Backsheets Exhibited High Overall Defect Rate of 11% in India: Kaushik Choudhury, DuPont

Globally, nearly a four-fold cumulative increase in PVDF outer-layer cracking defect rate has been observed, from 5 per cent to 23 per cent between year 4 and year 9 after installation… In India, the defect results are similar to global and backsheets exhibited a high overall defect rate of 11 per cent. Most of the backsheet defects were observed in 5+ years old projects (48 per cent defect rate), and a majority of the operating projects in India are less than 5 years old, the real impact is yet to be seen, believes Kaushik Roy Choudhury, Senior Scientist and Global Technology Leader, Dupont Photovoltaic Solutions, a leading global supplier of speciality materials like backsheets, metallisation pastes etc. In conversation with Manu Tayal, Associate Editor, Saur Energy International, Choudhury shared his views on various topics including how its global PV field reliability program help investors in taking decisions, kind of defects found in projects during their analysis, DuPont’s products offerings for the solar industry etc. Here’re the excerpts from that exclusive interview

Q. Shed some light on DuPont’s global PV field reliability program. 

The DuPont Global Field Reliability Program is a highly developed field inspection and analysis program that monitors material degradation and its impact on module performance. For nearly a decade, DuPont has collaborated with field partners, customers, downstream developers, universities, and national labs to perform these field inspections.

This program is one of the most thorough of its kind, guided by a multistep inspection protocol conducted by DuPont scientists and engineers at sites in North America, Europe, Asia, and the Middle East. Resulting data are analyzed using a variety of criteria— including component, material, mounting, time in service, and climate.

Q. How does this reliability program help solar project developers and owners who generally invested a huge amount in a project for the long term?

The program is intended to help buyers and investors understand the breadth of component degradation issues and module failures that can occur in the field. Based on the extensive field analysis and survey, DuPont has internally developed a recommended Bill of Materials (BoM) for crystalline silicon solar panels that are anticipated to demonstrate superior performance and reliability over time.

Specifying proven types of materials in projects can help improve the durability and reliability of solar panels over their lifetime, and, help to reduce the risk of premature power degradation or catastrophic panel failure that can diminish the internal rate of return (IRR), resulting in much lower returns on solar investments than expected for developers and project owners.

To this end, the program creates awareness and education on using the right materials and components in a solar project to help in better decision making for long term performance and returns. At the same time, the program also helps project owners holistically assess the ‘health’ of managed projects and implement effective O&M practices.

Q. As per your analysis on the field, what kind of defects you mainly observed in the solar power plants installed in the Indian region specifically? Up to what extent such defects can impact plant performance and their cost in the long term?

Globally, nearly a four-fold cumulative increase in PVDF outer-layer cracking defect rate has been observed, from 5% to 23% between year 4 and year 9 after installation. Deeper backsheet cracks have led to backsheet delamination, exposing the core layer to elements and leading in some instances to inverter tripping, ground faults, arcing and module fires. Backsheet cracking has been seen in hot-arid, cold-arid, temperate, and Mediterranean climate, so there is no clear correlation between cracking and climate. We have also seen significant cell and interconnect level defects.

In India, the defect results are similar to global and backsheets exhibited a high overall defect rate of 11%. Most of the backsheet defects were observed in 5+ years old projects (48% defect rate), and a majority of the operating projects in India are less than 5 years old, the real impact is yet to be seen.

The level of impact that these defects can have on immediate energy generation and on O&M costs, varies. For example, backsheet defects do not immediately show up as power production issues. However, they can, if left undetected or unattended, develop into significant electrical safety issues, sometimes leading to module fires. At that point, there is a sudden unexpected expense in O&M and possible module replacement which can run as high as ~10 times the scheduled budget for O&M. On the other hand, busbar and interconnect corrosion, and encapsulant discoloration lead to gradual power loss over years of operation.

Q. As the cost of module took significant share in the total cost of the solar plant. How important is the quality of the module used in the plant? Can quality and cost go hand in hand? Explain.

Solar panels represent approximately 50% of the total cost of a solar power plant and therefore it is critical for panels to reliably produce power for their 25-year expected lifetime or longer, even in demanding environments. This is where solar cell and panel materials play a crucial role.

Focusing on just immediate cost/watt-peak is very much a short-term approach. Instead, we believe that the industry should be focusing on a longer-term view and think in terms of anticipated cost/kilowatt-hour over the system’s expected lifetime of 25+ years. Shorter system lifetime, a decrease in five years or so, is anticipated to increase Levelized Cost of Electricity (LCOE) and inefficiency by over 30%. Conversely, by extending the system’s lifetime and performance by five years can help decrease the LCOE by 20%.

Q. Is DuPont’s Tedlar PVF Film-based Backsheet good for all the climatic conditions that India have? What is its defect rate?

DuPont™ Tedlar® PVF film-based backsheets have now been tested in the field in all kinds of climates (desert, tropics, temperate, marine, mountain) and maintain the lowest defect rates – even after 35 years in the field. The cumulative defect rates are less than 1% for installations ranging from 4-35+ years. Tedlar® based backsheets are field-tested and proven for 30+ years and ensure risk-free performance in the field.

Q. What kind of defects is generally found in the inner layer of a backsheet? In how much time such defects appear and their impact on the solar power plant?

Inner-layers of backsheets can exhibit cracking in the field, for certain materials. Inner layer cracks constituted 24% of the overall backsheet defects, the overall inner layer cracking tripled in 2020 compared to 2019 assessment. These cracks initiate at the inner layer and propagate through the module’s polyester core. They are frequently encountered in fluoroethylene vinyl ether (FEVE) and polyethylene terephthalate (PET) backsheets. This can directly impact power through increased leakage currents leading to delayed inverter starts, ground faults and fires.

Q. Do you find cases of degradation of material in glass backsheets as well, in how many years they appear? Any example?

Delamination and cracking were observed in multiple glass backsheets. Delamination appears to originate near edges of a module or at individual cells. Cracks likely originate at scratches or chips on the glass surfaces and edges or at stress risers introduced by the racking system. Interestingly, this defect has been observed in modules spanning different generations of technologies and ages. We have examples from Europe, North America and China.

Q. What is DuPont’s major unique selling proposition (USP) among customers as compared to close peers?

DuPont Photovoltaic Solutions is a leading supplier of speciality materials to the solar energy industry and represents a portfolio of product solutions with over 40 years of service that delivers proven power and lasting value for the fast-growing photovoltaics sector, including DuPont Solamet® metallization pastes, DuPont™ Tedlar® films as well as now DuPont™ Fortasun™ photovoltaic silicones.

DuPont has made a significant strategic investment in the growth of solar energy – by developing innovative material solutions across the value chain. We are not only a speciality PV material supplier to the industry, but we also collaborate with our partners to conduct technical audits at the plant level as well as develop and execute accelerated lab testing of solar materials, components and panels. We have built partnerships with leading research and academic institutes and work across the solar value chain to provide technical support including specifications for the bill of materials to source right solar panels.