Hail impact testing evaluates the ability of photovoltaic modules, roofing systems, automotive components, and other outdoor products to withstand high-energy impacts from ice projectiles. This technical guide explains the key hail impact test specifications defined by international standards such as IEC 61215-2, ASTM E1038, UL 2218, and EN 13583, covering test samples, procedures, parameters, and acceptance criteria. Understanding these specifications helps manufacturers, developers, and quality engineers ensure compliant, verifiable hail resistance before products enter the field.
Technical Overview
A hail impact test is a controlled mechanical-impact procedure in which ice balls of specified diameter, mass, and velocity are launched against a specimen to simulate hailstone strikes. The purpose is to verify that the product retains its structural integrity, sealing performance, and—depending on the product type—electrical and optical functions after exposure to representative hail loading. Because hailstone kinetic energy scales with the cube of the diameter and the square of the velocity, even small increases in ice ball size dramatically raise the severity of the test, which is why specifications define these parameters precisely.
Natural hailstones range from a few millimeters to over 75 mm in diameter, with terminal velocities of roughly 15 to 45 m/s. Laboratory specifications condense this range into discrete severity levels, typically from 12.5 mm up to 75 mm ice balls, delivering impact energies from less than 1 joule to more than 100 joules. The most widely applied hail impact test specifications include:
- IEC 61215-2 (MQT 17) – Hail impact test for terrestrial photovoltaic (PV) modules, the baseline for solar module design qualification.
- IEC 61730-2 – PV module safety qualification, which references hail impact requirements.
- ASTM E1038 – Determining the resistance of photovoltaic modules to impact by hailstones using propelled ice balls.
- ASTM E822 – Practice for mounting photovoltaic modules to replicate hail damage conditions.
- UL 2218 – Impact resistance of roof covering materials using dropped steel balls as a hail surrogate.
- EN 13583 – Determination of hail resistance for flexible waterproofing sheets.
- GB/T 9535 – Chinese national standard for terrestrial PV module design qualification, aligned with IEC 61215.
Tests are performed by accredited third-party laboratories operating under ISO/IEC 17025 quality management, or by manufacturers' in-house laboratories for research and pre-certification screening.
Testing Samples
Photovoltaic Modules
Crystalline silicon and thin-film PV modules, building-integrated photovoltaic (BIPV) laminates, solar tiles, and photovoltaic glass are the most frequently tested sample types. Specimens should be complete, production-representative modules with final framing, junction box, and encapsulation, since the glass, encapsulant, and cells act together as an impact system. Typical sample quantities are one to three modules per test level, plus a reference module for electrical benchmarking.
Roofing and Waterproofing Materials
Bituminous and polymer membranes, metal roofing sheets, concrete and clay tiles, shingles, skylights, and architectural glazing are tested to verify resistance to penetration, cracking, and delamination. Samples must include the full installed build-up—substrate, insulation, membrane, and fastening—to replicate real boundary conditions.
Automotive Components
Body panels, windshields and lamp lenses, paint and coating systems, radar and camera covers, and exterior trim parts are validated against OEM-specified hail severities. Specimens are conditioned and mounted at the installation angles used on the vehicle.
Aerospace, Rail, and Outdoor Equipment
Radomes, aircraft leading-edge skins, train cab windows, LED street luminaires, HVAC outdoor units, telecommunications enclosures, and EV charging stations are tested when hail exposure threatens safety or service continuity.
Testing Items
The following parameters and result items are specified and recorded in a hail impact test:
- Ice ball diameter, mass, and density (typically verified at approximately 0.85–0.92 g/cm³).
- Ice ball temperature, commonly –4 °C ± 2 °C at the moment of launch.
- Impact velocity and resulting kinetic energy, with velocity tolerance generally within ±5%.
- Number and location of impacts, applied to the most vulnerable points such as corners, edges, unsupported spans, cell centers, and busbar intersections.
- Specimen temperature and mounting orientation during the test.
- Post-test visual inspection for cracks, fractures, delamination, and permanent deformation.
- Electrical performance verification for PV modules, with maximum power degradation limited to 5% of initial values under IEC 61215-2.
- Insulation resistance and dielectric withstand verification after impact for safety-relevant products.
- Auxiliary diagnostics such as electroluminescence (EL) imaging to reveal hidden cell cracks in PV modules.
