Characterization of EVA degradation processes in Si-based PV modules by means of spatially-resolved luminescence spectroscopy

Transcription

1 Characterization of EVA degradation processes in Si-based PV modules by means of spatially-resolved luminescence spectroscopy 1

2 Degradation of PV modules Typical construction of a c-si PV module Frontglass EVA Cells EVA Backsheet Main problems of service life prediction of PV modules: Low sensitivity of measurement methods Non-destructive characterization necessary Occurrence of many different failure modes 1 Degradation scenarios of PV modules Degradation of electrical properties during DH 2 1 after Köntges, et al. (2014): Report IEA-PVPS T13-01:2014: 2 Köhl (2014): 29th EUPVSC 5DP

3 A very brief history of Polymer Luminescence Ashby Oxyluminescence from polypropylene Charlesby The Identification of Luminescence Centres in Polyethylene and other Polymers But: Complex changes of luminescence could not be correlated to the degradation of physical properties! 3

4 Since Polymer Luminescence at AG Röder: Theory Steffen Density of States Model of Polymer Luminescence P 4

5 Polymer Luminescence at AG Röder: Application to PV modules Identification spatial luminescence patterns in mini modules and full-scale PV modules after accelerated aging outdoor weathering Comparison PV modules of different manufactures to access performance/material differences Parallel aging under different conditions (Multiageing Chamber) Categorization crack damage of PV modules Correlation EVA-Luminescence with mechanical parameters Correlation EVA-Luminescence with crosslinking 5

6 Luminescence upon accelerated aging Sketch of the optical setup: spectrometer UV-laser fiber UV-filter lens dichroic mirror sample Luminescence shows a correlation to the aging duration from the beginning of accelerated aging. 6

7 2D Luminescence scanning of commercial PV modules Setup for 2D-photoluminescence detection (scanning) of embedding polymers in PV-Modules Detail: Scan head with excitation laser and collecting optics 7

8 Luminescence field inspection device 16

9 2. Spatially-resolved measurements on PV-Modules First step of analysis: integration of luminescence spectra and graphical presentation of the location dependent total intensity Wavelength [nm] Presentation with space-resolution via integration of the spectra Intensity [a. u.] Space on the Scan-axis [a. u.] Line-Scan with spectral information Line-Scan Total intensity 9

10 3. Luminescence patterns upon accelerated aging Dry heat (H), damp-heat (DH) Accelerated aging without UV 2000h H 2400h DH 4000h DH Accelerated aging with UV and DH aging followed by UV (DH+UV) 1000h UV 1500h UV 2750h DH + 700h UV 10

11 3. Influence of different materials (accelerated DH aging) DH aging results in similar patterns in most modules Only manufacturer C1 used SC-EVA a) C1 b) C2 c) C4 Other manufactors used fast/ultrafast cure EVA d) C5 e) C6 f) C7 11

12 3. Influence of different materials (accelerated UV aging) UV aging results in similar patterns in most modules The patterns are fundamentally different from DH aging a) C1 b) C2 c) C4 Luminescence of manufacturer C2 does not reduced to zero. Only manufacturer to use Ce-containing frontglass! d) C5 e) C6 f) C7 12

13 Luminescence patterns after outdoor weathering c-si- PV-Modules from 7 companies (data anonymized) 4 different weathering sites: Moderate, Germany:Cologne Alpin, Germany: Zugspitze, 2650 m Desert, Negev Israel Tropic, Indonesia 15

14 Luminescence patterns after outdoor weathering Similar patterns are observed in all modules (e.g. Isreal, 3 years) a) C1 b) C2 c) C3 d) C4 Patterns are most similar to those of accelerated aging with UV e) C5 f) C6 g) C7 Modules of manufacturer C2 deviate Patterns (and spectra) are from distinct others (as for: observed for UV aging). 1) Exclusive thermal aging 2) UV aging or outdoor weathering 14

15 5. Influence of outdoor weathering time Indonesia 2y Indonesiia 3y Indonesia 6y n.a. PV modules of manufacturer C5 Negev2y Negev 3y Cologne 2y Cologne 3y Cologne 6y n.a. Zugspitze 2y Zugspitze 3y 23

16 Intensity [a.u.] Intensity [a.u.] Correlation coeff. Luminescence intensity upon outdoor weathering Evaluation of the luminescence intensity on the center of the cell (No change of spatial patterns, no visible yellowing): Influence of temperature Influence of (UV) radiation Activation energy [kj/mol] Arrhenius-temperature-dose In: Indonesia, Is: Israel, K: Cologne, Z: Zugspitze UV-dose [kwh] The luminescence intensity correlates with the duration of exposure, the average temperature and the UV dose 16

17 5.Correlation of the luminescence intensity of different modules Intensity A good correlation exists for modules by manufacturers C5 and C6 Company Frontglass Encapsulation Cell Backsheet C1 G1 Solar glass E1 SC EVA poly R1 PVF 170 µm C2 G2 With Cer E2* FC EVA poly R2* TPT 290 µm C3 G3 Cer-free E3 UFC EVA poly R3 TPT 350 µm C4 G4 AR-glass E3 UFC EVA mono R3 TPT 350 µm C5 G5 Solar glass E4 FC EVA poly R4 PVF 290 µm C6 G6 Solar glass E5 FC EVA poly R4 PVF 290 µm C7 G7* n.a. E6* n.a. poly R5* n.a. Modules by manufacturer C2 show no correlation to all others Different materials show differences In luminesence 1) The luminescence intensity is specific for the material and the weathering location. 2) A good correlation between modules of similar composition is observed 3) Differences are observed for different materials The materials used by manufacturers C5 and C6 are similar. 17

18 Application of Luminescene to damage characterization normal outdoor exposure transport damage, dendritic fracture exposure damage (Zugspitze) c-si modules from different weathering sites, measurement after 2 years 25

19 7. Evaluation of damages Electroluminescence image (EL) Overlay of EL and FL Photoluminescence intensity Luminescence along cracks shows similar reduction like at the cell edges Schlothauer J., Jungwirth S., Röder B., Köhl M.: Photovoltaics International, 10 (2010)

20 Conclusions Luminescence intensity is an indicator for ageing time indoor and outdoor In PV modules the luminescence is distributed inhomogeneously Diffusion processes (mostly O 2 ) enable destruction of chromphores in the polymer resulting in decreased luminescence intensity The shape of the spectrum is different for DH and UV ageing Complex behaviour of the spectra after combined ageing procedures esp. outdoors UV aging and outdoor weathering cause similar luminescence patterns Spectral effects of UV and DH ageing can be separated also in case of outdoor weathered modules The EVA luminescence of different manufacturers correlates for different ageing methods, indicating that luminescence can be used to monitor the condition of the encapsulating EVA in PV modules Using minimized multi ageing chamber developed at HU Berlin different ageing parameters can be applied to one mini-module and differences in degradation behaviour can be analysed Luminescence can be used for crack inspection (e.g. age of cracks) It can be used for PV module inspection: in- and out-door

21 THANK YOU FOR YOUR ATTENTION Bernd Litzenburger Norbert Lenck Peter Bentz Financial support: Bundesministerium für Wirtschaft Und Energie (FKZ E) Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit (FKZ ) Sponsored by the industrial partners: Scheuten Solar, Schott Solar, Solarfabrik, Solarwatt, Solar World, Solon