Illuminated Thermography (IR)

• Description: Heat in the PV modules is detected using an infrared (IR) camera [1]. The later can be hand-held, or mounted on a drone, allowing for fast measurements of large areas.
• Equipment: IR-Camera, preferably mounted on a drone.
• Requirements: Stable sunny conditions for illumination, low wind conditions for drone flight.
• Gained insights: detection of hot spots, disconnected strings/modules, diode failures.   
  Hot spots are 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 [2,3]).
• Recommended frequency: once a year. If possible 1-2 times more in the first year after commissioning.        
  So far, regular IR imaging of alpine PV installations, as done at the Albigna hydropower dam [4], seems to have been the exception rather than the rule. Experience will show whether drone-based illuminated thermography might become a common preemptive measure: Early detection of hotspots allows for intervention before critical failure occurs. Since this might save an additional future on-site intervention, thermography imaging performed during annual inspection of PV plants could be advantageous in remote locations.
• Advantages:
  • Can be done during operation.
  • Contactless.
• Disadvantages:
  • Flying a drone needs expertise and practice.
• Effort:
  • Global: low. Relatively small and lightweight equipment, easily transportable to the site (even on foot).
  • Costs: 1800 to 2700 Euros per day.
  • Time: 30 min per hectare.
• Providers (non-exhaustive list):
  • Energie Netzwerk GmbH: https://www.energie-netzwerk.ch/photovoltaik-qualitaet
  • REECH AG: https://reech.ch/
  • TÜV Rheinland: https://www.tuv.com/world/en/aerial-inspection-of-pv-systems.html
  • Verband unabhängiger Energieerzeuger: https://www.vese.ch/drohnenthermografie/
  • Solarmarkt GmbH: https://www.solarmarkt.ch/de/services/services-fuer-bauherrschaften/qualitaetspruefung-mit-waermebilddrohne
• Links:
  • Brief explanation of illuminated thermography: https://www.zehndorfer.at/en/photovoltaics/ir-measurement
  • Establishing a Drone-based Maintenance Strategy: https://thedronelifenj.com/solar-pv-aerial-inspection-frequency/
• Additional notes: Combined with visual inspection and I-V curve measurement, this method forms a low effort solution to quantify the most likely failure modes reported in literature, namely discoloration, delamination, corrosion and breakage [5]. Despite higher UV-radiation in alpine regions, discoloration is expected to be less of an issue, thanks to lower temperatures, slowing the chemical reaction. However, these low temperatures, combined with high irradiation, lead to increased thermomechanical stress and materials being more brittle, increasing the risk of delamination and breakage [6,7]. As for the risk of breakage, it is also increased in alpine regions, since the mechanical loads through wind, snow cover, snow drift and ice formation are much higher than in the lowlands.

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References

1. Jahn U, Herz M, Köntges M, Parlevliet D, Paggi M, Tsanakas I, et al. Review on infrared and electroluminescence imaging for PV field applications. International Energy Agency (IEA); 2018.
2. Hügli A. Alpine untility scale PV: Challenges of Constructability and Operations 2025.
3. Heierli C. Interview about alpine PV: AXPO, Alpin Solar (Muttsee-Staumauer) 2025.
4. Szacsvay T. Untersuchung zum Alterungsverhalten von PVModulen einer hochalpinen PV-Anlage. Bern: REECH; 2024.
5. Rahman MM, Khan I, Alameh K. Potential measurement techniques for photovoltaic module failure diagnosis: A review. Renew Sustain Energy Rev 2021;151:111532. https://doi.org/10.1016/j.rser.2021.111532.
6. Schmidhalter F. Interview about alpine PV: Enalpin 2025.
7. Gassner A. Alpine PV: Stressors and module testing strategies 2025.