Ice Ball Impact Test Method: Standards, Equipment, and Procedures for Hail Impact Resistance Evaluat

The ice ball impact test method is a standardized laboratory procedure used to evaluate the resistance of photovoltaic modules, glazing, and other exterior materials to hailstone impacts using projectiles of calibrated size, mass, and velocity. Governed primarily by IEC 61215-2, GB/T 9535, and ASTM E1038, this test simulates severe hailstorm conditions to verify product durability, safety, and long-term reliability. This article explains the test principle, specimen requirements, equipment, step-by-step procedures, acceptance criteria, and typical applications.

Technical Overview

The ice ball impact test, also known as the hail impact test, is a destructive mechanical test in which spherical ice projectiles are propelled against a specimen at controlled velocities to simulate the effects of natural hail. It is most widely applied in the design qualification and type approval of terrestrial photovoltaic (PV) modules, where it forms an essential part of the environmental and mechanical stress test sequence defined in IEC 61215-2 (test MST 16), the Chinese national standard GB/T 9535, and ASTM E1038.

Natural hailstones vary in diameter from a few millimeters to well over 50 mm and can strike surfaces at velocities exceeding 30 m/s. Because field exposure to hail is random and unrepeatable, the test replaces natural hail with machine-made ice balls produced from clean water in precision molds. Each projectile is launched perpendicular to the specimen surface by a compressed-air launcher, and its velocity is measured immediately before impact. By standardizing the diameter, mass, temperature, and speed of the projectile, the method provides reproducible impact energies that allow different products, designs, and manufacturing batches to be compared on an equal basis.

The principal international and national references for this method include:

• IEC 61215-2, Terrestrial photovoltaic (PV) modules – Design qualification and type approval – Part 2: Test procedures (hail/ice ball impact test, MST 16)
• IEC 61215-1, which defines the pass criteria and visual defect categories applied after the test
• GB/T 9535 and the GB/T 61215 series, the Chinese national adoptions covering crystalline silicon and thin-film terrestrial PV modules
• ASTM E1038, Standard Test Method for Determining the Resistance of Photovoltaic Modules to Impact by Propelled Ice Balls
• EN 61215 series, the European implementation of the corresponding IEC test procedures

The canonical projectile parameters used in the IEC-based procedures are summarized below. Each impact delivers kinetic energy ranging from approximately 2 J for the smallest sphere to more than 60 J for the largest.

• 25 mm diameter, nominal mass 7.53 g, launch velocity 23.0 m/s, impact energy approximately 2.0 J
• 35 mm diameter, nominal mass 20.7 g, launch velocity 27.2 m/s, impact energy approximately 7.7 J
• 45 mm diameter, nominal mass 43.9 g, launch velocity 32.9 m/s, impact energy approximately 23.8 J
• 55 mm diameter, nominal mass 80.2 g, launch velocity 39.5 m/s, impact energy approximately 62.6 J

Testing Samples

Photovoltaic Modules

Crystalline silicon and thin-film PV modules with glass front sheets, glass-glass laminates, and flexible front encapsulation are the primary test subjects. Complete modules with their final frame configuration, junction box, and cables are tested so that all load-bearing and fracture-sensitive components are evaluated in their assembled state.

Building-Integrated Photovoltaics and Laminated Glazing

Glass laminates intended for curtain walls, skylights, canopies, and BIPV facades are tested because hail strikes on vertical and inclined architectural surfaces are a common service hazard. Polycarbonate and PMMA transparent covers used in greenhouses, walkways, and agrivoltaic installations are also frequently evaluated with this method.

Roofing and Cladding Components

Rigid roofing assemblies, transparent roof panels, protective covers for outdoor equipment, and coated metal or composite cladding elements may be assessed using propelled ice ball procedures adapted from the PV module standards or referenced in product-specific specifications.

Automotive and Transportation Exterior Parts

Exterior trim, sensor windows, light covers, and other components exposed to road debris and hail can be evaluated by vehicle manufacturers using ice ball impact techniques as part of internal durability specifications derived from the same general principle.

