Mulilo Sonnedix Prieska solar farm in South Africa header image

Spotlight on a solar scandal

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Millions of solar PV panels could fail or degrade prematurely and may even be at risk of fires. But no one knows exactly where they are or how big the problem is. Rectifying the faults could cost billions. E&T investigates.

In February 2020, the power output plummeted at one of South Africa’s proudest solar photovoltaic electricity generation sites, the Mulilo Sonnedix Prieska solar farm (see satellite image). It left many baffled. Usually, PV solar panels last between 20 and 30 years. So how could this happen after less than four?

Insiders claim accelerated backsheet degradation is to blame. The backsheet is part of a solar module which seals it from dust and moisture and provides electrical insulation. It is also necessary to protect interior components from mechanical and environmental stresses.

The Mulilo Sonnedix Prieska solar farm is among the largest in South Africa. If and why the plant’s backsheets have defects is hard to answer. All the managing director of the company that built the site could say was: “information is confidential”.

Mulilo Sonnedix Prieska PV plant in South Africa

Image credit: Google Earth; CNES/Airbus

Millions of solar PV solar panels, built with cheap materials less than a decade ago, could be affected, with a potentially large price tag for replacements attached. But across the industry, E&T’s investigation encountered vast levels of opaqueness of information and data on solar panel defects caused by early degradation. Companies that perform reliability tests refuse to name names and issue unreliable results on the extent of the problem.

E&T explored one specific legacy issue involving so-called AAA polyamide-based (PA-based) PV module backsheet technology. This was mostly used between 2010 and 2012, but also a little while after. We tested how much the industry and companies could share on a potentially monumental faux pas from a decade ago. The findings suggest: not much. This means that both the public and regulators are left in the dark over possibly substantial unknown safety risks.

Degradation can lead to cracks that can then cause module fires and electrical shorts. Jenya Meydbray, CEO at performance and reliability testing lab PV Evolution Labs, says the worst case is if panels catch fire. This can happen when panels suffer cracks and when there is moisture. “You can absolutely bridge the gap between the exposed conductor and the frame.”

Companies that perform reliability and defect evaluations cannot share specifics on the clients they help with costly replacement campaigns. Those that make backsheet products themselves have vested interests.

However, a 2019 field study by the PV section of global chemicals giant DuPont, which offers its own backsheet materials under the Tedlar brand, claimed that globally, there could be “over 12GW of field failures to date” from polyamide backsheet failure involving “widespread backsheet through-cracks”.

Failure on that scale would be concerning. The quoted 12GW figure is the equivalent of 37.5 million photovoltaic panels (based on a representative panel size of 320W).

A DuPont representative said “all these panels” should be unconditionally replaced. Nearly 88 per cent of PA-based backsheet panels could have defects between years six and ten, making them age around three times faster than panels without accelerated degradation issues.

If DuPont’s evaluation is right, safety risks should be at the forefront of regulators’ concerns. Cracks in the inner and outer layer of a panel can cause shorts, but also localised burn-throughs, as well as full-blown module fires. Are these concerns vindicated? Scientific research largely says yes.

2020 study on backsheet degradation

Image credit: Xiaohong Gu 2020, “Drivers for the cracking of multilayer polyamide-based backsheets in field photovoltaic modules: In-depth degradation mapping analysis”

In March 2020, the US National Institute of Standards and Technology (NIST) published a study showing that the worst cracking was often on the inner layer of the backsheet and analysing a chemical mechanism for how such cracks develop. Co-author Xiaohong Gu says the most important function of the inner layer is for dielectric insulation, so once a crack happens there will be a hazard. Defects can then propagate right through the backsheet, allowing moisture to enter and corrode the panel’s internal metallic components.

A 2018 paper by researchers from Case Western Reserve University in Ohio confirmed that climate and temperature are additional risk factors. “The addition of humidity and temperature variation formed up to three times as many cracks on a photodose basis compared to dry, constant temperature exposures” they found.

The chances are that British and wider European solar capacity are affected by premature degradation. E&T was told that this type of PA backsheet was largely produced between 2010 and 2012 and was pulled off the market between 2013 and 2014. A more precise evaluation was not possible as data was not obtainable, but those years were a time when solar installations grew rapidly across the continent.

Solar capacity data

Image credit: E&T

AAA PA backsheets became popular because of their alluring price point. The motivation was to improve raw material supply as demand could no longer be met with polyvinyl fluoride (PVF). Cheaper polyamide backsheets allowed panel manufacturers to meet growing demand from Europe. Annual installations of solar capacity in Italy, Germany, Spain and the UK exploded before falling back again (see graphic). In the UK, the government heavily subsidised the sector until 2013.

