Photovoltaic Glass Impact Resistance Testing: Standards, Methods and Applications

Photovoltaic glass impact resistance testing verifies that solar glass covers and finished PV modules can withstand hailstones, wind-borne debris, and accidental mechanical shocks throughout a 25-plus-year service life. This technical guide explains sample requirements, test items, and internationally recognized test methods based on IEC, UL, ASTM, EN, GB and JIS standards, as performed by accredited third-party laboratories and in-house quality teams worldwide.

Technical Overview

Photovoltaic (PV) glass is the outermost functional and protective layer of a solar module. In crystalline silicon modules it is typically a 2.0 mm to 4.0 mm soda-lime-silica glass, fully tempered or heat-strengthened, often with an anti-reflective (AR) coating and a textured or rolled surface. Because the front glass is continuously exposed to hail, wind-borne debris, falling objects, handling shocks and vandalism, its impact resistance directly determines module safety, reliability and long-term energy yield.

Impact resistance testing simulates these mechanical threats under controlled laboratory conditions and evaluates whether the glass cracks, punctures or breaks in a safe pattern. The most widely applied standards include the IEC 61215 series (design qualification, including the hail resistance test), the IEC 61730 series (safety qualification), UL 1703 and UL 61730 for the North American market, ANSI Z97.1 for safety glazing, EN 12150 and EN 12600 for heat-treated and laminated glass in Europe, GB 15763.2 and GB/T 5137.1 in China, JIS R 3206 in Japan, and ASTM C1048 for heat-treated flat glass.

• Verify resistance to cracking, penetration and fracture under defined impact energy levels.
• Confirm that any breakage occurs in a safe, small-fragment pattern rather than large shards.
• Confirm that impacted modules remain electrically safe, with insulation and dielectric integrity intact.
• Support product certification, factory quality control and bankability documentation for PV projects.

Testing Samples

Fully Tempered (Toughened) PV Glass

The most common test article is 3.2 mm or 4.0 mm fully tempered cover glass with low-iron content. For steel-ball drop testing, standard-size panels such as 610 mm × 610 mm coupons are typically prepared with cut and edge-finished boundaries representing production conditions.

Heat-Strengthened and Thin Glass

Heat-strengthened glass, increasingly used in lightweight and 2.0 mm thin-glass module designs, is tested to characterize its different breakage behavior. Because it fragments into larger pieces than tempered glass, its post-impact safety must be evaluated carefully.

Laminated and Double-Glass Configurations

Laminated PV glass—two glass plies bonded with EVA, POE or PVB interlayers, as used in bifacial double-glass modules—is tested for interlayer adhesion and post-breakage integrity, since the interlayer must retain fragments after fracture.

Coated and Textured Glass

AR-coated, patterned or rolled-glass samples are tested to confirm that surface treatments and textures do not degrade impact performance or cause coating spallation under impact.

Finished PV Modules

Full-size modules are submitted for type testing under IEC 61215-2 (hail resistance) and IEC 61730-2 or UL 61730 safety requirements, where impact tests are followed by visual, electrical and dielectric evaluations.

Testing Items

• Steel-ball drop impact resistance (rigid-body impact on bare glass panels).
• Hail impact resistance using calibrated ice balls fired at controlled velocities.
• Soft-body impact resistance using shot-bag or twin-tyre pendulum methods.
• Fragmentation (break pattern) test after induced fracture of tempered glass.
• Post-impact dielectric withstand, insulation resistance and wet leakage checks at module level.
• Post-impact power degradation and visual defect assessment at module level.

Testing Methods

Steel Ball Drop Test

A hardened steel ball of specified mass is dropped freely from a defined height onto the horizontally supported glass sample. Quality-control and certification procedures commonly use balls such as 227 g or 1040 g with drop heights of 1 m to 2 m, depending on the applicable standard and glass thickness. The specimen passes if it does not break, and any breakage mode is recorded for break-pattern analysis. Test parameters and sample quantities follow standards such as GB 15763.2, GB/T 5137.1 and ANSI Z97.1.

Hail Impact Test (Ice Ball Method)

Following the hail resistance test of IEC 61215-2, ice balls of specified diameter—25 mm as the standard reference size, with 35 mm or 45 mm options for severe-climate projects—are conditioned to approximately −4 °C and propelled by compressed air at controlled velocities (about 23 m/s for the 25 mm ball, higher for larger diameters). The ice balls strike the module at multiple defined positions covering corners, edges and cell areas. Pass criteria require no major visual defects such as through-cracks, with electrical and power-retention limits applied within the module test sequence.

Pendulum and Shot-Bag Impact Test

Soft-body impact methods evaluate glazing against human-body or debris loading. In the EN 12600 pendulum method, a twin-tyre impactor of 50 kg is released from heights of 190 mm, 450 mm or 1200 mm, and the glass is classified accordingly. Shot-bag drop methods under ANSI Z97.1 deliver defined impact energy to verify that fragments do not create hazardous sharp edges.

Fragmentation Test

To confirm safe breakage behavior of tempered glass, specimens are fractured with a pointed tool and the fragment count within a 50 mm × 50 mm counting zone is recorded, together with limits on maximum fragment dimensions. Minimum particle counts are thickness-dependent and are specified in standards such as GB 15763.2, EN 12150 and JIS R 3206.

Module-Level Impact and Post-Test Evaluation

Under UL 61730 and UL 1703 requirements, a hardened steel ball is dropped onto the module glass surface at designated locations. After impact, the module must show no exposure of live parts and must pass a dielectric withstand test, demonstrating that mechanical damage does not create an electrical hazard.

Applications

Impact resistance testing is applied across the entire PV value chain. Glass manufacturers use ball-drop and fragmentation tests for routine factory quality control and batch release, while module manufacturers rely on hail and safety impact tests for IEC, UL and GB certification of new products. Testing is equally critical for emerging designs, such as 2.0 mm lightweight glass and bifacial double-glass modules, where reduced thickness requires verified impact margins.

• Certification and bankability documentation for utility-scale and rooftop projects.
• Project-specific qualification for hail-prone or cyclone-exposed regions.
• Research and development of thinner glass, new coatings and new interlayer materials.
• Insurance claims support and root-cause failure analysis after storm or hail damage.
• Incoming material inspection and supplier comparison for module assembly plants.

FAQ

Q: Which standard governs hail testing for PV modules? A: IEC 61215-2 specifies the hail resistance test using ice balls fired at defined velocities, with 25 mm diameter at approximately 23 m/s as the standard condition; IEC 61730-2 references equivalent safety considerations.

Q: What sample sizes are required? A: For glass-level ball-drop tests, panels of approximately 610 mm × 610 mm are typical, while hail and safety impact tests are performed on full-size production modules.

Q: How do tempered and heat-strengthened glass differ in impact behavior? A: Fully tempered glass has higher compressive surface stress and fractures into small, relatively harmless particles, whereas heat-strengthened glass breaks into larger fragments but offers better post-breakage handling in laminated constructions.

Q: Can testing be performed on finished modules rather than bare glass? A: Yes. Module-level testing per IEC 61215-2, IEC 61730-2 and UL 61730 evaluates the glass together with encapsulant, cells and backsheet, and adds electrical safety checks after impact.

Q: How are ice balls prepared for hail testing? A: Ice balls are molded from water, conditioned in a freezing environment at approximately −4 °C, weighed and measured, and their launch velocity is verified before each impact to ensure repeatable kinetic energy.