Testing Items

Depending on the product standard and the purpose of the evaluation, the following items are typically verified as part of an ice ball impact test campaign:

• Projectile conformance: ice ball diameter, mass, surface quality, and temperature prior to launch
• Velocity verification: measured impact speed within the tolerance band of the standard, typically ±5% of the nominal value
• Impact point accuracy: strikes delivered at the prescribed locations on the specimen surface
• Post-impact visual inspection: detection of broken glass, cell cracks visible through the front surface, delamination, bubbles, or other major visual defects
• Electrical performance: measurement of maximum output power before and after impact to quantify degradation
• Electrical safety: dielectric withstand or wet leakage current verification after the mechanical insult
• Structural integrity: optional electroluminescence (EL) imaging to reveal hidden cell cracking

Testing Methods

Principle of the Test

Spherical ice balls manufactured from clean, preferably distilled or deionized water are accelerated by a compressed-air launcher and directed normal to the surface of the test specimen. The launch pressure is adjusted until the measured velocity at the target plane matches the value specified for the selected ice ball diameter. A defined pattern of impact points covering structurally critical and statistically vulnerable areas of the specimen is struck, after which the specimen is examined for damage and, where applicable, retested electrically.

Ice Ball Preparation

• Ice balls are molded from clean water in two-part spherical molds that produce smooth, crack-free spheres free of embedded air bubbles.
• The finished diameter and mass of each sphere are checked against the nominal values, and spheres exhibiting chips, cracks, or irregular surfaces are rejected.
• Ice balls are conditioned in a freezer at the low temperature specified by the applicable standard and are transferred to the launcher immediately before firing so that their temperature does not change appreciably in flight.
• Each sphere is used for one impact only; deformed or partially melted balls are never reused.

Apparatus and Calibration

• A compressed-air cannon or pneumatic launcher fitted with a barrel whose bore matches the ice ball diameter, equipped with a rapid-acting release mechanism.
• An optical velocity measurement system, such as paired light gates or a ballistic chronograph, positioned close to the specimen so that the speed at the moment of impact is recorded for every shot.
• A rigid support or mounting frame that holds the specimen at the required orientation, typically with the impact direction perpendicular to the face.
• Calibrated instruments for measuring ice ball dimensions, mass, and temperature, and for recording ambient conditions in the test area.
• The launch pressure for each velocity setting is established in advance by calibration shots, and the velocity of every impact is verified and documented.

Specimen Conditioning and Mounting

Specimens are normally tested at ambient laboratory temperature in the state in which they are supplied, complete with frames and accessories. The specimen is mounted so that the impact face is exposed to the launcher at the specified standoff distance, and the support conditions follow the applicable standard so that the response of the product, rather than the fixture, is being evaluated. Relevant identification data, orientation, and pre-test measurements such as maximum power are recorded before firing begins.

Impact Procedure

• Select the ice ball diameter and corresponding velocity appropriate to the required severity level and the product specification.
• Mount a conditioned ice ball in the launcher and fire it at a designated impact point, confirming that the measured velocity lies within the permitted tolerance.
• Repeat the process at each of the prescribed impact points, which typically include corners, edge regions, the geometric center, locations above individual cells, and areas above junction boxes or bypass diodes, as defined in the applicable standard.
• Any shot that misses the intended point, glances off an edge, or falls outside the velocity tolerance is repeated with a fresh ice ball.
• After the final impact, allow the specimen to stabilize, dry any residual moisture, and proceed to evaluation.

Post-Impact Evaluation and Acceptance Criteria

Following the impacts, the specimen is examined visually under good illumination for major defects such as broken front glass, cracked cells visible through the superstrate, delamination extending beyond allowable limits, or damage that endangers operation or safety. For PV modules, electrical measurements are repeated and compared with the baseline values recorded before the test; the degradation of maximum output power must remain within the limit defined by the applicable standard or product specification. Insulation or wet leakage tests are often performed afterward to confirm that the mechanical impacts have not compromised electrical safety. A specimen that exhibits no major visual defects, satisfies the electrical performance limits, and passes the safety verification is considered to have withstood the test.

