Hail Protection Performance Testing: Standards, Methods, and Applications

Hail protection performance testing evaluates the ability of photovoltaic modules, roofing systems, glazing, and other outdoor products to withstand hailstone impacts under controlled laboratory conditions. Performed in accredited third-party laboratories in accordance with standards such as IEC 61215-2, ISO 9806, UL 2218, ASTM E1038, and EN 13583, these tests simulate realistic hail events to verify structural integrity, electrical safety, and long-term weatherability. This article explains the test principles, sample requirements, test items, procedures, pass criteria, and typical applications of hail impact resistance testing.

Technical Overview

Hail protection performance testing, also referred to as hail impact resistance testing, is a laboratory procedure that reproduces the mechanical loading imposed by natural hailstones on products installed in exposed outdoor environments. Damage from hailstorms can range from surface dents and coating breaches to glass fracture, cell cracking, water ingress, and complete functional failure, making validated hail resistance a critical requirement for products such as photovoltaic modules, roof coverings, waterproofing membranes, and glazing.

The test principle is based on matching the kinetic energy of a natural hailstone impact. Kinetic energy is calculated as one half of the projectile mass multiplied by the square of its velocity. A standard 25 mm ice ball, with a mass of approximately 7.5 g, launched at 23 m/s delivers roughly 2 joules of impact energy, while larger hailstone simulations, such as an 85 mm ice ball traveling at approximately 44 m/s, can deliver well over 250 joules. By controlling projectile size, mass, velocity, and temperature, laboratories can reproduce hail events of defined severity with high repeatability.

Internationally recognized test frameworks include IEC 61215-2 (terrestrial photovoltaic module design qualification, hail impact test), IEC 61730-2 (PV module safety), GB/T 61215 series (Chinese national standards harmonized with IEC 61215), ISO 9806 (solar thermal collectors), ASTM E1038 (simulated hail impact on photovoltaic modules), UL 2218 (impact resistance of roof covering materials), and EN 13583 (artificial hard hail resistance of roof waterproofing sheets). Together, these standards define projectile specifications, impact velocities, target locations, and pass criteria for a wide range of product categories.

Testing Samples

Sample requirements depend on the product category and the applicable standard. In general, samples must be representative of normal production, complete with all functional layers, and submitted in sufficient quantity to allow pre-test baseline measurements, post-test evaluation, and, where required, high-severity testing in addition to the standard test level.

Photovoltaic Modules

Crystalline silicon and thin-film photovoltaic modules, including glass-backsheet and glass-glass constructions, building-integrated photovoltaic (BIPV) laminates, and bifacial modules. Typically, at least two full-size modules are required for the hail impact test according to IEC 61215-2, with one module serving as a control for baseline electrical characterization such as maximum power measurement, wet leakage testing, and electroluminescence imaging.

Roofing and Waterproofing Products

Asphalt shingles, concrete and clay tiles, metal roofing panels, bituminous membranes, thermoplastic and elastomeric sheets such as TPO, PVC, and EPDM, and insulated roof panels. For UL 2218 evaluation, samples are installed over a representative roof deck and underlayment system following the manufacturer's installation instructions, since the performance of the assembled system, rather than the material alone, determines the classification.

Glazing, Skylights, and Transparent Components

Laminated safety glass, tempered glass, polycarbonate and acrylic glazing, rooflights, greenhouse panels, and transparent protective covers. These samples are tested in the mounted orientation and support condition specified by the manufacturer, because edge retention and frame stiffness strongly influence impact behavior.

Automotive, Aerospace, and Outdoor Equipment Components

Vehicle body panels, windshields and fixed glazing, sensor and camera covers, outdoor electrical enclosures, telecommunication equipment housings, and composite panels. Testing is typically performed according to manufacturer specifications or industry standards adapted to simulate service hail exposure for the specific component.

Materials and Protective Components

Protective films, coatings, paints, encapsulants, and composite laminates used in exposed applications. Material-level testing supports research and development activities, comparative benchmarking of candidate materials, and input data for product-level design validation.

Testing Items

Typical test items and measured parameters in a hail protection performance test program include the following:

• Ice ball dimensional and mass verification (standard 25 mm diameter, approximately 7.5 g, with optional higher-severity diameters from 35 mm up to 85 mm)
• Ice ball temperature conditioning verification at approximately -4 °C prior to launch
• Projectile velocity calibration and measurement (23 m/s for the standard 25 mm ice ball, with a typical tolerance of ±5%)
• Multi-point impact testing at 11 defined positions on the specimen, covering corners, edges, the center, and areas near junction boxes or other sensitive features
• Pre-test and post-test maximum power (Pmax) measurement and degradation assessment for photovoltaic modules
• Visual inspection for broken glass, cracked cells, delamination, surface damage, and other major defects
• Wet leakage and insulation resistance testing after impact to confirm electrical safety
• Electroluminescence (EL) imaging to reveal hidden micro-cracks in solar cells
• Steel ball free-fall impact testing and classification (Class 1 through Class 4) for roof covering materials per UL 2218
• Post-impact watertightness verification for membranes, roofing assemblies, and glazing systems
• Low-temperature conditioning and impact testing to represent winter hail conditions for waterproofing products

Testing Methods

Ice Ball Propulsion Method

This method, applied in IEC 61215-2 (test MST 17), ISO 9806, and ASTM E1038, uses spherical ice balls manufactured from purified water and conditioned in a freezer at approximately -4 °C so that they are fully solid yet representative of natural hail. The ice balls are loaded into a pneumatic launcher, and compressed air propels them against the mounted specimen. Velocity is measured immediately before impact using optical measurement devices at the launcher exit, and the air pressure is adjusted until the required velocity is achieved within tolerance. For photovoltaic modules, 11 impacts are applied at standard-specified locations. Where higher hail severity is required, larger ice balls are used with correspondingly higher velocities; for example, a 35 mm ball is launched at approximately 28 m/s and a 45 mm ball at approximately 32 m/s, with diameters available up to 85 mm for severe hail simulation.

