14 th IEA PVPS Task 13 Meeting Bolzano, 6-8.4.2016 UV fluorescence imaging as fast inspection method for PV modules in the field A. Morlier, M. Köntges, M. Siebert, I. Kunze Institute für Solarenergieforschung Hameln/Emmerthal
Fluorescence (FL) detection UV-Light 310-400 nm UV-Light source ca. 30 W/m² UV-Light intensity CCD-Camera UV-Fluorescence 400-800 nm Highpass filter > 400 nm Measurement place should be protected from external light sources Field measurements possible at twilight/night Basic literature on the fluorescence effect: F.J. Pern, Sol. Energy Mater. Sol. Cells 41/42, 1996, 587-615 L. King, M.A. Quintana, J.A. Kratochvil, D.E. Ellibee and B.R. Hansen, Prog. Photovolt.: Res. App., 8: 241 256 (2000). doi: 10.1002 Detection of micro cracks with the fluorescence effect: Schlothauer, S. Jungwirth, B. Röder, M. Köhl, Photovolt. Int. 10 (2010), pp. 149-154 Detection of micro cracks with the fluorescence effect in the field: M. Köntges, S. Kajari-Schröder, I. Kunze, Proc. 27 th EUPVSEC Conference, Frankfurt, Germany, 2012. B. Kubicek, D. Mayrhofer, G. Eder, OTTI Symposium für Solarenergie, Bad Staffelstein, Germany, 2016
Fluorescence spectrum Increase of EVA fluorescence over aging time 1 Camera sensitivity 2 Aging time Blue sensor more adapted for shorter exposures Green sensor more adapted for longer exposures 1 A. Czanderna et al., Sol. Energy Mater. Sol. Cells 403, 101-181, 1996 2 F. Sigernes et al., Optics express 17 (22), 20211-20220 (2009)
Fluorescence/Additives relation 1 Peroxide 1 Antioxidant 2 UV Absorber 2 Light stabilizer (HALS) 9 Formulations: EVA #1, #5, #6, #7, and #8 only with one additive EVA #2, #3, #9 and #10 mixed 1 Adhesion promoter Peike C., et al., Proc. IEEE PVSC Conference 2013, 1579-1584
Origin of fluorescence/yellowing Additive mixtures EVA with HALS and Antioxidant: no chromophores Additives dominate fluorescence: UV-absorber and cross-linking agent Additive mixtures All additive mixtures fluoresce Peike C., et al., Proc. IEEE PVSC Conference 2013, 1579-1584
Lamination materials UV dose 331 +/- 17 kwh/m² UV-transparent silicone UV-transparent EVA Every material fluoresces, but with different intensities Silicone with UV-absorber Std. EVA
Lamination materials UV dose 331 +/- 17 kwh/m² UV-transparent silicone UV-transparent EVA Fluorescence quenching through O2 diffusion Silicone with UV-absorber Std. EVA
UV fluorescence over exposure time Initial measurement: Weak fluorescence intensity No discernable pattern
UV fluorescence over exposure time 58 days outdoor, namely 290 kwh/m² global irradiation dose First discernable patterns Necessity for highly sensitive capture UV-light should be better filtered Reflection UV-light source
UV fluorescence over exposure time 125 days outdoor, namely 584 kwh/m² global irradiation dose Discernable patterns
UV fluorescence over exposure time 301 days outdoor, namely 980 kwh/m² global irradiation dose Patterns easily discernable
UV fluorescence over exposure time 511 days outdoor, namely 1735 kwh/m² global irradiation dose Patterns really clearly discernable
Electroluminescence image 511 days outdoor, namely 1735 kwh/m² global irradiation dose Cell crack Edgewafer
UV fluorescence over exposure time 511 days outdoor, namely 1735 kwh/m² global irradiation dose Cell crack easily discernable Edge wafer warmer when functioning, higher UV fluorescence intensity
UV fluorescence after a fall 3 days indoor (1735 kwh/m²) 1. Module falls short indoor stay does not affect fluorescence 2. 3 days indoor stay 3. FL-measurement
UV fluorescence after a fall 3 days indoor and 7 days outdoor (1735 kwh/m² + 34 kwh/m²) As few as 7 days outdoor allow for discerning new cell cracks
UV fluorescence after a fall 3 days indoor and 14 days outdoor (1735 kwh/m² + 74 kwh/m²) New cell cracks already appear wide!
UV fluorescence after a fall 3 days indoor and 21 days outdoor (1735 kwh/m² + 113 kwh/m²) New cell cracks widen slowly
UV fluorescence after a fall 3 days indoor and 35 days outdoor (1735 kwh/m² + 175 kwh/m²) Old and new cell cracks discernible through fluorescence intensity
UV fluorescence after a fall 3 days indoor and 49 days outdoor (1735 kwh/m² + 237 kwh/m²)
UV fluorescence after a fall 3 days indoor and 77 days outdoor (1735 kwh/m² + 355 kwh/m²) Old neat cell cracks are discernible from the new ones up to 2.5 months Half height peak width [mm] Irradiation dose [kwh]
UV fluorescence quenching Modelling: cell crack Glass Lamination material Cell Backsheet
UV fluorescence quenching Modelling: partial delamination of the cell Glass Lamination material Crack Cell Backsheet Partial delamination Supposition: adhesion between cell and embedding material is reduced around the cell crack
UV fluorescence quenching O 2 diffusion two different processes 1. Along delamination, 2. Through massive material Laminationsmaterial Glass Crack Partial delamination O 2 diffusion fast Cell O 2 diffusion slow Backsheet
Hotspots UV-Fluorescence Visible light picture Lock-In thermography FL method identifies areas that are/were hot during functioning
Field measurement tool Transport in a car trunk possible 0.5 h assembling Adaptable to module size Easy to use for 2 persons In average 21 s/image, incl. placement, handling Example measuring conditions: up to 500 W/m², um 0 C
Field measurements Serial number fluoresces Module 3 years in the field Dark field Fluorescence image Dark field substraction blue+green channel Dark field substraction increases noise reduces overlighting between cells (blooming) increases constrast remarkably Dust/dirt fluoresces Speculation: colophonium from flux traces?
Correlation with snail trails Snail trails correlate with fluorescence quenching due to cracks
Junction box: different cases FL IR Cells over the junction box show locally more fluorescence Cells warmer at this position, as seen on IR Less artefacts than IR
Junction box: different cases Second backsheet layer laid under the cross connectors Only a portion of the cross connector is intensively fluorescing Supplementary layer of backsheet blocking O 2 Hot junction box and connectors
Conclusion UV fluorescence by daylight possible Minimal aging: ca. a summer ~500 kwh/m² Cell cracks, teared tabs, hot cells (parts) Discriminating between new and 2.5 months old cracks or older 1300 modules in a 8 h day with 2 operators This work is funded by the Land Lower Saxony & the federal ministry of economy (BMWi) under contract number 03257350D Fidelitas
Outlook UV fluorescence may be combined with EL UV fluorescence may complement EL images with informations on warmth production and cracking storyline Thank you for your attention!