A hail impact test evaluates how photovoltaic modules, aerospace transparencies, automotive parts, and other outdoor products withstand the kinetic energy of striking hailstones. By launching calibrated ice balls at controlled velocities, this procedure verifies structural integrity, electrical safety, and functional performance under severe weather conditions. This guide explains the applicable standards, required specimens, tested parameters, and the complete step-by-step hail impact test procedure.
Technical Overview
A hail impact test, also known as an ice ball impact test, is a mechanical robustness procedure that simulates the damage caused by natural hailstorms. Standardized ice balls are launched at a specimen using a compressed-air launcher, and the specimen is subsequently examined for cracks, delamination, breakage of internal components, loss of electrical insulation, and degradation of performance. Because hail is one of the most common causes of field failure for glass-fronted and externally mounted products, this test is a core requirement in many certification and qualification programs.
The physical basis of the test is kinetic energy: the energy delivered to the specimen equals one half of the ice ball mass multiplied by the square of its velocity. For the most widely applied condition, defined in the IEC 61215 series for terrestrial photovoltaic modules, a 25 mm ice ball with a mass of 7.53 g is fired at 23.0 m/s, delivering approximately 2.0 J of impact energy at normal incidence.
The hail impact test is governed by several recognized standards, including:
- IEC 61215-2 / EN 61215-2 (MQT 10) — design qualification and type approval of terrestrial photovoltaic modules, hail resistance test
- GB/T 61215 series, GB/T 9535 and GB/T 18911 — Chinese national adoptions covering crystalline silicon and thin-film photovoltaic modules
- UL 1703 and UL/IEC 61730-2 — safety standards for flat-plate photovoltaic modules and panels, which include hail impact provisions
- ASTM F320 — hail impact resistance of aerospace transparent enclosures such as aircraft windshields and cabin windows
- Customer or industry technical specifications for automotive, rail, and telecommunication hardware, typically executed by accredited third-party laboratories
Testing Samples
Photovoltaic Modules and BIPV Components
Full-size PV modules are the primary specimens, including glass-glass and glass-backsheet laminates, bifacial modules, flexible modules, thin-film products, and building-integrated photovoltaic (BIPV) panels. The specimen must be complete with frame and glazing identical to the production configuration, since framing strongly influences impact behavior. Typically one or two modules are tested, depending on the standard and the severity level required.
Aerospace Transparent Enclosures
Aircraft windshields, side windows, canopy transparencies, and other flight-critical glazed components are tested per ASTM F320. Specimens are usually flat panels or representative curved sections cut from production tooling, complete with the actual laminate construction, interlayers, coatings, and edge attachments used in service.
Automotive Exterior Parts and Sensor Covers
Body panels, headlamp and signal lamp lenses, mirror housings, radar covers, camera windows for driver-assistance systems, and roof-mounted antenna modules are increasingly evaluated for hail resistance. Specimens are complete components mounted on representative support structures so that the stiffness of the real installation is reproduced.
Rail Transit and Outdoor Electrical Equipment
Exterior equipment on rolling stock and trackside installations, such as front camera housings, sensor enclosures, display units, outdoor distribution cabinets, and telecommunication equipment housings, are tested to confirm weatherworthiness. Specimens should include the actual enclosure material, windows, gaskets, and internal mounting of sensitive components.
Testing Items
Depending on the product type and the referenced standard, a hail impact test program typically covers the following items:
- Resistance to a single impact from a standard ice ball at prescribed diameter, mass, and velocity
- Determination of the threshold impact energy that causes visible damage or functional failure, using graded severity levels
- Post-impact structural integrity: glass cracks, through-cracks, delamination, cell breakage, dents, and coating damage
- Electrical safety retention: dielectric withstand and wet leakage current performance for photovoltaic and electrical products
- Performance retention: maximum output power measurement of PV modules after impact, with degradation limits defined by the standard
- Functional verification: optical transmission, sensor function, sealing integrity, and operation of the component after impact
Testing Methods
Test Apparatus and Environmental Conditions
The core equipment is a pneumatic hail gun consisting of a compressed-air reservoir, a launching barrel, and a velocity measurement system using paired optical gates or photodiodes located close to the target plane. Ice balls are produced in precision molds filled with purified or deionized water and are frozen in a chamber, commonly at approximately -20 °C, until fully solid. Immediately before use, representative ice balls from each batch are checked for diameter, mass, clarity, and proper hardness. The specimen is stabilized at ambient laboratory temperature, typically around 23 °C, unless the applicable standard or specification requires a different conditioning temperature. Testing is conducted behind a protective barrier, as ice balls exit the launcher at high speed and fragments scatter on impact.
Step-by-Step Hail Impact Test Procedure
- Step 1 — Specimen receipt and identification: record model, serial number, materials, and construction details; assign a unique test identification; and photograph the specimen in its as-received condition.
- Step 2 — Pre-test inspection and measurement: perform visual inspection, verify dimensions and mounting features, and, for PV modules, record initial electrical measurements such as maximum power at standard test conditions where required by the standard.
