IEC 61730 Hail Impact Test: Requirements, Procedures, and Certification Guidelines for Photovoltaic

The IEC 61730 hail impact test is a critical safety evaluation that verifies whether photovoltaic modules can withstand mechanical damage from falling hailstones without compromising electrical safety. This article explains the technical basis of IEC 61730-2 MST 32, including ice ball specifications, impact energy levels, test procedures, pass criteria, and its role in PV module certification for hail-prone markets. Understanding these requirements helps manufacturers design durable, certifiable solar products and helps buyers select modules proven to survive severe weather.

Technical Overview

IEC 61730 is the international safety qualification standard for terrestrial photovoltaic (PV) modules, published in two parts: IEC 61730-1, which defines construction requirements, and IEC 61730-2, which defines the sequence of safety tests (MST tests). Within this sequence, the hail impact test (MST 32) subjects a fully assembled PV module to controlled impacts from artificially manufactured ice balls fired at high velocity, simulating the mechanical stress of a real hailstorm.

The purpose of the test is not merely to assess cosmetic damage. It is a safety test: hailstones striking the front glass or polymeric front sheet can cause cracks, delamination, cell fracture, or exposed conductive parts, any of which can create electric shock, fire, or performance hazards over the module lifetime. The test method is harmonized with the hail resistance test described in IEC 61215-2, and it uses the same ice ball launch equipment, target positioning, and impact energy classes.

The test severity is defined by the ice ball diameter, mass, and impact velocity. The standard severity levels most commonly applied are:

• 25 mm diameter, approximately 7.5 g, at 23.0 m/s, delivering about 2.0 J of impact energy
• 35 mm diameter, approximately 20.7 g, at 27.2 m/s, delivering about 7.7 J of impact energy
• 45 mm diameter, approximately 43.9 g, at 30.7 m/s, delivering about 20.7 J of impact energy
• 55 mm diameter, approximately 81 g, at 33.9 m/s, delivering about 46.6 J of impact energy

The 25 mm level is the default severity for general safety certification, while higher levels are selected when modules will be installed in regions with documented severe hail exposure or when project specifications, insurers, or buyers demand enhanced resilience.

Testing Samples

Crystalline Silicon Modules

Standard glass-front, polymer-backsheet modules based on monocrystalline or polycrystalline cells represent the majority of samples tested. The full-size production module, complete with frame, junction box, cables, and connectors, is tested exactly as it would be shipped and installed.

Glass-Glass and Bifacial Modules

Double-glass laminates, including bifacial designs, are evaluated for front-side impact resistance. The stiffer structure and heavier front cover of these constructions can change crack propagation behavior, so dedicated testing is essential for certification.

Thin-Film Modules

Cadmium telluride, CIGS, and amorphous silicon modules are tested with the same ice ball parameters. Their typically thinner glass and different laminate architecture make them sensitive to impact-induced fracture and edge chipping, which the test is designed to reveal.

Flexible and Lightweight Modules

Modules with polymeric front sheets or flexible substrates may be impacted while mounted on a representative rigid support structure, as specified by the manufacturer's installation instructions, because support conditions strongly influence impact response.

Building-Integrated PV (BIPV) Products

Glazing laminates, solar roof tiles, and façade elements installed in or on buildings often require elevated hail severity levels, since replacement after hail damage is costly and building codes in many hail-prone jurisdictions impose stricter impact requirements.

Testing Items

The hail impact test is evaluated through a defined set of inspections and measurements performed before and after the impacts:

• Visual inspection before testing, to record the initial condition and confirm the absence of pre-existing major visual defects
• Initial electrical performance measurement at Standard Test Conditions (STC) to establish the baseline maximum power
• Initial insulation resistance verification, confirming the module passes the insulation test prior to mechanical stressing
• Dimensional and mass verification of each ice ball, confirming diameter, sphericity, and mass within tolerance
• Velocity verification of each launched ice ball using calibrated speed measurement equipment at the impact plane
• Post-test visual inspection, checking for broken glass, cracked cells, torn front sheets, exposed live parts, and any other major visual defect
• Post-test maximum power measurement, with degradation evaluated against the allowable limit
• Post-test insulation test and wet leakage current test, confirming that electrical safety is preserved even in wet conditions after impact damage

Testing Methods

Sample Preparation and Conditioning

Complete modules are conditioned in the laboratory at controlled ambient temperature prior to testing. The module is mounted according to the manufacturer's declared mounting method, typically using the standard mounting holes or clamping zones, so that the support conditions reflect real installation. The front surface is oriented perpendicular to the launch barrel at every impact point.

