Degradation of Cross-linked Polyethylene and Cross-linked Polyolefin
Olga Eliseeva, Tim Peshek, Laura Bruckman, Roger H. French
Solar Durability & Lifetime Extension Center, Department of Materials Science and Engineering
Case Western Reserve University, Cleveland OH, USA
Results
Background
• Photovoltaic (PV) modules are expected to maintain a power output
within acceptable limits for over 25 years.
• Although some standards exist for PV wires, such as TÜV and UL
FTIR Spectra of Southwire
Norrish II mechanism
1. Light forms a free radical
2. The radicals breaks bonds
3. Forming smaller units
• The degradation of carbonyl results in vinyl and ketone groups
• carbonyl peak decreases and vinyl and ketone peaks increase
4703, a typical standard test in 720 hours in wet and dry UV is not
indicative of 25 years outdoors.
• No international standard established for wires
Experimental procedure
Wire Type
Southwire
General Cable
TÜV Cable
Composition
Single layer cross-linked polyethylene (XLP) insulation
Double layer ethylene propylene rubber (EPR) insulation
Chlorinated polyethylene (CPE) jacket
Thermoset polyolefin (XL-PE) insulation
Non-halogenated cross-linked polyethylene (XL-PO) jacket
composite
Height to Reference Peak Ratio
Data
Chamber
QUV Spray 1
QUV Spray 2
Q-Fog
Test
1.55 W/m^2/nm irradiance maximized a 340nm for
24 h of dry 5x UV at 70C
ASTM G154: Cycle 4: 1.55 W/m^2/nm irradiance maximized a
340nm for 8 h UV at 70⁰C and 4 h condensation at 50⁰C
Full Width at Half Height to Reference Peak Ratio
Prohesion test: 1h spray cycle at 24 ⁰C consists of .05% NaCl
and >4% ammonium sulfate mist and 1h drying cycle at 35° C
References
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Electr. Insul. Mag. 17, 14–22.
Gulmine, J.V., Akcelrud, L., 2006. FTIR characterization of aged XLPE. Polym. Test. 25, 932–942.
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thermally aged XLPE cable in the high-frequency range. Polym. Test. 25, 553–561.
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• FTIR Spectra of Southwire
• Expected to see a vertical decrease in the 1600cm^-1 region and an vertical as well as
a horizontal increase in the 1700cm^-1 region
• We observed what we expected
• Height to Reference Peak Ratio
• Expected to see a decrease but no clear trend emerged
• Full Width at Half Height to Reference Peak Ratio
• Expected to see an increase but no clear trend emerged
• Height to Baseline Ratio
• Expected to see a decrease
• We saw a decreasing tread with a single outlier at 1176 hours
Conclusion
Height to Baseline Ratio
• We can not compare our peaks to Carbon black, despite what the literature states, it begins
degrading around 1176 hours and does not make a good bases for comparison
• Generally we see the expected Norrish II mechanism of degradation, with a decease of the
carbonyl peaks and an increase of the vinyl and ketone peaks
• More analyzes need to be conducted at the 1176 hour mark, to examine why there is an increase
of the carbonyl region
Ongoing work
•
•
•
•
Find a component that does not degrade to use as a reference regain
Expand this analyses to the other two wires types
Identify mechanism of degradation for heat
Analyze the data for the other two test chambers
Acknowledgements
Thank you to Underwriters Laboratories for providing funding and support for this project, especially Liang Ji. Thank you to
First Solar for providing materials. Thank you to SURES for funding over the previous summer. Thank you to all members of
the VUV-lab group for their support.