Hail Impact Test Parameter Determination: Standards, Methods and Key Measurements

Hail impact test parameter determination establishes the measurable variables—ice ball diameter, mass, launch velocity and kinetic energy—that control the severity and reproducibility of hail resistance testing. Accurate determination of these parameters is essential for qualifying photovoltaic modules, building envelope products and automotive components against recognized standards such as IEC 61215-2, ASTM E822 and EN 13583. This article reviews the governing standards, applicable sample types, measurement items, calibration methods and typical applications of hail impact testing.

Technical Overview

Hail impact testing reproduces the mechanical loading imposed by natural hailstones by projecting man-made ice balls against a specimen at a controlled velocity. The severity of the test is defined by a small set of quantifiable variables: the ice ball diameter, the ice ball mass, the impact velocity, and the resulting kinetic energy calculated as E = 1/2mv². Parameter determination is the process of measuring and controlling these variables with traceable instruments and documented tolerances, which is what converts an impact demonstration into a repeatable, engineering-grade test.

Accredited third-party laboratories typically perform hail impact testing under standards published by IEC, UL, ASTM, EN, GB and JIS organizations. The most widely applied procedure for photovoltaic modules is the hail impact test (MQT 17) of IEC 61215-2:2016, which is also referenced by IEC 61730-2, UL 61730 and the Chinese national standard GB/T 9535. The key parameters that must be determined before and during the test include:

• Ice ball diameter and geometric tolerance
• Ice ball mass, effective density and structural integrity
• Launch velocity measured at or close to the impact plane
• Kinetic energy delivered per impact
• Ice ball and specimen temperatures
• Impact position, incidence angle and total number of impacts

Testing Samples

Photovoltaic Modules and Solar Collectors

Crystalline silicon and thin-film photovoltaic modules, either full size or representative laminates with production-grade glass, encapsulant, backsheet and frame, are the most common specimens. Glazed flat-plate solar thermal collectors can also be evaluated using ice sphere impact methods described in ASTM E822.

Building Envelope and Roofing Products

Waterproofing membranes tested over their designated substrate in accordance with EN 13583, together with roof tiles, skylights, architectural glazing, translucent façade panels, protective coatings and exterior cladding systems, form the second major sample group.

Automotive and Transport Components

Body panels, painted closures, windshields, lamp lenses, radar and LiDAR covers, and mirror housings are mounted on representative support structures so that impact response reflects real vehicle boundary conditions.

Aerospace, Electrical and Outdoor Equipment

Radomes, composite leading edges, antenna covers, outdoor telecommunications enclosures and EV charging equipment enclosures are tested to verify hail resistance in exposed service environments. Specimens are generally conditioned to a defined temperature before testing, and impacts are applied normal to the exposed surface.

Testing Items

The following items must be determined, verified and recorded for every hail impact test campaign:

• Ice ball dimensional verification — diameter measured with calibrated calipers or optical gauges against the standard tolerance
• Mass determination — each ice ball weighed on a calibrated balance, commonly required to fall within about ±5 % of the nominal mass for its size class
• Ice integrity check — rejection of balls containing cracks, large air pockets or visible inclusions that alter effective density
• Velocity determination — projectile speed measured immediately before impact using light barriers or equivalent timing devices
• Impact energy calculation — kinetic energy computed from measured mass and velocity for each shot
• Temperature conditioning — ice ball storage temperature, commonly at or below about −10 °C, and specimen conditioning temperature
• Impact location and count — verification of aiming accuracy and the prescribed number of impacts per specimen
• Post-impact evaluation — visual inspection, maximum power measurement and insulation or wet leakage testing for electrical products, with electroluminescence imaging optional for crack detection in photovoltaic devices

Testing Methods

Ice Ball Preparation and Verification

Ice balls are cast from distilled or deionized water in precision spherical molds and frozen under controlled conditions to produce clear, dimensionally accurate ice. Before use, every ball is conditioned at low temperature, inspected for defects, and its diameter and mass are measured and logged. Balls that deviate from tolerance or show internal cracking are discarded, because both variables directly change the delivered impact energy.

