Hail Impact Resistance Testing of Materials: Standards, Methods and Applications

Hail impact resistance testing evaluates the ability of materials and finished products to withstand high-velocity ice ball impacts that simulate natural hailstone strikes. Performed in accredited third-party laboratories in accordance with standards such as IEC 61215-2, ASTM E1038, UL and GB series specifications, this test is essential for validating the durability, safety and long-term reliability of photovoltaic modules, glazing, roofing systems, polymer sheets and automotive components deployed in hail-prone regions.

Technical Overview

Hail impact resistance testing is a destructive mechanical test that reproduces the loading conditions imposed by natural hail on exposed products and materials. Standardized spherical ice projectiles, cooled to a controlled sub-zero temperature, are accelerated by a compressed-air launcher against the surface of a test specimen at specified velocities and locations. By controlling projectile diameter, mass, velocity and temperature, the test delivers a quantified and repeatable impact energy that can be compared against the kinetic energy of real hailstones.

The test answers three fundamental engineering questions: whether the material fractures, delaminates or deforms beyond acceptable limits under hail loading; whether the product continues to perform its function after impact; and whether any damage introduces safety risks such as loss of electrical insulation or reduced structural integrity. For manufacturers, the results support design qualification, product certification, warranty substantiation and market access in hail-exposed climates. Testing is typically carried out by ISO/IEC 17025-accredited third-party laboratories to guarantee traceable, defensible data.

Applicable Standards

Hail impact testing is governed by internationally recognized standards, and the correct method is selected according to the product type and target market:

• IEC 61215-2 – Design qualification and type approval of terrestrial photovoltaic modules, including the ice ball hail impact test.
• IEC 61730-2 – Photovoltaic module safety qualification, covering mechanical impact robustness.
• ASTM E1038 – Determining the resistance of photovoltaic modules to hail by impacts with ice balls.
• UL 61730 / UL 1703 – North American safety standards for flat-plate photovoltaic modules that reference impact resistance requirements.
• GB/T 61215 series – Chinese national standards for photovoltaic module design qualification, aligned with the corresponding IEC documents.
• ISO/IEC 17025 – General requirements for the competence of testing and calibration laboratories performing the test.
• Additional end-user, OEM and industry technical specifications that define project-specific hail classes or impact energies.

Testing Samples

Photovoltaic Modules and BIPV Products

Crystalline silicon and thin-film modules, glass-glass and glass-backsheet laminates, bifacial modules, flexible modules and building-integrated photovoltaic (BIPV) components such as solar tiles and facades. These samples are evaluated for glass breakage, cell cracking and electrical performance retention.

Glass, Glazing and Transparent Covers

Tempered glass, laminated safety glass, coated low-emissivity glazing, skylights, greenhouse covers and sight windows. Testing focuses on fracture pattern, penetration resistance and post-impact structural stability.

Roofing, Cladding and Facade Materials

Roof tiles, metal roof sheets, asphalt shingles, composite panels, fiber-reinforced sheets and architectural cladding. Testing assesses denting, perforation, coating loss and water-tightness after impact.

Polymer Sheets and Films

Polycarbonate, PMMA (acrylic) and ETFE sheets, as well as protective films and encapsulant materials. Testing evaluates crack initiation, whitening, delamination and residual optical or mechanical properties.

Automotive, Rail and Aerospace Components

Exterior trim, mirror housings, sensor and radar covers, lamp lenses, sunroof glazing, rolling stock front panels and radomes. OEM specifications frequently define custom projectile sizes and impact energies beyond the public standards.

Testing Items

Depending on the specimen and applicable specification, the following parameters and results are typically reported:

• Hail impact resistance at specified ice ball diameter, mass, velocity and kinetic energy.
• Visual damage assessment: surface cracks, chips, spalling, delamination, denting and coating failure.
• Electrical performance retention for photovoltaic products, including maximum power degradation after impact.
• Insulation resistance and dielectric withstand after impact.
• Electroluminescence (EL) imaging to reveal hidden cell cracks not visible to the naked eye.
• Optical transmittance or haze change for transparent materials.
• Custom test programs with non-standard diameters, velocities, impact angles and specimen temperatures.

