Solar panels contain numerous precious metals and recyclable materials, though these materials had been tightly bonded with EVA during the manufacturing process, thus a rapid and economically valuable recycling method for solar panels has become one of the most difficult issues for each country.
Renewable energy industry including solar energy has been receiving substantial degree of spotlight as the awareness of environmental protection surges, however, how will the profound quantity of discarded solar panels be disposed when solar panels reach their EOL after 25 years? Solar panels contain glass, aluminum, silicon, copper, precious metals, and PET, which are formed with the latest hot-melt adhesive encapsulant, and may transport the materials back to the industry chain once properly recycled.
A breakthrough has been made amongst Chinese scientists recently, where the eco-friendly vacuum condensation technology has successfully eliminated backplanes and encapsulants, and recycled the metals within the cells.
Sun Yat-sen University and Shanghai Jiao Tong University have proposed the vacuum-gasification-condensation technology, which effectively recycles backplanes and encapsulants that respectively accounts for 5% and 10% of solar materials. The research team believes that the existing chemical solvent removal technology creates secondary pollution, and is unable to “add value” to backplanes and encapsulants.
The team crushed fragile materials, such as copper, tin, silicon, and silicon dioxide into 5mm granules using the vacuum tubular high temperature furnace (containing an ion vacuum gauge, a mechanical vacuum pump, and a diffusion pump), whereas soft materials like backplanes and encapsulants that are not easily crushed can also be cracked into 5-20mm granules.
The team speculated on the status of decomposition according to the weight inside the furnace. When the internal temperature of the furnace reaches to 490°C, the unchanged weight indicates that backplanes and encapsulants have completely decomposed and volatilized, and the decomposition procedure is at its fastest under the temperature of 460°C. The bond length of polymers such as backplanes and encapsulants is broken off under a temperature of 297-386°C, where the weight slowly mitigates.
As pointed out by the study, the pressure within the high temperature furnace is restored to the normal level when the temperature arrives at 505°C, where backplanes and encapsulants are not completely decomposed and vaporized, and 1.95kg of residue is left at the end, of which 42.35% is carbon, 36.99% is silicon, 11.41% is silver, and 6.63% is oxygen. The research team points out that a small trace of copper, iron, and zinc were also detected, and a part of the residue is discovered as aluminum due to the substantial amount of the particular material on the surface of solar cells. The research team believes that this method may perhaps expedite the development of solar recycling.
The existing regulations regarding the recycling of solar panels in Taiwan are as follows: first, each unit of solar panel is registered with a serial number, and the operator must pay for a solar panel recycling fee of NTD$1,000/KW in accordance with the relevant subsection of the “Development Act of Renewable Energy”, before registering online and collecting according to the specifications during recycling, where disposal personnel will arrive at the scene to pick up the discarded panels. As for smaller panels used for residence and RVs, one can dial the specific hotline to request personnel in assisting with the disposal procedure.
Operators are primarily using the thermal processing method (hot melt or hot knife) to separate glass from cells, before recycling the respective components. The research unit has successively developed pyrolysis and the stripping method, which are able to remove EVA of the glass on top of the photovoltaic panel that will facilitate glass recycling and reuse.
(Cover photo source: pixabay)