Steel Ball Free-Fall Method

Applied in UL 2218 for roof covering materials, this method uses a solid steel ball dropped from a defined height onto the specimen, delivering a concentrated impact that conservatively represents hailstone loading. Class 1 testing uses a 1.25 inch steel ball dropped from approximately 12 feet, while Class 4, the highest rating, uses a 2 inch ball dropped from 20 feet, with Classes 2 and 3 using intermediate sizes and heights. Specimens are installed over a representative deck, impacts are applied at vulnerable points such as edges, overlaps, ridges, and fastener locations, and each impact point is typically struck more than once to evaluate resistance to repeated hail hits. The covering passes if it exhibits no cracking, fracturing, tearing, rupture, or exposure of the underlying substrate that could allow water penetration.

Artificial Hard Hail Method

Specified in EN 13583 for bitumen, plastic, and rubber roof waterproofing sheets, this method subjects conditioned membrane specimens to artificial hard hail impact on a defined substrate, often at specified low temperatures to represent the most unfavorable service condition. After impact, specimens are examined for cracks, perforations, and loss of watertightness, and the results are used to characterize the hail resistance class of the waterproofing product for the European market.

Post-Test Evaluation and Pass Criteria

Following impact exposure, specimens undergo final measurements defined by the applicable standard. For photovoltaic modules tested to IEC 61215-2, the pass criteria are based on visual inspection showing no major defects, such as broken glass or visible cracks through the front cover, together with a successful wet leakage test. Many test programs additionally include maximum power measurement, where degradation is typically limited to 5% or less relative to the pre-test baseline, and electroluminescence imaging to detect internal cell damage that is not visible externally. All measurement instruments, including velocity sensors, temperature sensors, and electrical characterization equipment, must be calibrated and traceable to national or international measurement standards to ensure result validity.

Applications

Hail protection performance testing supports product certification, market access, risk management, and engineering development across multiple industries. Key applications include:

• Certification of photovoltaic modules to IEC 61215-2, IEC 61730-2, and the GB/T 61215 series, which is a market entry requirement in most regions and a prerequisite for incentive program eligibility
• Classification of roofing products under UL 2218 to demonstrate Class 1 through Class 4 impact resistance for building code compliance and insurance rating purposes in hail-prone regions
• Verification of waterproofing membrane performance under EN 13583 for European construction projects and CE marking support
• Qualification of solar thermal collectors to ISO 9806, including hail resistance of glazing and absorber assemblies
• Research and development optimization of glass thickness, encapsulant selection, module construction, and coating systems
• Site-specific risk assessment for utility-scale power plants, where high-severity testing with large-diameter ice balls reflects regional hail climatology
• Failure analysis and warranty investigations following field hail damage, using comparative laboratory reproduction of the event

By engaging accredited third-party laboratories, manufacturers obtain impartial test evidence that supports product datasheets, certification documents, insurance filings, and customer confidence in hail-exposed installations.

FAQ

Which standard applies to my product for hail protection testing?

Photovoltaic modules are typically tested to IEC 61215-2 or the harmonized GB/T 61215 series, with safety aspects covered by IEC 61730-2. Roof covering materials are classified under UL 2218, roof waterproofing sheets are evaluated to EN 13583, solar thermal collectors are tested to ISO 9806, and PV modules may also be assessed using the simulated hail procedure in ASTM E1038. The correct standard depends on the product type, target market, and regulatory or contractual requirements.

What ice ball size and velocity are used in the standard test?

The standard severity level for photovoltaic modules uses a 25 mm diameter ice ball, weighing approximately 7.5 g, launched at 23 m/s. Higher severity levels use progressively larger ice balls, from 35 mm up to 85 mm, each launched at a correspondingly higher velocity to represent severe hail events.

How many impacts are applied to a photovoltaic module?

According to IEC 61215-2, a total of 11 impacts are applied at defined positions on the module front surface, covering corners, edge regions, the central area, and locations near sensitive components such as the junction box.

What are the pass criteria for photovoltaic modules?

The module must show no major visual defects after impact and must pass the wet leakage test. In many test programs, maximum power degradation is also assessed and is typically required to remain within approximately 5% of the pre-test value, and electroluminescence imaging may be used to confirm the absence of hidden cell cracks.

How is UL 2218 different from ice ball testing?

UL 2218 uses a solid steel ball dropped from a specified height rather than a propelled ice ball, and it produces a numeric classification from Class 1 to Class 4 for roofing assemblies rather than a pass or fail result for an individual product. Class 4, using a 2 inch steel ball dropped from 20 feet, represents the highest level of impact resistance under this standard.

Can high-severity hail testing be performed beyond the standard level?

Yes. Accredited third-party laboratories can perform enhanced-severity testing using larger ice balls, such as 45 mm, 55 mm, or up to 85 mm, at correspondingly higher velocities. This is commonly requested for projects located in regions with documented severe hail exposure or as part of differential product positioning by manufacturers.