Testing Methods

Ice Ball Preparation and Conditioning

Ice projectiles are molded from deionized or distilled water into precise spherical forms, free of trapped air bubbles and surface defects. After demolding, the ice balls are conditioned in a freezer at approximately −10 °C, and their diameter and mass are verified before use. Proper conditioning is critical: ice that is too warm may deform on impact, while ice that is too cold can behave more aggressively than natural hail.

Launch System and Velocity Control

A pneumatic launcher accelerates the ice ball along a calibrated barrel toward the rigidly mounted specimen. Projectile velocity is measured immediately before impact using optical light gates, and it is maintained within a tolerance of typically ±5% of the specified value. Common test points derived from the international standards include:

• 25 mm ice ball at 23.0 m/s, corresponding to approximately 2 J of kinetic energy.
• 35 mm ice ball at 27.2 m/s, corresponding to approximately 7.5 J of kinetic energy.
• 45 mm ice ball at 30.7 m/s, corresponding to approximately 20 J of kinetic energy.
• Other standardized diameters ranging from 12.5 mm up to 75 mm, with corresponding velocities scaling from roughly 16 m/s to about 40 m/s.

Impact Procedure

The specimen is mounted in its normal orientation of use and impacted perpendicular to its surface at a predefined pattern of impact points. For full-size photovoltaic modules, this typically comprises 11 locations covering the corners, edges, center and areas near the junction box or other sensitive features, with one impact per location. Where visible damage occurs, additional impacts may be applied to characterize the failure. Specimens may also be conditioned at low temperature before testing to evaluate worst-case cold-impact behavior where required by the specification.

Post-Impact Evaluation

After testing, the specimen undergoes a structured evaluation: detailed visual inspection for major defects, electrical power measurement to quantify any performance loss, EL imaging of photovoltaic products to detect micro-cracks, and insulation or wet-leakage testing to confirm safety. Typical acceptance criteria require no major visual defects, maximum power degradation within the limit defined by the standard (commonly 5% or less), and intact electrical insulation. A comprehensive test report documents projectile parameters, impact coordinates, observed damage and conformity conclusions.

Applications

Hail impact resistance testing supports a wide range of industries and engineering decisions:

• Qualification and certification of photovoltaic modules for utility-scale solar plants and rooftop systems in hail-prone regions.
• Building product certification for glazing, skylights, roofing and facade systems exposed to severe weather.
• Automotive and commercial vehicle validation of exterior components, lighting systems and advanced driver-assistance sensor covers.
• Aerospace and railway applications where radomes, windows and exterior panels must survive airborne ice impacts.
• Research and development of impact-resistant materials, including chemically strengthened glass, laminated interlayers, tough polymers and energy-absorbing composites.
• Insurance, warranty and due-diligence assessments requiring independent, laboratory-verified hail durability data.

FAQ

What sample size is required for hail impact testing?

Photovoltaic testing is normally performed on full-size production modules. For materials such as glass, sheets or composites, representative panels of a negotiated size can be tested. Accredited third-party laboratories can confirm the appropriate sample dimensions and quantity for a specific standard or specification before testing begins.

How is the ice ball diameter and impact energy selected?

The severity is determined by the applicable standard or the hail class agreed with the end user. A 25 mm ball at 23.0 m/s is a common baseline for PV modules, while higher severities such as 35 mm or 45 mm balls are specified for products intended for severe-hail climates or premium durability ratings.

Can customized test conditions be applied?

Yes. In addition to standardized conditions, laboratories routinely perform tailored programs with non-standard projectile sizes, velocities, impact angles, specimen temperatures and impact locations to satisfy OEM or project-specific requirements.

What are the typical pass criteria?

For photovoltaic modules, the specimen must show no major visual defects, limited maximum power degradation as defined by the standard, and continued compliance with insulation requirements. For structural and transparent materials, criteria typically cover fracture, penetration, deformation limits and retained functionality.

How long does hail impact testing take?

Core testing and post-impact inspection are usually completed within a few working days, while full programs including specimen conditioning, electrical characterization, EL imaging and report issuance typically require one to two weeks depending on scope and queue conditions.

Why is EL imaging recommended after hail testing?

Cell micro-cracks caused by impact are often invisible to the naked eye yet can degrade long-term power output. Electroluminescence imaging reveals these hidden cracks, providing a more complete picture of hail durability and supporting robust pass or fail decisions.