Hail Impact Resistance Evaluation of Photovoltaic Modules: Standards, Methods and Acceptance Criteri

Glass-glass bifacial modules are tested with ice ball impacts directed at the front (illumination) side as required by the standard. Rear-side impact evaluation can be added as a customer-specified option, since both covers may be exposed to hail in tracking or high-tilt installations.

Thin-Film, Flexible, and Lightweight Modules

CdTe, CIGS, and amorphous silicon products, as well as flexible laminates with polymer front sheets, are evaluated with the same apparatus. For these products the failure modes shift toward front-sheet penetration and absorber damage, so post-test imaging and electrical checks are especially important.

General sample requirements include: one or two modules in as-delivered condition (including original packaging where relevant), complete product documentation (datasheet, drawing, bill of materials), and baseline characterization (visual inspection, power at STC, and electroluminescence imaging) performed before the impact test.

Testing Items

A complete hail resistance evaluation typically comprises the following items:

• Visual inspection before and after impact, evaluated against the major visual defect categories of IEC 61215-1 (broken glass, cracked cells, delamination, bubbles, backsheet holes, junction box damage).
• Maximum power determination at STC before and after testing (measurement per IEC 60904-1 with a solar simulator of class per IEC 60904-9), with degradation calculated relative to the initial value.
• Electroluminescence (EL) imaging before and after testing (per IEC TS 60904-13) to reveal hidden cell cracks that do not produce visible damage.
• Insulation resistance and, where required, wet leakage current testing per IEC 61730-2 to confirm that electrical safety is maintained after mechanical insult.
• Ice ball dimensional, mass, and velocity verification, including launcher calibration against the tolerances of IEC 61215-2.
• Optional extended evaluations such as infrared thermography for hot-spot screening and rear-side or oversized-ball impact campaigns for site-specific risk profiles.

Testing Methods

Sample Preparation and Baseline Characterization

The module is stabilized at laboratory ambient temperature, visually inspected, and electrically characterized. Power at standard test conditions and an EL image are recorded as the reference baseline. Any pre-existing anomaly is documented so that test-induced changes can be unambiguously attributed to the hail impacts.

Ice Ball Preparation and Launch Calibration

Ice balls are molded from purified water, conditioned in a freezer to approximately −10 °C, and inspected for sphericity, diameter, and mass within the tolerances of the standard. A compressed-air hail cannon propels each ball toward the module; impact velocity is measured with optical light gates just before contact and must fall within the specified tolerance (typically ±5%) of the target value. Aim points are confirmed with calibration shots onto a witness target prior to testing the module.

Impact Procedure

The module is rigidly mounted in its normal orientation and struck perpendicular to the surface at a minimum of 11 prescribed locations, covering the module corners, corners of selected cells, the central region, areas adjacent to the frame, and the zone above the junction box. The baseline severity is the 25 mm / 23.0 m/s ice ball specified in IEC 61215-2; enhanced severities using 35 mm to 75 mm ice balls at proportionally higher velocities and energies (from a few joules up to more than one hundred joules) are applied when project specifications or insurance requirements demand them. Each impact is documented with its location, measured velocity, and observed result.

Post-Test Evaluation and Acceptance Criteria

After the final impact, the module is re-inspected visually, re-measured for power at STC, and re-imaged by electroluminescence. Insulation and wet leakage tests verify continued electrical safety. The module is judged to pass when no major visual defect as defined in IEC 61215-1 is present, power degradation does not exceed the specified limit (typically 5% for this test), and no safety-relevant damage is detected. Any glass fracture over active cells, cell cracks producing dark EL signatures, or loss of insulation constitutes a failure requiring design remediation and retest.

Applications

Hail resistance evaluation supports a wide range of industry activities:

• Certification and design qualification of PV modules within the full IEC 61215 test sequence required for market access in most regions.
• Site selection and engineering for utility-scale and commercial plants located in hail-prone areas, where enhanced ball sizes are specified to match local meteorological records.
• Insurance underwriting, risk engineering, and lender due diligence, where documented hail test reports strengthen the technical bankability dossier of a project or product.
• Research and development of more resilient module architectures, including glass thickness optimization, encapsulant selection, frame and support design, and crack-tolerant cell interconnection.
• Comparative benchmarking by project developers, EPC contractors, and asset owners when qualifying module suppliers against specific procurement specifications.
• Forensic reference after real-world hail events, providing a standardized basis for judging whether observed field damage is consistent with the certified hail resistance class of the affected modules.

FAQ

Which standards govern PV module hail testing?

The primary standard is IEC 61215-2, test MQT 16, which is part of the international design qualification sequence for terrestrial PV modules. ASTM E1038 offers an equivalent ice-ball impact method frequently referenced in North America, and IEC 61730 / UL 61730 covers the electrical safety verification performed after the impact test.

What ice ball size and velocity are used in the standard test?

The baseline test uses a 25 mm diameter ice ball weighing 7.53 g launched at 23.0 m/s, corresponding to roughly 2 J of impact energy per strike. Larger ice balls from 35 mm up to 75 mm are available for enhanced-severity programs targeting high-risk sites.

How many impact points are applied?

A minimum of 11 impact locations is prescribed, distributed across the module corners, corners of selected cells, the central area, frame-adjacent regions, and the junction box zone, ensuring that both the strongest and most vulnerable structural areas are challenged.

What are the pass criteria?

The module must show no major visual defects, a maximum power degradation within the standard limit (typically no more than 5% versus the initial measurement), and continued compliance with insulation and wet leakage requirements. EL imaging is used to confirm the absence of significant hidden cell cracks.

Can hail resistance be verified for modules already installed in the field?

Direct ice-ball impact testing is a laboratory procedure performed on representative production samples. For fielded arrays, EL imaging, power measurements, and thermal inspection after a storm are used to assess damage, and the results are interpreted against the laboratory hail test classification of the installed module type.

How long does the evaluation take?

For a single module at standard severity, including baseline characterization, impact testing, and final measurements, results are typically issued within one to two weeks. Extended or multi-severity campaigns, or tests integrated into the full IEC 61215 sequence, require additional time as defined in the agreed test plan.