of molded plaques or cut sections. Glow-wire tests are particularly relevant for these current-carrying enclosures, since they simulate ignition from overheated electrical parts.

Cables and Wires

PV interconnect cables with cross-linked insulation and sheath materials are evaluated for flame propagation along a single vertical cable or along bunched cable trays, together with smoke density and halogen-acid gas emission where low-fire-hazard ratings are required.

Adhesives, Sealants, and Potting Compounds

Structural adhesives, silicone or polyurethane sealants, and encapsulant potting gels used inside junction boxes are tested as cured specimens to determine their contribution to fire load and their tendency to sustain combustion after removal of the ignition source.

Finished Module Assemblies and BIPV Components

Complete laminates, framed modules, and BIPV products such as photovoltaic glazing, roof tiles, and curtain-wall panels are subjected to large-scale fire tests on representative roof or wall mountings to assess spread of flame and resistance to burning brands in support of a system fire class.

Testing Items

Depending on the material, component, and intended application, a combustion performance evaluation program may include the following test items:

• Limiting oxygen index (LOI) — minimum oxygen concentration required to support candle-like combustion
• Horizontal burning classification (UL 94 HB, IEC 60695-11-10)
• Vertical burning classification at 50 W (UL 94 V-0, V-1, V-2, IEC 60695-11-10) and at 500 W (UL 94 5VA, 5VB, IEC 60695-11-20)
• Afterflame time, afterglow time, and flaming drip behavior
• Ignitability under a small flame source (ISO 11925-2, IEC 60695-11-2 needle flame)
• Glow-wire flammability index (GWFI) and glow-wire ignition temperature (GWIT)
• Time to ignition, peak heat release rate, and total heat release by cone calorimetry (ISO 5660-1, ASTM E1354)
• Smoke production rate, total smoke release, and specific extinction area
• Specific optical density of smoke (ISO 5659-2, ASTM E662)
• Carbon monoxide and carbon dioxide yields and identification of combustion gases
• Mass loss rate and residual char characterization
• Flame propagation on single and bunched cables (IEC 60332 series) and smoke emission of cables (IEC 61034)
• Spread-of-flame and burning-brand performance of finished modules (IEC 61730-2 fire test based on UL 790 / ASTM E108)
• Reaction-to-fire classification of BIPV construction products (EN 13501-1, GB 8624)

Testing Methods

Small-Scale Burning Tests (UL 94 / IEC 60695-11-10 and IEC 60695-11-20)

Vertical burning tests apply a 50 W premixed methane flame to the lower end of a 125 mm × 13 mm specimen twice for 10 s each. Afterflame duration after each application, total afterflame time across five specimens, afterglow, and ignition of surgical cotton placed beneath the specimen determine the V-0, V-1, or V-2 classification; V-0 is the most demanding rating and excludes flaming drips. The 500 W apparatus (5VA/5VB) applies a more severe flame five times for 5 s to vertical or horizontal plaques and is commonly specified for junction-box plastics. Specimens are conditioned at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for at least 40 h before testing.

Limiting Oxygen Index (ISO 4589-2, ASTM D2863, GB/T 2406.2)

A vertically mounted specimen is ignited at its top surface and burned in a controlled oxygen-nitrogen mixture flowing upward through a chimney. The oxygen concentration is adjusted in steps to find the minimum level at which combustion is sustained for 3 minutes or over 50 mm of specimen length. LOI values above 21 % indicate combustion is not sustained in normal air; flame-retardant PV plastics and backsheets typically target LOI values of 26 % to 32 % or higher.

Cone Calorimetry (ISO 5660-1, ASTM E1354)

A 100 mm × 100 mm specimen is exposed to a radiant flux of 25 to 75 kW/m² from a truncated cone heater and ignited with a spark igniter. Oxygen consumption calorimetry yields time to ignition, peak and average heat release rate, total heat release, effective heat of combustion, mass loss rate, smoke production, and yields of CO and CO₂. This method provides the most complete quantitative description of the fire behavior of backsheets, encapsulants, and laminated module coupons, and supports fire-hazard modeling of rooftop arrays.

Glow-Wire Testing (IEC 60695-2-10, -2-11, -2-12, -2-13)

A glowing nickel-chromium wire at temperatures from 550 °C to 960 °C is pressed against the specimen. GWFI tests whether the material self-extinguishes without igniting surrounding tissue paper, while GWIT determines the temperature 25 K above which ignition does not occur during a 30 s contact. These tests are standard requirements for plastics in junction boxes and other PV parts that may carry fault currents.

