Since 2018, Lithuanian manufacturer SoliTek has been investigating solar panel design for circularity via a European Commission Innovation Action project called Circusol, or “Circular Business Models for the Solar Power Industry.”
Funded by the EU Horizon 2020 program, Circusol aims to deliver circular PSS (product-service systems) business models with real environmental benefits and economic feasibility, validated in five real-life commercial demonstrations. Overall, the project brings together 15 partners from seven European countries and will conclude in November 2022.
One of the main research topics has been PV module ecodesign. Due to the booming PV market, the waste volumes derived from decommissioned PV installations are expected to increase in the near future. At the same time, current recycling practices are characterized by a significant loss of material quality (“downcycling”). Thus, SoliTek has been looking into the barriers and opportunities related to solar panel circularity, to propose alternative design options.
Key issues
Based on the knowledge and experience of Circusol partners, literature reviews, and a workshop with PV industry experts, design characteristics have been identified that make current-day solar panels difficult to recycle, repair, or reuse. These circularity hindering characteristics were divided into four categories (see Table 1).
The current sandwich structure of PV panels, which is filled with encapsulants, makes it difficult for recycling companies to open them. Consequently, a widely adopted shredding approach contaminates the silicon and glass streams, resulting in lower quality secondary materials. Moreover, the lack of traceability for panels and their materials means recycling facilities receive products without any background information.
Then there’s the diversity of materials applied, and their quality and concentration ranges. These create inefficiencies in recycling processes, complicating economic and environmental benefits, as well as repair or re-use opportunities.
| Design issues and circularity impacts | |||
| Current PV panel design issues |
Impact on recycling | Impact on reusability | Impact on repairing and refurbishment |
| Sandwich structure | Requires sophisticated and costly processes to recover high-quality materials. Dominant mechanical recycling processes recover low-quality materials. | Not possible as cells cannot be recovered intact due to lamination of encapsulants and glasses/back sheet. | Not possible to repair solar cells. |
| Lack of traceability of panels and their materials |
Difficult to make decisions about recycling facility establishment due to lack of information about panels and their compositions in specific regions/countries. | Difficult to evaluate potential due to lack of information related to panel materials, components, technology, etc., which could allow evaluating its second-usage value, applications, and markets. | Lack of easily accessible information that would allow better repairability/refurbishment (manufacturer recommendations on repairing, components specifics, etc.). |
| Diversity of panel components and materials | Panel manufacturers introducing recyclable or less toxic materials provide additional challenges for recycling companies to adapt their processes and adjust recovered materials management.
Future different types of panels could challenge recycling feasibility for high-value materials recovery. |
Different material combinations require evaluation for second-hand markets (toxic materials content compatibility with local country, availability to recycle such panels in the country, etc.). | Different repairability feasibility based on panel composition. |
| Diversity of panel sizes | Different panel dimensions and weights influence logistics and recycling machinery line feasibility to recycle them. | ||
| Evaluation of design for circularity solutions | ||||||
| Potential for recycling |
Potential for Re-use |
Potential for repair and refurbishment |
Required capital investment for the manufacturer | Change in solar panel BOM costs | Overall positive impact toward circularity |
|
| NICE encapsulation |
High | High | High | High | Low | High |
| ECA | Low | Medium | Low | Medium | Medium | Medium |
| LEAD-free ribbons | Low | Medium | Low | Low | Low | Medium |
| Fluorine-free back sheet |
Medium | Medium | Low | Low | Medium | Medium |
| RFID | Medium-High | High | High | Medium | Low | High |
Moreover, due to the lack of information about discarded panels, their composition, and their history, repaired panels are not “bankable” for second-life use because it is hard to estimate the remaining technical lifetimes and efficiencies.
The plethora of panel components and materials challenges the closed-loop strategies for both component and panel manufacturers. Globally, there are around 100,000 different panel types when all the slight changes like materials and nominal power, are taken into account.
Components such as iron-free glass, fluorine-free backsheets, and recyclable backsheets are being increasingly designed for circularity. But due to the high heterogeneity of panels and lack of traceability, it is almost impossible for recycling companies to sort and treat specific panels with circular components and materials separately.
Solutions to improve circularity
Building upon the abovementioned circularity issues, SoliTek proposes the following solutions: Radio Frequency Identification (RFID) tags, for better traceability of panel type, age and origin; New Industrial Solar Cell Encapsulation (NICE), which designs out encapsulation material; and electrically conductive adhesives, lead-free ribbons, and fluorine-free back sheets, to design out troublesome materials (e.g., lead and fluorine).
The advantages and disadvantages of these modifications have been analyzed from the perspective of SoliTek’s manufacturing operations to identify the most promising alternative designs, with both NICE and RFID tags being retained. NICE encapsulation was developed by Apollon Solar to protect solar cells by extracting oxygen and sealing cells tightly between glass. But by reducing “sandwich“ component layers, recycling companies can process panels with fewer difficulties.
RFID tags, whether attached as ultra-high frequency (UHF) tags or inserted as in-laminated near field communication (NFC) tags, allow for the collection of information about panels, like material composition, dates of repairs, etc. Information can be added directly into the tags or in the links associated with the tags, which is then communicated to an online database. It can be stored during the manufacturing phase and/or updated at any other given point with a phone (NFC tags) or dedicated reader (UHF tags).
Economic feasibility
Solitek produced PV modules incorporating the abovementioned technologies and adaptations, on a small scale, for testing in a climate chamber. Not all the UHF RFID tags attached to the panels survived the climate chamber tests. Thus, it is recommended that NFC tags are laminated into the tops of panels, which could protect them from environmental degradation.
NFC tags are relatively cheap (around €0.20/each), making their application increasingly interesting with continuous improvements in power. Lead-free ribbons proved to provide less adhesive strength. Additional experiments are thus required to optimize ribbon material ratios and panel manufacturing processes.
From a supply chain perspective, the most important solution to address circularity issues in PV panels is arguably the development of a database that would allow their characteristics to be traced.
For recycling facilities, this would make it easier to know what kind of (waste) product they receive, in terms of material composition, panel performance, and recycling/repair/reuse options. An increase in transparency and data availability on these topics could push the PV industry to keep improving the materials and components for PV panel circularity.
About the authors
Tadas Radavičius holds a Master’s degree in management. He is currently working on a Ph.D. looking at “circular processes management in energy sector companies.” He works as a project manager at SoliTek R&D.
Julius Denafas has worked for more than nine years in the field of industrial research and the production of high-efficiency c-Si solar cells and modules. He holds a Master’s degree in materials and manufacturing from Technical University of Denmark and a Ph.D. in the field of environmental engineering from Kaunas University of Technology. He has also been involved in seven European R&D projects related to PV and renewable energy.
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