Launcher Calibration and Velocity Determination

A compressed-air launcher fires the ice ball toward the clamped specimen, with launch velocity regulated through air pressure. Velocity is measured immediately upstream of the target using two light barriers separated by a known distance, from which speed equals distance divided by transit time. For each ball size, laboratories establish a pressure–velocity calibration curve and verify shot-to-shot repeatability, typically holding measured velocity within approximately ±5 % of the nominal value. Impact perpendicularity and aim point are also verified before formal testing.

Standard Parameter Combinations

IEC 61215-2 defines matched sets of diameter, mass and velocity that laboratories use as calibration targets; comparable values appear in GB/T 9535. Representative combinations include:

• 25 mm ball, approximately 6.8 g, 23.0 m/s, about 1.8 J
• 35 mm ball, approximately 20 g, 27.2 m/s, about 7.5 J
• 45 mm ball, approximately 42.5 g, 30.7 m/s, about 20 J
• 55 mm ball, approximately 77 g, 33.9 m/s, about 45 J
• 65 mm ball, approximately 125 g, 36.7 m/s, about 84 J
• 75 mm ball, approximately 193 g, 39.5 m/s, about 151 J

Where a product specification or regional hail climate demands a different severity, the required velocity is determined by rearranging the energy equation for the target kinetic energy of the selected ball mass, followed by launcher calibration at the resulting set point.

Test Execution and Evaluation

The conditioned specimen is rigidly mounted in its normal orientation and subjected to a defined number of impacts, commonly ten per photovoltaic module in IEC 61215-2, distributed over prescribed critical locations such as cells near the frame corners, quarter-line intersections and the area above the junction box. After the final impact, the specimen undergoes visual inspection for major defects, electrical performance measurement where applicable, and insulation or wet leakage verification to confirm that dielectric integrity has been maintained.

Applications

• Type approval and safety certification of photovoltaic modules under IEC 61215-2, IEC 61730-2, UL 61730 and GB/T 9535
• Enhanced hail resilience programs for modules destined for hail-prone regions using 45 mm to 75 mm ice balls
• Qualification of roofing membranes and waterproofing systems against hail loading per EN 13583 and related EN test methods
• Validation of solar collector cover materials following ASTM E822 practice
• Design verification of automotive glazing, painted panels and sensor covers exposed to roadside hail impact
• Comparative material studies on glass thickness, encapsulant selection, coating adhesion and composite layup
• Correlation of physical test results with finite element impact simulations for product development
• Root-cause analysis of field hail damage and insurance-related damage assessments performed by accredited third-party laboratories

FAQ

What is hail impact test parameter determination?

It is the systematic measurement and control of the variables that define hail test severity—ice ball diameter, mass, velocity, temperature, impact location and impact count—so that tests are accurate, repeatable and comparable between laboratories.

How is the impact velocity of an ice ball measured?

Velocity is measured just before impact using photoelectric light barriers spaced a known distance apart; the measured transit time yields the speed, which is then compared with the tolerance band required by the applicable standard.

Why must ice ball temperature be controlled?

Ice hardness and fracture behavior vary strongly with temperature. Conditioning balls at a defined low temperature, commonly at or below about −10 °C, ensures consistent mechanical response and therefore consistent energy transfer to the specimen.

Which hailstone size is most commonly used for solar panels?

The 25 mm ice ball at 23 m/s is the baseline requirement in IEC 61215-2, while larger sizes from 35 mm to 75 mm are specified when modules must demonstrate enhanced resistance for severe hail climates.

What are typical pass criteria after a hail impact test?

Acceptance is typically based on the absence of major visual defects such as glass breakage or cell cracks visible to the unaided eye, minimal or no degradation of maximum power output, and continued compliance with insulation resistance requirements.

Can hail impact testing be combined with other environmental tests?

Yes. Hail impact testing is frequently embedded within full qualification sequences that include thermal cycling, damp heat and humidity-freeze exposure, allowing assessment of how environmental aging affects subsequent impact resistance.