Solar panels with other backsheets also have problems. Next to polyamide, DuPont blames polyethylene terephthalate (PET) and polyvinylidene fluoride (PVDF) backsheets as a cause for accelerated degradation. Those panels will suffer 54 per cent and 42 per cent defect rates respectively within 6-10 years, according to its 2019 reliability report.

Discretion trumps transparency

When things go wrong it’s hard to find a guilty party. Many backsheet technology providers and module manufacturers that serviced the market between 2010 and 2013 went out of business. Insurance warranties from back then are sometimes poorly drawn up. DuPont’s spokesperson said in June the company was about to support a tier-two module maker in arguing that its insurance company should pay replacement costs at a site in Canada.

None of this is public. Asset holders are not keen to share information on defects “because it could help to devalue their projects”, DuPont’s technical representative says. E&T confirmed this aversion to transparency; when we emailed the owners of the 10 largest UK solar sites built between 2010 and 2012, we received no answer.

Industry players stay similarly quiet. Dupont, Heliolytix and PVEL, all performing reliability tests for clients, all refused to provide specific business names of PA backsheet component manufacturers, saying it’s bad for business. The companies have clients relying on discretion. DuPont’s spokesperson said naming specific firms selling or buying PA materials could “put firms out of business”.

E&T asked for comments from five market leaders in backsheet manufacturing that dominated in 2011, according to a report by analytics firm GlobalData: Germany’s Krempel group, Toyo Aluminium, Madico, Coveme and Jolywood. Only the Krempel group responded and said it had never sold PA-based backsheets in its 28-year history.

A Krempel representative says the Austrian firm Isovoltaic was the main supplier of PA backsheets back then. In 2010, the company advertised itself as a global market and technology leader in backsheet production.

But there were others. Uwe Hesmert, key account manager at Krempel, says that the German backsheet manufacturer Bischof und Klein served the market with PA backsheets, at least for a certain period, though in a smaller capacity than Isovoltaic. E&T approached the firm but received no response.

Hesmert says Coveme and Jolywood were never involved in PA backsheets to his knowledge, but he did name Suzhou SunShine New Materials Technology Co as another supplier. Dutch firm Royal DSM, a global science-based company, acquired the Chinese backsheet manufacturer in 2017.

Statistics on backsheet technology

Image credit: Dupont, EMF Solar

Isovoltaic was subject to a management buyout in 2016 and then formed a collaboration with plastics manufacturer Borealis, which launched a co-developed polypropylene backsheet in 2018. However, the new company, Isovoltaic Solinex, went into liquidation at the end of that year. It’s not clear who owns the firm’s intellectual property.

Lack of public records makes it extremely difficult to know where these defective polyamide backsheet panels ended up. Even DuPont’s representative admits this. The company has a vast internal database of solar projects where defects by degradation are tracked but can’t share it with third parties.

For DuPont, it’s easier to track components for clients as it has the module-maker stamp on the panel, or nameplate stamp. The serial number is also often used to trace back who manufactured the panels. “It is possible for those module makers to track back [component] products, not only to continents, but to different countries or factories, where they were produced in batches”, DuPont says. Without information from the sites, efforts to track components are in vain.

 “Unfortunately, there is no database where you could go to and say, there’s this field in southern Italy or northern Africa or wherever,” says Kaushik Roy Choudhury, global technical leader at DuPont. There is no concerted effort to track failures.

Is the UK affected by AAA PA backsheets? Dr Thomas Betts, an expert in applied photovoltaics at Loughborough University, thinks it’s definitely possible.

The UK Solar Trade Association (STA) also remains in the dark. A representative explained to E&T that the STA has no access to the data that would allow it to estimate the extent of the PA legacy issue for the country.

Module manufacturers will know what components they use, we were told. The public and the government won’t. Non-​transparency is exacerbated by the use of different backsheet components at the same site, where panels should be produced by a single manufacturer.

UK-based Marc Scambler, director at Amberside Energy, says: “Clearly there was a change of materials, but everything is under the same manufacturer’s part number. We’ve got photos of [solar] modules, looking at them from the rear, modules that are clearly different. Yet they have exactly the same sticker on them. The test houses have no record of changes in the bill of materials. This is where we saw issues.”

Scambler is dissatisfied with traceability of modules in the industry and criticises the inability to track the bill of materials. If there is data, “there is very little information on the modules. There’s certainly no bill of materials information”. Even data containing granular details of components has faults: “for instance, you can tell from the Excel files that there are two different types of modules. There could be slight differences in serial numbers that would indicate they’re coming from different batches.”