Ice Ball Manufacturing and Verification

Ice balls are molded from distilled or deionized water that has been boiled and cooled to remove dissolved air, producing clear, defect-free ice free of bubbles and cracks. The frozen projectiles are stored at a temperature between -10 °C and -40 °C. Before firing, each ice ball is checked for diameter, sphericity, and mass to confirm compliance with the severity class selected for the test. A shattered, chipped, or non-conforming ice ball is discarded.

Launch and Impact Procedure

A pneumatic hail cannon launches each ice ball at the module surface using compressed air. Optical velocity sensors positioned immediately in front of the module measure the speed of every projectile, and the measured velocity must fall within the tolerance band around the specified value; out-of-tolerance shots are repeated. Impacts are distributed across the module according to the standard's defined impact pattern, which covers 11 locations including module corners, edges, the centre of the module, and areas near the junction box and electrical terminations. One impact is delivered at each location, and the ice ball typically shatters on contact, dispersing its kinetic energy into the laminate.

Post-Impact Evaluation and Pass Criteria

After all impacts are completed, the module undergoes visual inspection, power measurement at STC, and insulation-related safety tests. To pass the IEC 61730 hail impact test, the module must meet all of the following conditions:

• No major visual defects, such as broken glass through which the interior is exposed, cracked cells visible through the front cover in a manner affecting safety, or delamination extending to functional safety relevance
• No exposed live parts or accessible conductive components resulting from the impacts
• Maximum power degradation within the allowable limit defined by the applied standard sequence
• Successful completion of the insulation test and wet leakage current test after impact
• Continued compliance with the construction and safety requirements of IEC 61730-1

A module that fails any of these criteria must undergo design modification, such as tempered glass of increased thickness, enhanced encapsulant selection, or revised framing, before retesting.

Applications

Hail impact testing under IEC 61730 supports a wide range of industry needs:

• Certification of PV modules for safety marks and market access in regions where hailstorms are common, including North America, Central Europe, India, Australia, and parts of China
• Utility-scale solar project qualification, where lenders, engineering firms, and owners specify elevated hail severity levels to protect long-term energy yield
• Insurance risk assessment, with underwriters increasingly requiring documented hail test evidence before covering plants in high-risk hail corridors
• BIPV and rooftop product approval, where building codes and municipal regulations reference hail impact performance for exterior construction elements
• Research and development, enabling manufacturers to compare glass types, encapsulants, cell layouts, and support structures under repeatable, quantified mechanical loading
• Quality control and failure analysis, reproducing field hail damage in the laboratory to validate root cause conclusions and corrective actions

FAQ

What is the difference between the hail test in IEC 61730 and IEC 61215?

The physical test method is essentially identical and harmonized between the two standards. The difference lies in the evaluation focus: IEC 61215 evaluates whether the module continues to perform (design qualification and performance), while IEC 61730 evaluates whether the module remains electrically safe after hail impact. Most certification programs apply both standards in a combined test sequence.

Which hail severity level should my module be tested to?

The 25 mm ice ball at 23 m/s is the standard default severity. Higher levels (35 mm, 45 mm, or 55 mm) are recommended when the installation site has a documented history of large hail, when project specifications demand it, or when insurability of the plant depends on demonstrated hail resistance.

How many impacts are applied to a module?

The standard procedure applies one ice ball impact at each of 11 defined locations on the module, covering corners, edges, the centre, and regions near the junction box and terminations. Additional impacts may be performed when specified by the client or required for investigative purposes.

Are the ice balls real hailstones?

They are artificial ice balls molded from deionized water to controlled dimensions and mass, stored at low temperature before launch. Their density, hardness, and impact behavior closely approximate natural hailstones, and their controlled consistency gives the test its repeatability.

What happens if a module fails the hail impact test?

Failure indicates that hail damage could compromise electrical safety or performance. Manufacturers typically respond by increasing front glass thickness or strength, adjusting encapsulant and cell design, or improving frame and support stiffness, after which the module is retested to demonstrate compliance.