Ignitability and Needle-Flame Tests (ISO 11925-2, IEC 60695-11-2)

A small propane flame is applied to the bottom edge or surface of a specimen for 15 or 30 seconds. Flame spread above a specified height within a defined time, flaming droplets, and ignition of filter paper below the specimen are assessed. This method also feeds directly into EN 13501-1 and GB 8624 classification of BIPV products.

Smoke Density Testing (ISO 5659-2, ASTM E662)

Specimens of 75 mm × 75 mm are exposed in a closed chamber to a radiant heat source of 25 kW/m² with or without a pilot flame, and light transmission across a defined optical path is recorded. Specific optical density (Ds), Ds(max), and VOF4 values characterize smoke obscuration, which is critical for halogen-free versus halogenated backsheet and cable formulations.

Module-Level Fire Testing (IEC 61730-2, UL 61730, UL 790 / ASTM E108)

For modules intended for rooftop installation, the finished product mounted on a representative deck is subjected to spread-of-flame tests and, for higher classes, burning-brand tests as defined for Class A, B, or C roof coverings. The tests evaluate whether an externally applied flame propagates across the module surface and whether the module resists penetration by burning brands. Test outcome depends not only on material flammability but also on module construction, framing, mounting method, and air gap.

Cable Fire Tests (IEC 60332-1-2, IEC 60332-3 series, IEC 61034)

Single PV cables are tested with a 1 kW premixed burner applied for 60 s to a vertically supported specimen, with charred extent and downward flame spread as acceptance criteria. Bunched-cable and smoke-emission tests apply where PV cabling is installed in bundles, trays, or building voids, and are frequently combined with halogen-acid and smoke-corrosivity measurements for low-fire-hazard cable grades.

Applications

Combustion performance test data for PV materials are used throughout the product life cycle and across the value chain:

• Safety certification of PV modules to IEC 61730 and UL 61730, including the module fire test sequence
• Flame-retardant material development and comparative selection of backsheets, encapsulants, and engineering plastics
• Incoming-material quality control and supplier qualification for flame-retardant grades
• Fire classification of BIPV glazing, tiles, and facades under EN 13501-1 and GB 8624 for building-code approval
• Compliance verification of PV cables for low fire propagation and low smoke emission in plant design
• Fire-risk assessment and loss-prevention documentation for rooftop PV systems on commercial and residential buildings
• Root-cause and failure analysis after field fire incidents, comparing recovered material behavior with reference data
• Academic and industrial research on halogen-free flame retardancy of EVA, POE, and PET-based PV polymers

Accredited third-party laboratories routinely conduct these tests and issue reports accepted by certification bodies, installers, insurers, and regulatory authorities worldwide.

FAQ

Why do PV materials need combustion testing if modules are mainly glass and aluminum?

Module cores contain combustible encapsulants, backsheets, plastics, and cable insulation. Fault currents, arc faults, and external fires can ignite these components; testing quantifies ignition resistance, flame spread, heat release, and dripping so that products and installations can be designed and certified with acceptable fire risk.

What is the difference between UL 94 V-0 and UL 94 5VA?

V-0 is a 50 W vertical burning classification based on short afterflame times and no flaming drips. 5VA and 5VB use a 500 W flame applied five times to thicker plaques and represent a substantially more severe exposure; 5VA additionally requires that the specimen not develop a hole. Junction-box plastics are commonly specified as 5VA or GWFI 960 °C.

What limiting oxygen index indicates a flame-retardant PV material?

LOI above 21 % means the material will not burn in normal ambient air. In practice, flame-retardant backsheets and engineering plastics for PV applications target LOI values of at least 26 % to 28 %, with premium grades exceeding 30 %.

Do BIPV modules require building fire classification?

Yes. When photovoltaic elements are integrated into roofs, facades, or glazing, they fall under construction-product fire regulations and must be classified, for example under EN 13501-1 (Euroclasses) or GB 8624 in China, using tests such as the single burning item test (EN 13823 / GB/T 20284) and the single-flame source test (ISO 11925-2 / GB/T 8626).

How do material-level tests relate to the module fire test in IEC 61730-2?

Material-level tests such as UL 94, LOI, and glow-wire ratings support material selection and are often quoted in technical data sheets, while IEC 61730-2 evaluates the finished module mounted on a representative roof deck using spread-of-flame and burning-brand methods derived from UL 790 / ASTM E108. The module fire class is therefore determined by the complete construction, not by any single material rating.

What sample preparation is required before testing?

Specimens are cut to method-specific dimensions, edges are finished free of flash, and conditioning is performed at 23 °C ± 2 °C and 50 % ± 5 % relative humidity for a minimum of 40 hours, or as specified by the applicable standard. For encapsulants and potting compounds, curing state must be defined and reported because cross-link density measurably influences burning behavior.