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Swiss researchers have studied three types of black ink coatings for metal ribbons used in building-integrated photovoltaic (BIPV) modules. They have compared their visual stability and their effect on electrical performance.
A group of researchers in Switzerland has investigated the visual stability and electrical performance of black interconnect coatings used in photovoltaic modules. These coatings are used to improve the aesthetic appeal of building integrated photovoltaic (BIPV) modules by minimizing their appearance on black backsheets.
“Interconnection concealment is often achieved through costly and inefficient manufacturing steps, such as applying colored strips or bands with manual positioning,” the researchers explained. “A possible solution to modify the appearance of metallic tapes is to coat them with ink. “Inkjet is one of the best technologies capable of addressing the precision, resolution and flexibility requirements for coating shiny metallic ribbons.”
In conversation with pv magazine , the corresponding author, Dr. Alejandro Borja Block, added that “the cost of the manual process could be around 3 CHF ($3.32)/module, while an automated process could be 0.15 CHF /module approximately. It is important to consider that when making these estimates many assumptions are made, such as the degree of automation of the equipment, the useful life of the equipment, the cost of consumables, the cost of energy used, the speed of the process, etc.
In the article “ Stability of black interconnect coatings for solar photovoltaic module applications ,” published in Solar Energy Materials and Solar Cells , the research team compared three types of metal tapes - One was a commercially available black tape with no information on the coating used and the other was a commercially available black tape with no information on the coating used. while the other two were coated in the laboratory with commercial UV-curable inkjet inks.
The scientists tested the three tapes in a sequence based on the industry standard IEC 62788-7-2. All coated tapes were cut into 3 cm long strips and then laminated onto conventional glass-backed sheet (G/BS) modules.
They then encapsulated the panels using three different encapsulants, with and without UV blockers. The three samples were left in the chamber for a total of 2,000 hours, equivalent to approximately 120 kWh/m2 of UVA and UVB (UVA+UVB) irradiance doses, corresponding to approximately two years of outdoor exposure in central Europe. .
“The most surprising observation that emerged from the data comparison was that the color change only appeared in UV-curable inkjet inks, not in commercial black ribbons,” the academics said. “Ink 1 produced the largest color change: a yellow halo appeared around the coated metal interconnects. This could indicate diffusion of the ink components within the encapsulant and degradation. Ink 2 produced a smoother but still noticeable color change.”
After this test, the researchers dug deeper into ink 1, as it showed the most significant color change. They did this in two ways: first, by isolating the ink and the pure 2-PEA molecule to investigate whether it played an important role in the observed degradation; secondly, creating a mini solar module and then coating its ribbons with the corresponding ink.
Pure component samples were aged for 24 hours and 10 days, or UVA + UVB doses of 1.5 and 15 kWh/m2, respectively. “The pure component of the ink and rinse, 2-PEA, polymerized after 1.5 kWh/m2 and turned yellow after 15 kWh/m2,” the group emphasized. “This is due to the creation of carbonyl bonds in the substance, which are related to the oxidation of the molecule under ultraviolet light. The carbonyl index increased by 22% after UV exposure of 15 kWh/m2.”
As for the sample coated module, it was aged for 6,000 hours or a UVA + UVB dose of 360 kWh/m2. “The use of the unstable ink investigated would represent a long-term aesthetic modification of the color, demonstrating potential long-term instability, but the electrical performance would be similar to a module without coated tapes (less than 3% energy loss). ”, noted the team.
Concluding their research, the scientists said they “advise against the use of 2-PEA monomer for aesthetic photovoltaic applications and suggest the use of UV-curable inks with aliphatic monomers, which have better non-yellowing properties, in combination with UV-blocking encapsulants.” ”. They also added that “UV-blocking encapsulants help mitigate photodegradation of 2-PEA in G/BS laminates, while not fully mitigating degradation of the ink itself.”
The team consists of academics from the Swiss Federal Institute of Technology Lausanne, the CSEM of Switzerland, the Center for Sustainable Energy, the Leoben Polymer Competence Center of Austria and the Academy of Sciences of the Czech Republic. |