Applications

The ice ball impact test method supports a broad range of engineering and commercial objectives:

• Design qualification and type approval of PV modules for utility-scale, commercial, and residential power plants under the IEC 61215 framework
• Research and development of stronger front glasses, encapsulants, cell interconnection schemes, and module architectures resistant to hidden cracking
• Incoming and outgoing quality control for glass suppliers and module manufacturers, including comparison of production batches
• Certification support for building-integrated photovoltaic products installed on facades and roofs exposed to hail-prone climates
• Durability assessment of greenhouse covers, skylights, transparent noise barriers, and outdoor equipment enclosures
• Project-specific verification, where developers and insurers require evidence of hail resistance beyond the standard severity levels, using larger or faster projectiles under agreed test plans
• Failure analysis, where the test is used to reproduce field damage mechanisms and validate corrective design actions

Accredited third-party laboratories routinely perform this test as part of full IEC 61215 sequences or as a stand-alone assessment for manufacturers, system developers, and certification bodies.

FAQ

What is the ice ball impact test used for?

It is used to demonstrate that a product, most commonly a photovoltaic module, can withstand the mechanical loading imposed by hailstones of a defined size and speed without suffering breakage, excessive power loss, or electrical safety hazards.

Which standards specify the ice ball impact test?

The principal references are IEC 61215-2 (test MST 16) together with IEC 61215-1 for pass criteria, the GB/T 9535 and GB/T 61215 series in China, ASTM E1038 in the United States, and the EN 61215 series in Europe.

How are the ice balls made and controlled?

They are cast in precision spherical molds from clean water, inspected for diameter and mass, and conditioned at a standardized low temperature in a freezer. Each ball is fired once, and its temperature and velocity are verified at the time of launch.

What ice ball sizes and velocities are used?

The standard series couples each diameter with a target velocity: 25 mm at 23.0 m/s, 35 mm at 27.2 m/s, 45 mm at 32.9 m/s, and 55 mm at 39.5 m/s, corresponding to impact energies of roughly 2 J, 7.7 J, 23.8 J, and 62.6 J respectively. The severity level is selected according to the product specification or the expected service environment.

How is the impact velocity verified?

An optical velocity measurement system located close to the specimen records the speed of every projectile, and the result must fall within the tolerance band of the standard, typically ±5% of the nominal velocity. Launch pressure is calibrated in preliminary shots and confirmed shot by shot.

Where on the specimen are the impacts applied?

The applicable standard defines a set of impact points covering structurally sensitive areas such as corners, edges, cell centers, and regions above junction boxes or bypass diodes. Each point receives a single calibrated impact unless a product specification requires otherwise.

What are the pass criteria?

A specimen passes if it shows no major visual defects such as shattered front glass or visible cell breakage, its maximum power degradation remains within the specified limit, and post-test insulation or wet leakage verification confirms continued electrical safety.

Can the test severity be increased beyond the standard levels?

Yes. For installations in exceptionally hail-prone regions or for premium product classes, test plans may specify larger ice balls, higher velocities, or additional impact points. These extended conditions should be agreed between the manufacturer, the purchaser, and the testing laboratory and documented in the test report.

How does the ice ball test differ from the mechanical load test?

The mechanical load test applies a quasi-static, uniformly distributed pressure to simulate snow and wind, whereas the ice ball test applies localized, high-speed dynamic impacts that concentrate energy on small areas. The two tests are complementary and are both included in the IEC 61215 sequence because they excite different failure modes.

What information appears in a typical test report?

A compliant report identifies the specimen and standard used, records the ice ball diameters, masses, temperatures, and measured velocities for every shot, documents the impact point map, and presents the visual, electrical, and safety inspection results together with an explicit statement of pass or fail.