Testing Methods
Ice Ball Preparation
Ice balls are molded from distilled or deionized water, free of bubbles and cracks, and conditioned in a freezer until they reach the specified temperature. Before use, each ice ball is measured for diameter and mass to confirm that density and dimensional tolerances comply with the applicable standard.
Launch and Measurement Apparatus
A pneumatic launcher—commonly called an ice ball gun—accelerates the ice ball using compressed air toward the clamped specimen. Optical light gates or an equivalent chronograph measure the velocity immediately before impact, and the kinetic energy is calculated and compared with the specified level. The launch direction is perpendicular to the specimen surface, and the impact point accuracy is typically required within a few millimeters.
Standard Test Sequence
- Condition specimens to the specified temperature and record initial measurements (visual, electrical, dimensional).
- Mount the specimen with support fixtures that reproduce the intended installation condition.
- Verify ice ball parameters and calibrate launcher velocity before each series.
- Apply impacts at the defined locations—for example, the 11-point pattern specified for PV modules in IEC 61215-2 MQT 17, using a 25 mm ice ball at 23 m/s (approximately 2 J) as the baseline severity, with higher classes such as 35 mm at 30.7 m/s (approximately 9.5 J) or 45 mm balls (20 J and above) for hail-prone sites.
- Perform post-test inspection: visual examination, EL imaging, maximum power measurement, and insulation testing as applicable.
- Issue a test report documenting parameters, impact coordinates, observed damage, and pass/fail judgment against the acceptance criteria.
Alternative Methods
For roofing products, UL 2218 replaces ice balls with steel balls dropped from heights of up to approximately 6 meters (20 feet), assigning impact resistance classes from Class 1 to Class 4. EN 13583 similarly provides a graded hail resistance determination for waterproofing sheets. These surrogate methods trade the physical realism of ice for repeatability and simpler equipment, and the applicable product standard dictates which method is authoritative.
Applications
Hail impact test specifications support a wide range of engineering and commercial objectives:
- Certification of PV modules under IEC 61215-2 and IEC 61730-2 for market access, incentive programs, and bankability reviews.
- Building envelope compliance, where impact-rated roofing and glazing are required by codes or insurers in hail-prone regions.
- Automotive validation of exterior components against OEM durability specifications for hail-exposed markets.
- Product development and benchmarking, comparing glass thickness, encapsulants, frame designs, and coating systems.
- Warranty substantiation and root-cause analysis following field hail events, using laboratory reproduction of the impact conditions.
- Procurement qualification, enabling project owners and EPC contractors to specify measurable hail resistance levels in technical requirements.
FAQ
Which standard governs hail impact testing for solar modules?
IEC 61215-2, test MQT 17, is the internationally recognized hail impact test for terrestrial PV modules. In China, GB/T 9535 defines the equivalent national requirement, and ASTM E1038 provides an alternative method based on propelled ice balls.
What ice ball size and velocity are used in the baseline test?
The baseline IEC 61215-2 test uses a 25 mm diameter ice ball at 23 m/s, delivering roughly 2 joules of kinetic energy. Higher severity classes—such as 35 mm at 30.7 m/s or 45 mm and larger balls for severe-hail regions—are specified when the installation site warrants greater impact energy.
What are the pass criteria for PV modules?
A module passes if it shows no major visual defects (broken glass in a hazardous manner, cracked backsheet, delamination), the maximum power degradation does not exceed 5% relative to the initial measurement, and it continues to pass the insulation and dielectric withstand requirements. EL imaging is commonly used to detect latent cell cracking.
Is hail impact testing mandatory?
It is mandatory within IEC-based PV certification schemes and is frequently required by building codes, insurers, and utility-scale tender specifications in hail-affected regions. Even where not legally required, it is strongly recommended as part of durability qualification.
How does the ice ball method differ from the steel ball method?
The ice ball method reproduces the actual density, brittleness, and energy transfer of natural hail, giving realistic damage patterns. The steel ball method, such as UL 2218 for roofing, offers excellent repeatability and simpler equipment but represents a harder, non-fracturing projectile. Product standards define which method applies.
How many samples are needed and how long does testing take?
Most specifications require one to three production-representative specimens plus reference measurements. After ice ball preparation and velocity calibration, the impact sequence itself is short; including pre- and post-test electrical characterization and EL imaging, a complete test is typically completed within a few working days.