Assessment: Electroluminescence Analysis Reveals 847 Hidden Cell Cracks After Hail Event

Assessment type: Insurance assessment / Damage analysis System size: 4.2 MWp monocrystalline PERC Region: Middle Franconia Period: Jul – Sep 2024

Assessment summary:

Hail event on June 28, 2024 (hailstone size up to 4.5 cm) over 4.2 MWp ground-mounted system
Visual inspection: only 23 modules with visible glass breakage (0.2% of total area)
EL testing (sample of 1,200 modules): 847 cell cracks, 214 modules with performance relevance
Extrapolation to entire system: 1,780 affected modules, yield reduction of 8.3% (P50 basis)
Insurance settlement: EUR 312,000 (module replacement + lost yield)

Why was an electroluminescence test required?

On June 28, 2024, a hailstorm with hailstone sizes of 3–4.5 cm struck a 4.2 MWp solar park in Middle Franconia (commissioned 2021, monocrystalline PERC modules, 9,240 modules total). The visual inspection after the event identified only 23 modules with visible glass breakage — a damage rate of just 0.25%.

Experience shows, however, that hail impacts with stone sizes exceeding 3 cm regularly cause hidden cell cracks (microcracks) that are not detectable visually or by thermography in the first months after the event, but lead to long-term performance degradation. The insurer therefore commissioned a systematic electroluminescence test.

Test scope and methodology

Parameter	Value
Modules tested (sample)	1,200 of 9,240 (13%)
EL camera	InGaAs sensor, 1024x1024 px, exposure 10 s
Test current	Isc (short-circuit current) of respective module
Test timing	At night (10:00 PM – 4:00 AM), July 12–15, 2024
Statistical confidence interval	95% at sample size n=1,200

What did the EL analysis reveal?

The electroluminescence images showed a significantly more extensive damage pattern than the visual inspection:

Damage category	Number of modules	Proportion of sample	Performance relevance
Class A: No findings	687	57.3%	None
Class B: Hairline cracks without deactivation	299	24.9%	Low (≤2% Pmax)
Class C: Cell cracks with partial deactivation	147	12.3%	Medium (2–8% Pmax)
Class D: Severe cell cracks / cell fragmentation	67	5.6%	High (>8% Pmax)
Total with findings	513	42.8%	—
Of which performance-relevant (C+D)	214	17.8%	Replacement recommended

Extrapolation to entire system (9,240 modules): At 17.8% damage rate (Class C+D), approximately 1,645 modules are performance-critically damaged. Considering the 95% confidence interval, the actual number lies between 1,480 and 1,810 modules. Average yield reduction of the entire system: 8.3% compared to P50 forecast.

How was the damage progression over time assessed?

For validation, a follow-up test was conducted in September 2024 (3 months after the hail event) on 50 Class B modules. Result: 12 modules (24%) had degraded from Class B to Class C — the cracks had propagated under thermal cycling. This confirms the well-known mechanism of "crack propagation" following mechanical pre-damage.

What economic damage was determined?

Expert damage calculation:

Item	Amount
Module replacement 1,645 modules (incl. installation, logistics)	EUR 247,000
Lost yield during replacement period (estimated 4 weeks, pro rata)	EUR 38,500
EL testing + assessment	EUR 26,500
Total damage (insured)	EUR 312,000

Expert assessment: Without EL testing, the insurance claim would have been limited to 23 modules (approx. EUR 3,500). The hidden number of undiscovered hail damage in the PV industry is considerable. The analysis shows that visually inconspicuous systems should be systematically tested by electroluminescence after hail events with stone sizes exceeding 3 cm — in this case, the damage rate was 71 times higher than the visually detectable damage.

Similar case? We can help.

Independent assessment by TUV-certified expert assessors — operating across Europe.

Request a consultation

Last updated: 2026-06-16 | Author: Christoph S. Prestele, TUV-certified expert assessor | PV-BESS-Assessor.com