As brilliant summer sunlight streams down upon central and southern Taiwan, the area’s photovoltaic (PV) panels are hard at work generating power. But these solar panels won’t last forever. Those made with current technology have a nominal service life of 20-some years, and natural disasters can shorten their life expectancy. If we accept the need for large-scale use of green energy to slow the progress of climate change, we must also give thought to what to do with retired solar panels.

Fu Yaw-shyan has been researching solar power for more than 20 years. Here, he makes a point about the industry’s ups and downs by holding up a now obsolescent thin-film solar cell.

An international mission

Solar panels primarily consist of glass (75%), aluminum (10%), and the copolymer ethylene vinyl acet­ate (EVA, 10%), along with smaller amounts of silicon, copper and silver. “Solar panels are able to withstand at least 20 years of wind, rain and sun because these materials are of high quality. They should be recycled and reused,” says Fu Yaw-shyan, a professor in the Department of Greenergy at National University of Tainan.

PV Cycle, a member-based PV takeback and re­cyc­ling scheme established by the European Union, is currently the world leader in solar panel recycling. Processors typically disassemble the aluminum frames of the panels, then shred the remaining material and heat it to vaporize the EVA polymers and backsheets. The process enables the recovery of most of the aluminum, silicon, copper, silver and glass in the panels.

Unfortunately, the panels’ backsheets typically contain fluorine, which is released when the backsheets are pyrolyzed. Flourine damages the ozone layer, so re­cyc­ling facilities have to install equipment to capture it, making the facilities as large as steel mills, and driving their construction costs to nearly NT$100 million. 

Fu says that Europe’s recycling industry isn’t as developed as Taiwan’s, and doesn’t bother recycling EVA and backsheets. Even if the Europeans went to the trouble of doing so, the materials have so little value that they would end up going into a landfill or being incinerated. Europe currently also lacks the technology to mechanically separate these materials from solar panels, which is why processors just burn them off. Fu resolved to find ways to fully recycle PV panels because he believes that wasting useful materials and letting them become a pollution concern is antithetical to the goals of green energy.

The quartz on the left can be refined into the metallurgical grade silicon (MGS) on the right. MGS is a key raw material for the PV and semiconductor industries.

A comprehensive recycling system

Fu’s background is in chemistry. After completing his PhD in 2001, he went to work for the Industrial Technology Research Institute investigating the solar energy applications of new materials. He then became a professor at National University of Tainan, where he continued his solar energy research. Fu has seen the ups and downs of solar at first hand throughout his more than 20-year research career.

When the international community began a big push into green energy, aiming for net zero carbon emissions by 2050, solar power entered a period of rapid develop­ment. Fu recognized that this growth was going to make PV panel re­cyc­ling a serious issue.

He established a research group to study the issue in 2017. With its background in chemistry, the group’s entry point was via chemical decomposition. But even though their research yielded results, they didn’t seek to commercialize their methods because the solvents required were themselves pollutants. They then looked into approaches using physical reduction, breaking the physical bonds between the materials and splitting the panels apart layer by layer. But this raised a new problem: as their recycling equipment warmed up, the adhesives used in the panels began sticking to everything. The group turned to Taiwan’s machine tool industry for help, using joint R&D efforts with a number of companies to draw on their deep well of expertise. Its most recent method has been to run the machines disassembling the panels at room temperature, which allows the aluminum frames, silicon, glass, EVA, polyvinylidene difluoride (PVDF) and valuable metals to be separated from one another while maintaining their original characteristics.

Fu’s team uses physical reduction to separate PV panels into layers, enabling them to be fully recycled. (process diagram courtesy of Liu Cheng-chen)

Cash-positive recycling

The team has also continued to investigate applications for recycled materials as a means of furthering the indus­try’s development. Andrew Hung, a core team member, says that many firms approached Fu about buying techno­logy while the group was still conducting its R&D. Fu has declined their offers because he feels that business being business, these companies would only extract and reuse the high-value materials, while dumping materials with lower commercial value, like glass and EVA, into the waste stream. He believes that finding a real way forward on the disposition of old PV panels means developing applica­tions for all of the recovered materials, so that those materials can be fed back into the industrial chain.

Fu says that Taiwan has the advantage of having a complete recycling ecosystem that enables companies here to transform waste materials regarded as trash in other countries into gold.