Commercial bias in evaluation

DuPont benefits from asset owners who decide in favour of costly solar panel replacements. It leaves plenty of room for speculation. When E&T asked Choudhury, DuPont’s senior technical expert, how the company came up with the 12GW defect figure, he could not explain. “I could be wrong on that [12GW] even, because it’s very difficult to get exact numbers on which polyamide backsheet were sold…”, he said.

Other PV reliability experts remain sceptical about the extent of the PA backsheet legacy problem quoted by DuPont. They surmise that companies like DuPont have an interest in selling their own backsheets and therefore have ample reason to overblow the issue.

Rob Andrews at Heliolytics, a firm that runs solar industry inspections through aerial infrared and deep analytics, cautions against overstating figures that could lead to a glut in panel replacements.

There is no need for fearmongering, says Andrews: “[faulty backsheet technology] is not universally leading to the need to fully repower modules. I don’t think it would be a proper characterisation that all these plants are going to have to get torn out or anything to that extent.” He also doesn’t think the issue demonstrates a broader crisis of reliability in the PV industry.


Vested Interests

E&T notes that DuPont has a commercial interest in persuading asset owners to replace solar panels. That makes it an imperfect organisation to give an impartial assessment. When DuPont published its 2019 global study, it sponsored a feature in the magazine Solar Power World. This appears to show an 88 per cent defect rate in PA panels six to ten years after installation. In contrast, “only Tedlar® PVF maintains lowest defect rates after 30+ years”.

One expert from a competitor business says there are caveats to DuPont’s analysis. DuPont generally measures sites that already have known issues. Defect ratios in DuPont’s documents are reflective of that sample, the insider told E&T.

“For over 35 years, the DuPont Tedlar PVF film based backsheets have and continue to maximize durability and reliability and minimise system defects” DuPont says on its website. In the latest NIST academic research on solar panel degradation, published in March, the in-depth degradation mapping analysis was also partly funded by DuPont. The firm’s commercial interest correlates with its focus on indicating defects in other companies’ backsheet technology. One year after DuPont shifted its focus to stress defects in PA-based backsheet panels in 2017, the company announced an expanded portfolio of products, including new Tedlar backsheet materials.

Without independent and transparent review from a third party on defects, it may be difficult to judge whose estimates are right – but if DuPont’s assumptions on health and safety issues are correct, should operators and the public be warned?

Unless the government demands information, DuPont won’t share it, the firm says, but “if there is any regulation around [to allow the regulator to track components] then we definitely could give out the identity of asset owners”, Choudhury said.

What did the solar panel sector learn from all this? The best advice is to increase robust testing, multiple insiders told E&T.

The sector may soon be able to demonstrate that it has taken that lesson to heart. Since polyamide backsheets were pulled seven years ago, there is renewed demand for cheaper PA backsheets today. US manufacturer Tomark-Worthen, founded by ex-employees of Madico, wants to reinvent the technology. It has developed a new kind of polyamide backsheet, promising to cut costs by 25-30 per cent compared with high-efficiency fluoropolymer products.

Some observers remain optimistic, saying the solar industry has come a long way and learned from its missteps. Kelly Pickerel, editor-in-chief at Solar Power World, adds that buyers of solar panels have become more knowledgeable about their rights in recent years. “They can demand certain bills of materials from module manufacturers and they can seek out modules that only use top-tier materials”.

While technology testing seems largely solved in 2020, health and safety issues still need to be addressed. Amberside Energy’s Scambler thinks the UK government does too little to enforce standards to ensure health and safety. These issues are obvious and need to be tackled.

E&T approached the Health and Safety Executive, a government body, for comments. At this point, nothing in HSE’s documents suggested it had looked at safety-related problems caused by accelerated degradation, but HSE told us that it investigated two incidents at a solar panel farm recently, “both of which were system-of-work issues and not equipment issues. During 2014/15 British Gas (BG) contacted HSE about fires originating in solar PV panels and causing consequential damage to buildings. BG alleged some PV array manufacturers were putting unsafe products on the market; however, this is a Trading Standards matter”. HSE is more concerned about workers who could fall from heights when installing panels – a common problem.

The issues thrown up by PA backsheets hold important lessons for testing and panel replacement. All solar panels degrade at some point. Then questions like recycling will become more pressing. Working out how to deal with early-degrading panels today could help in dealing with the rest in the future. And there is still time. The majority of PV panels are far from the end of their lifespan. 75 per cent of solar installed is less than five years old. Yet as more solar panels degrade, replacement costs and recycling considerations become more important. Operators looking ahead to decommissioning may note that Europe’s first solar panel recycling plant opened in France in 2018. 

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