IEC 61215 hail test vs Kiwa PVEL hail stress sequence: what each proves

The IEC 61215 hail test fires 11 ice balls of 25 mm at 23.0 m/s, about 2 J each, then checks for visible damage, insulation faults and power loss. Nearly every module passes. Kiwa PVEL and RETC use ice balls from 35 to 60 mm and report glass breakage, which is what separates modules for hail-prone sites.

What does the IEC 61215 hail test (MQT 17) test?

MQT 17 is the hail test in IEC 61215-2:2021, edition 2.0, published on 24 February 2021 by the International Electrotechnical Commission (IEC). MQT stands for module quality test.

The standard ball is 25 mm at 23.0 m/s, as the US Department of Energy (DOE) tabulates. RETC (Renewable Energy Test Center), a US test laboratory, puts the energy at about 2 joules (J) per impact, at 11 impact points. Larger balls are optional, but the DOE notes manufacturers rarely publish results at those sizes.

The introduction to IEC TS 63397 lists four requirements after the impacts. There must be no intermittent open-circuit fault and no major visual defect. Wet leakage current must stay within its initial limit, and power loss within the Gate No. 2 limit of IEC 61215-1:2021 (clause 7.2.3). The DOE describes the power bar as a loss of under 5%.

What does a pass prove, and what does it not?

A pass proves a floor: 11 impacts of about 2 J cause no visible damage, insulation fault or large power loss. The same IEC introduction says MQT 17 suffices where modules are unlikely to meet severe hail. It adds that the IEC 61215 series is not written to detect later power loss from invisible cell micro-cracks.

Three gaps matter for hail-prone sites:

• Energy. A 45 mm ball carries 20.7 J, about ten times the IEC ball.
• Sample size. RETC says the test often runs on one or two modules. Kiwa PVEL says its earlier two-module, 11-point test could only separate "atypically bad" from "normal" modules.
• Output. The result is pass or fail, with no ball size at which the glass breaks.

What does the Kiwa PVEL hail stress sequence add?

It adds larger balls and a breakage rate. Kiwa PVEL's Hail Stress Sequence (HSS) uses lab-made ice balls of 35 to 55 mm. It sits in the Product Qualification Program (PQP) behind the annual PV Module Reliability Scorecard, whose 12th edition, published on 27 May 2026, is the latest as of October 2026.

Under PQP version 11, each bill of materials (BOM, the exact set of module components) saw two ball sizes on two modules each. A 2.0 mm glass//glass BOM started at 40 mm, then two further modules took 35 mm if glass broke or 45 mm if not. Glass//backsheet BOMs started at 50 mm and moved to 55 mm if none broke or to 45 mm if glass broke. Load, thermal cycling and humidity-freeze steps after the hail became optional, because the power loss they revealed was small.

A Top Performer must not break glass at 40 mm or larger. As of October 2026, 23% of BOMs had an HSS failure in the 2026 Scorecard, meaning breakage at both ball sizes or a retest request.

Since April 2026 Kiwa PVEL's test page describes a test to failure called Hail-TTF. The same five modules take each size in turn until glass breaks. Sizes run from 35 to 45 mm for non-fully tempered glass and from 45 to 55 mm for fully tempered glass.

How does RETC test hail?

RETC's Hail Durability Test (HDT) is an optional sequence in its Thresher Test programme. RETC describes eight modules taking 10 impacts at five locations each, in four two-module groups with balls of 45, 50.8, 55 and 60 mm. All eight then take 50 thermal cycles between 85 °C and -40 °C and the IEC hot-spot test. Electroluminescence (EL) imaging, visual inspection and power measurement bracket each stage, and products are graded Class A (best) to D.

In RETC's 2024 report, Class A means under 1% power loss at the end, and a high achiever must also withstand at least 20 J. RETC's 2025 Hail Resiliency Curve Test fires ever larger balls until the glass breaks.

IEC has its own add-on, IEC TS 63397:2022. It applies 200 hours of damp heat, then hail, then dynamic load, thermal cycling and humidity freeze, and compares power loss with unhailed reference modules. IEC does not plan to add it to IEC 61215.

How do the main hail tests compare?

They differ most in ball energy, sample size and what is reported.

Is there a hail size rating for solar panels?

No single one. IEC gives pass or fail at 25 mm, Kiwa PVEL reports breakage by ball size and RETC grades Class A to D. Switzerland's cantonal fire insurers (VKF) have mapped IEC 61215 tests with 45, 55 and 65 mm balls to hail classes HW 3, HW 4 and HW 5 since October 2025.

Why do glass thickness and module construction matter?

Thin glass breaks first. As of October 2026, Kiwa PVEL's Scorecard shows 43% of 2.0 mm glass//glass modules breaking at 40 mm hail and 61% at 45 mm. The table adds the number of modules tested (n) from the Scorecard chart.

The thicker-glass n sums the chart's three groups. The comparison is not like for like. Under the version 11 sequence, the 61% describes BOMs that had already passed 40 mm. Kiwa PVEL's chart also shows more than 40% breakage at 50 mm for 3.2 mm glass//backsheet (n = 16) and 3.2 mm glass//2.0 mm glass (n = 14).