While the EVA recovered from PV panels isn’t as pure as virgin EVA (the bonding process results in metal contamination), the team was able to turn this to their advantage by developing products that use metal-doped EVA, such as antistatic shoes for use in clean rooms.

If the PVDF stripped from solar panels is processed by pyrolysis, it produces hydrofluorocarbons that damage the Earth’s ozone layer. Fu’s team is therefore looking for ways to take advantage of PVDF’s acid‡alkali resistance, evaluating the feasibility of using it in industrial paints, piping for industrial wastewater, or even water filters for reservoirs. If they deem an application highly promising, they examine it in greater depth.

glass recovered by the recycling process

Innovative thinking

The team’s goals go beyond recycling to finding ways to upcycle and recover materials. The glass that constitutes the bulk of a solar panel is a case in point. While most re­cyc­lers find it a burden because of its low resale value, Fu’s team has developed a method to turn it into a different kind of solar panel.

In traditional solar panels, flat glass plates are mounted in an aluminum frame to provide extra strength. Fu developed a method for turning recycled PV glass into channel glass, a construction material, and then added solar cells to the new product. Team member Dai Shyue-bin, who holds a PhD in physics, uses a namecard to demonstrate how channel glass works. While a flat namecard is pretty flimsy, it can hold more weight if you fold the ends over to create a squared-off u-shape. Dai says that’s the principle underlying channel glass.

Last September, Fu’s team and the CPC Corporation built a solar energy cabin from the team’s channel glass. Team member Dr. Liu Cheng-chen laughs, “The glass kept getting bashed by hammers during assembly, but the blows didn’t so much as scratch it. It’s clearly plenty strong.” The cabin also produced enough power to run the air conditioner inside, which has given the team greater confidence in promoting PV construction materials.

The group believes that if solar panels can be integrated into buildings, builders can provide generating capacity for just the cost of the construction materials. Fu thinks it would be feasible to install the team’s new panels in structures such as the noise barriers lining highways and along pedestrian walkways. In addition to lowering the cost of integrating PV power, this would also reduce the competition for land between PV installers and the public.

EVA recovered by the recycling process

Building a future for PV

The team has been researching PV panel recycling for five years, and is currently raising funds to cover the cost of certifying its PV building material. The group believes that obtaining both PV and construction certifications for its product will help broaden the PV industry’s outlook. The team is also testing out the automation of its recycling machines with the goal of building a fully automated production line that can be installed in a 40-foot shipping container. The success of that effort would enable PV re­cycl­ing facilities to be shipped anywhere in the world they are needed, saving the energy that would otherwise be used to ship decommissioned PV panels to a distant recycler. Such technology could open up new inter­national markets for Taiwan. 

Asked whether the team has struggled with any obstacles in the last five years, Fu laughs and says, “We’ve hit many, but we’ve pushed through them all.” Their recycling technology alone has undergone three major ­revisions, and many firms that were initially very supportive of their efforts have gotten tired of waiting and given up. The team is constantly dealing with the challenges of how to win grants and raise the technological barriers to entry.

For the last few years, the government has been encouraging universities to establish companies as a means of getting their research into the hands of industry. Fu’s team was the first from NUTN to do so. He and the other three core members of his team decided that they needed to raise millions of NT dollars to fund their operations, even if they had to sell their own homes to do so. Dai Shyue-­bin laughs and tells us that Fu is like a missionary, constantly encouraging team members to look on PV panel recycling as a vocation. Fu himself says, “I’m not sure this will ever turn a profit, but I’m happy to be doing it even so, because our work will benefit the environment.”       

silicon recovered by the recycling process

The team is doing its utmost to build a circular economy in PV cells by developing recycling methods and applications for recycled materials. From left to right: Dai Shyue-bin, Fu Yaw-shyan, Liu Cheng-chen, Ke How-wei, and Andrew Hung.

The team is aiming to fully automate its PV panel recycling system and make it small enough to fit inside a 40-foot container, to increase its export potential. (courtesy of Liu Cheng-chen)

Able to easily bear the weight of a 90-kilogram person, the team’s PV channel glass has a higher safety factor than the glass used for glass-curtain buildings.

The Taiwanese research team is striving to resolve the problem of PV panel waste and make green energy truly sustainable by finding ways to fully recycle solar panels.