Hail damage to the photovoltaic system: detect, document & settle

After a hailstorm many solar systems appear outwardly undamaged – yet they are not. Microcracks in the solar cells develop without visible glass breakage but lead to gradual yield loss and jeopardise insurance cover. This guide explains how to reliably detect hail damage, why thermography is the only legally sound documentation method and what operators must do immediately after a hail event.

Visible and invisible damage – why the first look is misleading

A hailstorm passes over your commercial PV system. The next morning you go up to the roof and see: the protective glass of the modules is intact. No crack, no impact mark. Was it just rain? Unfortunately not – and this situation is more dangerous than an obvious glass breakage.

Hailstones transfer kinetic energy to the module glass on impact. With sufficient energy the glass breaks immediately – this is visible and typically triggers an insurance report. With lower energy or smaller hailstones the glass remains outwardly intact but the solar cells underneath suffer Mikrorisse (Micro-Cracks). These are not detectable with the naked eye, not even when viewed directly in sunlight.

Microcracks interrupt the conductive connections between cell areas. This leads to two direct consequences: first, the power output of the affected cells drops immediately, though usually only slightly – too little to show up in normal monitoring. Second, the cracks spread through thermal cycles (heating up during the day, cooling at night) over months and years. What today means 2% power loss can be 15% or more after two years.

Particularly insidious: modern high-performance modules with thin glass and PERC cell technology are more susceptible to microcracks than older standard modules. A system that ran without problems for ten years can be significantly affected by a single hail event – without this being initially apparent.

Hail resistance classes – what your modules can withstand

International standard IEC 61215 defines hail resistance classes for solar modules from HW1 to HW5. The class indicates what hailstone diameter and what impact speed a module withstands without glass breakage. What the standard does not test, however, is microcracks. A module can pass the HW4 test and still have microcracks.

Klasse	Hagelkorndurchmesser	Aufprallgeschwindigkeit	Einsatz
HW1	12,5 mm	4,0 m/s	Wenig hagelgefährdete Lagen
HW2	16,3 mm	5,2 m/s	Standardgebäude
HW3	25 mm	8,2 m/s	Mindeststandard D/A/CH
HW4	35 mm	11,9 m/s	Hagelgefährdete Regionen
HW5	45 mm	14,0 m/s	Extremlagen, Solarparks

In Germany the hail frequency in southern Germany, parts of NRW and the Alpine foothills has been significantly above the long-term average in recent years. Climate projections by the DWD assume that extreme weather events will continue to increase. Anyone planning a new system today should plan for at least HW3, and HW4 for exposed locations.

Immediate measures after a hail event – what you need to do now

After a hailstorm the clock is ticking. Insurance contracts typically require a damage report within 72 hours. At the same time it is important not to take ill-considered measures that could worsen the damage or jeopardise the documentation.

Why thermography is the only reliable diagnostic method

Microcracks in solar cells cannot be proven across an entire site by any other practically applicable method. The electroluminescence test (EL) does provide more precise crack images at cell level, but requires the entire system to be shut down and is logistically barely feasible for ground-mounted systems.

Drone thermography to IEC TS 62446-3, by contrast, captures all modules of a system during live operation. Microcracks that generate electrical resistance appear in the thermogram as local thermal anomalies. The standard prescribes under which measurement conditions (minimum irradiance, wind speed, module operating state) images must be taken – only then are the results legally sound and insurance-compliant.

This report is the basis for the insurance settlement and – if necessary – for a court expert report. Without this evidence insurers can reduce or refuse payouts because the cause of damage is not clearly proved.

Insurance, duty obligations and what many operators do wrong

Most photovoltaic insurances cover hail damage under the natural hazards clause. But in practice disputes frequently lie between the damage and the payout – not because the insurer does not want to pay, but because Obliegenheitspflichten verletzt wurden.

Duty obligations are behavioural requirements that the insured must fulfil to maintain their insurance cover. For PV systems these typically include: regular visual inspections (often annual), recurring inspections of the electrical system per DGUV regulation 3 or DIN VDE 0105-100, and for systems above certain capacity classes a thermographic inspection per VdS recommendation every two years.

Anyone who has neglected these inspection obligations risks a payout reduction in the event of a claim. In the worst case the insurer argues that the damage would have been detected and limited earlier with proper maintenance. A current thermographic inspection – ideally from the 12 months before the damage event – is therefore valuable not only for damage documentation but also as evidence of fulfilled duty obligations.

Hail damage and manufacturer warranty – two different claims

Hail damage is generally kein Gewährleistungsfall against the module manufacturer. The product warranty covers manufacturing defects (delamination, snail trails, cell defects from production) but not external impacts such as hail, storm or vandalism. These belong in insurance settlement.

There is however an important exception: if a module does not meet the advertised hail resistance class – i.e. it fails at a hailstone size that it should tolerate according to the data sheet – a product defect exists. In this case there is a parallel claim against the manufacturer. This is difficult to prove in practice and requires an expert report that evidences the hailstone size of the event and identifies the module weakness.

Kosten der Thermografie nach Hagelschaden

The cost of a drone thermographic inspection for hail damage analysis depends on system size. For commercial rooftop systems between 50 and 500 kWp they are typically between €600 and €2,800 net. For solar farms from 750 kWp costs are calculated individually.

These costs are in most cases versicherungsfähig. Many PV insurers reimburse the cost of a professional damage diagnosis as part of the claims settlement – check with your insurer before commissioning the inspection. For insurers who make submission of an expert report a prerequisite for settlement, reimbursement is almost always provided.

Frequently asked questions