Sunday read: A PV band-aid


From pv magazine 06/2021

DuPont plans to launch a backsheet repair kit for modules in the field. What does it look like and how does it work?

Certain types of backsheet used by panel manufacturers are known to degrade in the field earlier than the expected lifetime of the PV system. To restore the electrical integrity of the PV panel, we have designed a backsheet repairing tape solution built upon a structure similar to Tedlar-based backsheet, with an adhesive designed to bond onto the underlying degraded backsheet.

DuPont has developed a specific Tedlar repair tape and teamed up with Suncycle GmbH and its subsidiary, sc-refit GmbH, who developed a robust application process designed to be compatible with on-site field intervention. First, the panels are dismounted and cleaned. After an inspection of the backsheet, the team uses a special device to apply the tape to the module. The edges around the frame and junction box are sealed before final inspection and remounting. The whole repair process is quite short – less than 10 minutes.

Can the repair kit be used only on polyamide, or on any type of backsheet?

The DuPont Tedlar PVF tape has been designed to use a thick rubber-based adhesive widely used in the construction industry – with a very long track record in the field. The adhesive is particularly well adapted to provide a broad latitude from the lamination processing standpoint – particularly relevant to bond over uneven, rough, and cracked surfaces. These include the type of polyamide-based backsheets observed in the field. Such adhesive can also be used to bond over “smoother” and cracked PVDF-based backsheet surfaces. The DuPont team and sc-refit are committed to keep optimising the tape, and process, to reduce the application cycle time without compromising the performance of the solution.

The repair solution can be applied to all sorts of backsheets, but all types of defects are not necessarily repairable. For example, when the backsheet damage results from a different dysfunction, such as broken cells generating hot spots, then repairing the backsheet will not successfully solve the underlying problem of the broken cell. In this case, it is preferable to replace the panel.

Can O&M service crews simply buy the kits and repair the backsheets, or do they need special training? Or are specialised maintenance crews necessary?

The repairing process involves a combination of a pre-engineered repair tape and a robust application process involving a special repair device that has been designed by our development partner sc-refit. Despite the robustness of the tape and the process, the personnel involved need to be properly trained to initially conduct a technical assessment of the reparability at the panel level, and to then deliver a consistent application process to protect the panels durably.

At this point, sc-refit will be delivering the repairing services in the EU. However, we’re also contemplating appointing additional accredited third-party service partners to accelerate the market introduction of the joint solution in the U.S., and possibly in India later. Only accredited partners will be granted the right to use the same tape and equipment package and fully trained by DuPont and sc-refit to ensure a consistent quality service.

How big do you see the market for your new product?

According to the DuPont field survey data, the majority of the polyamide-based backsheets will undergo catastrophic degradation over time, exposing over 10 GW of panels to such risk. For PVDF-based backsheets, the process of degradation is somewhat slower and may affect about 20% of the panels within their expected lifetime. But the market share of PVDF-based backsheets is quite large, exceeding 40% or so, as it keeps on being widely used by most panel manufacturers.

Considering the cumulative panels deployed in the field involving such backsheets, we may have over 60 GW of panels deployed. We estimate that about 20% to 30% of the panels with backsheet level degradation cannot be repaired, due to corrosion or cell cracking, for example – so the actual and addressable market may be around 5 GW to 6 GW per year at this point, and will keep increasing over time.

Who would be your direct customers?

Initially, panel manufacturers will be on the front line, dealing with the asset owners exposed to the PV panel level degradations. In the absence of repair solutions, they have to engage in a long “dialogue” to determine the extent of the problem and consider the replacement of the panels affected. In most cases, replacement involves only a sub-set of the panels deployed at the PV plant – while panels with no degradation of the semiconductor will be kept in-situ despite their probable backsheet degradation over time. Also, the warranty terms typically do not take into account the panel dismounting and the cost associated with the redesign of the plant if a newer generation of PV panels is used to replace old ones.

Partial or complete panel replacement is not a good approach to all parties from a cost perspective – and may not eliminate the risks if panels with a similar bill of materials are considered for replacement.

The on-site repair can address the PV panel manufacturer’s needs well by reducing their cost exposure while restoring the safety of their PV panels still operational from a power output perspective, extending their lifetime with minimal operational disruption of the PV plants.

From the asset owner’s perspective, repairing can also minimise the plant disruption and downtime associated not only with the dismantling and replacement of the panels but also the partial redesign of the plant that would be necessary with the use of newer PV panel generation.

Have you already been in contact with underwriters and lenders? Do they accept this as a low-risk revamping option for older arrays?

This may not be required as in most cases the cost of the repair will be supported by panel manufacturers, as long as PV panels are covered by warranty terms.

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