UV Fluorenscence (UV-F)

^{Created by M.L., OST, on 19.03.2025}

Description: UV-F detects the luminophores generated when EVA degrades under UV radiation. Oxygen diffusing into the EVA reacts with the luminophores and deactivates them (photobleaching). Therefore, moisture ingress and cell cracks are visible as darker regions in the fluorescence image [1].
Equipment: UV-light source to excite the luminophores, camera to record fluorenscence.
Requirements: Measurements to be performed in the dark (at night, or with a cover).
Gained insights: Cell (micro-) cracks, glass breakage, delamination, hot spots, hot cells. A history of UV-F measurements can give insights into encapsulant degradation/ageing.
Due to the combination of low temperatures and heavy mechanical loads (wind and snow), defects such as micro-cracks and glass breakage are expected to be more common in alpine regions [2–4]. Hot spots are also more likely to occur in alpine PV installations, due to their steep mounting angles, leading to increased self-shading, combined with higher irradiation levels (up to above 1600 W/m² [5,6]).
Advantages: Allows to differentiate between old and recent cell cracks.
Disadvantages: Limited to modules using materials that generate luminophores [1]; cracks on edge of cells not visible, due to oxygen ingress from gap between cells.
Effort:
- Global: medium.
- Costs: medium.
- Time: medium; 1 hour per 250 solar modules.
Providers (non-exhaustive list):
- Photovoltaikbuero: https://photovoltaikbuero.de/pv-know-how-blog/uv-fluoreszenz-an-photovoltaikmodulen/
- AIT Austrian Institute of Technology GmbH: https://energieforschung.at/projekt/anlagendiagnostik-und-modulanalyse-basierend-auf-standard-charakterisierungsverfahren-und-neu-entwickelten-messverfahren/
Links:
- Brief explanation of UV-F: https://isfh.de/flois/?lang=en
Additional notes:
- Since it takes a few days/weeks for the oxygen to diffuse into the EVA, very fresh cracks can not be detected. Therefore, it is important to wait some time before measuring UV-F after an event like a hail storm.
- Usage of a drone is possible, allowing to accelerate the measurement process.

[1] According to [1], these are typically UVA absorbing encapsulants, such as various types of EVA, thermoplastic silicones and crosslinking polyolefins.

*Source: W. Mühleisen, et al., 2019, Renewable Energy 134, Scientific and economic comparison of outdoor characterisation methods for photovoltaic power plants.* *CC BY 4.0*

References

Hermann W, Eder G, Farnung B, Friesen G, Köntges M, Kubicek B, et al. Qualification of Photovoltaic (PV) Power Plants using Mobile Test Equipment. International Energy Agency (IEA); 2021.
Gassner A. Alpine PV: Stressors and module testing strategies 2025.
Seigneur H, Schneller E, Lincoln J, Ebrahimi H, Ghosh R, Gabor AM, et al. Microcrack Formation in Silicon Solar Cells during Cold Temperatures. 2019 IEEE 46th Photovolt. Spec. Conf. PVSC, Chicago, IL, USA: IEEE; 2019, p. 1–6. https://doi.org/10.1109/PVSC40753.2019.9198968.
Schneller EJ, Seigneur H, Lincoln J, Gabor AM. The Impact of Cold Temperature Exposure in Mechanical Durability Testing of PV Modules. 2019 IEEE 46th Photovolt. Spec. Conf. PVSC, Chicago, IL, USA: IEEE; 2019, p. 1521–4. https://doi.org/10.1109/PVSC40753.2019.8980533.
Hügli A. Alpine untility scale PV: Challenges of Constructability and Operations 2025.
Heierli C. Interview about alpine PV: AXPO, Alpin Solar (Muttsee-Staumauer) 2025.