RETC's 2024 report says 2.0 mm glass is too thin to be fully tempered on most production lines. It adds that glass of 3.2 mm or more is fully tempered and roughly twice as resilient. The DOE advises at least 3.2 mm front glass.

Broken glass is the loss that counts. As of October 2026, every unbroken BOM in the Scorecard's hail data lost under 2% power. Glass//glass keeps cells near the neutral plane, and multi-busbar cells limit the damage when glass//backsheet modules crack. Two BOMs with extreme induced cracking lost 4.7% and 3.8%. The degradation calculator compares a one-off loss of that size with long-term degradation.

Bifacial buyers face a trade. RETC says the risk is worse for larger bifacial modules with 2.0 mm glass on both sides. Rear-side gain depends on ground reflectance (bifacial gain vs albedo) and should be weighed against the glass specification.

How much do module size, frame and mounting matter?

Larger formats add risk. IEC TS 63397 says the trend to larger cells and modules may add to hail power loss. The DOE says 60-cell modules limit damage while 72-cell and 144-cell formats may be at higher risk.

Edges matter too. Kiwa PVEL finds glass near edges and junction-box holes breaks more often than glass at the centre, which is why Hail-TTF aims there. The DOE favours stronger frames, rear support bars and framed over frameless modules.

The DOE says a steeper tilt reduces hail damage, which the stow section below covers.

How big is the hail risk in Europe and Hungary?

The European Severe Storms Laboratory (ESSL) logged a record 10,092 hail reports for 2024. It counts 243 days of large hail (2 cm or more) and 101 days of very large hail (5 cm or more) that year. For Hungary in 2024, ESSL lists hail reaching 8 cm on 22 June and 5 cm on 13 July. The same review records hail damage to solar panels in Italy and Austria. A peer-reviewed analysis of the same database counts 903 large-hail reports (2 cm or more) on 226 large-hail days in Hungary from 2000 to 2020. It notes that report quality varies by country.

The National Chamber of Agriculture (NAK) runs Hungary's hail suppression system with 986 ground generators that release silver iodide to shrink hailstones. NAK says hail can never be ruled out, and its damage figures are farmland claims, not solar parks.

HungaroMet names hail among the thunderstorm hazards at all three warning levels. Alerts usually come half an hour to three hours ahead, for areas of at least half an average county.

How does hail stow work on a solar tracker?

A hail stow rotates a single-axis tracker to a steep tilt before the storm, so hailstones strike at a glancing angle. The DOE cites a study of one tracker system where a 60° tilt raised survival likelihood from 82% to 99% versus flat panels. It adds that higher tilt raises wind load and that 60° is not practical on fixed-tilt systems, a trade covered in trackers vs fixed tilt.

The evidence comes from US sites. In March 2024 in Fort Bend County, Texas, three solar farms with 2.0 mm//2.0 mm dual glass and a 52° stow met radar-estimated hail of 40 to 100 mm. Damage was minor, from debris and from rows that failed to stow. Radar tends to overestimate hail size, and kWh Analytics warns that simple physics models may overstate the benefit of stow by 48% for hail of about 7.5 cm.

VDE Americas verified an Arkansas site in April 2025 where stow signalled within a minute of each alert. In the 2025 Solar Risk Assessment it recommends stow where the return interval for hail of 45 mm or more is under 100 years. Stow would use regional alerts plus a project-specific service. A kWh Analytics simulation put the cost of stowing at 60° through every severe thunderstorm alert at 0.1% of annual revenue for a Texas tracker site.

How do insurers treat hail damage to solar farms?

Insurers treat hail as a leading solar loss and have tightened terms. In kWh Analytics' US loss database, hail caused 73% of loss value from 6% of incidents, and the DOE calls severe hail the greatest contributor to insured solar losses worldwide. Kiwa PVEL says insurers now apply large deductibles, payout limits and exclusions, such as no cover for modules with cell cracks.

In Hungary, insurer Colonnade notes that hail damage means replacing panels, costly and slow for large parks, and advises higher-resistance panels at the design stage.

What this means for module selection and insurance in Hungary

• Treat the IEC pass as an entry ticket. It shows minimum hail qualification, not survival of the hail ESSL records in Hungary.
• Ask for the hail report of the exact BOM. Glass, frame, size and mounting all change the result. The DOE advises asking for proof of a test above the IEC minimum.
• Match test energy to site hazard. Hail of 8 cm exceeds every ball in the Kiwa PVEL and RETC programmes, and 5 cm sits near the top. No test result removes the need for a site hazard study, stow and cover.
• Price the options together. Thicker glass, tracker stow and tilt angle each change expected loss. Compare them with the policy's deductible, sub-limits and cell-crack terms.
• Ask the broker what is credited. Ask whether glass specification, verified stow and tilt change the premium, deductible or sub-limits.

Limits of this explanation

• Lab balls strike at set angles and speeds. Real hail is irregular, wind-driven and varies within one storm.
• Scorecard figures are as of October 2026 and change with each annual edition. Scorecard and Module Index results cover the BOMs that manufacturers chose to submit, and a changed glass supplier or frame can change the result.
• The loss, stow and insurance figures come from US insurers and laboratories. They show how the mechanisms work, not what Hungarian sites will pay or lose.
• This is not engineering or insurance advice. The methods page lists the data sources used across this site.