Hail Impact Testing Scheme: Standards, Test Methods, and Technical Requirements

Hail impact testing is a laboratory-based destructive test that simulates the kinetic energy of natural hailstones to evaluate how products such as photovoltaic modules, automotive glazing, and building envelope materials withstand hail strikes. This article presents a complete hail impact testing scheme, covering applicable standards such as IEC 61215-2 and ASTM E1038, sample types, test items, test methods, and acceptance criteria. It is intended to help manufacturers, project developers, and certification engineers establish a compliant, repeatable hail resistance verification program through accredited third-party laboratories.

Technical Overview

Hail impact testing reproduces the mechanical loading imposed by natural hailstones by launching engineered ice balls against a specimen surface at controlled velocities. The objective is to determine whether the product can absorb the corresponding impact energy without glass breakage, penetration, cracking, delamination, or unacceptable loss of performance. Because hail is one of the leading causes of field failure for outdoor products, particularly solar power plants located in hail-prone regions, this test has become a core element of design qualification, insurance due diligence, and product risk management.

The principal references for hail impact testing include IEC 61215-2 (terrestrial photovoltaic module design qualification, hail test MQT 17), ASTM E1038 (determining resistance of photovoltaic modules to hail by impact with ice balls), the regional adoptions EN 61215-2 and GB/T 61215.2, and EN 13583 (determination of hail resistance for flexible waterproofing sheets). Tests are typically performed by accredited third-party laboratories operating under ISO/IEC 17025 quality systems to ensure traceable and defensible results.

• Standard ice ball diameter: 25 mm, with a nominal mass of 7.53 g, for photovoltaic modules per IEC 61215-2
• Standard launch velocity: 23.0 m/s, verified within a tight tolerance of typically ±5% at the target plane
• Nominal impact energy: approximately 2 J delivered at the point of impact
• Enhanced protocols: 35 mm or 45 mm ice balls at correspondingly higher velocities for high-hail-risk deployment sites

Testing Samples

The scope of hail impact testing extends to any product exposed to atmospheric hail during its service life. Typical sample categories submitted to accredited third-party laboratories include the following.

Photovoltaic Modules and BIPV Products

Crystalline silicon and thin-film modules in glass-backsheet or glass-glass constructions, building-integrated photovoltaic laminates, solar roof tiles, and photovoltaic-thermal collectors. Full-size modules are tested in their as-manufactured configuration, including frame, encapsulant, and junction box.

Automotive Exterior Components

Windshields and panoramic roofs, headlamp and taillight lenses, radar and camera covers for driver assistance systems, painted body panels, and grille assemblies. Automotive programs are frequently executed against manufacturer-defined ice ball diameters, velocities, and impact zones.

Building Envelope and Roofing Products

Waterproofing membranes and shingles per EN 13583, skylights and translucent roofing panels, architectural glazing, polycarbonate and acrylic sheets, composite cladding, and coating systems.

Aerospace and Outdoor Electrical Equipment

Radomes and antenna housings, aircraft exterior panels, outdoor enclosures for power and telecommunications equipment, LED luminaire covers, and display signage intended for unsheltered installation.

Testing Items

A complete hail impact test scheme evaluates both structural integrity and functional performance before and after impact. Depending on the product category and applicable standard, the testing items typically include:

• Visual inspection before and after impact, covering glass breakage, surface cracks, delamination, and cell fractures
• Maximum output power (Pmax) measurement before and after impact to quantify power degradation
• Electroluminescence (EL) imaging to reveal hidden microcracks in photovoltaic cells
• Insulation resistance and wet leakage current verification to confirm electrical safety after impact
• Assessment of penetration, permanent deformation, and coating or seal damage
• Functional verification such as optical transmittance of sensor covers and watertightness of building products

Testing Methods

Ice Ball Preparation and Conditioning

Ice balls are cast from deionized water in precision molds of the specified diameter, producing spheres free of embedded air bubbles and cracks. Each ball is verified for diameter and mass before use. The balls are conditioned in a freezer at sub-zero temperature, typically in the range of -10 °C to -20 °C, so that they remain fully frozen at the moment of launch. Surface temperature is confirmed with an infrared thermometer, and each ball is launched promptly after removal from conditioning to prevent surface melting.

Launcher Calibration and Velocity Control

A pneumatic ice ball launcher using compressed air or nitrogen accelerates the ball through a barrel matched to the ball diameter. The launch pressure is calibrated against a velocity curve, and the actual velocity of each shot is measured immediately upstream of the target using light gates or a chronograph system. Impacts are delivered perpendicular to the specimen surface from a short, controlled standoff distance, and velocity deviations beyond the permitted tolerance invalidate the shot and require repetition.

Specimen Mounting and Impact Locations

Specimens are mounted in the orientation and support configuration defined by the applicable standard, reproducing realistic boundary conditions. For photovoltaic modules per IEC 61215-2, impacts are applied at a defined set of locations on the front surface, commonly 11 points covering the module corners, edges, center, and the region near the junction box, with one strike per location. Automotive, construction, and aerospace samples are tested at critical zones identified by the specification, and every impact coordinate is documented in the test report.

Post-Impact Evaluation and Pass Criteria

Following the impact sequence, the specimen undergoes visual inspection against major defect criteria, EL imaging, and repeat performance and safety measurements. Typical acceptance criteria for photovoltaic modules include absence of major visual defects, maximum power degradation within the limit defined by the standard, and continued compliance with insulation and wet leakage requirements. Glazing and construction products are commonly judged on the absence of penetration and the absence of damage in defined vision or protected zones.

Applications

Hail impact test results support a wide range of engineering, commercial, and regulatory decisions across industries:

• Design qualification and type approval of photovoltaic modules for utility-scale and commercial solar plants in hail-prone regions
• Enhanced hail resistance verification requested by insurers, lenders, and asset owners for project due diligence
• Research and development comparison of glass thickness, encapsulant materials, and module constructions
• Validation of automotive glazing, lighting, and driver assistance sensor covers for extreme weather robustness
• Certification and building code compliance of roofing membranes, skylights, and cladding systems
• Field failure analysis and root-cause verification following hailstorm damage claims

FAQ

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

The standard test per IEC 61215-2 uses a 25 mm diameter ice ball with a nominal mass of 7.53 g, launched at 23.0 m/s, delivering approximately 2 J of kinetic energy at the impact point.

Can the test simulate severe hailstorms with larger hailstones?

Yes. Enhanced protocols using 35 mm or 45 mm ice balls at proportionally higher velocities are routinely specified for high-hail-risk sites. These larger balls generate several times, and in the case of 45 mm balls more than ten times, the impact energy of the standard 25 mm test.

What are the typical pass criteria?

For photovoltaic modules, the specimen must show no major visual defects, power degradation within the limit set by the standard, and continued compliance with insulation and wet leakage tests. For glazing and building products, the typical criteria are no penetration and no functional damage in the specified zones.

Is hail impact testing mandatory for PV module certification?

Yes. The hail impact test is a mandatory sequence item (MQT 17) within IEC 61215-2 design qualification, and equivalent requirements exist in the regional adoptions EN 61215-2 and GB/T 61215.2.

How should samples be prepared and shipped?

Full-size production-representative samples should be supplied in the as-delivered configuration, packaged to prevent pre-test damage, and accompanied by manufacturer data sheets. The required sample quantity and impact point plan should be confirmed with the accredited third-party laboratory before shipment.