Hail Impact Testing Procedure: Standards, Process, and Evaluation Methods

Hail impact testing evaluates the ability of solar modules, automotive components, and building materials to withstand mechanical damage from hailstones under controlled laboratory conditions. This article explains the complete hail impact testing procedure, from sample preparation and ice ball calibration to impact execution and post-test evaluation, in accordance with IEC 61215, ASTM E1038, UL 1703, and GB/T 9535 requirements.

Technical Overview

Hail impact testing is a destructive mechanical test that simulates the localized, high-velocity loading produced by natural hailstones. Frozen ice balls of specified diameter, mass, and temperature are propelled against a test specimen using a calibrated pneumatic launcher, transferring kinetic energy comparable to that of a real hailstorm. The test verifies whether a product retains its structural integrity, functional performance, and electrical safety after hail exposure. It is most widely applied to terrestrial photovoltaic (PV) modules, but it is also used for automotive glazing, exterior body panels, roofing materials, skylights, and aerospace components. Accredited third-party laboratories typically perform the test under ISO/IEC 17025 quality systems to support certification and market access.

• Primary PV standard: IEC 61215-2 (Test MQT 10 – Hail impact), European adoption EN 61215-2
• PV safety standards referencing impact resistance: IEC 61730-2, UL 1703, UL 61730
• Chinese national standard for terrestrial PV modules: GB/T 9535
• ASTM E1038: determining resistance of photovoltaic modules to impact by hailstones
• OEM and industry technical specifications for automotive, construction, and aerospace products

Testing Samples

Photovoltaic Modules

Full-size crystalline silicon, thin-film, bifacial, double-glass, flexible, and building-integrated photovoltaic (BIPV) laminates. Two identical modules are normally submitted: one for the impact sequence and one retained as a reference for performance comparison.

Automotive and Transportation Components

Exterior body panels, hoods, windshields and side windows, headlamp and taillight lenses, camera and sensor covers, mirror housings, and EV charging station enclosures. These parts are frequently tested in a cold-soaked condition to reproduce the worst-case winter scenario.

Building and Construction Products

Roofing tiles and membranes, skylights, curtain-wall and facade glass, polycarbonate and acrylic glazing, greenhouse panels, exterior doors, and rolling shutters.

Aerospace and Outdoor Equipment

Aircraft skin panels, radomes, antenna covers, outdoor electronics enclosures, and telecommunications cabinets exposed to severe weather environments.

Testing Items

A complete hail impact evaluation typically includes the following measurement items, performed before and after the impact sequence:

• Visual inspection for cracks, delamination, bubbles, broken glass, and external surface defects
• Maximum power determination (Pmax) at Standard Test Conditions (1000 W/m², 25 °C cell temperature, AM 1.5 spectrum)
• Electroluminescence (EL) imaging to reveal hidden cell micro-cracks
• Insulation resistance and wet leakage current testing to confirm electrical safety
• Dielectric withstand verification where required by the applicable safety standard
• Hail impact execution at the specified ice ball diameter, mass, velocity, and temperature
• Post-test performance comparison and pass/fail judgment against the defined criteria

Testing Methods

Step 1: Sample Reception and Pre-Test Characterization

Upon receipt, the laboratory records specimen identification and dimensions, performs an initial visual inspection, and stabilizes the sample at the specified ambient conditions. Baseline measurements are then taken, including maximum power at STC, EL imaging, and insulation or wet leakage tests as applicable. These baseline data establish the reference against which post-impact degradation is judged.

Step 2: Ice Ball Preparation

Ice balls are molded from deionized water that is free of trapped air bubbles, in order to achieve uniform density and predictable fracture behavior. Common nominal diameters include 25 mm, 35 mm, and 45 mm. The ice balls are frozen and stored at approximately −20 °C (within the range specified by the applicable standard) until fully equilibrated, and each batch is checked for diameter, mass, and freedom from cracks before use.

Step 3: Equipment Setup and Velocity Calibration

The specimen is rigidly mounted on a support frame with the target surface perpendicular to the firing axis of a pneumatic hail cannon. Compressed air pressure is adjusted so that the ice ball reaches the required impact velocity, which is measured by photoelectric sensor gates located immediately in front of the specimen. For the standard 25 mm ice ball, IEC 61215-2 specifies a velocity of 23.0 m/s, with heavier severities such as 35 mm at approximately 27 m/s and 45 mm at approximately 31 m/s available by agreement. Calibration shots confirm that the measured velocity remains within the tolerance of the standard, typically ±5%.

Step 4: Impact Point Mapping and Test Execution

Impact locations are marked according to the standard, typically covering eleven points that include the module corners, edges, center, cell corners and boundaries, and areas above the junction box or electrical terminations. Each point is struck once with a single ice ball at the specified velocity. The entire sequence is documented with high-speed video or photography so that the impact energy, point of contact, and any immediate damage can be traced.

Step 5: Post-Test Inspection and Evaluation

After the final impact, the specimen undergoes a full repeat of the pre-test characterization. Pass criteria under IEC 61215-2 generally require that no major visual defects are present, maximum power degradation does not exceed 5% relative to the initial measurement, EL imaging shows no significant new crack patterns beyond the allowable limit, and insulation and wet leakage tests continue to be satisfied. For non-PV products, acceptance is judged against the client specification, such as absence of fracture, penetration, or functional failure.

Step 6: Data Analysis and Report Issuance

The laboratory compiles all records into a formal test report containing sample identification, the standard applied, ice ball parameters (diameter, mass, temperature, velocity), the impact location map, photographic evidence, pre- and post-test performance data, and a clear pass/fail conclusion. Reports issued by ISO/IEC 17025-accredited third-party laboratories are accepted for certification schemes, buyer declarations, and regulatory market access.

Applications

Hail impact test results support a wide range of engineering and commercial objectives:

• Type-approval and certification of PV modules under IEC 61215, IEC 61730, UL 61730, EN 61215, and GB/T 9535 for global market access
• Design verification of impact-resistant materials such as chemically strengthened glass, tempered glass, coated polycarbonate, and composite panels
• Validation of automotive exterior components against OEM durability and field-damage requirements
• Aerospace qualification of airframe and radome structures for flight through convective weather
• Insurance loss-prevention assessments and root cause analysis of field failures after hailstorms
• Incoming quality control and mass-production consistency checks for manufacturers

FAQ

What ice ball sizes and velocities are most commonly used?

• The default severity in IEC 61215-2 is a 25 mm ice ball at 23.0 m/s. Higher severities, for example 35 mm and 45 mm ice balls at correspondingly higher velocities, can be selected for products installed in severe-hail regions or where the buyer specification requires it.

How many samples are required for the test?

• For PV modules, one module for the impact sequence plus a reference module is generally sufficient, although full IEC 61215 certification requires additional modules for the complete test sequence. For components and materials, the sample quantity is defined by the client or the referenced product standard.

What is the typical turnaround time?

• The impact sequence itself is usually completed within one or two working days. Including pre-test and post-test electrical characterization, EL imaging, and report preparation, a typical project cycle is five to ten working days after the samples are stabilized.

What are the pass criteria?

• For PV modules: no major visual defects, maximum power degradation within the specified limit (normally 5%), no excessive new cracking in EL imaging, and continued compliance with insulation and wet leakage requirements. For other products: no fracture, no penetration, and no functional failure as defined by the applicable specification.

Can products other than solar modules be tested?

• Yes. Accredited third-party laboratories routinely develop custom hail impact protocols based on ASTM E1038 or OEM requirements for automotive, construction, aerospace, and outdoor electronics products.