Reshaping the Module: The Path to Comprehensive Photovoltaic Panel Recycling

Abstract

The market for photovoltaic modules is expanding rapidly, with more than 500 GW installed capacity. Consequently, there is an urgent need to prepare for the comprehensive recycling of end-of-life solar modules. Crystalline silicon remains the primary photovoltaic technology, with CdTe and CIGS taking up much of the remaining market. Modules can be separated by crushing or cutting, or by thermal or solvent-based delamination. Separation and extraction of semiconductor materials can be achieved through manual, mechanical, wet or dry chemical means, or a combination. Crystalline silicon modules are currently recycled through crushing and mechanical separation, but procedures do exist for extraction and processing of intact wafers or wafer pieces. Use of these processes could lead to the recovery of higher grades of silicon. CdTe panels are mostly recycled using a chemical leaching process, with the metals recovered from the leachate. CIGS can be recycled through oxidative removal of selenium and thermochemical recovery of the metals, or by electrochemical or hydrometallurgical means. A remaining area of concern is recycling of the polymeric encapsulant and backsheet materials. There is a move away from the use of fluorinated backsheet polymers which may allow for improved recycling, but further research is required to identify materials which can be recycled readily whilst also being able to withstand outdoor environments for multi-decadal timespans.

Circular economy priorities for photovoltaics in the energy transition

“…Offsetting virgin material demands can be accomplished in ways other than recycling, including high-yield, high-efficiency, reliable systems (thereby reducing replacement and total deployment needs); remanufacturing of components; and circular material sourcing. Other studies have cataloged detailed considerations of PV design for circular economy, current recycling status and challenges [25,27,[75][76][77]. In addition to these technological circular economy designs, policy and business paradigms could support a circular economy for PV [78,79].…”

Recycling of Discarded Photovoltaic Solar Modules for Metal Recovery: A Review and Outlook for the Future

“…31 In the case of CdTe, the cell deposition is done on the front sheet, while for CIGS, the rear sheet is used, and CdS on the CIGS layer is often used as a buffer layer. 23,32,33 Due to the expected growth of a heterogeneous waste PV stream comprising different structures, types, and compositions, recycling strategies should be robust and easily adaptable.…”

“…The basic structure of a solar (mono or multicrystalline) Si cell consists of an aluminum alloy frame, cover plate glass, back sheet, and crystalline silicon wafers (180–200 μm) laminated between two EVA sheets. A c-Si absorber layer (6 wt %) is connected by Pb-coated Cu wires and Ag grid wires on the front, while Al is on the back for current transfer. , The front layer is usually made of glass, and the back sheet (0.8 wt %) comprises polymers, fluorinated polymers such as polyvinyl fluoride (Tedlar), polyvinylidene fluoride, or ethylene chlorotrifluoroethylene . The back sheet is widely of three types, (a) KPK (PET/Kyner), (b) TPT (PET/Tedler), and (c) PPE (PET/EVA), and comprises C (54.9%–63.8%), H (4.3%–6.6%), O (24.5%–30.5%), N (0.2%), and F (0–9%) .…”

“…The elemental constituents of CdTe are CdTe (0.11%–0.13%), Cu (0.02%), SnO 2 (0.02%), and CdS (0.01%), while CIS (Cu, In, Se) modules consist of CdS (0.0003%), ZnO (0.035%), CuInS 2 (0.04%), and Mo (0.025). , CIGS is a modified CIS produced by replacing 15% of In with Ga to improve solar cell efficiency . In the case of CdTe, the cell deposition is done on the front sheet, while for CIGS, the rear sheet is used, and CdS on the CIGS layer is often used as a buffer layer. ,, Due to the expected growth of a heterogeneous waste PV stream comprising different structures, types, and compositions, recycling strategies should be robust and easily adaptable.…”

“…21,22 The front layer is usually made of glass, and the back sheet (0.8 wt %) comprises polymers, fluorinated polymers such as polyvinyl fluoride (Tedlar), polyvinylidene fluoride, or ethylene chlorotrifluoroethylene. 23 The back sheet is widely of three types, (a) KPK (PET/Kyner), (b) TPT (PET/Tedler), and (c) PPE (PET/EVA), and comprises C (54.9%−63.8%), H (4.3%−6.6%), O (24.5%−30.5%), N (0.2%), and F (0−9%). 24 The average composition of c-Si entails 75%−80% glass (front layer), 10% polymer (encapsulant and back sheet, SiN x ), 10% Al (mostly frame), 3%−5% Si (solar cells), and 1% Cu (connectors).…”