- Step 3 — Ice ball preparation: mold ice balls from purified water, freeze them to the conditioning temperature, and verify representative samples for diameter and mass against the specified nominal values, for example 25 mm and 7.53 g under IEC 61215-2.
- Step 4 — Launcher calibration: fire calibration shots through the velocity measurement gates and adjust the air pressure until the launch velocity is achieved at the target plane within the tolerance stated in the standard, for example 23.0 m/s for the 25 mm ball.
- Step 5 — Specimen mounting: fix the specimen to a rigid support frame in its normal service orientation, using the mounting points defined by the standard, and align the launcher barrel perpendicular to the impact surface at the specified standoff distance.
- Step 6 — Impact location marking: mark the prescribed impact points on the specimen. For PV modules under IEC 61215-2, eleven locations are defined, covering the glass corner, frame edges, corners of corner cells, the center of a corner cell, cell corners adjacent to the center, the module center, and the area above the junction box, with one impact delivered at each point.
- Step 7 — Execution of impacts: load a conditioned ice ball, confirm the velocity reading for each shot, and fire at each marked location in sequence. Each shot is documented with measured velocity, impact point, and observations such as shattering behavior of the ice ball or immediate visible damage.
- Step 8 — Post-test inspection: examine the specimen under adequate illumination for cracks, through-fractures, delamination, broken cells, exposed live parts, and damage to frames or edge seals. Photograph all impact locations and any defects found.
- Step 9 — Electrical and functional verification: repeat dielectric withstand and wet leakage tests for PV modules, re-measure maximum power output where required, and perform functional checks on optical, sensing, or sealing performance for other product categories.
- Step 10 — Reporting: compile the test report including specimen description, standard and severity level applied, ice ball parameters, measured velocities, impact location map, photographs, post-test measurement results, and a clear statement of compliance with the pass criteria.
Pass Criteria and Evaluation
Under IEC 61215-2, a module passes the hail test when inspection reveals no major visual defects, such as broken or badly cracked external surfaces, bends in the frame beyond acceptable limits, bubbles or delamination forming a continuous path between cells, or visible broken cells, and when insulation requirements such as the dielectric withstand and wet leakage tests continue to be met. For aerospace transparencies tested per ASTM F320, the evaluation focuses on the initiation of cracks, crazing, or interlayer damage at the specified impact energy. For automotive and electronic components, acceptance is defined by the customer specification and is usually based on the absence of through-cracks, retention of sealing, and preserved function after impact.
Extended Severity Levels
Where a product will be installed in regions with severe hail exposure, higher severity levels are applied by agreement between manufacturer, purchaser, and the accredited third-party laboratory. These levels use larger ice balls, commonly in the 35 mm to 50 mm class, with correspondingly higher impact energies, and may be combined with elevated or reduced specimen temperatures to bound the worst-case service condition. Impact energy is scaled by both the increased mass of the larger ball and the velocity specified for that diameter in the governing standard or specification.
Applications
Hail impact testing is applied across industries where products face outdoor weather exposure:
- Certification and type approval of crystalline silicon and thin-film photovoltaic modules for utility-scale, commercial, and residential power plants, particularly projects located in recognized hail corridors
- Qualification of building-integrated photovoltaic products, skylights, architectural glazing, and translucent roofing systems
- Aerospace qualification of windshields and cabin transparencies that must tolerate hail encounter during flight and ground operations
- Validation of automotive exterior components, lighting lenses, and camera or radar covers for advanced driver-assistance systems
- Verification of rail vehicle exterior equipment, outdoor electrical enclosures, telecommunications cabinets, and charging infrastructure installed in severe climates
FAQ
What ice ball sizes are used in a hail impact test?
The standard condition for photovoltaic modules is a 25 mm ice ball weighing 7.53 g, launched at 23.0 m/s. For severe-service qualifications, larger ice balls in the range of 35 mm to 50 mm or more may be specified, with the mass and velocity defined by the applicable standard or by agreement with the purchaser.
How many impact points are tested on a PV module?
Under IEC 61215-2, eleven impact locations are specified, distributed across structurally and electrically critical areas of the module, including corners, edges, cell corners, the module center, and the region above the junction box. One impact is delivered at each location.
Can a steel ball drop test replace the hail impact test?
No. Ice balls fracture on impact and transfer energy differently from a rigid steel ball, producing a different stress distribution in the target. The two tests are not equivalent, and certification standards require the ice ball method for hail resistance assessment.
Is the hail impact test destructive?
Yes. Specimens are subjected to high-energy impacts and are considered consumed by the test. Even specimens that pass are not returned to service, since hidden internal damage may compromise long-term reliability.
How long does the test take?
The ice ball freezing and conditioning stage typically requires at least 24 hours. Launcher calibration, the eleven-shot impact sequence, and post-test inspection and electrical verification are usually completed within one additional working day, with the full report issued shortly afterward by the accredited third-party laboratory.
Do all standards use the same test temperature?
No. IEC 61215-2 tests modules at ambient laboratory temperature with ice balls conditioned at subzero temperature before launching, while some customer specifications for automotive or rail components require impacts at low ambient temperature to represent winter hail events. The conditioning temperature must always follow the standard or specification cited in the test plan.