Hail Damage: The Loss That Does Not Show Up Immediately

Hail is the peril that causes the most significant insured solar losses in exposed regions, and it has an unpleasant characteristic: the worst damage is frequently invisible.

What modules are tested to

IEC 61215 requires modules to withstand impact from 25 mm ice spheres at around 23 m/s at defined points. Most quality modules pass comfortably, and some manufacturers test to larger stone sizes and publish the results.

Severe hail events exceed this. Stones of 40-50 mm are not unusual in parts of the US Great Plains, northern Italy, and increasingly elsewhere. At those sizes and velocities, the test standard is no longer the relevant reference.

Two damage modes

Glass fracture. Obvious. The module is compromised, moisture will enter, and it needs replacing. Easy to identify and to claim.

Cell microcracking without glass breakage. The problem. Impact energy transmits through the glass into the silicon, cracking cells while leaving the glass intact. From the ground the array looks fine. Output immediately after may be essentially normal, because cracked cells often still conduct.

Then thermal cycling does its work. Over subsequent months and years the cracks propagate, cell sections become electrically isolated, and output declines. By the time the loss is obvious, the claim window has usually closed and the connection to a specific weather event is difficult to establish.

Inspecting after an event

Do this even when nothing looks wrong.

Visual inspection first, but understand its limits. Look for glass fracture, frame deformation, and impact marks on surrounding surfaces – if the roof flashing and rooflights are dented, the modules took the same impacts.

Thermal imaging under load. Cracked cells that have become electrically isolated show as hotspots. Effective for damage that has already progressed, less so for fresh cracks that are still conducting.

Electroluminescence imaging is the definitive method. A current is applied to the module in darkness and the infrared emission photographed. Cracked cells appear as dark regions with clear crack patterns. It finds damage nothing else detects.

EL imaging historically required a laboratory, but field-portable systems now exist and drone-based EL is available in some markets. For a large array after a significant event, it is worth the cost – it is the difference between a documented claim and an argument.

Documenting for a claim

What makes a hail claim succeed:

• Pre-event baseline. Commissioning EL or thermal imagery, and string-level performance history. Without a baseline, an insurer can reasonably argue the cracks predate the event.
• Prompt post-event inspection with dated imagery and a report from a qualified inspector.
• Meteorological evidence. Local weather records or a hail verification service confirming stone size and timing at your location.
• Collateral damage photographs. Dented HVAC housings, damaged rooflights, marked flashings – corroborating evidence of impact severity.
• Performance data before and after, at string level.

Reducing exposure

For sites in genuinely hail-prone regions:

• Specify modules tested beyond the minimum. Some manufacturers publish results for larger stone sizes; thicker front glass and glass-glass construction generally perform better.
• Consider tilt. Steeper tilt presents a more oblique angle to falling hail, reducing impact energy. Not always compatible with other design goals, but worth weighing where hail risk is high.
• Understand your deductible structure. Percentage-of-value hail deductibles are common in exposed regions and can be large enough that moderate damage falls entirely to you.
• Stock spares. After a regional hail event, replacement modules of a specific model become scarce and slow. A small stock of matching modules turns a months-long outage into a week.

The pattern worth watching for

If your plant experienced hail two years ago, was inspected visually, declared fine, and has since drifted a few percent below expectation with no other explanation – commission EL imaging before concluding it is normal degradation.

Microcrack propagation produces exactly that signature, and finding it late is better than not finding it. Even outside a claim window, knowing the cause changes what you do next.