Hail-Resistant Solar Panels: Tests and Buying Checklist

Solar panels can withstand some hail, but a basic hail-test pass does not establish protection against every storm. For a hail-exposed project, compare the exact module bill of materials, impact-test conditions, mounting arrangement and operating strategy before selecting a product.

This guide is for rooftop and utility-scale PV buyers. It combines published laboratory findings with a practical document-review workflow. Laboratory results below belong to the named testing organizations; the worked purchasing example is illustrative.

What Does the Standard Solar Panel Hail Test Prove?

The commonly cited IEC 61215 baseline uses 25 mm ice balls at approximately 23 m/s, with 11 impacts at specified locations. DOE describes the basic pass in terms of no visible damage and less than 5% power loss. This is a summary, not the complete set of acceptance criteria: check the applicable standard edition and test report. Larger ice-ball conditions are also available. ^[1]

Source for diameter, mass and velocity: DOE. Energy is calculated as E = ½mv², with mass in kilograms, and rounded. These are controlled test conditions, not a prediction of every natural hailstone's speed or density. ^[1]

At these conditions, a 55 mm impact has about 23 times the energy of a 25 mm impact. That does not make one large strike equivalent to 23 smaller strikes: impact location, contact behavior and accumulated damage also matter.

Ask for the test conditions, not just “hail certified.” Specifying a diameter without velocity, mounting details and a defined pass criterion is an incomplete comparison.

What Independent Hail Tests Show

Kiwa PVEL's 2026 Reliability Scorecard reports glass breakage under 45 mm hail testing in 61% of tested 2.0 mm/2.0 mm glass modules, compared with 7% in its thicker-glass group. That group includes several constructions, not one universal glass specification. ^[2]

These are results from its tested population, not market-wide failure probabilities or a forecast for a particular project. PVEL also notes that alternative constructions had smaller sample sizes and that all three thicker-glass categories included some breakage at 50 mm. The purchasing lesson is to obtain the individual BOM report rather than infer performance from a category average.

Do invisible cell cracks always mean major power loss?

No. PVEL reports less than 2% power loss in all unbroken HSS-tested BOMs in its 2026 dataset. EL remains useful for documenting cell condition, but cracks alone do not establish a fixed degradation rate or automatic replacement need. ^[2]

Request before-and-after electroluminescence (EL) images, maximum-power measurements, visual findings and electrical safety results. If a report includes follow-on thermal cycling or hot-spot testing, check the actual sequence and results. RETC's published Hail Durability Test program includes these additional stress steps; they should not be assumed to be part of every hail test. ^[3]

When is testing to failure useful?

VDE and RETC's Hail Resiliency Curve approach tests samples to glass breakage and uses the results to characterize failure probability. This provides more detail than a single pass threshold. Request the tested BOM, sample count, impact locations, mounting configuration and uncertainty when comparing curves. ^[4]

Compare Glass, Frame and Mounting Together

Glass thickness is a useful screening factor, but it is not a complete product specification. Check the strengthening process and the entire module construction, including the rear layer, frame, dimensions and support arrangement.

• Glass: Confirm front and rear thicknesses and whether each pane is fully tempered or heat-strengthened.
• Frame and supports: Match the tested frame profile, support rails, clamp zones and mounting orientation.
• Impact locations: Check whether vulnerable regions near edges, corners and design features were evaluated. Do not assume that a strong center-impact result describes the whole module.
• Installation: Follow the model-specific manual for clamp type, engagement, torque and permitted spans.
• Weight: Include the proposed module mass in roof, racking and handling reviews.

A support bar or thicker glass may improve a particular design. Do not assign a universal percentage improvement without comparative testing. Likewise, a torque setting from another project should not replace the installation manual.

Verify That the Tested Panel Is the Panel You Will Receive

A model family can contain more than one bill of materials. A strong report is relevant only if its tested construction covers the proposed delivery.

1. Identify the report: Record the laboratory, report number, date, model designation, standard edition and test protocol.
2. Match the construction: Reconcile glass specifications, module dimensions, frame and other relevant BOM details with the quoted product.
3. Match the installation: Compare the laboratory mounting arrangement with the project layout and permitted installation conditions.
4. Check sampling: Ask how samples were selected, how many were tested and what production lots they represent.
5. Control changes: Include an agreed process for substitutions, supporting evidence and approval before shipment.

If detailed BOM information is confidential, request a laboratory or manufacturer statement linking the quoted configuration to the report, with controlled access for the project's technical reviewer.

Worked purchasing example: two “55 mm tested” offers

Illustrative scenario: Supplier A provides a one-page summary with no velocity or mounting description. Supplier B provides a report identifying impact conditions, the tested BOM, mounting arrangement, sample count and post-test results.

Supplier B offers a better basis for review, but neither offer should be approved solely on the “55 mm” label. First establish whether the tested configuration matches the delivered product and whether the evidence meets the site's requirements. Keep unresolved differences in the procurement record.

Check Whether Hail Stow Will Work at Your Site

Tracker stow can reduce exposure, but the target angle must account for hail direction, wind loading and equipment limits. Fixed rooftop arrays require a different response plan because their tilt cannot normally be changed before a storm.

Do not read tilt-angle calculations as guaranteed damage reductions. For vertically falling hail, a simplified model gives a normal kinetic-energy component proportional to cos²θ, where θ is module tilt from horizontal. The ratios are 25% at 60° and about 6.7% at 75°. These are geometric energy-component ratios, not measured reductions in breakage or insured loss.

Before accepting a stow strategy, document:

• The approved angle and wind/hail operating envelope.
• Weather-alert triggers and responsibility for activation.
• Measured time from alert receipt to confirmed row position.
• Backup power, communications failure behavior and position feedback.
• How conflicting wind and hail commands are resolved.

Use commissioning records to establish the required warning lead time. A generic number of minutes is not evidence that a particular plant will reach its protective position.

Use a Supplier Checklist Before Signing

Start with a site-specific hail assessment. A historical maximum is an observation, not a dependable upper limit for future storms. Set the design target with the project's technical adviser, considering the operating life and consequences of failure.

What to send the supplier

Please provide the hail-test evidence for the exact module model and BOM quoted for our project. Include report identity, test protocol, ice-ball diameter and mass, impact velocity and energy, impact locations, mounting arrangement, sample count, glass-breakage findings, before-and-after power and EL results, and applicable electrical safety results.

Please identify any differences between the tested configuration and the proposed delivery, along with installation restrictions, warranty exclusions and the process for approving BOM changes. Our request includes the site location, proposed layout, mounting spans and tracker details where applicable.

Keep warranty and insurance reviews separate

A test pass is not a promise of claim payment. Check the actual module warranty and project policy independently, including exclusions, deductibles, sublimits, operating obligations and required evidence. Do not assume either document defines coverage through a single hail-diameter threshold.

Retain serial-number maps, commissioning records and baseline condition evidence. After a storm, preserve weather and stow logs, photographs and inspection results. Qualified personnel should assess damaged equipment before electrical testing or return to service.